ACUS01 KWNS 190454
SWODY1
SPC AC 190452

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1152 PM CDT Fri Sep 18 2020

Valid 191200Z - 201200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Organized severe thunderstorms are not expected across the
contiguous United States today.

...Synopsis and Discussion...
An upper trough will move east across the northern Rockies with
shortwave ridging moving into the northern Plains. Cooling aloft
will overspread much of Montana and Wyoming late in the day and
overnight, with a surface trough and wind shift over eastern Montana
and Wyoming at 00Z.

Southerly winds will maintain a plume of 50s F dewpoints over the
Plains and into northeast Montana, although this air will be
originating out of a surface high over the eastern US. While various
point forecast soundings show a few hours of uncapped soundings over
parts of eastern Montana, the quality of the moisture is in
question. In addition, the zone of potentially uncapped air for
surface-based parcels will be narrow ahead of the cold front,
quickly becoming capped to the east. A storm or two may form after
00Z, possibly becoming elevated as they move north during the
evening over northeast Montana.

Cool profiles aloft may favor small hail or gusty winds with
isolated storms over northeast Montana, but aforementioned moisture
quality as well as relatively weak deep-layer shear suggest little
severe threat.

Scattered storms are also possible from central and eastern Idaho
into southwest Montana beneath the upper trough, with only very
small hail or localized gusty winds expected.

Elsewhere, developing Tropical Storm Beta will remain over the
western Gulf of Mexico, as will the more favorable instability and
shear.

..Jewell/Wendt.. 09/19/2020

$$
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ACUS01 KWNS 271248
SWODY1
SPC AC 271246

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0746 AM CDT Sun Sep 27 2020

Valid 271300Z - 281200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS LATE THIS
AFTERNOON/EVENING FOR EASTERN OK AND THE ADJACENT OZARK PLATEAU...

...SUMMARY...
Isolated severe thunderstorms are possible this afternoon and
evening across eastern Oklahoma and the adjacent Ozark Plateau.

...Eastern OK and the Ozarks late this afternoon/evening...
In response to the amplification of a midlevel trough over the Great
Plains, a surface cold front will surge southward to near the I-44
corridor in MO/OK by this evening, as a remnant lee cyclone moves
southward and weakens across the eastern TX Panhandle and northwest
TX. In advance of the front, boundary-layer dewpoints of 68-72 F
will continue advect northward from TX into central/eastern OK. The
moisture advection will occur beneath a cap associated with a warm
elevated mixed layer, which will contribute to MLCAPE around 2000
J/kg, but also likely limit any potential for warm sector storm
development.

Lift atop the frontal surface appears necessary for storm initiation
late this afternoon/evening near the I-44 corridor, with storms
subsequently spreading southeastward through tonight. The initial
convection will form close to the surface front, but there should be
a tendency for storms to become elevated to the cool side of the
boundary. The moderate buoyancy with midlevel lapse rates in excess
of 8 C/km and effective bulk shear near 40 kt will support some
supercell structures, with an attendant threat for isolated large
hail and/or strong outflow gusts with storms close to the surface
front. The severe threat will peak this evening, and then diminish
gradually overnight as the low levels stabilize and buoyancy
decreases. A Slight risk upgrade is still a possibility later today
for the area centered on eastern OK, primarily for large hail.

..Thompson/Jewell.. 09/27/2020

$$
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ACUS01 KWNS 281628
SWODY1
SPC AC 281627

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1127 AM CDT Mon Sep 28 2020

Valid 281630Z - 291200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OH TO THE
CENTRAL GULF COAST...

...SUMMARY...
Isolated strong/damaging wind gusts will be possible, mainly during
the late afternoon to early evening, from Ohio to the central Gulf
coast.

...OH to the central Gulf coast...
Within a large-scale trough over the Great Plains/MS Valley, an
initial mid-upper speed max will rotate north-northeast from IL/IN
into southern Ontario. Pronounced cyclogenesis is expected through
tonight from the Lake Huron vicinity north towards James Bay. The
trailing cold front will continue to move east across the OH Valley
to central Gulf Coast regions. Poor mid-level lapse rates are
expected within the majority of the warm sector, and the richer
low-level moisture (boundary-layer dewpoints in the low-mid 70s)
will be confined to the Gulf Coast. Thus, buoyancy will be rather
shallow and limited in magnitude to the north in the OH Valley
(MLCAPE < 250 J/kg), with moderate buoyancy (MLCAPE of 1500-2500
J/kg) expected near the Gulf coast.

Ongoing scattered to broken showers from the TN Valley north within
the zone of ascent along the cold front may deepen into low-topped thunderstorms by peak heating, most likely centered on the OH
Valley. Here, strong deep-layer shear may offset the limited
buoyancy/poor lapse rates aloft to yield a brief cluster capable of
producing locally strong gusts. Wind profiles will be weaker from AL
to southern LA, though thermodynamic profiles will be much more
favorable for deeper convection, with an attendant threat of
isolated damaging wind gusts during the late afternoon to early
evening.

..Grams/Darrow.. 09/28/2020

$$
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ACUS01 KWNS 291944
SWODY1
SPC AC 291942

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0242 PM CDT Tue Sep 29 2020

Valid 292000Z - 301200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM EASTERN
VIRGINIA TO NORTHERN FLORIDA...

...SUMMARY...
Isolated damaging winds will be possible through this evening from
north Florida across the Carolinas to eastern Virginia. A brief
tornado is also possible, mainly centered on eastern North Carolina
tonight.

...20z Update...

Only minor changes have been made to the ongoing outlook, mainly to
adjust/trim the 10% General Thunder line from NY southward through
FL based on the current position of the cold front. Elsewhere, 10%
General Thunder was also removed from parts of the Upper Midwest and
Great Lakes based on latest observational trends and calibrated HREF
guidance. While a thunderstorm or two cannot be completely ruled out
in these areas, coverage of any lighting flashes should be
minimal/sub-10%.

...Southeast and Mid-Atlantic vicinity...

The Marginal risk area has been trimmed on the western flank in
NC/SC/GA as convection continues to shift east/northeast along/just
ahead of the cold front. Otherwise, expect a few storms capable of gusty/locally strong winds will continue into the early evening
period. For more details, reference MCD 1723.

..Leitman.. 09/29/2020

.PREV DISCUSSION... /ISSUED 1111 AM CDT Tue Sep 29 2020/

...Delmarva to north FL...
Within an amplified large-scale trough from the Great Lakes to the
central Gulf Coast, a primary embedded impulse near the IL/IN border
will eject east to the northern Appalachians through early
Wednesday. Cyclogenesis will occur mainly tonight with the primary
surface cyclone ejecting north from the DE Valley towards VT. A
secondary lee cyclone over western NC should move towards the VA
Tidewater, with an attendant cold front to its south that will
progress east and reach the south Atlantic Coast by evening.

Upper 60s to low 70s boundary-layer dew points will remain pervasive
ahead of the cyclones/cold front, but boundary-layer heating will
likely be more pronounced from eastern VA to north FL. Given the
relatively meridional mid/upper-level flow regime and cooler
temperatures aloft lagging well west, high-level lapse rates will be
poor. This will likely hold MLCAPE to between 750-1500 J/kg north of
FL. Deep-layer winds will increase with approach of the amplified
trough, more substantially tonight, with relatively small low-level
hodograph curvature expected to persist into early evening. The
modest CAPE with an elongated hodograph due to the degree of
vertical speed shear should favor weak/transient supercell
structures within a broken line of convection along/just ahead of
the surface cold front during the late afternoon and evening. The
primary concern will be for locally strong gusts capable of
producing sporadic damaging winds. A brief tornado is also possible,
mainly centered on eastern NC tonight, with any deep convection that
can linger amid meager buoyancy as low-level hodographs enlarge.

$$
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ACUS01 KWNS 301631
SWODY1
SPC AC 301630

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1130 AM CDT Wed Sep 30 2020

Valid 301630Z - 011200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
The risk for severe thunderstorms is negligible through tonight.

...Extreme northern ME...
A shallow convective line in Aroostook County should progress into
New Brunswick by 1730Z. Despite being low-topped (<20 kft echo tops)
and no detectable lightning given poor mid to upper-level lapse
rates, extreme low-level shear provides some concern for a brief
tornado amid 66-68 F surface dew points. However, based on recent
radar reflectivity/velocity trends and the very limited
spatiotemporal extent of the threat, will refrain from adding a
severe risk area.

...Great Lakes...
Isolated to perhaps scattered thunderstorms are expected to persist
across the region as multiple embedded mid-level vorticity maxima
rotate through an eastern North America longwave trough. Steep
tropospheric lapse rates will support a risk for small hail in the
strongest storms through this evening. A gradual nocturnal decrease
in convection is expected outside of the immediate lakeshores.

...South FL...
Isolated thunderstorms should diminish this evening, with
redevelopment possible off the southeast coast during the early
morning as the surface front stalls over the FL Straits.

..Grams.. 09/30/2020

$$
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ACUS01 KWNS 011539
SWODY1
SPC AC 011537

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1037 AM CDT Thu Oct 01 2020

Valid 011630Z - 021200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe thunderstorms are not expected through tonight.

...Discussion...
Isolated low-topped thunderstorms are expected to mainly exist this
afternoon in association with a mid-level impulse over southwest
Lower MI shifting east towards the Lower Great Lakes. The risk for
waterspouts may continue across portions of Lake Erie and Michigan.

Otherwise, a maritime tropical air mass and weak shear environment
will persist south of a stalled front across south FL. Isolated
thunderstorms will be possible through the period, though storms
should be somewhat more concentrated this afternoon along the sea
breeze across southeast FL.

..Grams.. 10/01/2020

$$
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ACUS01 KWNS 021925
SWODY1
SPC AC 021923

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0223 PM CDT Fri Oct 02 2020

Valid 022000Z - 031200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe thunderstorms are not expected through tonight.

...20z Update...

Water-vapor imagery depicts a well-defined short-wave trough
ejecting northeast across eastern NY. Isolated thunderstorm
potential is primarily ahead of this feature, thus the 10% thunder
line has been adjusted to account for this movement.

No changes warranted regarding the potential for thunderstorms
across south FL.

..Darrow.. 10/02/2020

.PREV DISCUSSION... /ISSUED 1056 AM CDT Fri Oct 02 2020/

A generally quiet convective day is forecast across most of the
contiguous United States. Isolated lake-effect showers and
thunderstorms will continue to affect portions of northern NY and
possibly northern VT this afternoon and evening. Other scattered
thunderstorms are possible later today over parts of south FL. No
severe storms are expected.

$$
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ACUS01 KWNS 031252
SWODY1
SPC AC 031250

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0750 AM CDT Sat Oct 03 2020

Valid 031300Z - 041200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe thunderstorms are not expected today nor tonight.

...Synopsis/Discussion...
Mean ridging in the West, and troughing in the East, will continue
to dominate the CONUS upper-air pattern through this period. A
series of somewhat closely spaced shortwaves -- now located across
the central/northern Plains and Upper Midwest -- will dig into the
mean trough position from the upper Great Lakes to the lower
Mississippi Valley and northern Gulf, sharpening the cyclonic
curvature of the basal height/flow field through tonight.

At the surface, 11Z analysis showed a quasistationary front across
south FL, extending east-northeastward over the northern Bahamas and west-southwestward across the southeastern Gulf. This boundary --
both surface and in low levels through around 850 mb -- should drift
northward through the period and become more shallow in vertical
slope. Episodic, patchy areas of convection, with occasional
embedded thunderstorms, will occur in the low-level frontal zone and
southward through the Straits.

Elsewhere, a low was drawn between FRI-BIE, with weak cold front
southwestward across northwestern OK, the TX Panhandle and
northeastern NM. The low should move to south-central/central MO by
00Z, with front across southeastern/south-central OK, west-central
TX and southeastern NM. By 12Z the front should reach southern IL,
central AR, and portions of central/southwest TX. Moisture return
ahead of this front will be meager, with surface dew points
generally 40s to low 50s F, and an EML evident in the 12Z MAF RAOB
advecting over the region to cap the prefrontal warm sector.
Isolated thunder may occur in elevated convection today over MO
under cooler air aloft, northeast of the EML, and/or this evening
through tonight from the Ozarks to the Red River region.

..Edwards.. 10/03/2020

$$
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ACUS01 KWNS 031948
SWODY1
SPC AC 031947

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0247 PM CDT Sat Oct 03 2020

Valid 032000Z - 041200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe thunderstorms are not expected today nor tonight.

...20z Update...

The ongoing forecast remains on track. No changes are necessary with
this update. See discussion below for forecast details.

..Leitman.. 10/03/2020

.PREV DISCUSSION... /ISSUED 1115 AM CDT Sat Oct 03 2020/

...TX to IL...
A broad upper trough is present today over the eastern US, with
ridging across the west. Scattered showers and thunderstorms are
occurring this morning across the Ozarks of southern MO/northern AR.
This activity may persist into the mid afternoon before weakening.
Other convection is expected to form after dark across portions of
southeast OK and northeast TX - ahead of an approaching shortwave
trough. No severe storms are anticipated.

...FL...
A plume of deep moisture and sufficient CAPE is present over much of
the FL Peninsula today. This will maintain the risk of scattered
afternoon and overnight showers and thunderstorms.

$$
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ACUS01 KWNS 041244
SWODY1
SPC AC 041242

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0742 AM CDT Sun Oct 04 2020

Valid 041300Z - 051200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe thunderstorms are not expected across the U.S. through
tonight.

...Synopsis...
In mid/upper levels, a substantial mean trough over the eastern
CONUS is forecast to deamplify through the period. This will occur
as a series of nearly phased shortwaves -- now apparent in
moisture-channel imagery from the upper Great Lakes across the
middle Mississippi Valley to northeast TX -- eject eastward to the
Atlantic Seaboard and southern Appalachians region. One of those
shortwave perturbations -- now over IL -- will reach OH by 00Z, then
reach the northern Mid-Atlantic overnight.

At the surface, 11Z analysis showed a warm-frontal zone across he
southern FL Peninsula near Lake Okeechobee, forecast to drift
northward through the period. Isolated to scattered, episodic
thunderstorms are expected again this period across the FL Peninsula
and adjacent waters, as a rich moisture plume and weak but broad
low-level lift occur within and south of the frontal zone. Further
north, a low was drawn over IN between IND-HUF, with cold front
southwestward over central AR, north-central TX, the TX Permian
Basin, and southeastern NM. The low should remain weak and migrate
eastward toward the northern Panhandle of WV around 00Z, with the
front reaching eastern KY, middle TN, and southeast/south-central
TX.

...Ohio Valley region...
Isolated to widely scattered thunderstorms are possible from late
morning to afternoon, shifting eastward to northeastward across the
outlook area. Gusty winds are possible with the strongest activity,
but instability and shear should be insufficient for an organized
severe threat.

A field of large-scale lift (warm advection and DCVA) related to the aforementioned IL shortwave trough is contributing to showers across
parts of eastern IL and IN. From late morning into afternoon, as
the leading edge of this ascent field combined with frontal lift and
impinges on a modestly diurnally destabilizing warm sector, some of
the convection may deepen enough for lightning production. Forecast
soundings suggest 100-300 J/kg MLCAPE extending past the -20 deg C
isotherm, with buoyancy extending (and supporting some thunder
potential) behind the front. Though winds around 500 mb and higher
levels will be strong, only the very upper reaches of the convective
layer will extend into that regime, and only 20-30 kt effective-
shear magnitudes are forecast.

..Edwards.. 10/04/2020

$$
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ACUS01 KWNS 041933
SWODY1
SPC AC 041931

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0231 PM CDT Sun Oct 04 2020

Valid 042000Z - 051200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe thunderstorms are not expected across the U.S. through
tonight.

...20z Update...

The previous outlook remains on track and no changes are needed. See
discussion below for forecast details.

..Leitman.. 10/04/2020

.PREV DISCUSSION... /ISSUED 1115 AM CDT Sun Oct 04 2020/

...OH Valley..
No changes have been made to the ongoing forecast. Showers and a
few thunderstorms are possible mainly this evening over portions of
the upper OH Valley as a cold front approaches the region. Forecast
soundings suggest that minimal CAPE and shallow convective layer
will limit the coverage of lightning activity.

...FL...
Scattered showers and thunderstorms are possible this afternoon and
tonight over parts of FL and near the immediate Carolina coast.
Weak flow aloft should preclude organized severe storms.

$$
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ACUS01 KWNS 051539
SWODY1
SPC AC 051537

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1037 AM CDT Mon Oct 05 2020

Valid 051630Z - 061200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe thunderstorms are not expected through tonight.

Relatively dry and stable condition will preclude thunderstorms
across the vast majority of the contiguous United States today. One
exception will be along the coast of southeast MA for another 1-2
hours as an area of showers and thunderstorms drifts eastward and
out to sea. The other area of some risk for thunderstorms will be
across parts of the FL peninsula, where afternoon and evening storms
will be possible. No severe storms are expected.

..Hart.. 10/05/2020

$$
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ACUS01 KWNS 061557
SWODY1
SPC AC 061556

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1056 AM CDT Tue Oct 06 2020

Valid 061630Z - 071200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe thunderstorms are not expected today through tonight.

No changes have been made to the ongoing forecast. A progressive
shortwave trough will track southeastward into the western Great
Lakes region this evening, with cooling temperatures aloft and weak
forcing overspreading the area. Scattered showers and isolated
lake-enhanced thunderstorms will remain possible as this feature
moves across parts of WI/MI overnight. Other isolated thunderstorms
may occur this afternoon across parts of the FL peninsula and
coastal GA/SC/NC in a weakly unstable environment.

Otherwise, stable conditions with preclude thunderstorms over the
CONUS today.

..Hart.. 10/06/2020

$$
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ACUS01 KWNS 071602
SWODY1
SPC AC 071601

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1101 AM CDT Wed Oct 07 2020

Valid 071630Z - 081200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
AND EARLY EVENING ACROSS MUCH OF NEW YORK AND NEW ENGLAND...

...SUMMARY...
Strong wind gusts are possible later today from New York into much
of New England.

...Northeast...
The current forecast area appears to be on track, with no changes
made. A band of showers and thunderstorms is organizing from lake
Ontario northeastward along the St Lawrence Valley. This activity
will move quickly eastward across much of NY early this afternoon,
and across much of New England through early evening. Widespread
clouds are present ahead of the convection, which will limit
low-level lapse rates and CAPE. It is likely that these fast-moving
showers and storms will produce gusty and marginally damaging winds,
but it is uncertain how prevalent the risk of 50 knot winds will be.
Given the overall marginal thermodynamic environment, will maintain
the ongoing MRGL risk area. Activity should move off the New
England coast by mid-evening, ending the threat of gusty winds.

..Hart.. 10/07/2020

$$
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ACUS01 KWNS 081247
SWODY1
SPC AC 081245

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0745 AM CDT Thu Oct 08 2020

Valid 081300Z - 091200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS IN PARTS OF
NEAR-COASTAL SOUTHERN LOUISIANA...

...SUMMARY...
A tornado is possible over near-coastal southern Louisiana late
overnight.

...Synopsis...
In mid/upper levels, the northern-stream pattern is becoming more
zonal following the departure of a strong shortwave trough from New
England across the Canadian Maritimes. Meanwhile, a vorticity max
-- evident in moisture-channel imagery over west-central OK -- is
forecast to move slowly northeastward to the OK/KS/MO border area by
the end of the period, with trough southwestward across west-
central/southwest TX. As that occurs, Hurricane Delta is forecast
by NHC to turn northward across the western Gulf this period, toward
a mid-period day-2 landfall along the southwestern LA coastline.
See latest NHC advisories for specific track/intensity forecasts and
tropical watches and warnings related to Delta.

...Southern LA...
A tornado may occur the last few hours of the period from
outer-fringe convection associated with Hurricane Delta. This is a
marginal and conditional outlook predicated on:
1. Latest NHC forecasts of track, speed and expansion of the
supportive wind fields, juxtaposed with
2. Most probable outer reach of favorable, discrete to semi-
discrete convective modes that could become supercellular amidst
enlarging hodographs, and
3. Favorable inland migration of a maritime/tropical boundary layer
that, based on modified forecast soundings from several models,
would contain theta-e large enough to offset warm temperatures aloft
and yield surface-based buoyant parcels.

Such conditions are expected to spread well inland and include the diurnal-destabilization period Friday/day-2, but marginally may
spread as far north as roughly I-10 by the 12Z ending time of this
outlook period. Low-level shear and buoyancy each are expected to
diminish with inland extent overnight, even as they gradually
increase in an absolute sense at any given spot with Delta's
approach.

..Edwards/Goss.. 10/08/2020

$$
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Re: DAY1SVR: Day 1 Convective
By: Weather Alert to All on Thu Oct 08 2020 11:42 am

Can we some weather for New York here?HusTler
|13 Havens BBS
|12 (havens.synchro.net:23)

---
þ Synchronet þ Havens BBS havens.synchro.net
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ACUS01 KWNS 081947
SWODY1
SPC AC 081945

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0245 PM CDT Thu Oct 08 2020

Valid 082000Z - 091200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER COASTAL
LOUISIANA AFTER MIDNIGHT...

...SUMMARY...
A tornado is possible over near-coastal southern Louisiana after
midnight tonight.

...Discussion...
No change was made to the previous convective outlook.

..Smith.. 10/08/2020

.PREV DISCUSSION... /ISSUED 1119 AM CDT Thu Oct 08 2020/

...LA...
The affects of Hurricane Delta will begin to spread into coastal
areas of LA late tonight, but more likely on Friday. Model forecast
soundings suggest that vertical shear will increase before 12z in
this region, providing a conditional risk of rotating convection and
perhaps a tornado or two. However, CAM solutions suggest that more
cellular outer bands will remain offshore until the Day2 period.
Therefore the overall threat across southern LA appears MRGL through
12z.

$$
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HusTler wrote to Weather Alert <=-

Can we some weather for New York here?HusTler

Well, these alerts are mostly about severe weather that is forecast or that
has already happened. So, if you are not reading about New York, that is probably why. Lately, it has been all about places most likely to get hit
by hurricanes and typhoons.

That said, I am pretty sure that New York and New England got mentioned in
one of the 2, 3, or 4-8 day outlooks a day or two ago.



... 2 + 2 = 5 for extremely large values of 2.
--- MultiMail/??Unknow v0.43
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ACUS01 KWNS 091946
SWODY1
SPC AC 091944

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0244 PM CDT Fri Oct 09 2020

Valid 092000Z - 101200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
INTO TONIGHT FOR SOUTHEAST LA AND EXTREME SOUTHERN MS...

...SUMMARY...
A few tornadoes are possible across southern portions of Louisiana
and Mississippi later this afternoon into tonight.

...Discussion...
No change was made to the previous convective outlook.

..Smith.. 10/09/2020

.PREV DISCUSSION... /ISSUED 1125 AM CDT Fri Oct 09 2020/

...North central Gulf coast area through tonight...
Hurricane Delta will move northward and make landfall this evening
along the southwest LA coast, and continue inland toward northeast
LA overnight (please see the latest NHC advisories for additional
information). Though Delta will weaken as it moves over cooler
shelf waters and experiences more land influences, expansion of the
hurricane's wind field will lead to increasingly favorable
hodographs for supercells in the east-northeast quadrants of the
storm later today into tonight. A limiting factor thus far has been
the lack of a coherent eastern convective band. This suggests that
the tornado threat may be slow to develop today, and will likely
need peak afternoon destabilization in cloud breaks across southeast
LA. Still, effective SRH will increase to greater than 300 m2/s2
this afternoon into this evening as Delta approaches the coast, and
there will be sufficient buoyancy for a supercell/tornado threat in
the zone of somewhat larger CAPE across southeast LA.

