ACUS48 KWNS 120750
SWOD48
SPC AC 120748

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0248 AM CDT Sat Sep 12 2020

Valid 151200Z - 201200Z

...DISCUSSION...
Overall severe potential appears limited through the Day 4-8 period.
Broad upper ridging is forecast to persist across much of the CONUS
through Day 5/Wed, with any stronger westerly flow confined to the international border vicinity. By the second half of the period, the upper-level pattern is forecast to become more amplified and
progressive as a trough moves over the western states through the
weekend, and a series of troughs spread across the eastern U.S.
While guidance varies in timing, at least one cold front should
traverse parts of the Midwest mid-to-late week. However,
higher-quality moisture and instability are likely to be offset from
stronger forcing and shear, limiting severe potential.

Some severe threat, in the form of tropical cyclone-related tornado
activity could impact parts of the central Gulf Coast early in the
period as current T.D. 19 moves inland, as forecast by the National
Hurricane Center. However, uncertainty is too great at this time
frame to include severe probabilities.

..Leitman.. 09/12/2020
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ACUS48 KWNS 130832
SWOD48
SPC AC 130831

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0331 AM CDT Sun Sep 13 2020

Valid 161200Z - 211200Z

...DISCUSSION...
...Southeast States...

Some severe/tropical cyclone-related tornado threat could exist
across parts of MS/AL on Day 4-5/Wed-Thu. The National Hurricane
Center has current Tropical Storm Sally tracking slow north across
southern MS through Wednesday evening and across central/northern AL
on Thursday. Current guidance suggests low-level wind fields may
become more favorable as the system tracks more northerly and then northeasterly. However, instability is forecast to be very weak and
prolific rainfall may be more likely than severe
thunderstorm/tornado threats. Trends will continue to be monitored,
but uncertainty will preclude severe probs at this time.

...Northern/Central Plains into the Upper Midwest...

Medium range guidance is in fairly good agreement with respect to
the overall large-scale pattern through the period. A mean upper
trough will persist east of the Mississippi River through about Day
6/Fri. A more progressive pattern is then expected during the
weekend as a western shortwave trough moves east across the Pacific
Northwest and northern Rockies on Friday, and emerges over the
northern Plains around Day 8/Sun. This should result in surface low
pressure developing over the northern/central High Plains and
tracking east/northeast toward the Upper Midwest by the end of the
period. As this occurs, a cold front is likely to move across
portions of the Plains/Upper Midwest. Modest moisture return ahead
of this feature could provide enough instability for thunderstorm
activity late in the period, but timing of these features at this
time frame is uncertain, and trends will be monitored for any
increasing severe potential with time.

..Leitman.. 09/13/2020
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ACUS48 KWNS 140831
SWOD48
SPC AC 140830

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0330 AM CDT Mon Sep 14 2020

Valid 171200Z - 221200Z

...DISCUSSION...
In the D4/Thu through D5/Fri timeframe, the remaining circulation of
Tropical Cyclone Sally will migrate eastward across portions of
Georgia and South Carolina and may pose a risk for a tornado or two
and/or damaging convective wind. The track/timing of the system is
uncertain, however, and the low magnitude of the threat precludes
introduction of probabilities at this time.

Beyond that timeframe, an anticyclone will spread from the Great
Lakes eastward across the Northeast, which should maintain a nearly
stationary front along the Gulf Coast vicinity through most of the
forecast period. Only modest moisture return will occur in the
Plains ahead of the next trough that will migrate across the
northern Plains late in the forecast period. Thunderstorms are
expected, although confidence in a widespread severe threat is too
low to introduce any probabilities at this time.

..Cook.. 09/14/2020
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ACUS48 KWNS 161358
SWOD48
SPC AC 161357

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0857 AM CDT Wed Sep 16 2020

Valid 191200Z - 241200Z

...DISCUSSION...
At the beginning of the forecast period, models depict broad surface
ridging as a result of a >1035 hPa surface high in southeastern
Canada. The ridging will aid in keeping a relatively dry low-level
airmass entrenched across much of the central and eastern CONUS,
with a front from the northern Gulf of Mexico through the western
Atlantic keeping appreciable boundary-layer moisture south and east
of the U.S.

Over time, models gradually intensify a surface low over the
southern Gulf of Mexico that will reinforce northerly surface
trajectories across east Texas and the northern Gulf of Mexico.
This pattern will prevent deep moisture from returning inland over
the next few days while keeping the severe threat low.
Additionally, outside of a mid-level trough traversing the northern
Plains in the D5/Sun timeframe, an absence of mid-latitude systems
across much of the CONUS should also keep the severe threat
relatively low.

..Cook.. 09/16/2020
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ACUS48 KWNS 180850
SWOD48
SPC AC 180848

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0348 AM CDT Fri Sep 18 2020

Valid 211200Z - 261200Z

...DISCUSSION...
Deterministic medium-range guidance generally suggests that a
tropical cyclone over the western Gulf of Mexico should move slowly
along/near the TX Coast from Day 4/Monday through the middle of next
week, although predictability remains low at this extended time
frame. Refer to the latest forecasts from the National Hurricane
Center regarding the track and intensity of this system. At this
point, the potential for even weak destabilization to occur inland
is highly uncertain. Accordingly, the severe potential associated
with this tropical cyclone appears fairly low at this time, but some
chance cannot be ruled out along parts of the TX Coast into the
Southeast from Day 5/Tuesday onward. Otherwise, surface high
pressure is forecast to remain over much of the eastern CONUS next
week. This anticyclone, coupled with the tropical system over the
western Gulf of Mexico, is expected to limit substantial low-level
moisture return for most of the CONUS away from the Gulf Coast,
along with appreciable severe potential.

..Gleason.. 09/18/2020
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ACUS48 KWNS 190847
SWOD48
SPC AC 190845

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0345 AM CDT Sat Sep 19 2020

Valid 221200Z - 271200Z

...DISCUSSION...
Depending on the track of Tropical Cyclone Beta, there may be a
continued low-end severe risk along parts of the middle/upper TX
Coast into LA and perhaps the lower MS Valley from Day 4/Tuesday
through Day 6/Thursday. However, far too much uncertainty exists
regarding Beta's location at this extended time frame to include any
severe probabilities. Otherwise, severe potential across the
remainder of the CONUS will likely remain limited through Day
6/Thursday, as more substantial low-level moisture should be
confined to parts of coastal TX/LA and the lower MS Valley. By the
end of next week, large differences are apparent in guidance
regarding the synoptic-scale upper pattern across the CONUS. Some
potential for greater low-level moisture return appears possible
across parts of the MS Valley, Upper Midwest, and vicinity by next
Saturday, but predictability remains low.

..Gleason.. 09/19/2020
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ACUS48 KWNS 200832
SWOD48
SPC AC 200830

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0330 AM CDT Sun Sep 20 2020

Valid 231200Z - 281200Z

...DISCUSSION...
There are substantial differences in medium-range guidance regarding
the placement of Tropical Cyclone Beta across the vicinity of east
TX by Day 4/Wednesday. There might be a low-end severe risk across
parts of east TX into LA and perhaps the lower MS Valley/Southeast
on Day 4/Wednesday and Day 5/Thursday. However, shear and
instability are both forecast to be rather weak over these areas.
Otherwise, severe potential across the remainder of the CONUS should
remain limited through Day 6/Friday, as more substantial low-level
moisture will likely be confined to parts of east TX into LA and the
lower MS Valley/Southeast. By the end of the week and into next
weekend, guidance is coming into somewhat better agreement regarding
the placement and amplification of large-scale upper troughing over
the central CONUS. Some potential for greater low-level moisture
return appears possible ahead of this upper trough across much of
the central/eastern CONUS by Day 7/Saturday, but predictability
regarding any severe potential remains low.

..Gleason.. 09/20/2020
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ACUS48 KWNS 210853
SWOD48
SPC AC 210852

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0352 AM CDT Mon Sep 21 2020

Valid 241200Z - 291200Z

...DISCUSSION...
Depending on the progression of Tropical Cyclone Beta, some severe
threat may persist over parts of the lower MS Valley on Day
4/Thursday as it moves northeastward and merges with a weak
mid-level trough. Considerable uncertainty exists regarding Beta's
placement, and the marginal forecast shear/instability across the
lower MS Valley suggest no severe probabilities are warranted at
this time.

Farther west, an upper trough should advance eastward from the
Pacific Northwest to the northern/central Plains on Day 5/Friday.
Low-level moisture is forecast to gradually increase ahead of this
upper trough across parts of the Plains into the Upper Midwest and
MS Valley. Warm mid-level temperatures may keep the warm sector
capped across the Upper Midwest through much of the day Friday,
although deep-layer shear is forecast to be rather strong.

An isolated/marginal severe risk may exist this upcoming weekend
ahead of a cold front across a fairly broad portion of the CONUS
extending from parts of the southern Plains to the Great Lakes.
However, details remain unclear regarding the timing/amplitude of
the eastward-moving upper trough and related surface features.
Depending on this upper trough's evolution, some severe risk may
continue across parts of the eastern CONUS into early next week.
Regardless, far too much uncertainty exists to include 15% severe
probabilities at this extended time frame.

..Gleason.. 09/21/2020
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ACUS48 KWNS 230843
SWOD48
SPC AC 230842

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0342 AM CDT Wed Sep 23 2020

Valid 261200Z - 011200Z

...DISCUSSION...
Medium-range guidance is in reasonably good agreement that
large-scale upper troughing will develop and subsequently amplify
over the eastern CONUS this upcoming weekend into early next week.
Meanwhile, a highly amplified upper ridge will likely develop over
the western states in the same time frame. A surface cold front
associated with the upper trough is forecast to move across parts of
the Midwest, OH Valley, and Northeast from Day 4/Saturday through
Day 6/Monday. Although mid-level flow should be quite strong as the
frontal passage occurs, low-level moisture and related instability
are forecast to remain rather limited. This casts uncertainty on
whether any meaningful severe risk will develop across these
regions. A reinforcing cold front attendant to another, stronger
surface low may move across much of the central/eastern CONUS in the
Day 6/Monday to Day 8/Wednesday time frame. Deep-layer shear should
be strong as this second front progresses east-southeastward.
However, instability may once again be fairly weak. Too much
uncertainty exists regarding the both degree of instability and
robust storm development with either cold front passage to include
any 15% severe areas at this time.

..Gleason.. 09/23/2020
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ACUS48 KWNS 240851
SWOD48
SPC AC 240850

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0350 AM CDT Thu Sep 24 2020

Valid 271200Z - 021200Z

...DISCUSSION...
Large-scale upper troughing over the central CONUS is forecast to
amplify further on Day 4/Sunday. Large differences in medium-range
guidance emerge by early next week regarding the eastward
progression of this upper trough. If a slower solution verifies,
then organized severe thunderstorms would be possible along/ahead of
a cold front across parts of the southern Plains on Day 4/Sunday,
continuing into portions of the lower MS Valley, Southeast, and
possibly the Mid-Atlantic through at least Day 6/Tuesday. However,
if a faster eastward movement to the upper trough occurs, then
severe potential across these regions should be much less. Given
this uncertainty, no severe probabilities appear warranted through
the extended forecast period.

..Gleason.. 09/24/2020
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ACUS48 KWNS 250705
SWOD48
SPC AC 250703

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0203 AM CDT Fri Sep 25 2020

Valid 281200Z - 031200Z

...DISCUSSION...
Medium-range guidance is in relatively good agreement that upper
troughing will extend from Ontario southwestward into the central
Rockies early D4/Monday. Thereafter, model solutions quickly
diverge, showing both run-to-run variability as well as
model-to-model inconsistencies. Strong mid-level flow will accompany
this system, so the development of a few severe thunderstorms
appears possible once the upper trough interacts with the more moist
airmass across the eastern CONUS. However, this potential may be
mitigated by cloud cover and resulting limiting heating and
destabilization. Overall, predictability remains too low for much
forecast confidence at this range, but portions of the eastern CONUS
may eventually merit severe probabilities later in the forecast
cycle.

..Mosier.. 09/25/2020
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ACUS48 KWNS 260735
SWOD48
SPC AC 260734

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0234 AM CDT Sat Sep 26 2020

Valid 291200Z - 041200Z

...DISCUSSION...
Most recent medium-range model guidance is in relatively good
agreement that a dry continental air mass will cover much of the
CONUS early D4/Tuesday. A cold front will extent along the eastern
edge of this air mass, likely stretching from a low from western
Quebec southwestward along the Appalachians into the north-central
Gulf of Mexico. Showers and thunderstorms are likely ahead of this
front as it moves gradually eastward throughout the day D4/Tuesday.
Deep southwesterly flow will result in moderate vertical shear,
resulting in the potential for a few more robust/organized updrafts.
However, limited destabilization is currently expected to keep the
overall severe coverage low, precluding the need to outlook any
areas.