The threat for a couple of tornadoes will spread inland some
tonight, but should be tempered by diminishing buoyancy with time
and northward extent. The northern extent of the tornado threat
this afternoon into tonight will be delimited by a surface warm
front that will move northward. The warm front now extends from
southeast LA across southern MS/AL, and may provide a focus for
isolated strong storms this afternoon.

$$
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ACUS01 KWNS 101259
SWODY1
SPC AC 101258

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0758 AM CDT Sat Oct 10 2020

Valid 101300Z - 111200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE DEEP
SOUTH AND NORTHEAST/NEW ENGLAND...

...SUMMARY...
A few tornadoes are possible today into this evening across the Deep
South including parts of Alabama, Georgia, and Florida Panhandle.
Severe thunderstorms are also expected across parts of northern New
York and northern New England.

...Deep South including Alabama/Georgia/Florida Panhandle...
Tropical Cyclone Delta, which is centered over far west-central
Mississippi around sunrise, will continue northeastward. Although
the remnant circulation/low will tend to weaken, low-level winds on
its eastern periphery will remain strong (40-55 kt), with the
strongest core of south-southwesterly winds in the lowest 2-3 km AGL
expected to transition east-northeastward across Alabama/Florida
today, and toward Georgia and the nearby southern Appalachians by
evening.

Transient low-topped (including an absence of lightning flashes)
low-level mesocyclones have been noted through the early morning
hours within a zone of confluence across southwest Alabama and the
western Florida Panhandle. Potentially aided by cloud breaks and the
periphery of the eastward-advancing mid-level dry slot, a diurnal destabilization trend this morning into afternoon may modestly boost
low-level parcel accelerations and updraft intensity (albeit still
low-topped). Diurnal destabilization aside, a general northeastward
flux of low-level moisture will coincide with the entrance region of
the low-level jet, which should allow for a net east-northeastward
transition of the tornado threat today across additional parts of
Alabama toward western Georgia.

...Northeast/New England...
An upper-level trough centered near the border vicinity of northern Ontario/northern Quebec early today will steadily amplify and
progress eastward today toward northern New England. While surface
dewpoints are only in the 40s F early today, a steady influx of
modest moisture is expected into the region ahead of an east/southeastward-advancing cold front. Given the kinematic
scenario, low-level moisture/buoyancy should be adequate for the
development of stronger convection this afternoon. This should
initially occur over northern portions of New York into northern
Vermont/New Hampshire, while additional low-topped thunderstorms may
develop across/move out of eastern Quebec into Maine a bit later
this afternoon through early/mid evening. Very strong deep-layer west-southwesterly winds will support fast eastward-moving bands of
storms capable of wind damage and possibly some line-embedded
tornado risk.

...Western Washington...
A locally severe storm, including the potential for convectively
enhanced wind gusts, cannot be entirely ruled out early today in
general association with an eastward-moving/inland-spreading
shortwave trough and associated front. However, very limited
buoyancy, as sampled by the 12Z observed KUIL/Quillayute sounding,
suggests that any such severe potential should remain limited.

..Guyer/Goss.. 10/10/2020

$$
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ACUS01 KWNS 111624
SWODY1
SPC AC 111622

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1122 AM CDT Sun Oct 11 2020

Valid 111630Z - 121200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS LATE THIS
AFTERNOON INTO EARLY TONIGHT FROM SOUTHWEST MN TO EXTREME NORTHEAST
KS...

...SUMMARY...
Severe thunderstorms are possible late this afternoon and evening
across the Upper Midwest and Middle Missouri Valley. A brief/weak
tornado or two and isolated damaging gusts will be possible this
afternoon across parts of the Carolinas.

...MN/IA/eastern NE this evening through early tonight...
In association with a midlevel shortwave trough moving eastward from
WY/MT, a surface cold front will progress east-southeastward across
the northern/central Plains today and reach the upper MS Valley
overnight. A narrow corridor of low-level moistening is underway
ahead of the cold front (boundary-layer dewpoints of 56-60 F),
though the breadth and quality of the moisture return has been
limited by the influence of tropical cyclone Delta across the
Southeast. The modest low-level moistening is occurring beneath a
plume of steep midlevel lapse rates near 9 C/km, which is also
contributing to a strong cap. It appears that surface
heating/mixing, continued moisture advection, and focused ascent
along the front will all be necessary for thunderstorm initiation
this evening, starting around 23z near the MN/ND border and
developing southward toward eastern NE/western IA by late evening.

Strong/linear forcing for ascent along the front and storm motions
undercut by the front support rather rapid upscale growth into a
squall line, while the narrow corridor of buoyancy and cap will
limit the potential for pre-frontal storm development. The steep
midlevel lapse rates and MLCAPE of 1000-1500 J/kg will support some
potential for large hail, especially with any embedded supercells
given effective bulk shear in excess of 40 kt. Otherwise,
convection evolving quickly into a line suggests that damaging
outflow gusts will become the main threat this evening. The severe
threat will diminish gradually overnight as buoyancy diminishes and
convective inhibition increases with eastward extent.

...Carolinas this afternoon...
The remnants of tropical cyclone Delta will continue to move
east-northeastward from the southern Appalachians and weaken.
Vertical shear will remain at least marginally favorable for
supercells given lingering 30-40 kt southwesterly midlevel flow and
backed low-level winds/stronger low-level shear along a warm front
approaching the SC/NC border. The threat for a brief tornado or two
will be focused where the convection in central SC (along the
primary confluence band) moves northeastward and interacts with the
zone of somewhat stronger low-level shear along the warm front this
afternoon.

..Thompson/Squitieri.. 10/11/2020

$$
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ACUS01 KWNS 121603
SWODY1
SPC AC 121601

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1101 AM CDT Mon Oct 12 2020

Valid 121630Z - 131200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Organized severe thunderstorms are not expected through tonight.

...Great Lakes and OH Valley through this evening...
Within a largely zonal flow regime, a midlevel shortwave trough will
move eastward from the upper MS Valley to the Great Lakes/OH Valley
while gradually losing amplitude, as an upstream speed max
progresses eastward from the northern Rockies to the northern
Plains. Elevated convection is ongoing across WI in the zone of
ascent along a surface cold front and immediately downstream from
the midlevel trough, where lingering midlevel lapse rates near 8
C/km and MUCAPE of 500-1000 J/kg will support isolated, sub-severe
hail through midday. This regime will shift eastward over MI this
afternoon, though diminishing buoyancy aloft with eastward extent
suggests that the severe threat is minimal.

Farther south, low-level moisture advection in advance of the cold
front, as well as modest surface heating in cloud breaks beneath a
narrow plume of 7-8 C/km midlevel lapse rates, will support MLCAPE
of 250-500 J/kg this afternoon/evening across the OH Valley.
However, low-level flow will not be particularly strong (30 kt or
less), and the potential for strong/damaging gusts with shallow
frontal convection appears too low to warrant an outlook area.

..Thompson/Kerr.. 10/12/2020

$$
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ACUS01 KWNS 131925
SWODY1
SPC AC 131924

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0224 PM CDT Tue Oct 13 2020

Valid 132000Z - 141200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe thunderstorms are not expected across the contiguous United
States through tonight.

No major changes were made to the previous outlook. Only isolated,
general thunderstorm activity is expected along the northern tier of
states.

..Jewell.. 10/13/2020

.PREV DISCUSSION... /ISSUED 1056 AM CDT Tue Oct 13 2020/

...Synopsis...
A series of embedded shortwave troughs will move eastward across the
northern tier of the CONUS, within a zonal flow regime. The first
trough is moving over the lower Great Lakes/Appalachians as of late
morning. Warm advection in advance of this trough, in combination
with weak buoyancy (MUCAPE of 100-250 J/kg) rooted in the 850-700 mb
layer, will support some elevated convection and the potential for
isolated lightning flashes this afternoon across southeast New
England. An upstream trough approaching the upper Great Lakes could
also produce isolated lightning flashes this afternoon with very
weak buoyancy over eastern Upper MI and northern Lower MI.
Otherwise, a few low-topped thunderstorms will be possible this
morning along and west of the Cascades as an intense jet streak
approaches the WA coast. The left-exit region of this jet streak,
and associated steeper lapse rates/weak buoyancy, will spread inland
and affect northern MT and northwestern ND late in the period.

$$
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ACUS01 KWNS 141923
SWODY1
SPC AC 141921

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0221 PM CDT Wed Oct 14 2020

Valid 142000Z - 151200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM PARTS OF
EAST-CENTRAL MINNESOTA INTO NORTHWEST WISCONSIN...

...SUMMARY...
A strong/severe wind gust or two may occur this afternoon over
portions of the upper Mississippi Valley region.

No changes made to the previous outlook. A low-end/conditional
threat of a strong or severe gust remains possible with any shallow
convection that develops in association with the strong upper
vorticity maximum over the upper Mississippi Valley. Otherwise,
isolated lighting strikes are possible extending westward across the
northern High Plains, where gusty winds are ongoing.

..Jewell.. 10/14/2020

.PREV DISCUSSION... /ISSUED 1100 AM CDT Wed Oct 14 2020/

...Upper MS Valley this afternoon/evening...
A midlevel shortwave trough and associated surface cyclone over the
Dakotas will progress east-southeastward over the upper MS Valley
this afternoon/evening. This will occur within an amplifying
larger-scale trough over the north central CONUS (downstream from a
building ridge over the eastern Pacific). Cold midlevel
temperatures and steep lapse rates, in combination with daytime
heating in cloud breaks and residual boundary-layer dewpoints in the
40s, will support surface-based CAPE around 250 J/kg this afternoon
in the warm sector just south-southeast of the surface cyclone.
Surface heating/mixing and ascent within the left-exit region of the
mid-upper jet should support at least isolated thunderstorms this
afternoon. The combination of steep low-level lapse rates, 50 kt
midlevel flow and long hodographs will support some threat for
fast-moving cells capable of producing isolated strong/damaging
gusts. Gusty winds may also occur with low-topped, skeletal
convection along the trailing cold front into the northern High
Plains.

...Elsewhere...
A warm advection regime will persist into tonight across the Ozarks
in advance of a cold front moving southeastward across the central
Plains. There may be sufficient moistening for some elevated
showers late tonight in the vicinity of southwest MO, but elevated thunderstorms appear unlikely. Shallow convection is expected along
residual boundaries near the northeast FL/GA coasts and the middle
TX coast, but the threat for deep convection with lightning appears
minimal.

$$
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ACUS01 KWNS 151936
SWODY1
SPC AC 151934

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0234 PM CDT Thu Oct 15 2020

Valid 152000Z - 161200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe storms are not expected across the U.S. today.

...Discussion...

Only minor adjustments have been made to previous forecast which
still appears on track.

..Dial.. 10/15/2020

.PREV DISCUSSION... /ISSUED 1105 AM CDT Thu Oct 15 2020/

No changes have been made to the ongoing forecast. Scattered
thunderstorms will be possible later today over four areas.

1) Eastern MT into the western Dakotas this afternoon and evening,
ahead of a fast-moving shortwave trough tracking out of southern
Canada.

2) Southeast TX and southwest LA, behind a cold front surging
southward into the Gulf of Mexico.

3) South FL this afternoon where a moist but weakly sheared
environment is present.

4) Portions of The GA/SC/NC where weak low-level warm advection and
lift will aid in scattered showers and a few thunderstorms.

$$
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ACUS01 KWNS 191926
SWODY1
SPC AC 191925

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0225 PM CDT Mon Oct 19 2020

Valid 192000Z - 201200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe thunderstorms are not expected through tonight.

...Discussion...
Aside from a few minor line tweaks, no changes appear necessary to
the ongoing convective outlook.

..Goss.. 10/19/2020

.PREV DISCUSSION... /ISSUED 1045 AM CDT Mon Oct 19 2020/

A nearly stationary surface boundary extends from east TX into parts
of AR/TN/KY. Scattered showers and isolated thunderstorms have been
- and will continue to occur along and north of the front through
tonight. Abundant clouds and weak CAPE will limit updraft strength
and minimize the risk of strong/severe storms.

Scattered showers and thunderstorms will occur this afternoon over
much of the FL peninsula as a weak midlevel inverted trough affects
the area. Weak vertical shear and limited low-level convergence
should preclude organized severe storms in this area as well.

$$
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ACUS01 KWNS 201951
SWODY1
SPC AC 201949

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0249 PM CDT Tue Oct 20 2020

Valid 202000Z - 211200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe storms are not expected through tonight.

...Discussion...
Convection continues to evolve as expected across the areas
highlighted for thunder in the prior outlook. The thunder areas
over both coastal New England, and the upper Texas coast, are being
removed at this time, as it appears that potential for lightning has
diminished in these areas. Otherwise, aside from minor line
adjustments, no other changes appear necessary at this time.

..Goss.. 10/20/2020

.PREV DISCUSSION... /ISSUED 1120 AM CDT Tue Oct 20 2020/

A weak frontal zone extends from OK northeastward into the mid MS
and OH valleys. Scattered showers and occasional thunderstorms will
continue to affect this area through tonight. Other showers and
thunderstorms will affect parts of the FL peninsula, and the
immediate coastal areas of GA and the Carolinas. Finally, isolated
pockets of thunderstorms may occur today over portions of TX and
eastern MA. In all areas, weak thermodynamic parameters are
expected to preclude the risk of organized severe storms.

$$
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ACUS01 KWNS 231934
SWODY1
SPC AC 231932

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0232 PM CDT Fri Oct 23 2020

Valid 232000Z - 241200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
THE GREAT LAKES AND OHIO VALLEY...

...SUMMARY...
Threat for a few severe storms capable of damaging wind, hail and
perhaps a tornado will continue this afternoon into the early
evening over a portion of the Great Lakes and Ohio Valley.

...Discussion...
Forecast reasoning as laid out in prior outlooks remains reflective
of current convective/severe weather evolution across the outlook
area. Some minor line adjustments have been made to account for the
western edge of the outlook areas, to reflect progression of
advancing convection. Tweaks have also been made to the slight risk
area to account for counties currently within WW #501. Otherwise
however, Local severe risk will continue across the outlook area
through early evening.

..Goss.. 10/23/2020

.PREV DISCUSSION... /ISSUED 1120 AM CDT Fri Oct 23 2020/

...Great Lakes/OH Valley this afternoon/evening...
Within the northern stream, a shortwave trough will progress from
the upper MS Valley to the upper Great Lakes by this evening. An
associated surface cyclone in lower MI will gradually deepen and
move northeastward toward Lake Huron, as a trailing cold front
translates southeastward across Lower MI, the mid MS Valley, and the
southern Plains.

12z regional soundings support the possibility of both low-level
moisture advection from southwest-to-northeast toward Lower MI in
advance of the cold front, and downward mixing of moisture from
aloft with daytime heating. The net result should be boundary-layer
dewpoints increasing into the low-mid 60s in southeast Lower MI and
the upper 60s across the lower OH Valley. Some weak elevated
convection is ongoing in the warm sector across the lower OH Valley,
along the corridor of the low-level jet and where convective
inhibition is weak for parcels originating near 850 mb. Additional
warm sector convection will be possible through the day as the low
levels destabilize with heating/mixing.

The primary focus for thunderstorm development will be the zone of
ascent along and just ahead of the cold front through the afternoon.
MLCAPE is expected to range from 1000-2000 J/kg (greatest across the
lower OH Valley) in advance of the cold front, while low-midlevel
flow/shear will be stronger toward lower MI. The net result will be
an environment favoring bands of storms capable of producing
damaging winds with sufficiently strong downdrafts and momentum
transfer. A tornado cannot be ruled out with embedded rotating
storms given effective SRH close to 150 m2/s2 and effective bulk
shear near 35 kt, and marginally severe hail may also occur with
midlevel lapse rates of 7-7.5 C/km. The severe threat will diminish
by late evening across OH as the boundary layer stabilizes and the
primary shortwave trough passes farther to the north.

...East TX area through this evening...
Convection has organized as an MCS across north TX this morning with
a leading convective line and weak MCV. The downstream environment
across southeast TX appears conducive to maintaining some form of
this convection through the afternoon, with the southwest extent of
the convection limited by more substantial midlevel capping.

$$
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ACUS01 KWNS 240545
SWODY1
SPC AC 240543

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1243 AM CDT Sat Oct 24 2020

Valid 241200Z - 251200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe thunderstorms are not forecast across the contiguous U.S.
today or tonight.

...DISCUSSION...
An upper-level trough will dig southeastward into the northwestern
U.S. today, as west to southwest mid-level flow remains in place
from the Great Plains to the Eastern Seaboard. A shortwave trough
will move eastward across the Southeast. At the surface, a cold
front will move southeastward across the Mid-Atlantic, southern
Appalachians and central Gulf Coast states. Ahead of the front, weak instability is forecast today, which should result in scattered
thunderstorm development across much of the Southeast into the
Carolinas. The weak instability should keep convection below severe
limits. Elsewhere across the continental United States, thunderstorm development is not expected today or tonight.

..Broyles/Cook.. 10/24/2020

$$
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ACUS01 KWNS 251241
SWODY1
SPC AC 251240

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0740 AM CDT Sun Oct 25 2020

Valid 251300Z - 261200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Organized severe thunderstorms are not expected through tonight.

...Synopsis/Discussion...
In mid/upper levels, heights will fall across much of the central/
southern Rocky Mountains, Great Basin and Southwest through the
period, as substantial troughing now over the interior Northwest
digs southeastward and intensifies further. This will result in a
broad fetch of southwest flow aloft from AZ across the southern/
central High Plains to the upper Great Lakes. Strong cooling aloft
ahead of the western CONUS trough will steepen low/middle-level
lapse rates across the Four Corners region today into this evening,
combining with weak but sufficient low-level moisture to yield
MLCAPE in the 100-400 J/kg range. Well-mixed afternoon boundary
layers beneath strengthening midlevel currents may promote strong
gusts in a few cells, but organized severe potential appears too
minimal for an outlook.

At 11Z, the surface chart showed a wavy frontal zone, moving slowly
toward the south as a cold front across NC and quasistationary
elsewhere across northern GA, eastern AL, and the LA shelf waters of
the Gulf. Frontolysis is underway and will continue on the western
segment of this boundary over TX coastal waters and deep south TX,
while frontogenesis already drawn over the South Plains and Red
River regions also continue. The latter front will sharpen and sag
southward across the southern Plains through the period. By 12Z, a frontal-wave low may develop near ACT, with the cold front arching southwestward to westward across the southern Hill Country, Edwards
Plateau and Trans-Pecos regions. A stationary to very slow warm
front will extend from the wave over the Arklatex region. Late
overnight and northwest of the surface front, increasing elevated
moisture and isentropic lift within a strengthening warm-advection
plume will combine with frontal forcing, to increase chances for
thunderstorms embedded within an earlier-developing precip plume.

Meanwhile, a weak southern-stream perturbation now over the
Carolinas will continue to move east-northeastward and offshore from
the Tidewater area by this evening. General-thunder potential will
diminish quickly behind this trough, in a region of strong mid/upper
drying shown on moisture-channel imagery. Farther south, isolated, disorganized thunderstorms will be possible in a very moist and
weakly capped air mass, but with marginally supportive midlevel
lapse rates, across parts of southern/central FL.

..Edwards/Mosier.. 10/25/2020

$$
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ACUS01 KWNS 261244
SWODY1
SPC AC 261242

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0742 AM CDT Mon Oct 26 2020

Valid 261300Z - 271200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Organized severe thunderstorms are not expected across the U.S.
mainland today or tonight.

...Synopsis/Discussion...
The main mid/upper-level feature influencing this outlook is a
positively tilted, synoptic-scale trough -- apparent in moisture-
channel imagery from SD across southern WY and UT to southern CA.
The southwestern part of this trough -- with an embedded/closing low
currently located over UT -- will break southward through the
period, with the 500-mb low hooking south-southwest then east to
southern AZ by 27/12Z. As that occurs, the associated cyclone aloft
will deepen and become more symmetric, with strong mid/upper-level
difluence over the southern/central High Plains. Downstream, a
broad fetch of low-level warm advection and moisture transport will
combine with elevated frontal lift to support thunder potential
north of the surface front described below, and that will include
some thunder-accompanied freezing/frozen precip.

At 11Z, the surface analysis revealed a wavy frontal zone offshore
from the Carolinas and GA, extending across northern FL, then
westward over the northern Gulf to near GLS and CLL. In the latter
area, this boundary was being overtaken by an intense but slow-
moving cold front, drawn from western KY across southeastern AR and south-central TX, to the Big Bend and Trans-Pecos regions and
central NM. This front extended into a low between ABQ-GUP, then
southwestward across southern AZ to northwestern Sonora,
northeastern Baja and southwestern CA near SAN. This front will
penetrate southward well into northern MX through the period, while
moving slower across south TX and the lower Mississippi Valley.

...West-central/northwest TX to near the Red River...
Steep midlevel lapse rates above the nearly saturated elevated
frontal surface will foster MUCAPE around 1000-1500 J/kg over parts
of this region through midday, before columnar cooling in low/middle
levels reduces buoyancy. With 40-55 kt effective-shear magnitudes
evident in modified RAOBs and forecast soundings, any sustained/
discrete cells may produce small hail, and brief hail approaching
severe limits cannot be ruled out. However, the very isolated/
transient nature of this potential, with generally messy convective
modes, precludes an unconditional severe-hail outlook.

..Edwards/Mosier.. 10/26/2020

$$
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ACUS01 KWNS 272120
SWODY1
SPC AC 272118

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0418 PM CDT Tue Oct 27 2020

Valid 272000Z - 281200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe thunderstorms are not expected across the contiguous United
States through tonight.

No changes were made from the existing Day1 outlook.

..Jewell.. 10/27/2020

.PREV DISCUSSION... /ISSUED 1024 AM CDT Tue Oct 27 2020/

...West TX/OK...
A deepening upper low over southeast AZ will track slowly eastward
today into the southern High Plains. Widespread low-level warm
advection will lead to showers and isolated thunderstorms over west
TX and much of OK, with much of this precipitation atop sub-freezing
surface temperatures.

...Southeast LA to the FL Panhandle...
Tropical Storm Zeta is moving offshore and away from the Yucatan
Peninsula today. An increasingly moist and marginally unstable air
mass will spread inland tonight across the central Gulf Coast
region, with the potential for isolated thunderstorms after
midnight. The outer bands of the system are forecast to remain
primarily offshore tonight, with an increasing severe risk in parts
of this area tomorrow.

$$
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ACUS01 KWNS 281959
SWODY1
SPC AC 281958

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0258 PM CDT Wed Oct 28 2020

Valid 282000Z - 291200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THROUGH TONIGHT
FROM SOUTHEAST LA/MS TO SOUTHERN AL/WESTERN FL PANHANDLE...

...SUMMARY...
Hurricane Zeta may spawn a few tornadoes this afternoon through
tonight from extreme southeast Louisiana/Mississippi into southern
Alabama and the western Florida Panhandle.

...Southeast Louisiana...southern Alabama...Florida Panhandle...
A tornado watch has been issued until 05Z in anticipation of
increasing convection and shear associated with Hurricane Zeta.
Low-level shear will continue to increase along and east of the
center track later this afternoon and evening. MLCAPE 500-1000 J/kg
is already in place well inland, which should maximize time for
cells to attain rotation and pose a tornado threat.

..Jewell.. 10/28/2020

.PREV DISCUSSION... /ISSUED 1115 AM CDT Wed Oct 28 2020/

...Southeast LA this afternoon to AL/GA through tonight...
Hurricane Zeta is expected to make landfall late this afternoon
along the LA coast to the south of New Orleans (please see latest
NHC advisories for details). The weakening remnants of Zeta will
then accelerate northeastward through tonight across AL/GA, to the
east of a deep midlevel low over the southern Plains. An influx of
tropical moisture and associated buoyancy will continue through the
day along the north central and northeast Gulf coast as Zeta
progresses north-northeastward.