00Z guidance has come into better agreement regarding the potential
development of an upper low over the Southeast on D5/Wednesday. The
eastward progression of this low (and evolution of an attendant
surface low) could contribute to severe potential across the
Carolinas. However, more consistency within the guidance is still
needed for greater overall forecast confidence.

From D6/Thursday through D8/Saturday, dry and stable conditions are
currently forecast for the majority of the CONUS.

..Mosier.. 09/26/2020
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ACUS48 KWNS 270842
SWOD48
SPC AC 270840

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0340 AM CDT Sun Sep 27 2020

Valid 301200Z - 051200Z

...DISCUSSION...
Upper troughing is expected to persist across the central and
eastern CONUS from D4/Wednesday through the weekend. Stable
continental air mass and surface ridging associated with this upper
troughing will likely keep thunderstorm potential confined to south
FL. The only exception is early D4/Wednesday near a surface low over
the Carolinas. Persistent upper ridging is also expected to preclude thunderstorm development over the western CONUS.

..Mosier.. 09/27/2020
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ACUS48 KWNS 280709
SWOD48
SPC AC 280708

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0208 AM CDT Mon Sep 28 2020

Valid 011200Z - 061200Z

...DISCUSSION...
A series of shortwave troughs are forecast to rotate through the
broad upper troughing expected to persist across the central and
eastern CONUS through the weekend. Stable continental air
accompanying these shortwaves will help reinforce the continental
air mass already expected to be in place. At the same time, upper
ridging is expected to remain in place across the western CONUS.
This relatively stagnant upper pattern is not favorable for
thunderstorms across the majority of the CONUS. The only exception
is across central and southern FL where more low-level moisture will
likely persist.

..Mosier.. 09/28/2020
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ACUS48 KWNS 290843
SWOD48
SPC AC 290841

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0341 AM CDT Tue Sep 29 2020

Valid 021200Z - 071200Z

...DISCUSSION...
Medium-range model guidance is in good agreement that upper
troughing will be in place across much of the central and eastern
CONUS early D4/Friday. A shortwave trough is currently expected to
traverse this trough, moving across the northern/central Plains on
D4/Friday before continuing across the mid MS and OH Valleys on
D5/Saturday. Another shortwave trough may follow quickly in the wake
of the first.

This series of shortwaves will help maintain a stable continental
air mass across the majority of the central and eastern CONUS. Some thunderstorms do appear possible on across portions of the southern
Plains on D5/Saturday and the Lower MS Valley on D6/Sunday, ahead of
a cold front sweeping southward/southeastward. Marginal instability
is currently expected to limit coverage of severe thunderstorms.

..Mosier.. 09/29/2020
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ACUS48 KWNS 300858
SWOD48
SPC AC 300856

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0356 AM CDT Wed Sep 30 2020

Valid 031200Z - 081200Z

...DISCUSSION...
Upper pattern characterized by western CONUS ridging and eastern
CONUS troughing will likely persist through the weekend before then
losing amplitude and trending a bit more progressive early next
week. Overlap between any instability and strong vertical shear is
expected to be minimal, with medium-range guidance providing no
indications of widespread severe thunderstorms. Thunderstorms do
appear possible on across portions of the southern Plains on
D4/Saturday and the Lower MS Valley on D5/Sunday, ahead of a cold
front sweeping southward/southeastward. Thereafter, predictability
and forecast confidence are limited due to large differences within
the model guidance.

..Mosier.. 09/30/2020
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ACUS48 KWNS 010745
SWOD48
SPC AC 010744

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0244 AM CDT Thu Oct 01 2020

Valid 041200Z - 091200Z

...DISCUSSION...
Upper pattern is expected to trend towards a less amplified western
CONUS ridge/eastern CONUS trough configuration early next week.
Medium-range guidance has come into better agreement and several
shortwave troughs are expected to move within the eastern upper
trough. However, the general expectation is for the better low-level
moisture to remain displaced south of the stronger forcing for
ascent and stronger vertical shear.

..Mosier.. 10/01/2020
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ACUS48 KWNS 020743
SWOD48
SPC AC 020741

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0241 AM CDT Fri Oct 02 2020

Valid 051200Z - 101200Z

...DISCUSSION...
Large-scale mid-level ridging appears likely to persist within the
westerlies across the northern mid-latitude eastern Pacific into
western North America through the middle of next week, with broad
downstream troughing east of the Rockies into the western Atlantic.
Toward the middle of next week, there could be some re-amplification
of the ridging along an axis near the Canadian/U.S. Rockies, ahead
of a large developing mid-level trough approaching the Pacific
Coast. As this occurs, the large-scale downstream troughing may
amplify along a negatively tilted axis from Hudson Bay into western
Atlantic.

While embedded short wave developments remain much more uncertain,
this regime appears likely to maintain a west-northwesterly to
northwesterly mid-level flow across much of the nation. The
development of a southerly return flow of moisture off the Gulf of
Mexico appears unlikely, maintaining generally dry and/or stable
conditions with low convective potential.

..Kerr.. 10/02/2020
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ACUS48 KWNS 030803
SWOD48
SPC AC 030802

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0302 AM CDT Sat Oct 03 2020

Valid 061200Z - 111200Z

...DISCUSSION...
Medium-range models continue to indicate that initially broad
large-scale ridging, across the northern mid-latitude eastern
Pacific into western Northern America, may undergo amplification
while shifting eastward during the early to middle portion of the
coming work week. As this occurs, a significant short wave impulse,
digging within increasingly northwesterly flow to its east, appears
likely to contribute to substantive trough amplification along a
negatively tilted axis from the Hudson Bay vicinity into the western
Atlantic by late next week. This probably will be accompanied by
another substantive cold intrusion across the Great Lakes into the
Northeast, and a building surface ridge beneath increasingly
confluent mid-level flow, east of the Mississippi Valley and across
much of the Gulf Coast states. This should maintain/reinforce
generally dry and stable boundary-layer conditions across all but
the Florida Peninsula. Even if trends depicted in the latest
(03/00Z) ECMWF (which include the faster inland progression of a
significant mid-level trough on the leading edge of a strong zonal
flow emanating from the mid-latitude Pacific, and deeper surface
troughing across the higher plains by early next weekend) are
correct, convective potential appears low through this period.