Some more cellular convection has been observed this morning over
the northern Gulf. An increase in low-midlevel flow and vertical
shear will occur as Zeta approaches the coast as the mid 70s
boundary-layer dewpoints spread inland with muted daytime heating,
which will increase the threat for supercells/tornadoes in the outer northeastern and eastern convective bands. The more favorable
phasing of buoyancy/vertical shear will occur this afternoon/evening
from extreme southeast LA into southern AL/western FL Panhandle.
Poor lapse rates near the warm core center of Zeta and diurnal
stabilization should gradually limit the threat farther inland
overnight, though strong wind profiles and marginal CAPE rooted near
the surface may still support an isolated tornado overnight into GA,
to the southeast of the center.

$$
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ACUS01 KWNS 291632
SWODY1
SPC AC 291630

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1130 AM CDT Thu Oct 29 2020

Valid 291630Z - 301200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THROUGH TONIGHT
FROM THE CAROLINAS INTO SOUTHEAST VA...

...SUMMARY...
Isolated severe convective gusts and perhaps a tornado may occur
this afternoon into tonight from the Carolinas into southeast
Virginia.

...Carolinas into southeast VA through tonight...
The remnants of tropical cyclone Zeta will move quickly
east-northeastward over VA and reach the Atlantic coast by about mid
afternoon. Strong wind profiles/shear will accompany this system
across VA until it moves offshore, but buoyancy will be quite
limited in the poor lapse rate environment with the weakening warm
core cyclone. Thus, only isolated damaging convective gusts and/or
a brief tornado may occur prior to 21z. Thereafter, the synoptic
midlevel trough over AR will progress eastward to the southern
Appalachians by tonight, and to the Mid-Atlantic coast by the end of
the period. An associated, weak surface cyclone will move eastward
along the VA/NC border, along a baroclinic zone in the wake of Zeta.
A separate round of convection is expected to form this evening
across the Piedmont in the zone of ascent near the surface cyclone
and along the cold front trailing southward. The convection will
subsequently spread east-northeastward across the Carolinas and
southeast VA overnight.

Lapse rates aloft will remain rather poor, but lingering
boundary-layer dewpoints in the low 70s will support at least weak
buoyancy rooted at the surface (SBCAPE around 500 J/kg) overnight.
Long, relatively straight hodographs with effective bulk shear in
excess of 70 kt and ground-relative winds of 50 kt within a few
thousand feet of the surface will support a threat for isolated
damaging gusts with the overnight convection.

To the south, bands of convection persist from the FL Big Bend into
southeast GA along a confluence zone trailing south-southwestward
from Zeta. Gusty outflow winds may occur with the heavier
convective cores during the next few hours given 40 kt low-level
flow in area VWPs. However, poor lapse rates will limit updraft
intensity, and relatively moist profiles suggest that strong
downdrafts are also unlikely. Given the marginal thermodynamic
profiles and some weakening of low-level flow expected this
afternoon, the threat for severe/damaging winds appears to be quite
small.

..Thompson/Moore.. 10/29/2020

$$
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ACUS01 KWNS 311238
SWODY1
SPC AC 311236

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0736 AM CDT Sat Oct 31 2020

Valid 311300Z - 011200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Isolated thunderstorms should remain confined to parts of the
southern Florida Peninsula today. Severe thunderstorms are not
expected.

...Synopsis and Discussion...
An upper trough will amplify over the central CONUS and MS Valley
through tonight, while a surface cold front also surges eastward.
Low-level moisture will likely remain insufficient to support any
thunderstorms across these regions. The only appreciable risk for
thunderstorms today appears to be confined to portions of the
southern FL Peninsula, where a weak easterly wave and modest
low-level convergence along sea breeze boundaries should be present.
Although MLCAPE may increase to 1000-1500 J/kg this afternoon across
south FL, weak shear is expected to limit thunderstorm organization.

..Gleason.. 10/31/2020

$$
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ACUS01 KWNS 011238
SWODY1
SPC AC 011237

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0637 AM CST Sun Nov 01 2020

Valid 011300Z - 021200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FAR EASTERN NC...

...SUMMARY...
A tornado and locally damaging wind risk exists across the eastern
North Carolina vicinity between about 1 to 5 PM EST.

...Eastern NC vicinity...
Scattered showers are ongoing from SC to central VA within a
low-level warm advection regime. The southern portion of this
activity should develop into thunderstorms around midday as richer
low-level moisture characterized by mid 60s surface dew points along
the SC/far southern NC coast are advected north. With surface
temperatures expected to warm into the mid 70s, MLCAPE should
briefly reach 500-1000 J/kg before convection spreads offshore by
early evening.

Low-level hodographs will become increasingly enlarged as a swath of
40-45 kt 850-mb winds shift east and overlap the confined warm
sector ahead of the leading cold front. 0-1 km SRH appears likely to
reach 150-250 m2/s2 and would be conducive to a supercell or two
capable of producing a tornado along with locally damaging winds
across mainly far eastern NC, including the Outer Banks.

...Central FL...
Isolated to scattered slow-moving thunderstorms should develop as
low-level convergence strengthens along an intensifying cold front
this afternoon and evening. Poor mid-level lapse rates yielding thin
and weak buoyancy amid little lower-level shear will be limiting
factors to an organized severe risk.

..Grams/Gleason.. 11/01/2020

$$
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ACUS01 KWNS 012000
SWODY1
SPC AC 011959

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0159 PM CST Sun Nov 01 2020

Valid 012000Z - 021200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS COASTAL
NORTH CAROLINA...

...SUMMARY...
Severe risk will gradually decrease over the next 1 to 2 hours
across far eastern North Carolina and the Outer Banks, as storms
move offshore.

...Discussion...
As storms continue moving eastward across coastal North Carolina in
conjunction with the advancing cold front, organization has been
limited -- with storms primarily oriented in quasi-linear manner.
Though limited/local risk for a stronger wind gust, or brief
tornado/waterspout is still evident, this potential will diminish
from west to east over the next couple of hours, as storms move
offshore.

Elsewhere, showers and a few embedded thunderstorms are ongoing
across the Florida Peninsula ahead of the cold front, but any severe
risk here would be isolated/minimal this afternoon.

Finally, a few lightning flashes persist over portions of
south-central Pennsylvania, the adjacent Maryland/West Virginia
Panhandles. However, as convection crosses the ridges, downsloping
suggests that lingering lightning should further diminish with time.
As such, a thunder area will not be introduced for this region.

..Goss.. 11/01/2020

.PREV DISCUSSION... /ISSUED 1032 AM CST Sun Nov 01 2020/

...Eastern North Carolina/coastal southeast Virginia...
Large-scale trough amplification will continue to occur today into
tonight over the Great Lakes/Ohio Valley toward the Eastern
Seaboard. Low-level moisture characterized by low/mid 60s F surface
dewpoints continues to increase/stream northward across coastal
North Carolina ahead of increasingly organized convection near/ahead
of a wind shift and sharpening front.

Short-term anticipations are that a low-topped quasi-linear
convective line (much of it with little or no lightning flashes)
will continue to evolve early this afternoon across
east-central/northeast North Carolina into coastal southeast
Virginia, with the possibility that semi-discrete thunderstorms will
precede this band across the immediate coast of North Carolina
(within 50-70 miles of the Atlantic). MLCAPE may briefly reach
500-1000 J/kg before convection spreads offshore by early evening.

Low-level hodographs will become increasingly enlarged as a swath of
40-45 kt 850-mb winds shift east and overlap the confined warm
sector ahead of the leading cold front. Locally damaging
convectively enhanced winds will be a concern with the linearly
organized convection or the convection preceding it. Given that 0-1
km SRH appears likely to reach 150-250 m2/s2, a supercell or two
capable of producing a tornado will also be possible mainly across
far eastern North Carolina including the Outer Banks.

...Central Florida...
Slow-moving thunderstorms are occurring late this morning about 50
miles west of the west-central Florida coast, with other showers/few thunderstorms also occurring near the east-central Florida coast.
Modest destabilization will support development across/into other
parts of the interior. While gusty thunderstorm winds may occur,
poor mid-level lapse rates and minimal deep-layer/low-level shear
will likely preclude an organized severe risk.

$$
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ACUS01 KWNS 021621
SWODY1
SPC AC 021620

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1020 AM CST Mon Nov 02 2020

Valid 021630Z - 031200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe thunderstorms are not expected.

...NV/AZ/UT...
Relatively dry and stable conditions will prevail over most of the
US today, except a small part of the southwest states. A weak upper
low is currently over central CA, with a zone of mid-level lift and
cooler temperatures aloft affecting portions of southern NV,
northwest AZ, and vicinity. This will likely be sufficient for
pockets of showers and isolated thunderstorms through this evening.
No severe storms are expected.

..Hart.. 11/02/2020

$$
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ACUS01 KWNS 031248
SWODY1
SPC AC 031246

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0646 AM CST Tue Nov 03 2020

Valid 031300Z - 041200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Isolated thunderstorms may occur today across parts of northern
Arizona, eastern Nevada, and Utah. Severe thunderstorms are not
expected.

...Synopsis and Discussion...
As a weak upper trough/low migrates slowly eastward from CA across
the Great Basin today, isolated thunderstorms may occur across parts
of the southern Great Basin. Limited moisture and weak instability
should preclude organized severe thunderstorm potential across this
area. Thunderstorms are not forecast across the remainder of the
CONUS, as dry and/or stable conditions should prevail.

..Gleason.. 11/03/2020

$$
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ACUS01 KWNS 031932
SWODY1
SPC AC 031930

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0130 PM CST Tue Nov 03 2020

Valid 032000Z - 041200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Isolated thunderstorms may occur today across parts of Arizona,
eastern Nevada, and Utah. Severe thunderstorms are not expected.

...20Z Update...
Very minor adjustments were made the thunder line across AZ based on
the location of the shortwave trough and current lightning trends.
Otherwise, previous forecast discussion (appended below) remains
valid with no change in forecast reasoning.

..Mosier.. 11/03/2020

.PREV DISCUSSION... /ISSUED 1025 AM CST Tue Nov 03 2020/

Scattered showers and thunderstorms are expected to affect portions
of the desert southwest today, in vicinity of a weak upper low
moving across the area. Cool temperatures aloft and sufficient
mid-level moisture will promote convection, but weak shear and
limited CAPE will preclude organized severe storms.

Otherwise, no thunderstorms are anticipated across the CONUS today.

$$
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ACUS01 KWNS 041625
SWODY1
SPC AC 041623

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1023 AM CST Wed Nov 04 2020

Valid 041630Z - 051200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Isolated general thunderstorms are possible late tonight and early
Thursday morning across parts of south Florida.

...Synopsis/Discussion...
A progressive/low-amplitude large-scale pattern and a general
absence of appreciable low-level moisture will result in minimal
thunderstorm potential through tonight. Across southern Florida,
gradual low-level moistening via easterly flow will allow for the
development of weak buoyancy tonight. Convection could become deep
enough for isolated thunderstorms late tonight into the early
morning hours of Thursday in vicinity of the Florida Straits/far
southern Florida. Elsewhere, low-topped convection will likely
accompany an inland-moving front tonight in coastal Washington. It
currently appears that thermodynamic profiles will not be conducive
for charge separation and lightning flashes.

..Guyer.. 11/04/2020

$$
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ACUS01 KWNS 051943
SWODY1
SPC AC 051941

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0141 PM CST Thu Nov 05 2020

Valid 052000Z - 061200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe thunderstorms are not expected across the contiguous U.S.
through tonight.

...Discussion...
No changes appear to be necessary to the ongoing convective outlook.

..Goss.. 11/05/2020

.PREV DISCUSSION... /ISSUED 1030 AM CST Thu Nov 05 2020/

...Synopsis/Discussion...
Thunderstorm potential through tonight will be relegated to two
general areas. Across southern Florida and near the eastern Florida
coast, gradual moistening will continue to occur with diurnal
heating and moderate buoyancy (albeit weak mid-level lapse rates)
contributing to thunderstorm potential. In the West, an upper trough
will dig southeastward and approach coastal portions of
Oregon/northern California tonight. As a frontal band approaches and
moves inland, thermodynamic profiles will trend more favorable late
tonight (09-12Z) for the possibility of low-topped convection
capable of lightning.

$$
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ACUS01 KWNS 061937
SWODY1
SPC AC 061935

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0135 PM CST Fri Nov 06 2020

Valid 062000Z - 071200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe thunderstorms are not expected across the U.S. mainland.

...Discussion...
With convection evolving as anticipated, no substantive changes to
the outlook appear necessary at this time.

..Goss.. 11/06/2020

.PREV DISCUSSION... /ISSUED 1009 AM CST Fri Nov 06 2020/

No changes have been made to the ongoing thunderstorm forecast.
Scattered showers and very isolated thunderstorms are occurring
today off the Atlantic coast of SC/GA/FL. A few of these storms may
affect the immediate coastline, or parts of south FL, this afternoon
and evening. However, confidence is low that storms can spread very
far inland. Other thunderstorms over the central Gulf of Mexico may
spread slightly inland this afternoon and evening over parts of
southern LA. Finally, isolated lightning strikes may occur along the
coast and over the coastal ranges of central CA later today. In all
areas, weak CAPE and limited shear profiles are expected to preclude
severe storms.

$$
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ACUS01 KWNS 071236
SWODY1
SPC AC 071235

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0635 AM CST Sat Nov 07 2020

Valid 071300Z - 081200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
EASTERN ARIZONA AND WESTERN NEW MEXICO...

...SUMMARY...
Strong to isolated severe wind gusts may accompany thunderstorms
across parts of eastern Arizona and western New Mexico later this
afternoon and early evening.

...Synopsis...
In mid/upper levels, a high-amplitude pattern is expected through
this period, anchored by longwave troughing over the western CONUS.
Within the associated cyclonic flow, a complex synoptic to shortwave
evolution is expected. A strong synoptic cyclone -- now centered
over northern CA -- is forecast to pivot eastward over the Sierra
today, reaching northern NV, then weakening overnight. The
associated/basal shortwave trough will split eastward over southern
CA to central AZ by 06Z. This perturbation then should eject
rapidly northeastward over the Four Corners to central CO by 12Z,
while weakening rapidly. Meanwhile, a strong trough -- now evident
in moisture-channel imagery over central/southern BC -- will dig
southward across the Pacific Northwest as a closed low. This
feature will become the main anchoring synoptic cyclone, centered
over southeastern OR by the end of the period, with associated
cyclonic flow covering most of the West and Great Plains.

Elsewhere, a broad area of negatively tilted troughing, with several
embedded vorticity maxima, will persist from the Arklatex across the central/southeastern Gulf, influencing both general thunderstorm
potential in parts of the Southeast and the winding path predicted
for what now is T.D. Eta. Supercell/tornado-favorable wind fields
related to Eta, juxtaposed with favorable convection, are not
forecast to expand into south FL and the Keys until day 2. Refer to
NHC advisories for latest tropical watch/warning info and track/
intensity forecasts for Eta.

...Southwest CONUS...
A loosely organized belt of somewhat low-topped convection, with
isolated to widely scattered embedded thunderstorms, is forecast to
develop mid/late afternoon over southeastern AZ, extending northward
over higher altitudes north of the Mogollon Rim as it shifts
eastward over the outlook area. The main concern will be strong to
isolated severe gusts.

A combination of gradual diurnal/diabatic heating and low-level warm
advection ahead of the basal shortwave trough will contribute to
destabilizing the boundary layer throughout the day. Moisture
remains rather scant across much of the outlook area; however,
available surface obs to the south in MX, as well as GPS PW data,
indicate at least marginally favorable moisture will advect across
the region as well, ahead of a cold front now located across
southeastern portions of NV/CA. Relatively maximized low-level
convergence along/ahead of the front, impinging upon the moistening/ destabilizing layer, should compel convective development by mid-
late afternoon. Pockets of 100-400 J/kg MLCAPE are possible in and
near the outlook area.

Strengthening deep-layer winds -- aligned just to the right of the
frontal zone -- will boost speed/bulk shear steadily through the
day. Time series of forecast soundings and isotach cross sections
show intense mid/upper winds lowering to just a few km AGL before
frontal passage. This supports the potential for evaporationally
aided downdrafts to convey momentum from those faster-flow areas
through a well-mixed layer to the surface, in a few locales.

Though minimal, surface-based buoyancy above an inverted-v boundary-
layer thermodynamic profile may develop as far north as the Four
Corners region late this afternoon into evening, in a brief time
window before nocturnal surface cooling at those relatively high
altitudes remove the SBCAPE. The wind potential there, while
nonzero, still appears too conditional and short-lived to place in a categorical outlook. The threat also will diminish with eastward
extent into central NM for similar reasons.

..Edwards/Kerr.. 11/07/2020

$$
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ACUS01 KWNS 071931
SWODY1
SPC AC 071930

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0130 PM CST Sat Nov 07 2020

Valid 072000Z - 081200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS EASTERN
ARIZONA AND WESTERN NEW MEXICO...

...SUMMARY...
Strong wind gusts may accompany thunderstorms across parts of
eastern Arizona and western New Mexico late this afternoon and early
evening.

...20Z Update...
No changes appear warranted in this Outlook update cycle. Additional
heating this afternoon in conjunction with a strong wind field and
the arrival of stronger forcing for ascent should lead to an
increase in thunderstorms across eastern Arizona/western New Mexico,
some of which may produce strong/locally severe-caliber winds.

..Guyer.. 11/07/2020

.PREV DISCUSSION... /ISSUED 1025 AM CST Sat Nov 07 2020/

...AZ/NM...
A large upper low over central CA will track slowly eastward today,
with lift and mid-level moisture spreading across much of the Great
Basin and Four Corners area. A few pockets of thunderstorms will
affect this general area later today, with one area of likely
convective development across eastern AZ. Vertical mixing and
northward advection of moisture is expected to result in pockets of
afternoon surface dewpoints in the upper 40s to lower 50s. While
clouds are persisting in parts of the region, a few pockets of
heating will yield max CAPE values around 500 J/kg. This, combined
with relatively fast flow aloft, could result in gusty winds in the
strongest cores. The threat should diminish a few hours after
sunset.

...Southern CA...
A potent shortwave trough is rotating inland toward the LA Basin
today. This is expected to result in a few thunderstorms -
primarily along the mountain ranges north of LA. Cold temperatures
aloft could result in small hail in the stronger cells, but
organized severe storms are not anticipated.

$$
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ACUS01 KWNS 081243
SWODY1
SPC AC 081242

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0642 AM CST Sun Nov 08 2020

Valid 081300Z - 091200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER THE
SOUTHERN FLORIDA PENINSULA AND KEYS...

...SUMMARY...
A tornado threat may develop from late this afternoon through
tonight across south Florida and the Keys, as Tropical Storm Eta
approaches.

...Synopsis...
A high-amplitude mid/upper-level pattern will exist over the CONUS
through the period, anchored by a big, complex, cold-core cyclone
over the West, and an anticyclone moving slowly east-southeastward
over/off the Mid-Atlantic region. To the south and southwest of the anticyclone, an elongated, quasistationary mid/upper trough and
cyclonic-shear zone is evident in moisture-channel imagery from the
Arklatex across the central Gulf to near Tropical Storm Eta. The
Gulf/Arklatex part of this perturbation will weaken through the
period, as the eastern part merges with Eta. The resultant combined
cyclone will become the dominant vorticity component of the trough,
effectively forming the southern, cut-off member of a Rex-like
pattern configuration, in tandem with the synoptic anticyclone to
the north-northeast.

At the surface, 11Z analysis showed a pronounced cyclone over the
SD/MT/WY border area, with cold front south-southwestward across
east-central CO, central NM, and northwestern MX. The cyclone
should move northeastward across Lake Manitoba late tonight, as the
front proceeds eastward across the High Plains and portions of the
Upper Midwest. By 12Z, the front should extend near a line from INL-ONL-GLD-TCC-ELP, generally moving slower with southward extent.
A dryline now developing over western portions of NE/KS/TX will
sharpen gradually, but also, will be overtaken in the central High
Plains by that cold front. General thunderstorms are possible late
in the period near the front, in the outlined area, but with
inadequate moisture/instability for an organized severe threat.

...Eta: South FL, Keys...
Increasingly influenced by (and part of) the aforementioned mid/
upper perturbation, T.S. Eta is forecast by NHC to exit central Cuba
later this morning and turn northwestward to westward over the
Straits and Keys of FL through the period. As it does so, this
cyclone is forecast to spread a strengthening low-level wind field
(in space and time) across south FL and the Keys, with enlarging
low-level hodographs. Under current NHC progs, the most-favored
sector of the vortex, north through northeast of center, will shift
from east-west across the outlook area this evening and overnight,
apace with the westward component of Eta's translation vector.
Hodographs will enlarge and become more-favorably oriented during
that process. Still, concerns about low-level instability and
convective character -- especially with a good deal of dry air aloft
being entrained into the blended system per moisture-channel imagery
-- preclude more than a marginal unconditional probability of
tornadoes at this juncture.

Refer to the latest NHC advisories and maps for tropical-related watches/warnings, as well as track/intensity forecasts for Eta.

..Edwards/Kerr.. 11/08/2020

$$
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ACUS01 KWNS 081959
SWODY1
SPC AC 081958

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0158 PM CST Sun Nov 08 2020

Valid 082000Z - 091200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS SOUTHERN FLORIDA/FLORIDA KEYS...

...SUMMARY...
A tornado threat is expected from late this afternoon through
tonight and early Monday across south Florida and the Keys as
Tropical Storm Eta approaches.

...20Z Update...
Have upgraded portions of near-coastal southern Florida and the
Upper Florida Keys for what is anticipated to be an increasing
tornado risk this evening into the overnight and early morning hours
of Monday. While 18Z observed soundings from Miami and Key West were
not indicative of overly strong low-level SRH (50-150 m2/s2),
low-level winds are expected to steadily strengthen through late
afternoon into tonight as Eta approaches and potentially further
strengthens.

..Guyer.. 11/08/2020

.PREV DISCUSSION... /ISSUED 1026 AM CST Sun Nov 08 2020/

...South FL...
TS Eta is moving slowly northwestward toward the FL Straits.
Radar/satellite imagery show an area of heavier precipitation on the
north side of the center. This area is forecast by most CAM
solutions to approach the coast of southeast FL and the upper Keys
after dark. Current observations and forecast solutions suggest
that this activity will not be particularly organized, with
relatively weak UH tracks/convective elements noted. Nevertheless,
low-level shear will maximize during this period, which appears to
be of greatest concern for a tornado or two this forecast period.
The main time of concern will be roughly from 00-06z. Based on
current guidance, will maintain MRGL risk, but will continue to
monitor observational/model trends.

$$
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ACUS01 KWNS 091250
SWODY1
SPC AC 091249

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0649 AM CST Mon Nov 09 2020

Valid 091300Z - 101200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
SOUTH FLORIDA AND THE KEYS...AND OVER PORTIONS OF THE
CENTRAL/SOUTHERN PLAINS...

...SUMMARY...
A tornado or two may occur today over parts of south Florida or the
Keys on the back side of Tropical Storm Eta. Marginally severe hail
or gusts cannot be ruled out tonight over portions of the
south-central Plains.

...Synopsis...
In mid/upper levels, a longwave trough will persist over the western
CONUS, but with some important synoptic to subsynoptic developments.
A currently upstream trough over the Gulf of AK and southern AK
will dig southeastward to BC and the Pacific Northwest by the end of
the period. As that occurs, the broad, marginally closed cyclone
now over the Great Basin will eject east-northeastward across the
central Rockies to the adjoining High Plains. By 12Z tomorrow, the
associated 500-mb low should be located over the northwestern KS/
southwestern NE area, with trough south-southwestward over
southeastern NM. Elsewhere, a broad mid/upper cyclone over the
southeastern Gulf, southern FL, the northwestern Caribbean, and
central/western Cuba, has enveloped the circulation of T.S. Eta,
which should become the dominant midlevel vorticity max for the
broader cyclone.