..Kerr.. 10/03/2020
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ACUS48 KWNS 040801
SWOD48
SPC AC 040800

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0300 AM CDT Sun Oct 04 2020

Valid 071200Z - 121200Z

...DISCUSSION...
Medium-range models indicate that an initially strong, zonal
mid/upper jet, emerging from the northern mid-latitude Pacific, may
undergo considerable amplification while progressing inland across
the U.S. Pacific coast next weekend. This may include the evolution
of a large and deep mid-level trough across the Great Basin into the
Great Plains, and significant surface cyclogenesis to the lee of the
Rockies by late next weekend. This may be preceded by a developing
tropical cyclone over the Gulf of Mexico, which may eventually
accelerate northward or northeastward, inland ahead of the
amplifying trough in the westerlies.

Spread among the various model output concerning these developments
at this extended range remains quite large. However, increasing
severe weather potential appears at least a possibility, perhaps
most notably by Sunday across parts of the Great Plains. Even then,
though, while the boundary layer over the northwestern Gulf of
Mexico probably will have seasonably high dew points, the
extratropical cyclogenesis may occur rather far inland of the Gulf
coast (over the central or northern Great Plains), and low-level
moisture return through the Great Plains may just be commencing.

..Kerr.. 10/04/2020
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ACUS48 KWNS 050837
SWOD48
SPC AC 050835

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0335 AM CDT Mon Oct 05 2020

Valid 081200Z - 131200Z

...DISCUSSION...
Medium-range models continue to indicate that an initially strong,
zonal mid/upper jet, emerging from the northern mid-latitude
Pacific, will undergo considerable amplification late this week
through next weekend. It appears that this will include the
evolution of significant large-scale troughing migrating inland of
the Pacific coast, across the Great Basin, Rockies and Great Plains
by early next week. By next Sunday, deepening surface troughing and
embedded cyclogenesis to the lee of the Rockies may contribute to
potential for the development of a substantive southerly return flow
off the Gulf of Mexico, which could continue into Monday. This
could contribute to sufficient destabilization to support the
evolution of organized severe storms across parts of the Great
Plains into Mississippi Valley, in the presence of strong vertical
shear.

However, considerable spread exists within and among the various
models concerning the synoptic and sub-synoptic developments, at
this extended range. And latest model output suggests that
deep-layered low-level moisture return may be complicated by the
preceding inland migration of a tropical cyclone late this week into
early next weekend.

This cyclone (currently Tropical Depression Twenty-Six) is forecast
to intensify to hurricane strength across the Gulf of Mexico within
the next few days, then migrate inland across the north central
Gulf coast by Friday night before weakening. It too could be
accompanied by a risk for severe weather, in the form of tornadoes.
However, reinforcement of potentially cool air across much of the
Gulf States, in the days prior to landfall, contributes to
uncertainty concerning the extent of this potential inland of
immediate coastal areas.

..Kerr.. 10/05/2020
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ACUS48 KWNS 060835
SWOD48
SPC AC 060833

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0333 AM CDT Tue Oct 06 2020

Valid 091200Z - 141200Z

...DISCUSSION...
Medium-range models continue to indicate substantial amplification
within a belt of westerlies emanating from the mid-latitude Pacific
this coming weekend into early next week. This still appears likely
to include the evolution of large-scale mid/upper troughing across
and east of the Canadian and U.S Rockies by Sunday. This likely
will be accompanied by deepening surface troughing and embedded
cyclogenesis across the Canadian Prairies and U.S. Great Plains,
before shifting northeastward and eastward, toward Hudson Bay and
across the Mississippi Valley by late Monday.

This is expected to be preceded by the inland migration of Hurricane
Delta Friday night, which will pose the most substantive initial
potential for severe weather (in the form of tornadoes) during this
period. However, as is typically the case with features the scale
and nature of tropical cyclones, the extent of this risk, at this
extended range, remains unclear due to a number of uncertainties.
One in particular concerns relatively dry/potentially cool low-level
air associated with surface high pressure, which appears likely to
encompass much of the East and Gulf Coast states prior to landfall
of Delta. An elevated influx of moisture and associated rain
falling into this air mass may further reinforce stable
boundary-layer conditions preceding Delta. And this could mitigate
the risk for tornadoes inland of perhaps a small corridor near
coastal areas, before Delta weakens.

Thereafter, the most appreciable severe weather potential associated
with the extratropical cyclogenesis is probably Sunday into Monday,
before diminishing by Tuesday. The high latitude nature of the
stronger cyclogenesis (i.e. across the northern Great
Plains/Canadian Prairies into the west of Hudson Bay), and the
likely dependence on substantive moisture return from the Gulf of
Mexico for appreciable destabilization, contribute to uncertainty
which remains sizable concerning the extent of this risk.

..Kerr.. 10/06/2020
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ACUS48 KWNS 070831
SWOD48
SPC AC 070830

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0330 AM CDT Wed Oct 07 2020

Valid 101200Z - 151200Z

...DISCUSSION...
Medium-range guidance continues to indicate considerable
amplification within the westerlies across the mid-latitude Pacific
into North America this weekend into early next week. However,
there has been considerable spread within the output concerning the
short wave developments. This persists and appears to increase,
particularly through the early to middle portion of next week in the
latest model runs.

The pattern still appears likely to include the evolution of
large-scale mid-level troughing inland of the Pacific coast, through
the Canadian Prairies and U.S. Great Plains by Sunday. This
probably will be accompanied by deepening surface troughing to the
lee of the Rockies, and embedded surface cyclogenesis Sunday through
Sunday night, which may provide the focus for the most appreciable
severe weather potential during this period. Where forcing for
ascent may be most conducive, across the northern Great Plains, the
extent of this potential remains unclear due to uncertain low-level
moisture return, in the wake of inland migrating Hurricane Delta.

The remnants of Delta might still pose some risk for severe weather
east of the lower Mississippi Valley on Saturday, but
weak/negligible boundary-layer instability will probably remain a
mitigating factor, particularly as low-level wind fields and shear
weaken.

Otherwise, elsewhere through the remainder of the period, low
pattern predictability is a major issue, but guidance, in general,
appears to suggest that any severe weather potential may remain
relatively minor.