At the surface, 11Z analysis showed a cold front across portions of northeastern/central MN to a weak low in the ONL/YKN area, then
southwestward to another low near LHX. The Arctic frontal branch
extended from there northwestward over northwestern CO to the
northern Rockies, while a Pacific front extended from the southern
low south-southwestward over south-central NM. A dryline was drawn
from the southern low southward close to the eastern NM/TX line,
then across the Big Bend area of TX. By 00Z, the combined cold
front should extend from the western Lake Superior/MN Arrowhead
region to western IA, central KS, through a low over the
southwestern KS/southeastern CO area, then south-southwestward over
far west TX. The front will overtake the dryline generally from
north-south this evening and overnight. By 12Z, the front should
reach eastern Lower MI, southwestern WI, to a weak low over
northwestern MO, then across eastern KS to west-central TX and
northern Coahuila.

...South FL/Keys...
T.S. Eta is forecast by NHC to take a broadly cyclonically curving
and generally southwestward track through the period, around the
broader cyclone noted above. The T.S. should shift toward a
position over the southeastern Gulf that will effectively render it
a meandering, cutoff low amidst weak steering flow on days 2-3. See
latest NHC advisories for tropical watch/warning info and specific track/intensity guidance.

Forecast wind radii and existing/progged convective structure
indicate that Eta will remain asymmetric this period with convective
bands well east and northeast of center, across the outlook area.
Weak lapse rates and marginal instability -- as sampled by available central/southern FL RAOBs since 06Z -- are expected to continue, but
with typically rich near-surface moisture for a tropical cyclone,
and sufficient SRH (especially for any rightward/deviant motions of
sustained, deeper cells) to support a threat for a brief tornado or
two. Outer/peripheral convection associated with Eta may continue
to affect parts of this area well into tonight. However, as the
system pulls away westward, low-level flow, boundary-layer shear,
and hodograph size each will decline gradually with time over land,
likewise ramping down the already marginal supercellular tornado
potential.

...Central/southern Plains...
Isolated to scattered thunderstorms are expected to develop this
evening and especially overnight across western parts of the outlook
area, near the front and dryline, with greater convective coverage
likely over the more-strongly frontally forced KS portion. Activity
should spread eastward and northeastward across the remainder of the
area overnight, with the most intense cells offering a threat for
marginally severe hail and or gusts.

Strengthening deep-layer shear and lift with time will be the most
favorable factors, while instability remains modest. Time series of
forecast soundings suggest steep low/middle-level lapse rates above
a nocturnally stabilizing airmass near the surface, with increasing
moisture in and just atop the boundary layer. This will support
500-800 J/kg MUCAPE, locally/briefly reaching near 1000 J/kg, amidst
40-50 kt effective-shear vectors. The most favorable juxtaposition
of CAPE-shear parameter space and greatest coverage probabilities
appears to be over parts of central/south-central KS this evening.
Large-scale ascent should decrease southward across OK into greater
moisture, as will frontal forcing, while forecast soundings show a
warm nose or "CAPE robber" around 500 mb. This leads to questions
over coverage, but with the potential for isolated strong-severe
convection as far south as west-central OK.

..Edwards/Kerr.. 11/09/2020

$$
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ACUS01 KWNS 101949
SWODY1
SPC AC 101948

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0148 PM CST Tue Nov 10 2020

Valid 102000Z - 111200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE MID MS VALLEY/UPPER MIDWEST...

...SUMMARY...
Thunderstorms capable of producing damaging to severe winds and a
few tornadoes will remain possible this afternoon and evening from
parts of Missouri northeastward into portions of far eastern Iowa,
Illinois, and Wisconsin.

...20Z Update...
A QLCS will continue moving northeastward across IL and into
southern WI this afternoon and evening in tandem with a progressive
shortwave trough over the Upper Midwest. Damaging winds will remain
a concern given the linear mode and strength of the low/mid-level
flow per area VWPs. There is also some potential for a few tornadoes
with embedded circulations within the line, particularly in close
proximity to a deepening surface low that will develop from far
eastern IA into WI through this evening. For more information on the
near-term severe threat across this area, see Mesoscale Discussion
1780.

..Gleason.. 11/10/2020

.PREV DISCUSSION... /ISSUED 1015 AM CST Tue Nov 10 2020/

...Mid MS Valley...
Water vapor loop shows a strong shortwave trough and associated
mid-level speed max rotating across the central Plains into MO/IA.
This feature will result in strong surface cyclogenesis as a surface
low deepens along a cold front extending from northern MO into WI.
The corridor along and just east of the low/front will be the area
of concern for strong/severe thunderstorms today.

Thunderstorms are ongoing this morning along the front over MO.
Convection is expected to intensify and build northward toward the
surface low by early afternoon. CAM solutions indicate that the
bowing convective structures will not be substantially undercut by
the front, suggesting the activity will remain primarily
surface-based. This supports a risk of damaging wind gusts in the
stronger cores. Forecast soundings show strengthening low-level
shear across the threat area through the afternoon as the deepening
low helps to back/enhance near-surface winds. This could promote
the development of a few semi-discrete supercells along the line,
posing a risk of a few tornadoes.

The activity will track northeastward across Lake MI this evening
and eventually into northern Lower MI. Thermodynamic parameters
will be rather weak over this area, but there is some potential for
a lingering risk of locally strong/damaging wind gusts.

...FL...
Relatively strong deep southeasterly flow is present today across
the FL peninsula. A moist and moderately unstable air mass is also
in place across the region, with broken sunshine this afternoon
helping to steepen low-level lapse rates. Local VAD profiles show
25-35 knot winds in the 0-3km layer. Most CAM solutions show
relatively fast-moving thunderstorms affecting the region, posing a
risk of locally gusty/damaging wind gusts.

$$
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ACUS01 KWNS 111939
SWODY1
SPC AC 111938

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0138 PM CST Wed Nov 11 2020

Valid 112000Z - 121200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER WESTERN
PORTIONS OF THE FLORIDA PENINSULA...

...SUMMARY...
A few tornadoes are possible across parts of Florida mainly
northeast through southeast of the center of Hurricane Eta.

...20Z Update...

...FL...
As discussed in recently issued MCD 1971, convection within one of
the outer bands of Hurricane Eta has undergone some strengthening,
primarily from the western FL Keys northeastward into the
southwestern portion of the FL Peninsula. Lightning data confirms
this strengthening, with the cells about 20-30 miles north-northwest
of MTH show appreciable lightning density. Temperatures have warmed
into the low/mid 80s and mesoanalysis indicates about 1000-1500 J/kg
of MLCAPE. However, contrasting these thermodynamic improvements are
the weakening kinematic fields. The 18Z sounding from MFL indicates
0-1 km storm-relative helicity around 170 m2/s2, down from 220+
m2/s2 on the 12Z sounding. Even so, this parameter space remains
adequate for a few stronger storms capable of producing locally
strong wind gusts and perhaps a brief tornado or two. The 2% tornado
risk was expanded eastward to account for this band of storms. A 5%
wind area was also added to portions of central/south FL.

...NC/VA...
No changes needed to this portion of the outlook. Damaging wind
gusts still appear possible within any of the stronger cells.

..Mosier.. 11/11/2020

.PREV DISCUSSION... /ISSUED 1022 AM CST Wed Nov 11 2020/

...FL...
Hurricane Eta is moving slowly northward across the eastern Gulf of
Mexico, with outer bands affecting the western coast of the FL
Peninsula. A few of the convective elements in these bands have
shown indications of weak low-level rotation. Local VAD profiles
and forecast soundings show ample low-level shear for a risk of a
few spin-ups this afternoon. However, CAM solutions suggest that
coverage of more discrete cells will be sparse. Nevertheless, will
maintain the ongoing forecast with no changes.

...NC/VA...
Water vapor imagery shows a subtle shortwave trough over middle
TN/northern AL moving across the southern Appalachians. This
feature will begin to affect parts of VA/NC later this afternoon
with slightly strengthening low/mid level winds and vertical shear.
Scattered thunderstorms are expected to affect this region through
the day, with the increasing shear likely resulting in a few weakly
rotating storms. Forecast hodographs are not particularly favorable
for tornadoes, but one or two of the storms could become
sufficiently organized to produce locally gusty/damaging winds.

$$
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ACUS01 KWNS 121622
SWODY1
SPC AC 121621

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1021 AM CST Thu Nov 12 2020

Valid 121630Z - 131200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
THE EASTERN CAROLINAS...

...SUMMARY...
A few strong to severe storms are possible this afternoon across the
eastern Carolinas.

...NC/SC...
The remnants of Eta are tracking northeastward over southeast GA.
Ahead of this system, widespread showers and occasional
thunderstorms are affecting the Carolinas in advance of an
approaching upper trough. Recent radar/observational trends show a
surface cold front surging southward across NC. This feature is
effectively narrowing the corridor of any risk of strong/severe
storms to the coastal counties. Even here, widespread clouds will
limit destabilization and minimize the risk. Nevertheless, vertical
shear profiles are sufficiently strong to pose some risk of
gusty/damaging wind gusts or a brief tornado if storm-scale rotation
can become established. The primary threat should end by late
afternoon as the surging cold front moves offshore.

..Hart/Cook.. 11/12/2020

$$
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ACUS01 KWNS 131945
SWODY1
SPC AC 131943

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0143 PM CST Fri Nov 13 2020

Valid 132000Z - 141200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe thunderstorms are not expected through tonight.

...20Z Update...
The overall forecast remains on track with no changes needed.

..Mosier.. 11/13/2020

.PREV DISCUSSION... /ISSUED 1029 AM CST Fri Nov 13 2020/

...Southern Plains through Middle Mississippi Valley...

The atmosphere will destabilize in the 850-400 mb layer tonight from
a portion of the southern Plains into MO due to modest positive
theta-e advection accompanying a strengthening southerly low-level
jet. Forcing for ascent will increase in association with the
low-level jet and an approaching low-amplitude shortwave trough,
contributing the development of thunderstorms from northwest TX into
MO later tonight. Activity will remain elevated above a stable
surface layer with no severe weather expected.

...Western States...

Isolated thunderstorms are expected today from the Pacific NW and
the northern Rockies as steeper lapse rates and strong forcing for
ascent spread inland in association with a progressive shortwave
trough and its attendant upper jet.

$$
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ACUS01 KWNS 141257
SWODY1
SPC AC 141256

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0656 AM CST Sat Nov 14 2020

Valid 141300Z - 151200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE OZARKS
REGION INTO PARTS OF THE MID-SOUTH...

...SUMMARY...
Thunderstorms will offer damaging to severe gusts and the threat of
a few tornadoes, this afternoon into tonight, from the Ozarks region
into parts of the Mid-South.

...Synopsis...
On the large scale, broadly cyclonic mid/upper-level flow over the
western CONUS transitions downstream to zonal in the East. With
time today, the contributing series of numerous vorticity maxima and
embedded shortwave troughs -- now evident in moisture-channel
imagery across the Rockies, Great Basin and High Plains -- will
phase better. The result will be a sharpening synoptic trough,
moving eastward over much of the Great Plains by 00Z. By 12Z
tomorrow, this trough should extend from most of the length of MB
across the eastern Dakotas and eastern NE, to eastern OK and east
TX.

At the surface, 11Z analysis showed a marine warm front over the
northern Gulf and northwestward into north-central TX, and a
developing synoptic warm front across parts of central/southwestern
NE, northwestern to southeastern KS, and the western Ozarks. The
northern boundary will become better-defined with time today as
precip shifts off to its northeast, and as increasingly modified
Gulf trajectories moving through the frontolytic marine boundary
approach the region. Meanwhile, cold frontogenesis over the central Rockies/High Plains will advance eastward across the central Plains
today.

The warm front will move northeastward across parts of MO and the
lower Ohio Valley from this evening through overnight. A
frontal-wave low should develop from midday into the afternoon, near
or just north of the warm-front/cold-front triple-point over the
central Plains. The deepening low should eject northeastward over
IA around 00Z, with cold front trailing across northwestern MO, northern/western OK, and the TX Panhandle. By 12Z, the center of a well-developed synoptic surface cyclone should reach central Upper
MI, with occluded/cold front arching equatorward through lower MI,
IN, western/mid TN, central parts of MS/LA, and south-central TX.

...Ozarks and vicinity to Mid-South...
Multiple rounds of convection will cross the outlook area through
the period, with the morning activity generally nonsevere and in an
elevated, warm-advection regime. Small hail cannot be ruled out.
One or two bands of thunderstorms are expected to develop along and
ahead of the cold front this afternoon through evening over western/
central parts of the outlook area and shift eastward, with damaging
gusts, isolated marginally severe hail, and the potential for a few
tornadoes. More-isolated convection forming in the warm sector,
from the Ozarks southward to southern AR, also may become
surface-based before outrunning the destabilization plume.

This pattern will present the classic cool-season tradeoff between
stronger deep-layer flow and low-level shear to the north, and
greater moisture/instability but weakening large-scale lift to the
south. By afternoon, cooling midlevel temperatures should begin
over western parts of the "slight" and "marginal" areas as the
mid/upper trough amplifies and approaches, preceded by related DCVA
and strengthening deep shear. This process will spread eastward
into tonight above and just ahead of the cold front. Forecast
soundings in the north part of the surface-based buoyancy across MO
(see below) contain very large hodographs (effective SRH at least
briefly exceeding 500 J/kg) amidst 55-65-kt effective-shear
magnitudes. This supports supercell and QLCS_embedded vortices each
capable of producing tornadoes, as well as severe gusts. LEWP/bow configurations also will contribute to the wind threat.

Meanwhile, the warm-sector boundary layer should destabilize from southwest-northeast behind morning clouds/convection from
southwest-northeast over eastern OK AR and the Ozarks, from a
combination of diurnal heating and theta-e advection. A
northward-narrowing corridor of upper 50s to 60s F surface dew
points will support a similarly narrowing plume of 500-1000 J/kg
MLCAPE. Albeit briefly (before being overtaken by the front),
surface-based effective-inflow parcels may extend as far northeast
as central and southeastern MO this evening, and as far east tonight
as near the Mississippi River vicinity in the Mid-South tonight.
Given the strength of the wind fields before convection runs out of
supportive instability late in the period, the 5% and 15% wind areas
each have been expanded somewhat southeastward over more of the
Mid-South. Concerns over initiation timing and sparse convective
coverage, and fast northeastward translation of any cells forming in
the area before they can mature to severe levels, support a modest
eastward nudge to severe probabilities in eastern OK.

..Edwards/Leitman.. 11/14/2020

$$
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ACUS01 KWNS 141959
SWODY1
SPC AC 141958

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0158 PM CST Sat Nov 14 2020

Valid 142000Z - 151200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
MISSOURI AND ARKANSAS...

...SUMMARY...
Thunderstorms may produce damaging winds and the threat of a few
tornadoes this evening into tonight over parts of Missouri and
Arkansas.

...20Z Update...
The only appreciable change to the ongoing forecast has been to
expand the Marginal/Slight risk areas a little westward in
central/western MO based on latest observational and short-term
guidance trends. It still appears likely that surface-based
convective initiation along/ahead of a cold front across this area
will occur after 00Z this evening. Both damaging wind gusts and a
few tornadoes may occur with these initially semi-discrete storms,
before transitioning to more of an isolated strong/gusty wind threat
as storms congeal into one or more bowing line segments with
eastward extent later in the evening/overnight.

..Gleason.. 11/14/2020

.PREV DISCUSSION... /ISSUED 1017 AM CST Sat Nov 14 2020/

...MO/AR...
Latest water vapor loop shows an amplifying upper trough over the
central Rockies. This system will intensify and move into the
Plains this evening - and into the mid MS Valley overnight. At the
surface, a cold front will extend from central IA/MO into northeast
OK by evening. This boundary will provide the focus for
thunderstorm development.

Present indications are that thunderstorms will begin to form -
mainly after dark - from southeast IA into central MO and northwest
AR. Moisture/instability will be very limited in the northern parts
of the risk area, limiting a more robust severe event. However from
central MO southward into northwest AR, forecast soundings suggest
dewpoints approaching 60F and moderately steep mid-level lapse
rates. This should yield sufficient CAPE for a few vigorous
updrafts with supercells possible for a few hours. Very strong
vertical shear would suggest a risk of all hazards in these
fast-moving storms, including a few tornadoes. Storms will likely
organize into bowing segments tonight and move into a progressively
more stable air mass. Nevertheless, the potential for locally
damaging wind gusts could be maintained as far east as southern IL
and western KY/TN.

$$
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ACUS01 KWNS 151631
SWODY1
SPC AC 151629

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1029 AM CST Sun Nov 15 2020

Valid 151630Z - 161200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS PARTS OF OH AND
THE NORTHEAST/MID-ATLANTIC STATES...

...SUMMARY...
Strong to severe wind gusts will remain possible with low-topped
showers and thunderstorms from the Lower Great Lakes to the
Northeast and Mid-Atlantic States through early tonight.

...Lower Great Lakes to Mid-Atlantic/Northeast...
Scattered thunderstorms are ongoing across southeast Lower MI into
western OH with a history of widespread strong to isolated severe
wind gusts. This initial activity may struggle to further intensify
owing to boundary-layer dew points in the lower 50s within a narrow
spatial corridor ahead of this convection. It should eventually
outpace this narrow wedge of surface-based instability as it spreads
east/north of Lake Erie later this afternoon.

A more pronounced squall line is expected to develop around 21-23Z
from central NY to central VA and sweep east-northeast across the
Northeast and New England coast through early tonight within an
intense shear/minimally buoyant environment. This squall should
develop as the robust cold front impinges on low-level moisture
advecting north from the Carolinas/South Atlantic Coast. Between
00-03Z, mid 50s boundary-layer dew points should reach as far north
as eastern PA into southern New England along the track of secondary cyclogenesis. While low-level lapse rates will probably remain
weaker relative to the Lower Great Lakes region, the comparatively
richer low-level moisture should compensate. It is plausible that
lightning generation may be confined to areas farther north amid
scant elevated buoyancy and greater large-scale ascent.
Nevertheless, the presence of a low-topped squall line amid 50-60 kt
925-mb winds suggest strong to severe wind gusts are possible even
in the absence of lightning. As such, this region has been upgraded
to Slight Risk.

..Grams/Dean.. 11/15/2020

$$
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ACUS01 KWNS 161941
SWODY1
SPC AC 161940

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0140 PM CST Mon Nov 16 2020

Valid 162000Z - 171200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe thunderstorms are not expected across the contiguous U.S.
through tonight.

...20Z Outlook Update...

...Pacific Northwest...
Convection associated with weak CAPE is evident within a warm
frontal precipitation band overspreading the region. The southern
edge of the heavier precipitation (west of the Cascades) is
currently near the Columbia River and forecast to shift north of the
Puget Sound vicinity by around 03-05Z, with substantive lower/mid
tropospheric drying into its wake.

Despite the presence of the convection, initially warm and saturated thermodynamic profiles appear to be inhibiting the development of
lightning. Even near the leading edge of the mid-level drying, warm
layers aloft still appear inhibitive, and an area of offshore
lightning (roughly near 45N/126W) between 16-17Z appears to have
been short lived.

...South Florida...
Relatively warm and dry mid-levels, coupled with generally weak
low-level convergence, continues to inhibit thunderstorm
development. However, models indicate at least some increase in
low-level convergence along coastal areas near/north of Palm Beach
later this afternoon through tonight, which might still support the
risk for an isolated weak thunderstorm or two, in the presence of
weak instability.

..Kerr.. 11/16/2020

.PREV DISCUSSION... /ISSUED 1015 AM CST Mon Nov 16 2020/

...South FL...
Isolated showers currently east-southeast of the Space Coast should
increase in coverage as they spread southwestward along/ahead of a
weakly convergent cold front pushing south from central FL. Rather
poor 700-500 mb lapse rates between 4-5 C/km as sampled by regional
12Z soundings will be a limiting factor to sustaining charge
separation, but adequate buoyancy exists for a risk of isolated
thunderstorms.

...Coastal WA...
A pronounced low-level warm advection regime will shift north from
the Columbia Valley today. Scant elevated buoyancy may develop as
850-mb dew points rise to around 9 C this afternoon. Very isolated
lightning could accompany deeper showers through early evening.

$$
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ACUS01 KWNS 171941
SWODY1
SPC AC 171939

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0139 PM CST Tue Nov 17 2020

Valid 172000Z - 181200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe thunderstorms are not expected across the contiguous U.S.
through tonight.

...20Z Update...

...Coastal Pacific Northwest...
Isolated lightning flashes are still expected later tonight into
early Wednesday morning along the coastal portions of WA, OR, and
far northern CA ahead of an approaching shortwave trough.

..Mosier.. 11/17/2020

.PREV DISCUSSION... /ISSUED 1006 AM CST Tue Nov 17 2020/

...Western WA to coastal OR...
Increasingly onshore low-level trajectories may yield sufficient
moistening for the development of scant surface-based buoyancy,
mainly across portions of western WA later this afternoon. Isolated,
low-topped thunderstorms may form amid scattered showers with
sufficient effective bulk shear for a risk of small hail and locally
gusty winds. Another round of potential isolated thunderstorms may
develop towards the end of the period (09-12Z) along the OR coast as
a mid-level vorticity maximum embedded within the broader northeast
Pacific trough approaches the coast.

...Far South FL...
Isolated low-topped showers near the northern Bahamas should
translate southwest across the FL Straits today. The 12Z Miami
sounding continued to sample relatively warm/dry mid-levels above
600 mb which should serve to limit deep convective development amid
weak low-level convergence. Further drying of the boundary layer
later today will suppress all convection to south of the Keys by
this evening.

$$
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ACUS01 KWNS 181626
SWODY1
SPC AC 181624

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1024 AM CST Wed Nov 18 2020

Valid 181630Z - 191200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe thunderstorms are not expected through tonight.

...Northwest...
As the mean mid-level trough spreads inland from the northeast
Pacific, cold advection will help steepen lapse rates to support
isolated thunderstorms outside of the immediate coast. Thunder
potential will likely maximize during the late afternoon and evening
within three corridors.

The first is across the northern Sacramento Valley where convection
is already ongoing near Redding. The presence of 51-54 F surface dew
points and weak boundary-layer heating should yield meager MLCAPE up
to about 300 J/kg. An elongated hodograph might support weak
mid-level updraft rotation in the strongest cells this afternoon,
although low-level wind fields will likely decrease and become
slightly veered as the lead shortwave impulse shifts towards eastern
OR/WA. Small hail is possible, but the narrow spatiotemporal window
for more favorable hodographs coincident with adequate
instability/ascent appears limited enough to preclude tornado/hail probabilities.

The leading shortwave impulse may briefly support isolated thunder
near the OR/WA/ID border area during the late afternoon in a very
marginally supportive thermodynamic environment. Otherwise, the next
primary shortwave impulse that should reach the OR coast this
evening will sustain potential for isolated thunder centered on
western OR from the coast to the Cascades.

..Grams.. 11/18/2020

$$
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ACUS01 KWNS 191939
SWODY1
SPC AC 191937

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0137 PM CST Thu Nov 19 2020

Valid 192000Z - 201200Z

...NO THUNDERSTORM AREAS FORECAST...

...SUMMARY...
The risk of general thunder is negligible through tonight.

...20Z Outlook Update...
Lightning detection has indicated occasional lightning flashes in a
localized area near the northern Oregon coast within the past hour.
However, the window of opportunity for additional brief/weak
thunderstorm development west of the Cascades may be at its maximum
now through about 22-00Z, as the destabilizing influence of further boundary-layer warming is increasingly countered by warming aloft,
associated with the continuing eastward progression of the mid-level
cold pool. Any additional development may tend to become more
focused along the western slopes of the Washington Cascades, aided
by modest upslope flow, but coverage probably will remain
sparse/isolated.

..Kerr.. 11/19/2020

.PREV DISCUSSION... /ISSUED 0930 AM CST Thu Nov 19 2020/

...Northwest...
While the probability of thunder appears to be less than 10 percent,
three areas of nonzero probability appear to exist. The first is
near the ND/SD border area with a corridor of elevated convection in association with a shortwave impulse moving across the northern
Great Plains. While a couple flashes occurred in southeast MT
earlier this morning, effective inflow layers should become
increasingly elevated with eastern extent, thereby decreasing
potential for charge separation.