..Kerr.. 10/07/2020
--- SBBSecho 3.11-Linux
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ACUS48 KWNS 080901
SWOD48
SPC AC 080859

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0359 AM CDT Thu Oct 08 2020

Valid 111200Z - 161200Z

...DISCUSSION...
Medium-range guidance indicates that the westerlies will undergo
considerable further amplification during this period. It appears
most certain that mid-level ridging will build along a sharpening
axis just west of the U.S. Pacific coast into British Columbia.
Downstream, ensemble output depicts broad mean troughing east of the
Rockies through the Atlantic Seaboard by late next week, but
solutions are rather dispersive concerning embedded short wave
developments.

Greatest certainty exists concerning mid/upper trough amplification
along a negatively tilted axis east of the Rockies through the upper Mississippi Valley late this weekend into early next week. This is
forecast to be accompanied by significant surface cyclogenesis
across Saskatchewan into the vicinity of Hudson Bay, with a trailing
cold front surging across and east of the U.S. Great Plains.

The most appreciable severe weather potential with this system still
appears to exist on Sunday, across eastern portions of the northern
Great Plains into the upper Mississippi Valley. The extent of
northward moisture return in the wake of Delta remains uncertain,
and could remain fairly marginal for vigorous convective
development. However, a plume of initially steep lapse rates
associated with elevated mixed-layer air may still contribute to a
pre-frontal corridor of sufficient conditional and convective
instability to support severe thunderstorm development. Aided by
40-50+ kt mean lower/mid tropospheric flow, severe wind gusts may be
the primary hazard across the eastern Dakotas into Minnesota and
parts of the middle Missouri Valley.

With the suppression of the elevated mixed layer, severe weather
potential east-northeastward into the upper Great Lakes region on
Monday still looks more marginal due to less favorable thermodynamic
profiles. Through the remainder of the period, pattern
predictability remains problematic, but severe weather potential
still appears generally low at this time.

..Kerr.. 10/08/2020
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ACUS48 KWNS 090847
SWOD48
SPC AC 090845

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0345 AM CDT Fri Oct 09 2020

Valid 121200Z - 171200Z

...DISCUSSION...
A highly amplified upper trough over the Plains should move eastward
across the Midwest and Great Lakes on Day 4/Monday. A surface cold
front is likewise expected to sweep eastward across these regions.
Strong deep-layer shear will accompany the upper trough, but modest
low-level moisture return ahead of the front should tend to limit
the amount of instability present across the warm sector. A marginal
severe threat may still develop Monday afternoon across portions of
the Midwest/Great Lakes, but the overall severe risk may be tempered
by the lack of greater instability.

The cold front is forecast to move off the East Coast on Day
5/Tuesday, with strong mid-level westerly winds confined mainly to
the northern/central CONUS thereafter. Low-level offshore flow
should be generally be maintained across the southern states, which
should greatly limit instability across a large majority of the
CONUS. Accordingly, organized severe thunderstorm potential from Day
5/Tuesday through the end of the forecast period appears low.

..Gleason.. 10/09/2020
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ACUS48 KWNS 100817
SWOD48
SPC AC 100815

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0315 AM CDT Sat Oct 10 2020

Valid 131200Z - 181200Z

...DISCUSSION...
A strong mid-level westerly jet is forecast to remain confined to
parts of the northern/central CONUS through at least the middle of
next week. Greater low-level moisture will likely remain displaced
farther south, with minimal severe potential evident across the
CONUS through Day 6/Thursday. Large-scale upper trough amplification
appears possible across parts of the central/eastern CONUS by late
next week, but model differences regarding the evolution of this
upper trough are substantial. If a slower, more amplified upper
trough were to develop as some guidance suggests, then an organized
severe risk could materialize across some portion of the eastern
states around Day 7/Friday into Day 8/Saturday. However,
predictability remains far too low to include any severe
probabilities at this extended time frame.

..Gleason.. 10/10/2020
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ACUS48 KWNS 110831
SWOD48
SPC AC 110830

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0330 AM CDT Sun Oct 11 2020

Valid 141200Z - 191200Z

...DISCUSSION...
Quasi-zonal westerly mid-level flow across much of the
northern/central CONUS on Day 4/Wednesday should transition to a
more amplified pattern as large-scale upper troughing develops over
the central CONUS. Further amplification of this upper trough
appears likely across the eastern CONUS from Day 5/Thursday through
the upcoming weekend. Minimal low-level moisture return ahead of an eastward-advancing cold front across the central/eastern states
should keep organized severe thunderstorm potential low through at
least mid week. Model differences regarding the evolution of the
upper trough increase over the eastern states from Day 6/Friday
onward. Still, if a slower, more amplified upper trough were to
develop as some guidance suggests, then an organized severe risk
could materialize across some portion of the eastern states around
Day 6/Friday into Day 7/Saturday. However, predictability remains
far too low to include any severe probabilities at this extended
time frame.

..Gleason.. 10/11/2020
--- SBBSecho 3.11-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (21:1/175)

ACUS48 KWNS 120757
SWOD48
SPC AC 120755

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0255 AM CDT Mon Oct 12 2020

Valid 151200Z - 201200Z

...DISCUSSION...
Medium-range guidance is in reasonable agreement that a large-scale
upper trough will amplify as it moves across the eastern CONUS from
Day 4/Thursday into Day 5/Friday. A related surface cold front
should also advance across the eastern states in this time frame.
Modest destabilization ahead of the front may occur Friday across
parts of the Carolinas and vicinity. Depending on the timing of the
upper trough and cold front, an isolated/marginal severe threat
could develop across this area given adequate forecast shear. But, predictability still remains low. In the wake of the cold front
moving off the East Coast, severe potential appears low across the
CONUS on Day 6/Saturday. The evolution of another large-scale upper
trough over the central CONUS and Midwest/Great Lakes region appears
highly uncertain late this upcoming weekend into early next week.
Some low-level moisture return may occur ahead of this feature, but
far too much uncertainty in the synoptic-scale upper pattern
currently exists to confidently assess organized severe thunderstorm
potential at this extended time frame.