A lightning flash or two is also possible across parts of western to
southern MT during the late afternoon but predominately 20s surface
dew points will limit appreciable surface-based buoyancy. Finally,
low-topped showers will likely persist across coastal portions of WA
and northwest OR. Mid-level warm advection is underway in the wake
of shortwave trough passage earlier this morning, although this
process should be temporarily curtailed as a weak mid-level impulse
over the northeast Pacific approaches this evening. The weak forcing
for ascent coupled with generally increasingly marginal
thermodynamic profiles should limit thunder potential.

$$
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ACUS01 KWNS 201938
SWODY1
SPC AC 201936

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0136 PM CST Fri Nov 20 2020

Valid 202000Z - 211200Z

...NO THUNDERSTORM AREAS FORECAST...

...SUMMARY...
The threat for thunderstorms appears negligible through tonight.

...20Z Outlook Update...
The previously issued outlook is being maintained with no changes.

..Kerr.. 11/20/2020

.PREV DISCUSSION... /ISSUED 1016 AM CST Fri Nov 20 2020/

...Synopsis...
A largely quiescent pattern will continue over the CONUS through
this period, with zonal flow over the northern tier of states and
weak flow aloft over the Gulf coast/Southeast. A few convective
showers will be possible across south FL in an easterly flow regime
as a post-frontal air mass modifies over time, though a pronounced
temperature inversion in the 850-700 mb layer should limit any
thunderstorm potential. Farther west, low-level moisture is
returning northward into east TX, but substantial convective
inhibition and a lack of forcing for ascent will preclude
thunderstorms.

Gradual moistening in a frontal zone oriented roughly along the I-44
corridor from MO into OK could lead to the development of weak
buoyancy rooted in the 850-700 mb layer from 06-12z. Only weak
ascent and some convective inhibition are expected along the front
until near or after the end of this forecast period, which suggests
that any elevated convective showers over southwest MO should remain
too shallow/weak for lightning production until the day 2 period.

$$
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ACUS01 KWNS 210549
SWODY1
SPC AC 210548

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1148 PM CST Fri Nov 20 2020

Valid 211200Z - 221200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
The risk for severe thunderstorms appears negligible across the U.S.
through tonight.

...Synopsis...
A shortwave trough is forecast to amplify and move southeastward
from the northern Rockies this morning into the central Plains by
late tonight. At the surface, a cold front will sag southward across
the southern Plains and Ozark Plateau, as a weak surface wave
develops along the boundary and moves northeastward toward the
mid-MS Valley by Sunday morning.

...South-central Plains into the Ozark Plateau/Mid-MS Valley...
In advance of the primary shortwave trough moving into the central
Plains, one or more lower-amplitude vorticity maxima will likely
traverse the central Plains into the mid-MS Valley this afternoon
into tonight. Ascent attendant to these features will likely result
in the development of primarily elevated convection to the north of
the cold front. The most robust convection is currently anticipated
from northeast OK into the Ozark Plateau this evening, where modest
low-level moisture and relatively steep midlevel lapse rates may
support MUCAPE up to 500 J/kg. Small hail may occur with the
strongest storms, but the severe risk appears low at this time.
Convection should spread into the mid-MS Valley late tonight.

...South FL...
While very dry air aloft and a warm layer based roughly around 700
mb will continue to suppress attempts at deep convection during much
of the day, a gradual increase in moisture/instability across south
FL may support the potential for isolated thunderstorm development
by late afternoon/evening, primarily across the southeast portion of
the peninsula.

..Dean.. 11/21/2020

$$
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ACUS01 KWNS 211947
SWODY1
SPC AC 211946

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0146 PM CST Sat Nov 21 2020

Valid 212000Z - 221200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe thunderstorms are not expected today or tonight.

...20Z Update...
Recent surface analysis places a low over northeast OK, with a cold
front extending southwestward from this low back across the southern
TX Panhandle and into southeast NM. The cold front also extends east-northeastward across northern AR and into the TN Valley. Modest
warm-air advection across the western portion of this frontal zone
will continue to contribute to showers and occasional thunderstorms
from northern OK through the Ozark Plateau. This corridor of showers
and thunderstorms will gradually shift southward as the cold front
moves southward throughout the remainder of the period.

..Mosier.. 11/21/2020

.PREV DISCUSSION... /ISSUED 1017 AM CST Sat Nov 21 2020/

...Synopsis...
A series of low-amplitude shortwave troughs will move eastward from
the Four Corners to the lower OH Valley, in advance of an amplifying
northern stream trough over the upper-middle MO Valley. The
northward return of boundary-layer dewpoints in the low-mid 60s
across east TX will contribute to weak buoyancy along a frontal zone
from southern OK into the Ozarks. A few elevated thunderstorms are
expected later today into tonight atop the frontal surface, in
association with embedded speed maxima progressing eastward from
northern NM/southern CO. Other isolated thunderstorms may also
occur this afternoon into tonight along the path of the embedded
speed maxima, originating with weak buoyancy over the higher terrain
over northern NM/southern CO and spreading eastward above the
shallow cool air mass over the southern High Plains.

Otherwise, continued low-level air mass modification and some
cooling in the 850-700 mb layer noted from 00z to 12z at Miami may
allow sufficiently deep convection for isolated lightning flashes
near the southeast FL coast.

$$
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ACUS01 KWNS 221942
SWODY1
SPC AC 221940

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0140 PM CST Sun Nov 22 2020

Valid 222000Z - 231200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe thunderstorms are not expected across the U.S. today or
tonight.

...20Z Update...
Forecast outlined in the previous outlook (discussion below) remains
valid, with no changes needed to the ongoing general thunderstorm
areas.

..Mosier.. 11/22/2020

.PREV DISCUSSION... /ISSUED 1021 AM CST Sun Nov 22 2020/

...Synopsis...
A midlevel shortwave trough over the middle and upper MS Valley will
progress eastward over the OH Valley by tonight, as an associated
surface cyclone develops northeastward from the lower OH Valley this
morning to the lower Great Lakes overnight. East of the surface
cyclone and a trailing cold front, a moistening low-level air mass
will spread northward across the southeast Atlantic coast today, and
into southern New England late in the period. Ongoing convection
along the FL Atlantic coast will develop gradually northward toward
eastern NC tonight, and will reach southern New England before 12z.
The greater threat for more concentrated or organized storms should
remain just off the NC coast tonight, in proximity to the Gulf
Stream.

Otherwise, a lead shortwave trough over CA/southern NV this morning
will eject northeastward through this evening, in advance of a
shortwave trough that will move inland over CA/NV by the end of the
period. A gradual increase in low-midlevel moisture and ascent in a
warm advection regime will contribute to weak buoyancy and the
threat for isolated lightning flashes overnight in the vicinity of
the San Juan Mountains in southwest CO.

$$
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ACUS01 KWNS 231954
SWODY1
SPC AC 231953

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0153 PM CST Mon Nov 23 2020

Valid 232000Z - 241200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe thunderstorms are not forecast through tonight across the
contiguous United States.

...Discussion...
The only changes made to the previous forecast are 1) remove the
5-percent wind probabilities near Cape Cod and 2) shift the
thunderstorm risk east off the New England coast except for far
eastern Maine. Elsewhere, the forecast is on track.

..Smith.. 11/23/2020

.PREV DISCUSSION... /ISSUED 1004 AM CST Mon Nov 23 2020/

...Southeast New England to coastal ME the next few hours...
One midlevel shortwave trough will move off the Mid-Atlantic coast
by midday and over ME by mid-late afternoon. A band of slightly
elevated convection is moving across southeast MA and coastal ME in
advance of the midlevel trough and associated surface cyclone/cold
front. Isolated strong/damaging winds will be possible with
near-surface-based convection approaching Nantucket through about
17z, while the threat for thunderstorms will end across coastal ME
by about mid afternoon.

...Central Rockies this evening to the Plains overnight...
A midlevel trough over CA/NV will move eastward toward the Four
Corners by late tonight. Steep midlevel lapse rates and modest
moistening near 700 mb will support a few thunderstorms over the
higher terrain of northern NM and western CO late this afternoon
into early tonight. Very weak midlevel convection this morning over
northeast KS and southeast NE is unlikely to pose much threat for
lightning. The threat for a few elevated thunderstorms will
increase overnight (06-12z) from the TX Panhandle into western
OK/southern KS as midlevel lapse rates steepen and moisture
increases in the 850-700 mb layer.

$$
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ACUS01 KWNS 241952
SWODY1
SPC AC 241951

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0151 PM CST Tue Nov 24 2020

Valid 242000Z - 251200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE NORTHEAST
TX PANHANDLE INTO NORTHEAST OK...

...SUMMARY...
Severe thunderstorms are expected from the Texas Panhandle into
Oklahoma through this evening. More isolated severe storms are
possible overnight from northeast Texas into Arkansas. Large hail
and damaging winds will be the main threats, along with a couple of
tornadoes.

...20z Update - Southern Plains/Ark-La-Tex...

Only minor adjustment have been made to the 10% general thunderstorm
line across parts of the Plains based on latest trends and CAMs
guidance. Otherwise, the ongoing outlook is on track. Strong
thunderstorms have developed across parts of the OK/TX Panhandles
this afternoon where temperatures have warmed into the 60s and
MLCAPE has increased to around 500 J/kg near and east of current
convection. Additional storms are expected to develop with time as
the surface low and cold front develop eastward toward western OK
over the next couple of hours. Large hail, damaging gusts, and a
tornado or two still appear possible through this evening across the
Slight risk area. Most recently, 1 inch hail has been reported with
storms in Beaver County, OK. For more details, reference MCD 1807.

..Leitman.. 11/24/2020

.PREV DISCUSSION... /ISSUED 1027 AM CST Tue Nov 24 2020/

...Parts of the southern Plains to the Ark-La-Tex through tonight...

A midlevel shortwave trough over NM this morning will progress
eastward to northwest TX and western OK by late evening, and then
continue northeastward to MO/AR by the end of the period. The
midlevel trough will be preceded by a surface cyclone that will
develop eastward from the TX Panhandle this afternoon to western OK
this evening, and then northeastward to MO overnight. A narrow
corridor of mid-upper 50s boundary-layer dewpoints will return
northward to the east of a dryline, where a few cloud breaks could
allow pockets of surface heating as far north as west central or
northwest OK by mid-late afternoon.

Storm development appears probable by mid afternoon in the TX
Panhandle near the triple point, and storms will subsequently spread
eastward into west central and northwest OK late this
afternoon/evening, generally along and north of I-40. Deep-layer
shear will support supercells, but rather modest low-level shear and substantial forcing for ascent in the left-exit region of the
mid-upper jet suggest that some upscale growth into clusters or line
segments is also probable. Thus, there will be some threat for a
tornado or two relatively early in the convective evolution across
northwest OK, in proximity to the surface boundaries and where
low-level lapse rates/CAPE will be largest. Isolated very large
hail will be a threat with supercells given steep lapse rates and
500 mb temperatures colder than -17 C, and damaging winds will
become more of a concern this evening as convection grows upscale.

A separate zone of convection is expected overnight from northeast
TX into southeast OK and western AR, both in pre-frontal warm
advection and along the cold front as it encounters richer low-level
moisture and weakening convective inhibition. Convection will
likely remain elevated near and north of I-40, with more
surface-based convection closer to northeast TX. Vertical shear
will be strong in this corridor, but there will be a tendency for
the stronger forcing for ascent to begin passing north of the more
unstable warm sector late in the period. Overall, isolated severe
storms may occur overnight from northeast TX into AR, but it is
still not clear that a more concentrated severe threat will evolve
in this corridor, so low severe probabilities will be maintained in
this update.

$$
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ACUS01 KWNS 261301
SWODY1
SPC AC 261259

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0659 AM CST Thu Nov 26 2020

Valid 261300Z - 271200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE
SOUTHEAST STATES TODAY AND EASTERN TEXAS AND LOUISIANA TONIGHT...

...SUMMARY...
A few strong to locally severe thunderstorms could occur today
across the Southeast States including southeast Alabama and southern
Georgia. Isolated severe hail may occur with thunderstorms that
develop across parts of far eastern Texas into Louisiana late
tonight.

...Southeast States...
Bands of storms, including some embedded/weak transient supercells
overnight, continue to persist across southern Alabama and central
Georgia early this morning near/ahead of an
east/southeastward-moving cold front. While convergence will tend to
weaken during the day, modest diurnal destabilization and some
additional pre-frontal moistening from the south-southwest may help
sustain storms today from southeast Alabama into central/southern
Georgia and possibly parts of the Florida Panhandle. Deep-layer
shear will be sufficiently strong (35-40 kt effective) for some
well-organized storms and possibly a few weak/transient supercells,
although low-level winds within the lowest 1-2 km AGL will continue
to weaken today. While an overly organized severe risk is not
expected, a few stronger/locally severe storms capable of wind
damage could occur through the afternoon.

...Far east/southeast Texas and Louisiana late tonight...
As an initial response to the amplifying trough approaching the
southern Rockies late tonight, increasing elevated moisture
transport is expected late tonight near/north of a near-coastal warm
front and ahead of a cold front advancing southeastward across the
southern Plains. Somewhat steeper mid-level lapse rates will
overspread this nocturnal increase in low-level moisture, with the
possibility of 1000 J/kg MUCAPE in some locations by late tonight.
In the presence of long straight hodographs, these elevated
late-night storms could pose a marginally severe hail risk on an
isolated basis.

..Guyer/Broyles.. 11/26/2020

$$
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ACUS01 KWNS 261934
SWODY1
SPC AC 261932

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0132 PM CST Thu Nov 26 2020

Valid 262000Z - 271200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS LATE THIS
AFTERNOON ACROSS PARTS OF THE FLORIDA PANHANDLE...SOUTHERN GEORGIA
AND SOUTH CAROLINA...AND TONIGHT ACROSS PARTS OF SOUTHEASTERN TEXAS
AND SOUTHERN LOUISIANA...

...SUMMARY...
Isolated damaging winds with thunderstorms remain possible in narrow
corridor across parts of the Florida Panhandle through southern
Georgia and far southern South Carolina this afternoon. Isolated
large hail will be possible, mainly overnight, near the northwest
Gulf coast.

...20Z Outlook Update...
Some adjustments to the categorical and probabilistic lines have
been made, mainly to account for the ongoing progression of the
synoptic and sub-synoptic features.

As expressed in the prior discussion appended below, support for
severe storms across the Southeast remains quite marginal. However,
5 percent severe wind probabilities have been extended along a
narrow corridor of modest prefrontal boundary-layer destabilization,
from parts of the western Florida Panhandle into far southern South
Carolina.

..Kerr.. 11/26/2020

.PREV DISCUSSION... /ISSUED 1028 AM CST Thu Nov 26 2020/

...Southeast AL/southwest GA this afternoon...
Occasional weak supercell structures will remain possible within a
band of convection drifting southeastward along a surface cold
front. Ascent along the front will be aided by weak embedded speed
maxima aloft moving over the lower MS/TN Valley regions, in concert
with the diurnal heating cycle. However, low-level shear will be
weak and deep-layer shear will be on the lower margins for
supercells, in an environment with MLCAPE near 1000 J/kg. Thus, any
severe threat should be confined to isolated wind damage this
afternoon, prior to the storms weakening this evening.

...Southwest LA coast this afternoon into southeast TX overnight...
Low-level moisture is beginning to return northward toward the
northwest Gulf coast, and a few thunderstorms are ongoing across the
northwest Gulf along the warm front/buoyancy gradient. Moisture
will spread inland this afternoon into tonight in a weak warm
advection regime, with the potential additional influence of a
subtle speed max aloft moving east-northeastward from northwest
Mexico. A few thunderstorms will develop inland over southwest LA
this afternoon, with more substantial storm development expected
farther west and north in southeast TX after 06z tonight. Low-level
shear will not be particularly strong, but effective bulk shear of
40-50 kt, midlevel lapse rates of 7-8 C/km, and MUCAPE near 1500
J/kg could support isolated hail near 1" with slightly elevated
convection.

$$
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ACUS01 KWNS 271256
SWODY1
SPC AC 271255

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0655 AM CST Fri Nov 27 2020

Valid 271300Z - 281200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM SOUTH TEXAS
TO SOUTHERN MISSISSIPPI...

...SUMMARY...
Isolated, marginally severe thunderstorms are possible from South
Texas to southern Mississippi today.

...Synopsis...
The mid/upper-tropospheric pattern over the CONUS features a
positively tilted synoptic trough, extending from far northwestern
ON across MN, much of NE, through a col over central CO, to a closed
cyclone over central AZ. That portion of this trough located
poleward of the col will split eastward rapidly through the period,
reaching portions of New England and the coastal Mid-Atlantic by
12Z. Meanwhile the closed cyclone -- though not completely cutoff
-- will move eastward far slower, its center reaching east-central
NM by 12Z.

At the surface, 11Z analysis showed a cold front from Lake Michigan
across central/southwestern MO, northeast/central TX, and the TX Big
Bend area. This front is forecast to move southeastward by 00Z to
OH, middle TN, central MS, southwestern LA, the middle/upper TX
Coast, and deep south TX. By 12Z the front should reach central/
southern GA, southern LA, the northwest Gulf just offshore from the
mid/upper TX Coast, and slightly southward through deep south TX.
In doing so, it will overtake the western segment of a diffuse,
stationary to warm frontal zone analyzed initially across southern
GA, extreme southern portions of MS/AL, south-central LA, and east
TX.

...South TX/Rio Grande Valley to southern MS...
Scattered showers and widely scattered to scattered embedded
thunderstorms are expected through this evening -- mainly ahead of
the front but also along and behind it. Isolated, marginally severe
hail/gusts are possible, with the gust threat being along and ahead
of the front. The strongest convection should shift offshore
along/ahead of the front, and any prefrontal outflow pushes, late
this afternoon into this evening.

Regional radar mosaics, satellite imagery and lightning data reveal
a broad, gradual increase in convective coverage and areal extent
the past few hours from Coahuila to the Mississippi River portion of
the MS/LA border. This activity is building within a low-level
warm-advection plume, with rich boundary-layer moisture theta-e over
south TX to southwestern LA. Weak boundary-layer lift in the warm
sector appears to be keeping surface-based development subsevere in
character, despite the presence of 40-50-kt effective-shear vectors
and MLCAPE estimated in the 1000-2000 J/kg range. Abundant, multi-
level cloud cover also is apparent in IR imagery. That cloudiness
will impede diurnal heating substantially today, with peak MLCAPE
not much higher than at present.

Still, with large-scale ascent forecast to increase gradually ahead
of the slow-moving AZ/NM cyclone, and a favorable parametric
juxtaposition of shear, moisture and buoyancy across the region,
maintaining a marginal risk appears justified for this outlook
cycle. Upscale aggregation/clustering of convection is forecast by
some convection-allowing guidance across southeast TX near or just
ahead of the cold front; such a process may boost wind potential
locally should a sufficiently strong cold pool arise. Otherwise,
the gust threat will be brief and with downbursts in the most
intense multicells. Hail near severe limits is possible, but its
size and frequency will be limited by lack of stronger
1) Deep-layer lapse rates, and
2) Low-level shear for developing and maintaining low-level
mesocyclones, though transient supercell characteristics are
possible.

..Edwards/Broyles.. 11/27/2020

$$
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ACUS01 KWNS 271951
SWODY1
SPC AC 271949

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0149 PM CST Fri Nov 27 2020

Valid 272000Z - 281200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
OF THE WESTERN AND CENTRAL GULF COAST REGION...

...SUMMARY...
Isolated, marginally severe thunderstorms are possible from South
Texas to southern Mississippi today.

...20z Update - Western and Central Gulf Coast...

The only changes to the ongoing Marginal risk area have been to
remove northern portions of the area from TX into LA/MS based on the
current position of the surface front. Otherwise, the ongoing
forecast remains on track. Refer to MCD 1817 and the previous
outlook below for more details.

..Leitman.. 11/27/2020

.PREV DISCUSSION... /ISSUED 1020 AM CST Fri Nov 27 2020/

...Western and Central Gulf Coast...
Morning water vapor loop shows a compact upper low over AZ moving
toward the southern Plains. Relatively fast west-southwesterly flow
aloft extends from northern Mexico into parts of TX/LA/MS/AL where
low-level warm/moist advection is resulting in scattered showers and thunderstorms. This activity is forecast to continue through much of
the day as a weak surface cold front sags southward across the
region. Forecast soundings show MUCAPE values around 1000 J/kg from
southern AL into LA, with higher values farther southwest in TX.
This, combined with sufficient deep-layer shear may result in
transient rotating/bowing structures and an associated risk of gusty
winds or a brief spinup. However, low-level flow is weak and lapse
rates are not particularly steep. Therefore, the overall severe
threat remains marginal.

$$
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ACUS01 KWNS 011626
SWODY1
SPC AC 011624

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1024 AM CST Tue Dec 01 2020

Valid 011630Z - 021200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe thunderstorms are not expected through tonight.

...Synopsis/Discussion...
A highly amplified large-scale pattern over the CONUS includes an east/northeastward-moving deep cyclone over the Eastern Seaboard,
New England, and Quebec, in addition to a southeastward-digging
trough over the High Plains. Initially, a few lightning strikes
could occur mainly over Downeast Maine through early afternoon via
weak near-coastal elevated instability, prior to the cold front
exiting the region later this afternoon.

Elsewhere, air mass modification will steadily occur over the
western Gulf of Mexico through tonight in advance of the
aforementioned High Plains upper trough and ahead of a cold front
that is expected to reach the I-35 vicinity of central Texas by 12Z
Wednesday. Moist advection beneath steepening mid-level lapse rates
will support the possibility of isolated thunderstorms along the
middle/upper Texas coastal plain late tonight, primarily in the
09-12Z time frame (and beyond). A few rotating storms could occur
off the middle Texas coast in the predawn hours of Wednesday, but
the immediate near-shore/inland potential should remain low prior to
12Z Wednesday.

..Guyer.. 12/01/2020

$$
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ACUS01 KWNS 021945
SWODY1
SPC AC 021944

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0144 PM CST Wed Dec 02 2020

Valid 022000Z - 031200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF NEAR-COASTAL SOUTHEAST TEXAS AND SOUTHWESTERN/SOUTH-CENTRAL
LOUISIANA...

...SUMMARY...
Isolated severe thunderstorms are possible over portions of
near-coastal southeast Texas and southwestern/south-central
Louisiana.

...Discussion...
No change was made to the previous convective outlook.

..Smith.. 12/02/2020

.PREV DISCUSSION... /ISSUED 1025 AM CST Wed Dec 02 2020/

...Western Gulf Coastal Plain...
Thunderstorms continue to develop/intensify offshore of the
middle/upper TX coast late this morning as the boundary layer air
mass over the northwest Gulf of Mexico continues to slowly modify.
Advection of higher theta-e air inland has resulted in MLCAPE of up
to 500 J/kg along the middle TX coast with higher values offshore.
Afternoon MLCAPE should average 500-750 J/kg near the coast, and
when combined with westerly deep-layer shear of 45-50 kts contribute
to a favorable environment for supercell structures or perhaps small
bowing segments. The primary uncertainty remains the degree of storm
coverage inland in advance of the eastward moving cold front, and
latest CAM guidance continues to suggest the more organized storms
should remain mostly offshore. Nevertheless, some risk for a couple
of storms capable of producing damaging winds, hail and possibly a
tornado will exist near the coast as large-scale forcing for ascent
strengthens over the area this afternoon/evening.

$$
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ACUS01 KWNS 031944
SWODY1
SPC AC 031943

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0143 PM CST Thu Dec 03 2020

Valid 032000Z - 041200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
The risk for severe thunderstorms is low across the U.S. through
tonight.

...Discussion...
No change has been made to the previous convective outlook.

..Smith.. 12/03/2020

.PREV DISCUSSION... /ISSUED 1030 AM CST Thu Dec 03 2020/

...Gulf Coast...
A highly amplified large-scale pattern will persist through tonight,
including a slow eastward evolution of a currently closed trough
over the Ozarks toward the Mid-South through tonight. In association
with richer moisture, scattered thunderstorms are expected to be
most common over the open Gulf of Mexico waters off of Louisiana/Mississippi/Alabama and eventually off the Florida
Panhandle tonight, but a few thunderstorms will also be possible
over inland areas of the region this afternoon and tonight in
vicinity of a northward-extending surface trough. Organized severe
storms are unlikely. While a stronger storm or two could conceivably
occur near coastal Louisiana (Plaquemines Parish) or near coastal
parts of Mississippi/Alabama this evening into the overnight, latest
thinking continues to be that inland destabilization will be limited
and that the stronger/more organized storms will likely remain
offshore through late tonight.

$$
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ACUS01 KWNS 041958
SWODY1
SPC AC 041957

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0157 PM CST Fri Dec 04 2020

Valid 042000Z - 051200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS EASTERN
NORTH CAROLINA...

...SUMMARY...
A tornado or two and isolated severe wind gusts will be possible
across eastern North Carolina, mainly from late evening into the
overnight. Otherwise, a couple of strong wind gusts remain possible
over a portion of the Florida Panhandle and southwest Georgia this
afternoon.

...20Z Update...
Only change this outlook update cycle was to shift low severe
probabilities northward into southwest Georgia. A semi-organized
band of showers/embedded thunderstorms has evolved and surface
temperatures have warmed to near 70F with some low 60s F surface
dewpoints, exceeding some earlier guidance in both regards.
Reference Mesoscale Discussion 1832 for additional short-term
details.

..Guyer.. 12/04/2020

.PREV DISCUSSION... /ISSUED 1028 AM CST Fri Dec 04 2020/

...Eastern North Carolina...

A vigorous shortwave trough situated across AR and western TN will
transition to a negatively tilted wave as it continues through the
southern Appalachians late this afternoon and into the Carolinas
tonight. In response to the strong forcing for ascent attending this
feature, a surface low will deepen as it moves from SC this evening
to off the southeast VA coast late tonight. By mid evening this low
will be situated near the central SC/NC border with trailing cold
front extending southwestward through the central FL Panhandle. A
warm front/coastal boundary should advance inland through a portion
of eastern NC with dewpoints rising to around 60F in the warm sector contributing to weak instability with 500-1000 J/kg MLCAPE. Farther
west across central NC, instability will remain meager (100-200 J/kg
MUCAPE). However, given the strength of mesoscale forcing along the
portion of the cold front near the surface low track, some potential
will exist for a narrow line of low-topped convection to develop
this evening. This activity will be embedded within a strong
kinematic environment with 50 kt flow just above the surface,
suggesting some of the convection could produce strong to damaging
wind gusts. Farther east in the warm sector across eastern NC,
greater instability and strong vertical shear profiles will support
potential for a few supercells and bowing segments with an attendant
threat for a couple of tornadoes and isolated damaging wind
overnight.

...Florida Panhandle...

As of late morning a warm front was situated near the coast of the
FL Panhandle with a cold front moving through the western Panhandle
into the central Gulf. As the small warm sector develops northward,
weak instability with 400-800 J/kg MLCAPE will evolve inland. The
convection currently developing along the warm conveyor belt may
undergo some intensification this afternoon as the boundary layer
destabilizes. Vertical wind profiles are supportive of a couple of
rotating updrafts and bowing segments. The deeper forcing for ascent
will remain north of this region which combined with the modest
thermodynamic environment should remain limiting factors for a more
robust severe threat.

$$
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ACUS01 KWNS 051231
SWODY1
SPC AC 051230

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0630 AM CST Sat Dec 05 2020

Valid 051300Z - 061200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe thunderstorms are not expected across the U.S. through the
Day 1 forecast period.

...Discussion...
A high-amplitude, complex upper pattern will continue to evolve
across the U.S. today, to include four distinct features -- an
evolving upper low shifting northward across New England, a
short-wave trough digging southeastward across the Upper Midwest, an
upper low moving east-northeastward out of Mexico into Texas, and
finally a short-wave trough that will move inland over the
Northwest.

At the surface, cold/continental high pressure will prevail across a
majority of the country, with the predominant feature by far being a
rapidly developing low that will shift northeastward just off the
New England coast, roughly in tandem with the aforementioned upper
feature crossing this region.

Given the overall lack of unstable air over the country, risk for
thunderstorms will remain minimal in most areas. A few lightning
flashes may occur over Cape Cod and vicinity, and over the adjacent
Atlantic waters, in tandem with ongoing surface cyclogenesis.
Showers and isolated thunderstorms will be possible across parts of
south Florida and the Keys, and areas offshore, as a trailing cold
front associated with the northeastern U.S. surface low moves
southward across the area. Elevated convection, including a few
lightning flashes, can also be expected across parts of East Texas
and into western Louisiana and the Arklatex, though more widespread
convection will remain over the western Gulf of Mexico. Finally, a
stray lightning flash may occur over the Northwest, as the upper
system moves onshore. In all areas, no severe weather is expected.

..Goss.. 12/05/2020

$$
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ACUS01 KWNS 051956
SWODY1
SPC AC 051955

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0155 PM CST Sat Dec 05 2020

Valid 052000Z - 061200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe thunderstorms are not expected across the U.S. mainland
through tonight.

...20Z Update...
Only adjustment was to remove the thunderstorm area near coastal
southern New England as the risk for any near-shore elevated
convection is low and will be further diminishing. Otherwise, see
prior discussion below.

..Guyer.. 12/05/2020

.PREV DISCUSSION... /ISSUED 1030 AM CST Sat Dec 05 2020/

...Discussion...

A few thunderstorms remain possible mainly near the TX coast as a
series of weak impulses move northeast along southeastern periphery
of an upper low situated over northern Mexico. Very sparse lightning
flashes also cannot be ruled out farther west toward central through
northwest TX from mid-level convection. Here, steeper 700-500 mb
lapse rates exist in the presence of strong mid-level ascent
associated with vorticity maxima rotating through the upper low
circulation.

$$
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ACUS01 KWNS 061147
SWODY1
SPC AC 061146

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0546 AM CST Sun Dec 06 2020

Valid 061300Z - 071200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SOUTH FL AND THE
KEYS...

...SUMMARY...
Locally damaging winds and a brief tornado are possible across south
Florida and the Keys late tonight to early tomorrow morning.

...South FL and the Keys...
A shortwave trough over east TX will phase with a trough ejecting
east from IL as an upstream impulse digs south from northwest
Ontario. This evolution will aid in initial weak cyclogenesis over
the northeast Gulf tonight, followed by secondary cyclogenesis over
the Gulf Stream east of the Carolinas tomorrow morning. Poor
tropospheric lapse rates will be a limiting factor with buoyancy
likely to remain weak despite 14-16 g/kg mean-mixing ratios.
Nevertheless, consensus of guidance suggests a belt of strengthening
850-mb flow will become centered across south FL and the Keys by
09-12Z. This should occur in tandem with convective clusters across
the eastern Gulf spreading towards the region late in the period,
supporting a low probability damaging wind and tornado threat.

..Grams.. 12/06/2020

$$
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ACUS01 KWNS 061955
SWODY1
SPC AC 061954

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0154 PM CST Sun Dec 06 2020

Valid 062000Z - 071200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS SOUTHERN
FLORIDA...

...SUMMARY...
Locally damaging winds and a brief tornado are possible across south
Florida and the Keys late tonight through early Monday morning.

...20Z Update...
Will maintain severe probabilities for what is anticipated to be an
increasing potential late tonight (mainly after 06Z) for a couple of thunderstorms capable of localized wind damage and/or a tornado.
This will be as a cluster of storms likely moves in from the Gulf of
Mexico and/or as other semi-discrete storms develop ahead of any
such cluster.

..Guyer.. 12/06/2020

.PREV DISCUSSION... /ISSUED 1019 AM CST Sun Dec 06 2020/

...South Florida...

Southern-stream shortwave trough situated over TX late this morning
will phase with a northern-stream trough and accelerate through the
Southeast States tonight. Stalled front located just south of the FL
Keys will return to deep South FL tonight. This will result in a
small, moist warm sector spreading inland, while a southwesterly
low-level jet strengthens across this region late tonight in
response to the approaching shortwave trough.

The atmosphere across south FL will undergo modest destabilization
as upper 60s to near 70F dewpoints advect inland. However, very weak
lapse rates (generally less than 5.5 C/km) will contribute to a
marginal thermodynamic environment with MLCAPE below 800 J/kg.
Numerous showers and thunderstorms will develop within the region of
isentropic ascent north of the front, and widely scattered to
scattered surface-based storms are also possible along and south of
this boundary later tonight. Vertical wind profiles will strengthen
with 40+ kt effective bulk shear, along with increasing 0-1 km
hodograph size as the low-level jet evolves late tonight. A couple
of bowing structures and embedded supercells are possible with an
attendant threat for a few damaging gusts and a brief tornado. Due
to the expected limiting factors imposed by an anticipated marginal thermodynamic environment, will maintain MRGL risk category this
update but continue to monitor for a possible SLGT upgrade in later
outlooks.

$$
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ACUS01 KWNS 071956
SWODY1
SPC AC 071954

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0154 PM CST Mon Dec 07 2020

Valid 072000Z - 081200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe thunderstorms are not expected across the U.S. mainland
through tonight.

...20Z Update...
Have introduced a general thunderstorm area for what is anticipated
to be a low/isolated potential for thunderstorms the remainder of
the afternoon into evening across central/eastern South Carolina and
nearby small parts of Georgia/southeast North Carolina. Forcing for
ascent related to a southeastward-digging vort max and thermodynamic
profiles conducive for charge separation should allow for at least isolated/episodic low-topped thunderstorms as convection spreads east-southeastward through evening.

..Guyer.. 12/07/2020

.PREV DISCUSSION... /ISSUED 1003 AM CST Mon Dec 07 2020/

...Discussion...

Band of scattered showers and thunderstorms developing along a cold
front has moved off the southeast FL coast. Otherwise, a large area
of high pressure will maintain offshore flow and stable conditions
across the U.S. through the remainder of the period.

$$
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ACUS01 KWNS 081939
SWODY1
SPC AC 081937

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0137 PM CST Tue Dec 08 2020

Valid 082000Z - 091200Z

...NO THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Thunderstorms are not expected through early Wednesday.

...20Z Update...
Dry and stable conditions will persist throughout the period.
Previous forecast of no thunderstorms remains valid.

..Mosier.. 12/08/2020

.PREV DISCUSSION... /ISSUED 1000 AM CST Tue Dec 08 2020/

Relatively dry and stable conditions will preclude thunderstorms
across the contiguous United States today.

$$
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ACUS01 KWNS 132000
SWODY1
SPC AC 131958

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0158 PM CST Sun Dec 13 2020

Valid 132000Z - 141200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
SOUTHEAST TEXAS AND SOUTHWEST LOUISIANA...

...SUMMARY...
A few damaging wind gusts and a couple tornadoes will remain
possible across parts of southeast Texas and southwest Louisiana
through the early evening.

...20Z Update...
No changes have been made to the Slight Risk across parts of coastal
southeast TX and southwest LA. A band of pre-frontal showers and
thunderstorms should move northeastward across this area through the
remainder of the afternoon. Any isolated damaging wind and tornado
threat should remain focused along/near the coast, as widespread
precipitation aided by low-level warm advection has hampered the
northward advance of a warm front inland across southeast TX and
southern LA. For more information on the near-term severe threat
across this region, see Mesoscale Discussion 1845. It remains
unclear whether sufficient destabilization will occur farther north
into central LA and southwestern MS to support surface-based storms.
Any strong/gusty threat across this area will likely remain marginal
and quite isolated.

Farther east, mid to upper 60s surface dewpoints should advance
northward across southern AL and the western FL Panhandle late
tonight into early Monday morning ahead of a surface low and related
cold front moving generally eastward across the Southeast. Even
though low-level moisture will be increasing across these areas, it
appears that instability will be tempered by a low-level inversion
and poor low/mid-level lapse rates. With stronger forcing for ascent
attendant to a shortwave trough likely remaining to the north of
this region, robust convective development late tonight may not
occur. Have opted not to include low severe probabilities across
southern AL and the FL Panhandle given these potentially limiting
factors.

..Gleason.. 12/13/2020

.PREV DISCUSSION... /ISSUED 1023 AM CST Sun Dec 13 2020/

...Southeast Texas into southwest Louisiana...

Late this morning a warm front extends from a weak surface low in
southeast TX, eastward to near Palacios TX and into the northwestern
Gulf. The front will move north through the day, likely reaching the
Houston metro early this afternoon and continuing into the southwest
LA coastal area by late afternoon. Rich low-level moisture with
upper 60s to 70 F dewpoints reside along and south of the warm
front, and will contribute to MLCAPE from 800-1200 J/kg. Numerous
showers and scattered thunderstorms are developing across southeast
TX within corridor of isentropic ascent north of this boundary. This
activity will remain elevated with minimal severe risk. A somewhat
greater threat for severe storms should evolve this afternoon. Some
CAMs suggest surface-based storms will develop along confluence
boundaries just offshore. A couple of these storms might move inland
and interact with the warm front where low-level hodographs with
200-400 m2/s2 storm relative helicity and strong effective bulk
shear will support potential for supercells capable of producing a
tornado or two. Otherwise, additional surface based storms will be
possible as the cold front advances southeast and interacts with the
moist warm sector. Storms might eventually evolve into linear
structures along the cold front this evening as they spread east
into LA with a threat for mainly a few strong to damaging wind
gusts. The marginal thermodynamic environment with weak lapse rates
and widespread low clouds, along with tendency for deeper forcing
for ascent to remain north of warm sector, could potentially serve
as limiting factors for a more robust severe threat.

$$
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ACUS01 KWNS 141959
SWODY1
SPC AC 141958

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0158 PM CST Mon Dec 14 2020

Valid 142000Z - 151200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
The strong/gusty wind threat associated with thunderstorms has
decreased across eastern North Carolina. Minimal thunderstorm
potential is evident across the rest of the contiguous United States
through tonight.

...20Z Update...
A surface cold front is in the process of clearing the NC Coast, and
any isolated strong/gusty wind threat associated with convection is
quickly moving offshore. Therefore, low severe wind probabilities
have been removed from eastern NC with this update. Thunderstorms
are not expected across the remainder of the CONUS through the end
of the period owing to dry and/or stable conditions.

..Gleason.. 12/14/2020

.PREV DISCUSSION... /ISSUED 1008 AM CST Mon Dec 14 2020/

...Eastern NC...

Late this morning a cold front extends from a weak surface low over
the northern Coastal Plain of NC, through central GA, the central FL
Panhandle and into the eastern Gulf. Quasi-stationary front extends
from the surface low through northeastern NC and into southeast VA.
The low will track northeast and offshore by early afternoon, while
the cold front continues east and off the Atlantic Coast by mid
afternoon. Warm sector dewpoints across eastern NC have risen to the
low to mid 60s F, but instability remains limited due to widespread
clouds and showers with MUCAPE from 200-400 J/kg for parcels lifted
from near 850 mb. The ongoing area of showers with a few embedded
thunderstorms developing along the warm conveyor belt will continue
east during the day. Some potential will exist for this shallow
convection to become surface based as it encounters a warmer and
more unstable boundary layer across eastern NC, though instability
will remain very marginal. Given very strong vertical wind profiles
with 60 kt as low as 0.5 km AGL, some of this higher momentum air
could be transported to the surface within the higher reflectively
rain bands as the surface layer destabilizes farther east. However,
tendency is for the accompanying shortwave trough to deamplify with
only weak cyclogenesis inland which, combined with the very marginal thermodynamic environment, should limit overall severe threat.

$$
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ACUS01 KWNS 161957
SWODY1
SPC AC 161956

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0156 PM CST Wed Dec 16 2020

Valid 162000Z - 171200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
COASTAL NORTH CAROLINA...

...SUMMARY...
Isolated strong to severe thunderstorms will remain possible across
parts of coastal North Carolina and west-central Florida this
afternoon.

...20Z Update...
An isolated damaging wind and brief tornado threat should continue
for the next couple of hours along/near the NC Coast and Outer
Banks. Strong low-level shear is present to the northeast of a
deepening surface low across this region, which should continue to
prove favorable for updraft rotation. Although instability should
remain fairly weak, strong low-level warm/moist advection should
support surface-based storms where dewpoints can increase into the
low to mid 60s. Severe probabilities have been adjusted to account
for the northeastward movement of a band of convection located near
and north of the surface low. For more information on the short-term
severe risk across eastern NC, see Mesoscale Discussion 1853.

Widespread precipitation has limited the degree of instability
across much of the central FL Peninsula this afternoon. The
potential for an isolated strong to damaging wind gust should remain
confined along/near parts of the west-central FL Gulf Coast through
the remainder of the afternoon as storms move onshore. Upper 60s to
low 70s surface dewpoints are present across this area and slightly
greater destabilization has occurred in the presence of moderate
deep-layer shear.

..Gleason.. 12/16/2020

.PREV DISCUSSION... /ISSUED 1054 AM CST Wed Dec 16 2020/

...NC...
An intense shortwave trough is tracking across the lower MS and TN
valleys today, with large-scale forcing overspreading much of the
southeast US. Surface cyclogenesis is currently occurring off the
SC/NC coast. Latest radar loop shows a line of showers and
thunderstorms developing in vicinity of the surface low/warm front.
These storms are expected to track northward today and affect the
coastal counties of eastern NC. Most model solutions keep
surface-based CAPE over the Sound and Outer Banks. Nevertheless,
strong vertical shear may support supercell structures in this
activity, with a risk of locally damaging wind gusts or a brief
tornado. This threat should end by 23z as storms move out to sea.

...FL...
Scattered thunderstorms are occurring this morning over the
northeast Gulf of Mexico, along and ahead of an approaching cold
front. There is considerable doubt that storms can maintain this
strength as they move ashore into west-central FL this afternoon,
due to the limited moisture/instability over that region. While a
storm or two may produce gusty winds, the overall severe threat
appears marginal.

$$
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ACUS01 KWNS 171552
SWODY1
SPC AC 171551

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0951 AM CST Thu Dec 17 2020

Valid 171630Z - 181200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Isolated non-severe thunderstorms will be possible today in south
Florida and in California.

Latest water vapor loop shows multiple shortwave troughs affecting
the US today, but relatively dry/stable conditions will limit the
risk of thunderstorm activity to small parts of south FL and central
CA. In both areas, large-scale forcing is weakening through the day
and the risk of deep convection will diminish through the afternoon.
No severe storms are expected.

..Hart/Leitman.. 12/17/2020

$$
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ACUS01 KWNS 181937
SWODY1
SPC AC 181936

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0136 PM CST Fri Dec 18 2020

Valid 182000Z - 191200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Thunderstorm development will be possible late tonight from parts of
the Texas Hill Country northeastward to the Arklatex. No severe
thunderstorms are expected.

...20Z Update...
No changes have been made to the ongoing forecast.

..Gleason.. 12/18/2020

.PREV DISCUSSION... /ISSUED 1016 AM CST Fri Dec 18 2020/

...Synopsis...
Low-level moisture, characterized by dew points in the mid 50s to
lower 60s, will gradually increase across portions of
southern/eastern TX through tonight ahead of a positively-tilted
upper trough and surface cold front. The cold front will move east
and should extend from central WI southwest to central TX by 12z
Saturday. Steepening mid-level lapse rates will contribute to MUCAPE
of 400-600 J/kg, primarily after 06z. An area of showers and
thunderstorms is expected to develop across central/eastern TX late
tonight as modest height falls and low-level warm advection
increase. Weak elevated instability should preclude a severe risk
with these thunderstorms.

$$
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ACUS01 KWNS 191258
SWODY1
SPC AC 191256

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0656 AM CST Sat Dec 19 2020

Valid 191300Z - 201200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS TODAY ACROSS
PARTS OF THE MIDDLE/UPPER TEXAS COAST...

...SUMMARY...
Isolated strong to severe thunderstorms may occur today across parts
of the middle/upper Texas Coast.

...Synopsis...
A generally progressive upper-air pattern will prevail through the
period, with broadly cyclonic flow spreading eastward from the
central to eastern CONUS. The most important feature aloft will be
a positively tilted trough -- initially evident in moisture-channel
imagery from northern WI across eastern NE to far west TX and
adjoining northern MX. This perturbation will maintain positive
tilt while moving eastward and gradually weakening. By 00Z the
trough should extend from Lower MI across the Ozarks to south-
central TX. By 12Z tomorrow, it should reach southeastern ON,
eastern KY and AL.

Surface analysis showed weak lows over TX between MWL-SPS and
between DRT-LRD, connected by a cold front. The current south TX
low, or a new one, should move northeastward just of the mid/upper
TX Coast this afternoon, turning eastward along or just south of the
LA Coast tonight. Mesoscale convective effects may modulate the low
track southward and/or somewhat faster. The trailing cold front
will move across the TX Coast and northwestern Gulf, while extending
southwest of the low. A weaker inland version of the front, and a
collocated surface trough, will extend northeastward from the low.

...Mid/upper TX coastal plain...
Scattered thunderstorms are expected to develop, increase in
coverage and spread across the outlook area from mid/late morning
into the afternoon, offering the potential for isolated strong-
severe gusts and marginally severe hail. A tornado cannot be ruled
out as well.

The bulk of convection should occur in the form of a primary band
developing in a zone of relatively maximized low-level lift near the
front. With weak CINH in place, isolated thunderstorms also are
possible farther east near the immediate coast and over the Gulf.
This evolution should occur as the zone of lift encounters a
boundary layer steadily destabilizing from a combination of:
1. Warm/moist advection of a still-modifying marine layer from the
Gulf, and
2. Muted diurnal heating, amidst considerable cloud cover.

Although the CAPE-shear parameter space will be optimized offshore,
deep shear will increase over the outlook area as the mid/upper
trough approaches, with 40-50-kt effective-shear magnitudes becoming
common. Well-curved but marginally sized hodographs are expected,
supporting 0-1-km SRH in the 100-200 J/kg range. Modest low/middle
level lapse rates will keep peak preconvective MLCAPE around 500-800
J/kg inland near the coast, decreasing substantially northward. A
few high-res mesoscale progs indicate that weak surface-based
buoyancy (i.e., MLCAPE 200-500 J/kg) briefly may extend as far
northward as parts of the HOU metro, immediately before the main
area of convection moves through. As such, the marginal line has
been adjusted somewhat northward in this area.

Late this afternoon into evening, the convective band should shift
eastward over the Gulf, Golden Triangle region of southeast TX, and
portions of southwestern LA. This activity should outpace the
eastward extent of inland surface-based destabilization east of the
HOU area. By then, the most intense convection (including supercell
potential) will be relegated to the Gulf -- where the most well-
modified and unstable inflow air will reside -- posing some threat
to the various offshore interests.

..Edwards/Smith.. 12/19/2020

$$
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ACUS01 KWNS 192000
SWODY1
SPC AC 191959

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0159 PM CST Sat Dec 19 2020

Valid 192000Z - 201200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Thunderstorms will continue to shift eastward from the upper Texas
Coast into Louisiana this afternoon into tonight.

...20z Update - Middle/Upper Texas Coast...

A line of storms along the middle/upper TX Coast to southwest LA
will continue to shift east/southeast the remainder of the
afternoon. Thunderstorms will likely continue across southern
portions of LA into tonight. Ongoing convection has at times shown
some weak and transient areas of rotation embedded within the
broader line, but has remained sub-severe. Weak instability and a
bit of a warm layer in the 850-700 mb layer (contributing to poor
lapse rates) is likely limiting stronger/more organized convection.
The strongest portion of the ongoing line, near Galveston Bay as of
1945Z will continue to shift east/southeast and offshore the coast
within the next 15-30 minutes. Thus, any low-end severe threat has
moved offshore and will remain over the offshore waters of the Gulf,
and the Marginal risk has been removed with this update.