..Gleason.. 10/12/2020
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ACUS48 KWNS 130803
SWOD48
SPC AC 130802

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0302 AM CDT Tue Oct 13 2020

Valid 161200Z - 211200Z

...DISCUSSION...
A marginal/isolated severe threat may develop across parts of the
Carolinas on Day 4/Friday ahead of an eastward-moving upper trough
and surface cold front. However, the forecast combination of
instability and shear do not appear sufficient to include a 15%
severe area at this time. The cold front will clear nearly the
entire East Coast on Day 5/Saturday as the upper trough pivots
northeastward across the western Atlantic and Canadian Maritimes,
with little severe potential evident across the CONUS. The evolution
of another upper trough over the central CONUS late this upcoming
weekend into early next week still remains uncertain. Some
deterministic guidance shows a more amplified solution, which would
encourage the development of a stronger and more poleward surface
low. Depending on the timing/placement of the upper trough and the quality/northward extent of substantial low-level moisture return,
some severe risk may develop from late Day 6/Sunday through the end
of the period across parts of the southern Plains into the mid/lower
MS Valley as a cold front moves southeastward across these regions.
Regardless, predictability is too low to delineate any severe areas
at this extended time frame.

..Gleason.. 10/13/2020
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ACUS48 KWNS 140830
SWOD48
SPC AC 140828

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0328 AM CDT Wed Oct 14 2020

Valid 171200Z - 221200Z

...DISCUSSION...
Severe thunderstorm potential appears minimal across the CONUS on
Day 4/Saturday as a surface low develops northward across New
England into Canada, and a cold front clears all of the East Coast
except for south FL. There is still substantial model disagreement
in medium-range guidance regarding the degree of low-level moisture
return across parts of the southern/central Plains and lower/mid MS
Valley this upcoming weekend into early next week. These model
discrepancies mainly stem from disagreement in the evolution of
another upper trough over the north-central CONUS through early next
week. A slower evolution and eastward movement would potentially
allow for greater low-level moisture return across the central
states. Some severe threat could possibly develop across a part of
this broad region from late Day 5/Sunday through the end of the
forecast period, with a surface cold front serving as a focus for
convection. Regardless, there remains too much uncertainty regarding
the synoptic-scale pattern aloft from Day 6/Monday onward to include
any severe probabilities.

..Gleason.. 10/14/2020
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ACUS48 KWNS 150854
SWOD48
SPC AC 150852

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0352 AM CDT Thu Oct 15 2020

Valid 181200Z - 231200Z

...DISCUSSION...
An upper trough embedded within the mid-level westerlies is forecast
to move from the north-central states into the Northeast and Canada
on Day 4/Sunday. Although low-level moisture return may occur to the
south of this feature across the southern Plains vicinity, the
potential for organized severe storms appears low. Medium-range
guidance has come into somewhat better agreement regarding the
evolution of the mid/upper-level jet across the northern/central
CONUS in the early to middle portion of next week. Still,
differences remain in both the northward extent and quality of the
low-level moisture return across the central CONUS. Some guidance
suggests potential for isolated severe storms across parts of the southern/central Plains into the mid MS Valley and perhaps the
Midwest from Day 5/Monday into at least the middle of next week.
However, too much uncertainty exists regarding this severe potential
to include any probabilities at this time.

..Gleason.. 10/15/2020
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ACUS48 KWNS 190856
SWOD48
SPC AC 190854

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0354 AM CDT Mon Oct 19 2020

Valid 221200Z - 271200Z

...DISCUSSION...
...Thursday/Day 4 to Saturday/Day 6...
On Thursday, an upper-level trough is forecast to move across the
Intermountain West as southwest flow remains over the central U.S. A
cold front is forecast to advance southeastward into the Upper
Midwest as a low-level jet moves into the region from the southwest. Thunderstorms will be possible along the western edge of the
low-level jet from the central Plains northeastward into the upper
Mississippi Valley from late afternoon into the evening. Instability
is forecast to be weak suggesting any severe threat would remain
marginal.

On Friday and Saturday, the medium-range models move a cold front
southeastward across the mid Mississippi Valley and into the
southeastern U.S. Thunderstorms are expected to develop along parts
of the front both Friday and Saturday afternoon. However,
instability is expected to be weak which will again keep any severe
threat marginal.

...Sunday/Day 7 to Monday/Day 8...
Model solutions sharply diverge late in the Day 4 to 8 period. Some
solutions show an upper-level trough in the western U.S. with others
having the trough further to the east into the Great Plains. If the
model solutions with the trough further east verify, then
thunderstorms would be possible ahead of the trough on Sunday and
Sunday night from the mid Mississippi Valley and Ohio Valley
southwestward to the southern Plains. Under this scenario, the front
would move southeastward across the Ohio and Tennessee Valleys on
Monday. Isolated severe thunderstorms would be possible along parts
of the front on Monday. However, the models are forecasting weak
instability in most areas suggesting any severe threat would be
marginal.

..Broyles.. 10/19/2020
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ACUS48 KWNS 200856
SWOD48
SPC AC 200854

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0354 AM CDT Tue Oct 20 2020

Valid 231200Z - 281200Z

...DISCUSSION...
...Friday/Day 4 to Monday/Day 5...
On Friday, the medium-range models are in reasonable agreement,
moving an upper-level trough across the Intermountain West. At the
surface, a cold front is forecast to move southeastward into the
Ohio and mid Mississippi Valleys. Although instability is forecast
to be weak ahead of the front, a marginal severe threat can not be
ruled out Friday afternoon in pockets that destabilize the most.

On Saturday, the models continue in reasonable agreement with an
upper-level trough in the western U.S. and west-southwest mid-level
flow from the Great Plains to the Great Lakes. At the surface, a
cold front is forecast to be located from the lower Mississippi
Valley into the southern Appalachians. Instability along the front
is forecast to be very weak, suggesting that the severe threat could
be limited Saturday afternoon.

...Sunday/Day 6 to Tuesday/Day 8...
Model solutions diverge in the latter half of the Day 4 to 8 period.
Some solutions develop an upper-level trough across the southern
High Plains by Monday with other solutions keeping the trough
further west in Desert Southwest. The faster solutions suggest that
a large area of precipitation will develop from parts of the
southern Plains northeastward to the Ohio Valley from late Sunday
night into Monday. If this scenario pans out, then thunderstorms
would be possible along the northern edge of the moist sector on
Monday from parts of Texas east-northeastward to the Tennessee
Valley. The faster solutions suggest the thunderstorm potential
would continue into Tuesday as a cold front moves across the
southern Appalachians and Southeast. Under this scenario,
instability would be relatively weak along and ahead of the front
keeping any severe threat marginal. Predictability remains low late
in the Day 4 to 8 period.