Additional strong cells are possible into parts of southwest LA, but
this activity appears to be largely elevated and outpacing low level
moisture return, and thus surface-based instability. As such, severe
convection is not expected further east along the LA coast.

..Leitman.. 12/19/2020

.PREV DISCUSSION... /ISSUED 1030 AM CST Sat Dec 19 2020/

...Middle/Upper Texas Coast...
A shortwave trough over Texas/Oklahoma will continue to spread
generally eastward and reach the Tennessee Valley and middle Gulf
Coast late tonight. In advance of a southeastward-moving cold front
across northeast/central Texas, multi-layer cloud cover remains
prevalent late this morning as middle 60s F surface dewpoints slowly
spread inland along the middle/upper Texas coast. Modest
destabilization will steadily occur through early/mid-afternoon, but
the persistent cloud cover and increasing showers/thunderstorms will
probably limit the spatial extent of appreciable pre-frontal
destabilization over inland areas. Regardless, an increase in
surface-based deep convection is possible along the immediate coast
this afternoon. Moderately strong deep-layer/low-level shear would
support some supercells, with locally damaging winds and/or a brief
tornado possible.

It is probable that near/pre-frontal storm mergers across the
coastal plain should lead to an offshore shift of a convective band
by late afternoon/early evening. Accordingly, the most intense
convection should be relegated to the western Gulf of Mexico
tonight.

$$
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ACUS01 KWNS 201950
SWODY1
SPC AC 201949

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0149 PM CST Sun Dec 20 2020

Valid 202000Z - 211200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE
WESTERN FLORIDA PENINSULA...

...SUMMARY...
Isolated severe thunderstorms may affect parts of the western
Florida Peninsula late this afternoon and evening.

...20z Update - Western FL Peninsula...

The Marginal risk remains unchanged with this update. A strong storm
offshore Manatee County showed weak to moderate rotation over the
past hour or so. The storm has since weakened as it approaches the
coast, where instability is much weaker than further west over the
eastern Gulf waters. Nevertheless, as moisture continues to increase
ahead of a surface cold front, some modest increase in instability
is expected along the western Florida peninsula. Thunderstorms
should increase in coverage and move inland through this evening,
and a few strong storms are possible. For more details concerning
the short-term risk, see MCD 1860.

..Leitman.. 12/20/2020

.PREV DISCUSSION... /ISSUED 1029 AM CST Sun Dec 20 2020/

...Western Florida Peninsula...
Clusters of thunderstorms are ongoing over the eastern Gulf of
Mexico west/southwest of the Tampa/St Petersburg area at midday.
This inland-spreading precipitation will tend to delineate the
northward extent of modest surface-based destabilization this
afternoon as mid/some upper 60s F surface dewpoints otherwise expand
northward across the southern/central Florida Peninsula through early/mid-evening. Although the passing shortwave trough will tend
to weaken into tonight, residually strong low/mid-level winds will
support the possibility of well-organized storms/few supercells near
and across the western Florida Peninsula as additional moistening
and destabilization occur. A few damaging wind gusts and/or a
tornado could occur late this afternoon and evening.

$$
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ACUS01 KWNS 211936
SWODY1
SPC AC 211935

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0135 PM CST Mon Dec 21 2020

Valid 212000Z - 221200Z

...NO THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe thunderstorms are not expected through tonight.

...Synopsis...

A surface cold front has shifted south/southeast of the FL peninsula
and will clear the Keys within the hour. Thunderstorm activity
associated with this front remains well offshore and to the east FL
over the Bahamas. Thunderstorms are not expected for the remainder
of the period, and no changes are necessary.

..Leitman.. 12/21/2020

.PREV DISCUSSION... /ISSUED 1022 AM CST Mon Dec 21 2020/

...Synopsis/Discussion...
Deep convective potential is expected to essentially be nil over the
CONUS through tonight. A semi-amplified but progressive large-scale
pattern will prevail, highlighted by a prevalent upper trough over
the Great Lakes/Northeast States, while another shortwave
trough/associated front moves inland over the Pacific Northwest. A
cold frontal passage has ended the early day thunderstorm potential
across southern Florida. A stray lightning flash cannot be
conclusively ruled out near coastal Washington later this
afternoon/early evening. However, even with steepening mid-level
lapse rates, thermodynamic profiles are likely to remain very
marginal for lightning generation, with associated thunderstorm
probabilities remaining below 10 percent.

$$
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ACUS01 KWNS 222001
SWODY1
SPC AC 221959

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0159 PM CST Tue Dec 22 2020

Valid 222000Z - 231200Z

...NO THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Thunderstorms are generally not expected through tonight.

...20Z Update...
A few lightning flashes have occurred early this afternoon across
parts of northern Utah near an eastward-advancing cold front.
However, limited thunderstorm potential (sub-10 percent) is
perceived across the region the remainder of the afternoon/evening.

..Guyer.. 12/22/2020

.PREV DISCUSSION... /ISSUED 1016 AM CST Tue Dec 22 2020/

Relatively dry and stable conditions are expected to preclude
organized thunderstorms across the CONUS today. An isolated
lightning flash or two is possible in the Black Hills vicinity this
afternoon and evening as a strong shortwave trough approaches. This
activity should be very sparse, and may not reach sufficient depth
for charge separation.

$$
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ACUS01 KWNS 231251
SWODY1
SPC AC 231250

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0650 AM CST Wed Dec 23 2020

Valid 231300Z - 241200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE CENTRAL
GULF COAST REGION...

...SUMMARY...
A threat for damaging gusts and a few tornadoes will shift eastward
across the central Gulf Coast region, this afternoon through
tonight.

...Synopsis...
The dominant upper-air feature over the CONUS will remain a high-
amplitude, progressive, synoptic-scale trough -- initially apparent
in moisture-channel imagery from MB south-southwestward across the
central High Plains to Chihuahua. Reinforced by several shortwaves
and vorticity maxima, the associated cyclonic-flow field will shift
westward and expand through the period, covering most of the land
between the Rockies and Appalachians by 00Z. By then, the major
trough should extend from MN-NM, where it will be reshaped by a
strong, basal shortwave perturbation now digging southeastward over
UT. By 12Z, the synoptic trough should extend from the upper
Mississippi Valley across MO to central/southwest TX.

At the surface, a primary low was analyzed over southern MN. A cold
front extended from there over western IA, eastern KS, western OK,
the TX Panhandle, and central NM. The low should reach northern WI
or western Upper MI by 00Z and begin occluding, with cold front
extending across southern IL, northeastern AR, and east to south-
central TX. By 12Z, with the occluded low over eastern Lake
Superior, the cold front should be sweeping eastward to
southeastward near an axis from DTW-JKL-MOB and across the
northwestern Gulf. A secondary surface low may develop along the
cold front tonight, over parts of MS and AL, as the basal mid/upper-
level shortwave perturbation pivots eastward over central TX.

...Central Gulf Coast and vicinity...
Widely scattered to scattered thunderstorms should form by mid/late
afternoon and expand in coverage this evening, in two primary early
episodes:
1. A cold-frontal band across parts of AR and northeast/east TX,
shifting eastward across AR/LA. This activity initially will offer a
marginal severe threat as it impinges on a boundary layer somewhat
destabilized by both muted diurnal heating and synoptically forced
theta-e advection.
2. A nearly front-parallel but warm-sector low-level convergence
zone from southeast TX to northern LA, likewise shifting eastward
but not as quickly as the front. As such, the first should overtake
the second tonight, probably across portions of MS to southern LA,
forming a single primary thunderstorm band.

The combined, primary thunderstorm band, in turn, should shift
eastward along or just ahead of the front over southeastern LA, MS,
and portions of AL and the western FL Panhandle by 12Z. Late
tonight, a few thunderstorms also may move ashore in the western FL
Panhandle within a newer prefrontal convergence zone developing over
the adjoining Gulf.

Damaging gusts will be possible throughout the outlook area, along
with at least a marginal supercellular and/or QLCS tornado threat
for most of the distance inland. The greatest juxtaposition of a
favorably modified moist boundary layer with strengthening ambient
shear and low-level hodographs will be across the "slight" area this
evening and tonight. Surface dew points in the low/mid 60s F --
apparent in the partly modified warm sector over the northwestern
Gulf now, should spread inland as far north as southern AR this
afternoon and southern portions of MS/AL tonight, offsetting
marginal lapse rates enough to yield around 300-800 J/kg MLCAPE.
Meanwhile the approaching trough and its mass response will lengthen
the deep-shear vector and enlarge hodographs, with effective
shear/SRH values around 45-50 kt and 150-300 J/kg respectively,
where sustained surface-based inflow appears most probable.

Already modest boundary-layer lapse rates and low-level CAPE will
diminish with northward/inland extent across the central Gulf Coast
region, but isolated severe gusts and/or a tornado cannot be ruled
out even near the north edges of the "marginal" area where MLCAPE
less than 200 J/kg is expected. The blended severe regime should
reach the western FL Panhandle by 12Z, then continue into day-2 from
there eastward and southeastward across parts of FL/GA.

..Edwards/Smith.. 12/23/2020

$$
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ACUS01 KWNS 271246
SWODY1
SPC AC 271245

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0645 AM CST Sun Dec 27 2020

Valid 271300Z - 281200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Isolated thunderstorms are possible overnight along the central
California coast.

...Central CA coast overnight...
A midlevel shortwave trough near 36 N and 132 W will progress
eastward toward the central CA coast by 12z Monday. Cooling
midlevel temperatures and steepening low-midlevel lapse rates will
accompany this trough as it approaches the coast, in the zone of
ascent within the left-exit region of the mid-upper jet. Satellite
imagery and lightning detection data have revealed a few
thunderstorms with the trough over the eastern Pacific, and the
threat for isolated thunderstorms is expected to increase along the
central CA coast tonight, mainly after about 03-06z.

..Thompson.. 12/27/2020

$$
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ACUS01 KWNS 271942
SWODY1
SPC AC 271941

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0141 PM CST Sun Dec 27 2020

Valid 272000Z - 281200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Showers, possibly with a few embedded lightning flashes, will spread
across a portion of the southern/central California coast tonight.

...Discussion...
No changes are being made to the ongoing outlook; a few lightning
flashes remain possible near the southern California coast tonight.

..Goss.. 12/27/2020

.PREV DISCUSSION... /ISSUED 1021 AM CST Sun Dec 27 2020/

...Southern/central CA coast...
A vigorous shortwave trough near 35 N and 130 W will progress
east-southeast and reach the southern/central CA coast by 12Z
tomorrow. Cooling mid-level temperatures and steepening low to
mid-level lapse rates will accompany this trough as it approaches
the coast, in the zone of ascent within the left-exit region of a
100+ kt 500-mb jet. Lightning detection data have revealed sporadic thunderstorms just ahead of the trough over the eastern Pacific.
While buoyancy will remain scant, a threat for isolated
thunderstorms is expected along the coast between 06-12Z. This
activity will remain low-topped with the intense southwest flow
aloft holding at or above the EL, minimizing the risk for severe
storms.

$$
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ACUS01 KWNS 281934
SWODY1
SPC AC 281933

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0133 PM CST Mon Dec 28 2020

Valid 282000Z - 291200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe thunderstorms are not expected through early Tuesday.

No changes have been made to the outlook. See the previous
discussion below for more information.

..Dean.. 12/28/2020

.PREV DISCUSSION... /ISSUED 1033 AM CST Mon Dec 28 2020/

...Southern CA...
Low-topped showers with isolated thunderstorms will remain possible
into this evening within a steep low to mid-level lapse environment
amid meager buoyancy. The thunder threat will subside from west to
east along the coast as the final impulse embedded within the
broader shortwave trough (currently just offshore of Santa Barbara
county) moves southeast towards San Diego.

...Northern OK and southern KS...
Strengthening warm/moist advection between 850-700 mb may yield
scant MUCAPE by 09-12Z. A swath of elevated convection is expected
to develop during this time frame and sporadic lightning flashes
will be possible.

$$
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ACUS01 KWNS 291933
SWODY1
SPC AC 291931

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0131 PM CST Tue Dec 29 2020

Valid 292000Z - 301200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS CENTERED OVER
PORTIONS OF NORTHWESTERN TEXAS AND SOUTHWESTERN OKLAHOMA...

...SUMMARY...
A couple storms producing marginally severe hail are possible this
evening into early tonight across a portion of northwest Texas into
southwest Oklahoma.

...Discussion...
No changes to the ongoing outlook are necessary at this time.

..Goss.. 12/29/2020

.PREV DISCUSSION... /ISSUED 1012 AM CST Tue Dec 29 2020/

...Northwest TX and far southwest OK...
A shortwave trough just off the southern CA coast will dig southeast
and reach the southern Gulf of CA overnight, while a northern-stream
shortwave trough moves east-southeast from southern Saskatchewan to
MN. In the wake of the northern-stream wave, a cold front will surge
into the southern Great Plains this evening through the overnight.

The northwest extent of low to mid 50s boundary-layer dew points are
already prevalent from the Permian Basin into southwest OK, and will
gradually moisten into the mid to upper 50s amid persistent surface south-southeasterlies. By late afternoon, a dryline should take
shape across west TX, intersecting with a slow-moving
warm/quasi-stationary front near the southern TX Panhandle that
should extend northeast across western OK. The HRRR appears more
aggressive than other CAM guidance with convective development along
the dryline and front during the early evening as its parent RAP
depicts greater surface-based buoyancy than the NAM. A somewhat more
probable scenario is for convective development tonight as the High
Plains frontal surge impinges on the richer low-level moisture,
predominately rooted above the surface. Strong speed shear within
the cloud-bearing layer may prove favorable for at least transient
mid-level updraft rotation in a few cells. Weak MUCAPE and moderate
mid-level lapse rates will probably limit hail size between small to
marginally severe magnitudes.

$$
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ACUS01 KWNS 302000
SWODY1
SPC AC 301958

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0158 PM CST Wed Dec 30 2020

Valid 302000Z - 311200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS PORTIONS OF
SOUTHERN AND EASTERN TEXAS...

...SUMMARY...
Isolated severe hail and damaging winds, along with a brief tornado
will be possible through tonight across parts of east-central to
Deep South Texas.

...Discussion...
With convection continuing to evolve largely as laid out by the
reasoning in prior outlooks, only minor line adjustments appear
necessary to the forecast at this time.

..Goss.. 12/30/2020

.PREV DISCUSSION... /ISSUED 1030 AM CST Wed Dec 30 2020/

...East-central to Deep South TX...
No appreciable change appears needed to the cat 1/MRGL risk area,
although an adjustment has been made to expand the underlying
wind/tornado probabilities for this afternoon's convective threat in east-central/southeast TX.

A shortwave trough over western Chihuahua will gradually progress east-southeast towards the Coahuila/Durango border area through 12Z
tomorrow. In the wake of a northern stream shortwave trough, a
surface cold front will move southeast across eastern to south TX
through the period. The movement of the front will slow later
tonight in response to weak cyclogenesis near the lower TX, in the
zone of ascent downstream from the northern Mexico trough. This
pattern will also maintain a broad southerly low-level jet across
the TX coast that should diurnally weaken through sunset before
strengthening again late tonight, with a continued inland transport
of mid to upper 60s boundary-layer dewpoints.

The severe threat will probably occur within two phases, one this
afternoon across a portion of east-central/southeast TX and the
other overnight towards the middle TX coast. A pre-frontal
confluence arc of convection is ongoing just ahead of the impinging
cold front across central TX. A few cloud breaks ahead of this arc
should yield thin MLCAPE increasing to between 500-1000 J/kg. While
guidance generally suggests low-level flow will subside somewhat
this afternoon (with the RAP appearing more aggressive than the
NAM/ECMWF), modest hodograph curvature might prove sufficient for a
lower-end supercell or two capable of producing all hazards. The
undercutting nature of the front will further limit longevity of any surface-based supercell. After a potential lull in the severe threat
this evening, the risk for a severe storm or two should slowly
increase after 06Z tonight as deep-layer and low-level shear
gradually strengthen in the confined warm sector near the lower to
middle TX coast. The bulk of a greater tornado threat should still
await until after 12Z in the D2 period.

$$
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ACUS01 KWNS 311240
SWODY1
SPC AC 311238

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0638 AM CST Thu Dec 31 2020

Valid 311300Z - 011200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS TODAY INTO
EARLY TONIGHT FROM THE UPPER TX COAST TO SOUTHWESTERN MS...

...SUMMARY...
A few tornadoes, damaging winds, and isolated large hail will be
possible today along the upper Texas coast, and through tonight
across parts of Louisiana, Mississippi, and Alabama.

...Upper TX coast today to MS/AL overnight...
A midlevel closed low south of the Big Bend will eject northeastward
toward the Ozarks by early Friday, in response to an upstream
shortwave trough digging south-southeastward from northern CA toward northwestern Mexico. At the surface, a 1004 mb low as of 12z will
develop inland across the upper TX coastal plain today along a
quasi-stationary front, and the low will continue
north-northeastward toward the Ark-La-Tex tonight. The warm sector
(with boundary-layer dewpoints in the mid-upper 60s) will spread
inland to the east of the cyclone and contribute MLCAPE of 500-1000
J/kg today across extreme southeast TX/southwest LA, and into
tonight across southern MS and southwestern AL.

Thunderstorm development this morning will be focused along the
front near the developing surface cyclone along the upper TX coastal
plain. Convection will spread northeastward through tonight as the
cold front surges eastward across LA/MS to the south and southeast
of the cyclone. Effective bulk shear of 45-60 kt will be favorable
for organized severe storms on the nose of a 70-90 kt midlevel jet,
and low-level shear/hodograph curvature (effective SRH of 200-300
m2/s2) will be maximized in the northern portions of the warm sector
in conjunction with a southerly 40-50 kt low-level jet.

The combination of linear forcing for ascent along the cold front
and substantial cross-boundary flow and deep-layer shear vectors
will support a somewhat broken band of supercells and line segments.
Embedded supercells will also be possible in a loose band along a
secondary moisture plume from the southeastern Gulf of Mexico toward southwestern AL by tonight. Surface-based buoyancy and the strong
vertical shear will support the potential for a few tornadic
supercells, damaging gusts, and isolated marginally severe hail.
However, the magnitude of the tornado threat could be tempered some
by rather modest low-level lapse rates inland, and less-than-ideal
phasing with the ejecting midlevel trough and surface cyclone
glancing the northwest side of the surface warm sector.

..Thompson/Gleason.. 12/31/2020

$$
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ACUS01 KWNS 312044
SWODY1
SPC AC 312043

Day 1 Convective Outlook AMEND 1
NWS Storm Prediction Center Norman OK
0243 PM CST Thu Dec 31 2020

Valid 312000Z - 011200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM THE SABINE
RIVER VALLEY AREAS EASTWARD/NORTHEASTWARD ACROSS THE CENTRAL GULF
COAST STATES...

AMENDED TO ADD MRGL RISK AREA TO A PORTION OF THE EASTERN CAROLINAS

...SUMMARY...
Thunderstorms -- a few of which will likely be severe, with
tornadoes and damaging winds as the primary hazards -- will continue
from the Sabine River Valley vicinity across southwest Louisiana
through this afternoon, and then will expand across the rest of
Louisiana into Mississippi and Alabama this evening and tonight.

...Discussion...
Thunderstorms continue across portions of east Texas at this time,
and will continue spreading into western Louisiana over the next few
hours. While severe risk has remained muted thus far, the
environment downstream from the ongoing storms has become steadily
more supportive of severe/rotating storms -- both thermodynamically
and kinematically -- over the past few hours, as shown by changes in
the LCH RAOBs from 12Z to 18Z.

Thus, the ongoing outlook reasoning and areas appear to remain
representative of the evolving situation, with the only changes
which appear necessary at this time being to trim western fringes of
the areas to account for convective advance.

...Northeastern South Carolina/southeastern North Carolina...
A small cluster of thunderstorms has developed in marginally
unstable air near the northeastern South Carolina coast. Ample
shear observed across this area suggests limited/local risk for
gusty winds or a brief tornado late this afternoon. Please refer to
SWOMCD #1896 for additional short-term details.

..Goss.. 12/31/2020

.PREV DISCUSSION... /ISSUED 1028 AM CST Thu Dec 31 2020/

...Upper TX coast to MS/AL...
A mid-level closed low over western Coahuila will amplify as it
advances north into OK by early Friday, in response to an upstream
shortwave trough digging south-southeast from southern CA to Sonora.
At the surface, a 1004 mb cyclone should track north from the
Middle/Upper TX coast to northeast TX. By 06Z, this cyclone will
become increasingly occluded, yielding a T-shaped surface pattern
with the apex of the warm sector across the Ark-La-Miss as a cold
front sweeps east across the western Gulf and a west/east-oriented
warm front advances north across central portions of MS/AL. The warm
sector characterized by boundary-layer dewpoints in the mid-upper
60s will spread inland to the east of the cyclone and contribute to
MLCAPE of 500-1000 J/kg across extreme southeast TX/southern LA
through this afternoon, and into tonight across central/southern
portions of MS and AL.

Thunderstorm development has been focused near and offshore of the
Upper TX coast this morning, with multiple supercells noted
offshore. Convection will spread northeast through tonight along and
just ahead of the surging cold front. An additional swath of
convection will likely develop separately downstream across the
central Gulf coast by early evening and persist north over eastern
MS and AL through tonight within a robust low-level warm advection
regime.

Greater low-level shear and enlarged hodograph curvature will
initially be confined to the TX/LA portion of the outlook region
this afternoon before spatially expanding this evening as flow
fields strengthen downstream of the amplifying low. The combination
of linear forcing for ascent along the cold front and substantial cross-boundary flow of deep-layer shear vectors will support broken
bands of supercells and line segments, capable of producing
tornadoes and damaging winds. However, the magnitude of the tornado
threat should be tempered some by rather modest low-level lapse
rates inland, and less-than-ideal phasing with the ejecting
mid-level trough and surface cyclone glancing the northwest side of
the warm sector. 12Z HREF and recent HRRR guidance remain subdued
with the intensity and coverage of rotation potential within
simulated cells, lowering confidence for identifying a corridor of
10 percent or greater probability of significant tornadoes.

$$
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ACUS01 KWNS 011254
SWODY1
SPC AC 011252

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0652 AM CST Fri Jan 01 2021

Valid 011300Z - 021200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM EASTERN
ALABAMA AND PARTS OF THE FLORIDA PANHANDLE TO PARTS OF SOUTH
CAROLINA...

...SUMMARY...
Isolated strong-severe gusts and perhaps a tornado are possible from
eastern Alabama and parts of the Florida Panhandle to parts of South
Carolina.

...Synopsis...
In mid/upper levels, a binary cyclone system is evident in moisture-
channel imagery, within a large area of cyclonic flow covering most
of the Rockies and central CONUS. The leading cyclone is centered
over southeastern OK, and is expected to eject northeastward and
weaken through the period. By 00Z, the cyclone should be located
over IL, while beginning to phase with a northern-stream shortwave
trough now moving southeastward across northern SK. The low will
devolve into an open-wave trough thereafter, accelerating east-
northeastward to western NY and Lake Ontario by 12Z tomorrow.
Meanwhile, the upstream 500-mb low -- now over Sonora -- will pivot
across northern MX, becoming a strong, open-wave trough over the
southern Plains and northeastern MX by 12Z.

At the surface, 11Z analysis showed the main low (related to the
eastern mid/upper cyclone) over eastern OK between MLC-FSM, with an
elongated area of low pressure winding eastward along a wavy
occluded front over central AR. The triple point was drawn near the northeastern corner of MS, with warm front across northern/eastern
AL, central GA, southern SC and offshore NC. The cold front
extended across western AL to the central Gulf. The original/
occluded low should move northeastward across the Ozarks to IL,
close to the mid/upper cyclone center, while continuing to fill.

Meanwhile, a low should form today over the northeastern AR/western
KY/MO Bootheel/southern IL region and move northeastward toward the
lower Great lakes overnight, itself becoming the anchor of the
primary surface cyclone, while also increasingly stacked with
respect to the circulation aloft. The trailing cold front will move
slowly eastward as the upper low weakens and pulls away. This
boundary should be located over eastern TN, southwestern AL and the
central Gulf by 00Z. By 12Z the front should reach the western
Carolinas, GA and the central/eastern FL Panhandle. Cold-air
damming will retard warm-frontal advance over the southern
Appalachians/western Carolinas region, but the front should move
northeastward up the coastal Tidewater area through the period.

...Southeast...
Isolated to widely scattered thunderstorms will remain possible
within a loosely organized band of convection along/ahead of the
front over portions of AL, GA and the FL Panhandle, in a nominally
favorable CAPE/shear parameter space. The northeastern extent of
this activity may reach parts of SC this evening before weakening.
A tornado cannot be ruled out in any sustained supercell or wrapping
notch on an embedded quasi-linear segment, and isolated strong-
severe gusts also are possible.

Warm and moist advection will continue in the boundary layer ahead
of the primary convective swath, offsetting the modest lapse rates
aloft enough to yield a narrow corridor of around 500 J/kg of
preconvective MLCAPE today. Hodographs will be less elongated and
more looped with southeastward extent, but also smaller with time
and eastward extent over GA/SC. Effective shear will diminish
southward and southeastward into higher theta-e as well, as the
mid/upper cyclone fills and ejects northeastward away from the
region as a deamplifying wave. The resulting dampening mass
response will decrease low-level convergence with time, leading to
concerns about coverage and persistence of the strongest convection.
Given those factors, weaknesses of both low/middle-level lapse
rates and lift at various scales may preclude sufficiently
persistent deep convection to organize more than a marginal/
conditional severe threat.

..Edwards/Leitman.. 01/01/2021

$$
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ACUS01 KWNS 020051
SWODY1
SPC AC 020050

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0650 PM CST Fri Jan 01 2021

Valid 020100Z - 021200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM SOUTHEAST
GEORGIA THROUGH EASTERN SOUTH CAROLINA...

...SUMMARY...
A strong wind gust or two and a brief tornado remain possible this
evening from southeast Georgia into eastern South Carolina.

...Southeast Georgia through eastern South Carolina...

Band of relatively shallow convection with only a few embedded
lightning flashes persists along the warm conveyor belt from the
central FL Panhandle northeastward through the Middle Atlantic
region. The best chance for any additional severe weather this
evening exists from southeast GA, northeastward along and south of a
warm front situated across central SC. Surface based-convection in
this region will remain within vertical wind profiles sufficient for
a couple of rotating updrafts or bowing segments. The thermodynamic
environment in this region is very marginal, and a cooling surface
layer suggests most updrafts will probably remain slightly elevated. Nevertheless, a strong wind gust and a brief tornado cannot be ruled
out primarily through about 03Z.

..Dial.. 01/02/2021

$$
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ACUS01 KWNS 021254
SWODY1
SPC AC 021252

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0652 AM CST Sat Jan 02 2021

Valid 021300Z - 031200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE EASTERN
FLORIDA PANHANDLE INTO SOUTHEASTERN GEORGIA...

...SUMMARY...
Isolated strong to briefly severe thunderstorms may develop this
afternoon and evening, from the eastern Florida Panhandle into
southeastern Georgia.

...Synopsis...
A strongly amplified, progressive, split-flow pattern dominates the
CONUS this morning, the most prominent feature being a synoptic-
scale trough from the western Ozarks region southwestward across OK
and west-central TX, to north-central MX. This feature is expected
to evolve a broadly closed 500-mb cyclone today over OK. The
circulation center should reach the Ozarks of southern MO by 00Z,
while a basal vorticity max now over north TX ejects over parts of
AR and the Mid-South region. As the parent trough deamplifies
considerably, and a strong, compact shortwave trough digs
southeastward from the northern Rockies to the central High Plains,
the mid/upper low should reach the OH/IN border region by 12Z
tomorrow.

At the surface, 11Z analysis showed an occluded low over NY near
SYR, with a triple-point low near BID and cold front southwestward
to eastern NC, becoming quasistationary to a weak frontal-wave low
near AAF. The slow-moving cold front extended from there
southwestward across the central Gulf. Another weak low should form
along the front over the northern Gulf today and ripple
northeastward along the boundary over the FL Panhandle and portions
of GA today, delaying eastward shift of the frontal zone to its
northeast until the low passes. The low should reach eastern NC by
the end of the period. The front to its south will shift slowly eastward/southeastward, reaching eastern SC and the northwestern FL
Peninsula by 12Z.

...FL Panhandle/Southeastern GA...
Isolated strong-severe gusts are possible today into this evening in
a corridor of thunderstorms along/ahead of the front, from the
northeastern Gulf to parts of southeastern Georgia.

As the mid/upper low ejects northeastward, largely abeam of this
region, peripheral height gradients should tighten enough to
strengthen both winds aloft and deep shear. Simultaneously, mass
response to the distant passing wave will strengthen low-level mass
convergence and theta-e advection within a pre-existing belt from
the northeastern Gulf across the central/eastern FL Panhandle and
parts of southern GA. Forecast soundings indicate boundary-layer
theta-e will be just enough to yield marginal but uninhibited MLCAPE
in the 300-800 J/kg range, amidst 40-50 kt effective-shear
magnitudes favorable for at least transient supercellular
characteristics. Forecast hodographs show about 150-250 J/kg 0-1-km
SRH, with somewhat smaller effective SRH.

The main limiting factors will include weak lapse rates (including
within the boundary layer), leading to modest buoyancy, and the
band-parallel nature of cell motion, contributing to messy
convective modes. A strong preponderance of convective guidance
indicates more-westward axis of the convective corridor, especially
during the diurnal to early evening period when inflow-layer
buoyancy will be relatively maximized. As such, the outlook area is
shifted slightly back toward the front.

..Edwards/Leitman.. 01/02/2021

$$
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ACUS01 KWNS 021937
SWODY1
SPC AC 021935

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0135 PM CST Sat Jan 02 2021

Valid 022000Z - 031200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS LATE THIS
AFTERNOON ACROSS PARTS OF SOUTHEASTERN GEORGIA...

...SUMMARY...
A strong storm or two could still impact parts of southeast Georgia
late this afternoon, and pose at least some risk for severe weather.

...20Z Outlook Update...
Within a narrow plume of tropical moisture return, emanating from
near the Bay of Campeche, a convectively generated or enhanced
perturbation appears to be in the process of migrating inland off
the northeastern Gulf of Mexico. One associated small but sustained thunderstorm cluster is now progressing northeast of the Valdosta GA
area, within southwesterly deep-layer mean wind fields that are
still only modestly strong (around 40 kt, including around 30+ kt at
850 mb), but sheared.

This convection is currently rooted above rain-cooled air, but
latest objective guidance does indicate at least weak mixed-layer
CAPE developing along a zone of differential surface heating, from
near the southern flank of this convection northeastward across the
Waycross GA area. It might not be out of the question that
increasing inflow of this air mass may contribute to new,
intensifying convection in closer proximity to the differential
heating zone, where the environment may be more conducive for
activity to organize and support some severe weather risk late this
afternoon.

Otherwise, severe weather potential appears generally negligible,
particularly as latest objective analyses indicate that the boundary
layer remains stable across coastal waters between Tampa and the
Florida Big Bend, and a considerable distance into the northeastern
Gulf of Mexico.

..Kerr.. 01/02/2021

.PREV DISCUSSION... /ISSUED 1028 AM CST Sat Jan 02 2021/

...FL/GA...
A moist and marginally unstable air mass remains in place today over
parts of FL/GA/Carolinas, along and east of a surface cold front.
Scattered showers and a few thunderstorms will occur along the front
this afternoon and tonight. The overall prospects of severe storms
are low today, due to considerable cloud cover and limited
instability. Nevertheless, there is some chance of a strong storm or
two to move ashore over the FL Panhandle this afternoon and track
into southern GA. Gusty winds or a brief tornado are the main
threats.

Elsewhere across the nation, relatively dry and stable conditions
will preclude thunderstorms today.

$$
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ACUS01 KWNS 031219
SWODY1
SPC AC 031217

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0617 AM CST Sun Jan 03 2021

Valid 031300Z - 041200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe storms are not expected through tonight.

...Synopsis/Discussion...
In mid/upper levels, a progressive, split-flow pattern will
predominate, with a southern stream diverted around two
perturbations:
1. A leading cyclone -- now evident in moisture-channel imagery
over IN, forecast to move east-northeastward to New England and the
northern Mid-Atlantic region by 12Z tomorrow.
2. A trailing shortwave trough -- initially located over the
central High Plains -- that should pivot east-southeastward across
the Ozarks to the Tennessee Valley by 12Z.
Meanwhile, a strong northern-stream shortwave trough -- now over
parts of BC/WA -- will move across the northern Rockies and amplify,
reaching MB and the eastern Dakotas by the end of the period.

At the surface, a frontal-wave low was analyzed at 11Z near EWN, and
is expected to move northeastward and offshore by 16Z, while the
trailing cold front also moves east of the Outer Banks. Convection
with isolated embedded thunder potential, associated with the low/
front over the Outer Banks vicinity, should move offshore during the
next few hours. The cold front also will move southeastward down
the FL Peninsula, reaching southeastern FL and the Keys late
overnight into early morning. Weak convergence and poor low/middle-
level lapse rates should preclude thunderstorms along the FL segment
of the front.

..Edwards.. 01/03/2021

$$
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ACUS01 KWNS 031951
SWODY1
SPC AC 031950

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0150 PM CST Sun Jan 03 2021

Valid 032000Z - 041200Z

...NO THUNDERSTORM AREAS FORECAST...

...SUMMARY...
The risk for thunderstorms appears negligible across the U.S.
through tonight.

...20Z Outlook Update...
A few lightning flashes were noted with convection near the
northwestern Washington international border vicinity this morning.
This appeared to be near the southwestern periphery of the mid-level
cold core associated with a short wave perturbation, which is now
inland and in the process of progressing east of the Cascades.
Warming mid-levels in its wake likely will suppress any further such development across Pacific Northwest coastal areas through at least
12Z Monday.

..Kerr.. 01/03/2021

.PREV DISCUSSION... /ISSUED 1016 AM CST Sun Jan 03 2021/

Tranquil weather is expected over most of the CONUS today. Weak
convergence along a cold front may result in a few showers over
central and south FL, but thunderstorms are not expected over land
areas.

$$
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ACUS01 KWNS 051943
SWODY1
SPC AC 051942

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0142 PM CST Tue Jan 05 2021

Valid 052000Z - 061200Z

...NO THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe thunderstorms are not expected today.

...Discussion...
No changes to the ongoing outlook are being made in this update.

..Goss.. 01/05/2021

.PREV DISCUSSION... /ISSUED 1021 AM CST Tue Jan 05 2021/

...SC...
An intense mid/upper jet is moving eastward across the Carolinas
today, with an area of enhanced lift tracking over the region. The
pockets of coldest temperatures aloft are beginning to move
offshore, and 12z model guidance suggests that re-development of
showers behind the system will be quite isolated. While there is a
chance of a few lightning flashes over SC later today, the risk does
not appear to warrant a 10% thunderstorm outlook.

$$
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ACUS01 KWNS 061955
SWODY1
SPC AC 061953

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0153 PM CST Wed Jan 06 2021

Valid 062000Z - 071200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
EASTERN TEXAS...

...SUMMARY...
Thunderstorm capable of damaging winds, hail, and a couple tornadoes
are possible this afternoon and evening from southeastern Texas into
southern Louisiana.

...Discussion...
The ongoing outlook areas/reasoning continue to represent current
expectations, with storms now ongoing over eastern Texas, a few of
which are severe at this time.

The main changes at this point will be to adjust areas on the
western fringe of the outlook, to represent convective progression
which has occurred since the prior outlook. Expect severe risk to
continue this afternoon, and then diminish into the evening as a
combination of airmass stabilization, and given weaker instability
to the east of ongoing storms.

..Goss.. 01/06/2021

.PREV DISCUSSION... /ISSUED 1018 AM CST Wed Jan 06 2021/

...SE TX...
Latest water vapor loop shows an intense shortwave trough digging
into OK/TX. An 80+ knot mid level jet will rotate into the base of
the trough this afternoon and nose eastward across southeast TX and
the LA coast. This will result in increasing large scale forcing
and destabilization over this region, and aid in the development of thunderstorms.

Storms have already begun to form along/ahead of the advancing cold
front over central TX. Southerly low level winds ahead of the front
will help transport low/mid 60s dewpoints northward, leading to
sufficient afternoon CAPE for a few strong/severe storms. Forecast
soundings show MLCAPE values around 1000 J/kg and strong deep-layer
shear. Cooling temperatures aloft will promote the risk of hail in
the stronger cells. Near-ground shear is not expected to be
particularly strong, and linear/bowing structures are shown in most
12z CAM solutions. Therefore, it appears damaging winds are the
main threat but with some risk of a tornado or two. Storms should
move off the TX coast after dark, but strong convection may occur
along and just off the LA coast through the night and possibly
spread inland again over southeast LA towards dawn.

$$
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ACUS01 KWNS 071934
SWODY1
SPC AC 071933

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0133 PM CST Thu Jan 07 2021

Valid 072000Z - 081200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Isolated thunderstorms are possible over parts of the Southeast, and
along the Pacific Northwest coast.

...Discussion...
The only change to the outlook is to move the thunder line further
east across the Florida Panhandle to coincide with the back edge of
the ongoing convection.

..Broyles.. 01/07/2021

.PREV DISCUSSION... /ISSUED 1010 AM CST Thu Jan 07 2021/

...Southeast...
Scattered showers will continue to affect parts of AL/FL/GA/SC this
afternoon and tonight. Rich low-level moisture and instability is
generally confined to areas offshore, with very little thunderstorm
activity expected through the remainder of the period over land.
Nevertheless, there is a corridor from the FL panhandle eastward
into coastal GA/SC where a few lightning strikes will be possible.

...Pacific Northwest...
Another storm system will approach WA/OR/CA tonight, with the
potential for scattered thunderstorms offshore and along the coastal
ranges.

$$
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ACUS01 KWNS 081931
SWODY1
SPC AC 081930

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0130 PM CST Fri Jan 08 2021

Valid 082000Z - 091200Z

...NO THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Thunderstorm potential appears minimal over the U.S. mainland.

...20Z Update...
No changes have been made to the prior outlook.

..Gleason.. 01/08/2021

.PREV DISCUSSION... /ISSUED 0932 AM CST Fri Jan 08 2021/

...Synopsis...
Within the southern stream of a split flow regime, one shortwave
trough and an associated surface cyclone will move eastward off the
southeast Atlantic coast, while an upstream trough moves inland from
OR to the Great Basin. A surface cold front has moved across south
FL and the warm sector with the cyclone will likely remain offshore
of NC. Otherwise, a small cluster of lightning flashes along the OR
coast has diminished as of 1530z. Weak surface-based buoyancy will
be possible in the short term in a narrow corridor along the
immediate coast, though warming midlevel temperatures by late
morning into midday suggest that any thunderstorm threat will be
ending soon.

$$
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ACUS01 KWNS 091238
SWODY1
SPC AC 091236

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0636 AM CST Sat Jan 09 2021

Valid 091300Z - 101200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Isolated thunder may occur this afternoon and evening over parts of central/south Texas and New Mexico, and tonight over coastal areas
of northwestern California and southwestern Oregon.

...Synopsis/Discussion...
A complex, progressive, somewhat split-flow pattern will prevail in
mid/upper levels. Continental/polar air in the boundary layer, left
behind the last substantial cold-frontal passage, will render the
low-level air mass by itself unsuitable for supporting thunderstorms
over the CONUS from the Rockies eastward. However, isolated thunder
-- from convection rooted well above the surface -- may develop over
parts of the southern Rockies region (perhaps associated with winter
precip) and parts of central/south TX, this evening and overnight.
Isolated thunder also is possible late tonight over parts of the OR
and nearby CA coastlines.

The main two upper-air features relevant to convective potential
will be:

1. A strong shortwave trough now apparent in moisture-channel
imagery over the Great basin. This feature will dig southeastward
across the Four Corners region today, evolving a closed (or very
nearly so) 500-mb low this evening and overnight over NM. By 12Z,
the trough should extend from the central High Plains across far
west TX to north-central MX, with primary vorticity lobe likely
positioned between FST-ELP. A preceding swath of strong large-scale
DCVA/lift in midlevels will cross NM overnight, beneath strongly
difluent mid/upper flow, steepening 700-500-mb lapse rate quickly to
near 8 deg C/km. Where saturation occurs near the base of that
layer, CAPE may develop, straddling the -20 deg C isotherm.
Forecast soundings indicate MUCAPE will remain less than 100 J/kg,
and any resulting thunder should be very sporadic. This outlook
area appears the most marginal and uncertain of the two associated
with this perturbation, in terms of lightning-coverage potential,
due to a lack of more-robust theta-e beneath the zone of intense
midlevel cooling.

Meanwhile, a very immaturely modified, yet still marginally moist,
return-flow air mass will spread over the relatively stable boundary
layer across parts of southwest through central/southeast TX
tonight. Lapse rates steepened by warm advection and moistened at
the base of the buoyant layer will yield 100-400 J/kg MUCAPE, rooted
largely in the 600-750-mb layer. Buoyancy sill be activated by
parcels isentropically lifted to LFC, within a large area of precip
(some of it becoming snow in northwestern areas) and embedded
convection.

2. A weaker shortwave trough that now forms the basal perturbation
of a synoptic cyclone over the northeastern Pacific, south of AK.
The basal trough -- currently located west of CA between 143W-146W
-- is progged to split eastward from what is now the coldest, most lightning-active part of the cyclone. This southern lobe then
should penetrate the mean larger-scale ridge as it reaches the
northwestern CA/southwestern OR coastline around 09Z. In the few
hours before this trough reaches the coast, sufficient midlevel
cooling may occur to foster MUCAPE up to about 200 J/kg, including
some icing layers potentially supporting lightning generation. Any
thunder threat will be isolated, decreasing quickly with inland
extent.

..Edwards.. 01/09/2021

$$
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ACUS01 KWNS 091956
SWODY1
SPC AC 091954

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0154 PM CST Sat Jan 09 2021

Valid 092000Z - 101200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Isolated thunderstorms will be possible overnight across parts of
central/south Texas.

...Discussion...
No change was made to the previous convective outlook.

..Smith.. 01/09/2021

.PREV DISCUSSION... /ISSUED 1022 AM CST Sat Jan 09 2021/

...Synopsis...
A midlevel shortwave trough near the Four Corners will continue
moving southeastward toward far West TX by Sunday morning.
Low-midlevel moisture and buoyancy are quite limited across the
southern Rockies area with this trough. Farther east, a relatively
cool/dry air mass persists across the Gulf of Mexico in the wake of
a prior frontal passage. Much of the moisture return to TX will be
above the cool air mass at the surface, and forecast soundings
suggest some potential for weak buoyancy rooted near 700 mb
overnight across central/south TX. Thus, a few elevated
thunderstorms will be possible tonight in the zone of ascent/warm
advection in advance of the midlevel trough.

Otherwise, a shortwave trough over the eastern Pacific will approach
the Pacific Northwest coast late tonight and gradually weaken while
moving into the mean ridge position. The primary cold core will
pass to the north of this area, and the only weak buoyancy will be
rooted above the surface in the pre-frontal warm conveyor belt. The
overall thunderstorm threat appears too marginal to justify an
outlook area.

$$
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ACUS01 KWNS 101231
SWODY1
SPC AC 101230

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0630 AM CST Sun Jan 10 2021

Valid 101300Z - 111200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Sporadic non-severe thunderstorms are possible over south Texas and
southern Louisiana.

...Synopsis...
In mid/upper levels, the large-scale pattern will be characterized
by a broad cyclone over the Gulf of Alaska, mean ridging from CA
across the northern Rockies and northwestern Canada, and a complex,
split-flow regime of mean troughing over the central CONUS. The
principal southern-stream perturbation, around which the flow
splits, is evident in moisture-channel imagery over eastern NM and
far west TX, with a nearly closed cyclone around a 500-mb low
located over southeastern NM. The low should close fully through
the remainder of this morning and move eastward across west TX,
reaching the area between CDS-ABI by 00Z. By 12Z, the low should be
near TXK, along a deamplifying shortwave trough, then becoming an
open wave again and weakening across the Mid-South on day 2.

At the surface, a distinct low should develop off Padre Island by
around 18Z, from a trough analyzed at 11Z near a BRO-CRP-SAT axis.
The low should move east-northeastward from there across the
northwestern Gulf, and remaining south of the mainland through the
rest of the period. By 12Z, the low should be located south of
southeastern LA, with warm front arching to just south of the moth
of the Mississippi River, then southeastward over the east-central
Gulf. A cold front will trail south-southwestward from the low
across the northwestern Gulf.

...South TX...
Isolated to widely scattered thunderstorms are possible today across
much of south TX, within a broad plume of elevated, low-level warm
advection and moisture transport wrapping toward the mid/upper low.
This activity will be supported by elevated MUCAPE in the 200-500
J/kg range, rooted around 750-850 mb in southern areas and 650-750
mb from the Edwards Plateau across south-central TX.

A main convective swath -- perhaps a southward extension of the zone
of elevated frontogenetic lift now passing the AQO/SAT/COT corridor
-- should evolve through the day just inland from the lower TX Coast
and shift eastward. This activity should remain elevated and non-
severe over land, behind the developing surface cyclone. The
convection should increase in coverage and intensify after reaching
the Gulf surface low and encountering a higher-theta-e, more
surface-rooted inflow layer of the warm sector. Forecast soundings
suggest that deep shear and CAPE may become favorable for a severe
threat affecting offshore interests well south of the upper TX and
LA Coasts, but should not extend inland/north of the warm front, due
to lack of boundary-layer buoyancy.

..Edwards/Mosier.. 01/10/2021

$$
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ACUS01 KWNS 111929
SWODY1
SPC AC 111928

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0128 PM CST Mon Jan 11 2021

Valid 112000Z - 121200Z

...NO THUNDERSTORM AREAS FORECAST...

...SUMMARY...
The risk for thunderstorms appears negligible across the CONUS.

...Discussion...
No change was made to the previous convective outlook.

..Smith.. 01/11/2021

.PREV DISCUSSION... /ISSUED 0947 AM CST Mon Jan 11 2021/

Relatively dry and stable conditions are expected to preclude
thunderstorm development across the CONUS during the forecast
period.

$$
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ACUS01 KWNS 131954
SWODY1
SPC AC 131953

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0153 PM CST Wed Jan 13 2021

Valid 132000Z - 141200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe thunderstorms are not expected through tonight.

...20z Update...

The ongoing forecast remains on track. No changes have been made
with this update. See previous discussion below for forecast
details.

..Leitman.. 01/13/2021

.PREV DISCUSSION... /ISSUED 1019 AM CST Wed Jan 13 2021/

...Southeast States...
A southern-stream upper low is moving across LA/MS today, with its
associated mid level speed max approaching the southeast states.
Lift in the left-exit region of this jet will continue to result in
scattered showers across parts of MS/AL/GA this afternoon and
evening. While an isolated lightning flash is possible, it is
likely to stay below the 10% criteria for a general thunderstorm
outlook.

Later this evening, increasing large-scale ascent will shift
eastward into the Carolinas. Forecast soundings suggest a slightly
deeper unstable layer, along with a deeper moist layer. This may be
sufficient for a better chance of lightning flashes after dark over
parts of SC and southern NC.

$$
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