..Broyles.. 10/20/2020
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ACUS48 KWNS 230830
SWOD48
SPC AC 230828

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0328 AM CDT Fri Oct 23 2020

Valid 261200Z - 311200Z

...DISCUSSION...
A positive-tilt large-scale trough over the western U.S. on Monday
will likely evolve into a closed mid-level low and meander eastward
into the southern Great Plains by the Wednesday-Thursday (day 6-7)
timeframe. Medium-range model guidance varies on the
timing/placement of mid-level low and subsequent surface reflection
over the lower MS Valley. Given the model predictability concerns
during the latter half of the extended period, a
predictability-too-low highlight will be maintained. If strong
storms develop during the late Wednesday through Friday period next
week, the potential at this point would focus over the lower MS
Valley and central Gulf Coast.

..Smith.. 10/23/2020
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ACUS48 KWNS 240850
SWOD48
SPC AC 240849

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0349 AM CDT Sat Oct 24 2020

Valid 271200Z - 011200Z

...DISCUSSION...
Medium-range models show a mid-level low over the southern Rockies
on Tuesday. This feature is forecast to move eastward across the
south-central U.S. during the middle part of next week, and
subsequently to the southern Appalachians/Carolinas late in the work
week. Models continue to differ on the evolution of the low/trough
with substantial model spread. Confidence is relatively low in the
quality of a returning warm sector across the central/northeast Gulf
Coast and possibly into the Carolinas during this timeframe.
Therefore, a predictability-too-low highlight characterizes the Wednesday-Friday (day 5-day 7) period.

..Smith.. 10/24/2020
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ACUS48 KWNS 250820
SWOD48
SPC AC 250819

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0319 AM CDT Sun Oct 25 2020

Valid 281200Z - 021200Z

...DISCUSSION...
The primary features influencing potential for tornadoes and
damaging gusts in the extended period will be 1) tropical cyclone
Zeta impacting the central Gulf Coast and 2) its subsequent movement
as it becomes embedded within strong flow as a mid-level low over
the south-central U.S. moves eastward towards the southern
Appalachians through Thursday (day 5). Model guidance exhibits
considerable spread during the Wednesday-Thursday period such that
the combination of uncertainty in the timing/track of Zeta and the
merging of the frontal system render predictability-too-low
highlights for the time being across the central Gulf Coast and
parts of the Southeast/Mid-Atlantic states on Thursday. By the
latter half of the extended period, a front will probably move
offshore the Southeast and a tranquil pattern for organized severe
will likely ensue.

..Smith.. 10/25/2020
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ACUS48 KWNS 260857
SWOD48
SPC AC 260856

Day 4-8 Convective Outlook CORR 1
NWS Storm Prediction Center Norman OK
0356 AM CDT Mon Oct 26 2020

Valid 291200Z - 031200Z

CORRECTED FOR DAY

...DISCUSSION...
The potential for severe thunderstorms will focus on Thursday (day
4) from the FL Panhandle northward into the southern Appalachians
and perhaps into the Mid-Atlantic states, as Zeta accelerates to the
northeast ahead of a mid-level low. Considerable uncertainty
remains regarding Zeta's track and the degree of destabilization
that can occur. In wake of Zeta, a cold front will sweep eastward
across the Southeast and move into the western Atlantic early Friday
(day 5). Model guidance is in good agreement in depicting no
appreciable return of a destabilizing warm sector into the Gulf
Coast states and eastern U.S. As a result, a quiescent pattern for
severe activity will likely begin Friday (day 5) and continue
through the end of the extended period.

..Smith.. 10/26/2020
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ACUS48 KWNS 270833
SWOD48
SPC AC 270832

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0332 AM CDT Tue Oct 27 2020

Valid 301200Z - 041200Z

...DISCUSSION...
A quiescent period for severe thunderstorms will begin on Friday
(day 4) and continue through next Tuesday (day 8) as the large-scale
upper-air pattern features a mean trough over the eastern U.S. for
much of the extended period. Dry offshore flow will occur over the
Gulf of Mexico through the period and lead to hostile conditions for thunderstorm development.

..Smith.. 10/27/2020
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ACUS48 KWNS 280709
SWOD48
SPC AC 280708

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0208 AM CDT Wed Oct 28 2020

Valid 311200Z - 051200Z

...DISCUSSION...
Models are in very good agreement in depicting a large-scale trough
to develop over the Midwest on Saturday, and subsequently over the
lower Great Lakes and Northeast Sunday through Monday. A ridge is
forecast to develop over the central U.S. in wake of the departing
eastern U.S. trough by Tuesday with a low-amplitude pattern
beginning by the end of the extended period. Dry/stable conditions
in the low levels will exist across much of the CONUS as a result of
the upcoming pattern and result in very low to nil
severe-thunderstorm potential.

..Smith.. 10/28/2020
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ACUS48 KWNS 290812
SWOD48
SPC AC 290810

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0310 AM CDT Thu Oct 29 2020

Valid 011200Z - 061200Z

...DISCUSSION...
Medium-range model guidance is in good agreement in showing the
development of a large-scale mid-level trough over the eastern U.S.
on Sunday (day 4) before exiting the East Coast into the western
Atlantic on Monday (day 5). A low-amplitude/zonal-flow pattern will subsequently overspread and influence conditions across much of the
Lower 48 on Tuesday (day 6). Models vary considerably by late in
the extended period regarding the upper-level pattern. In summary,
a low-potential severe highlight will characterize the extended
period.

..Smith.. 10/29/2020
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ACUS48 KWNS 310724
SWOD48
SPC AC 310723

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0223 AM CDT Sat Oct 31 2020

Valid 031200Z - 081200Z

...DISCUSSION...
The extended range forecast will feature a changing pattern from
zonal flow during the midweek period followed by an amplifying
large-scale trough over the West Coast towards the end of next week.
Relatively dry/stable conditions will prevail across much of the
contiguous United States and result in very low severe weather
potential for the entire extended period.

..Smith.. 10/31/2020
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ACUS48 KWNS 010729
SWOD48
SPC AC 010728

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0128 AM CST Sun Nov 01 2020

Valid 041200Z - 091200Z

...DISCUSSION...
Low potential will characterize the risk for organized severe
thunderstorms during the Wednesday through Sunday (days 4-8). A
low-amplitude upper-air pattern will gradually transition to a more
amplified pattern by the end of the work week as a trough develops
over the West Coast. Dry/stable conditions across much of the
contiguous United States will preclude the development of organized
severe thunderstorms.

..Smith.. 11/01/2020
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ACUS48 KWNS 020844
SWOD48
SPC AC 020843

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0243 AM CST Mon Nov 02 2020

Valid 051200Z - 101200Z

...DISCUSSION...
Medium-range model guidance is in good agreement in showing the
development of a large-scale trough over the West Coast late in the
work week. Models exhibit appreciable variability during the latter
part of the extended period in both the evolution of the large-scale
trough and the northward return of low-level moisture from the Gulf
of Mexico into the central U.S. The risk for organized severe
thunderstorms will gradually increase during the Sunday into Monday
(days 7-8) but uncertainty is high by this timeframe. Will opt to
describe late Sunday (day 7) through Monday (day 8) with a predictability-too-low highlight.

..Smith.. 11/02/2020
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ACUS48 KWNS 030951
SWOD48
SPC AC 030949

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0349 AM CST Tue Nov 03 2020

Valid 061200Z - 111200Z

...DISCUSSION...
Severe potential should remain low through day 4 and 5
(Friday-Saturday) as offshore flow persists over the Gulf keeping
richer low-level moisture confined to the Gulf Coast region. An
exception could be later day 5 when some of the global models
indicate south FL could be impacted by a tropical cyclone. However,
solutions differ considerably regarding the strength and trajectory
of this feature.

Days 6-7 (Sunday-Monday) Upper pattern will amplify with a large
upper trough becoming established across the western U.S. by day 6.
By day 7 a significant shortwave trough is forecast to eject
northeast through the central Plains into the upper MS Valley. While
the associated lee cyclone will contribute to the return of modified
CP air through the pre-frontal warm sector, it remains unclear if
moisture return will be sufficient for a more robust severe threat.
A better chance for severe storms might evolve by day 7 from a
portion of the central and southern Plains into the middle MS Valley
region as the strengthening cold front advances southeast and
interacts with a moistening boundary layer.

..Dial.. 11/03/2020
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ACUS48 KWNS 040924
SWOD48
SPC AC 040922

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0322 AM CST Wed Nov 04 2020

Valid 071200Z - 121200Z

...DISCUSSION...
Day 4 (Saturday) Lee cyclogenesis will occur across the central and
northern High Plains, especially during the last half of the period
as a significant shortwave trough moves through the base of a
synoptic upper low and emerges over the central High Plains late
Saturday night. The northward advection of modified CP air will
commence, but boundary layer moisture and instability are expected
to remain insufficient for a threat of severe storms.

Day 5 (Sunday) Tropical cyclone Eta is forecast by the National
Hurricane Center to approach southern FL Sunday evening and might
undergo some strengthening, but predictability is not sufficient to
introduce severe probabilities at this time.

Elsewhere,in association with a shortwave trough ejecting northeast
through the central Plains, a lee cyclone will move northeast,
reaching ND during the evening with trailing cold front extending
southward through the northern and central Plains. Modified CP air
will continue advecting northward through pre-frontal warm sector
contributing to weak instability over the northern Plains and upper
MS Valley region. Thunderstorms might develop along this front
within a strongly sheared environment from the eastern Dakotas into
MN by evening. However, the anticipated marginal thermodynamic
environment could remain a limiting factor for a more robust severe
threat.

Day 6 (Monday) Some threat for strong to severe storms might exist
as storms develop along a cold front from the Midwest into the
central Plains. Some severe threat might also persist across FL
depending on track and magnitude of a tropical cyclone associated
with remnants of Eta. In both of these scenarios, predictability and
confidence in a more substantial severe threat remain low at this
time.

..Dial.. 11/04/2020
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ACUS48 KWNS 050943
SWOD48
SPC AC 050941

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0341 AM CST Thu Nov 05 2020

Valid 081200Z - 131200Z

...DISCUSSION...
...Sunday/Day 4 to Monday/Day 5...
The medium-range models have a large upper-level low pressure system
in the western U.S. on Sunday, with southwest mid-level flow across
the central U.S. This general pattern is forecast to gradually shift
eastward on Monday. A moist airmass is forecast to be in place for
both Sunday and Monday across the Southeast. Although thunderstorms
could develop in the Southeast in areas that heat up the most, a
severe threat is not expected due to weak instability.

...Tuesday/Day 6 to Thursday/Day 8...
On Tuesday, the models quickly eject the upper-level system
northeastward out of the Rockies and into the central U.S.
Thunderstorms will be possible ahead of the system Tuesday afternoon
and evening along a front which is forecast to be located in the mid Mississippi Valley by 00Z Wednesday. Instability could be strong
enough for a marginal or isolated severe threat Tuesday afternoon.
On Wednesday, the models move the upper-level system across the
Great Lakes. If the timing of the system is correct, then a
potential for thunderstorms may develop along parts of the eastern
Seaboard. Instability is forecast to be weak along the east coast on
Wednesday which should minimize any severe potential. On Thursday,
the models move an upper-level trough quickly eastward across the
Rockies. While some moisture return could occur in the southern
Plains ahead of the system, instability is again forecast to be
weak. This would minimize any severe threat ahead of the system.

..Broyles.. 11/05/2020
--- SBBSecho 3.11-Linux
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ACUS48 KWNS 061001
SWOD48
SPC AC 060959

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0359 AM CST Fri Nov 06 2020

Valid 091200Z - 141200Z

...DISCUSSION...
...Monday/Day 4 and Tuesday/Day 5...
An upper-level low pressure system is forecast to move eastward
across the Four Corners region on Monday and into the southern
Plains on Tuesday. Some moisture return is expected ahead of the
approaching system in the southern Plains, where thunderstorm
development will be possible Monday night into Tuesday. Although an
isolated severe threat will be possible in the southern Plains, weak instability should keep any threat isolated. The potential for
thunderstorm development is forecast to continue into Tuesday
evening across the lower Missouri Valley and Ozarks but weak
instability is again expected to keep any severe threat isolated.

...Wednesday/Day 6 to Friday/Day 8...
On Wednesday and Thursday, the medium-range models move the
upper-level trough into the Great Lakes and maintain southwest
mid-level flow across much of the continental United States. A moist
airmass is forecast to be in place along the eastern Seaboard where thunderstorm development will be possible on Wednesday. The models
keep the airmass weakly unstable Wednesday afternoon along most of
the Eastern Seaboard suggesting that any severe threat will remain
marginal. On Thursday and Friday, the models quickly move an
upper-level trough across the Great Plains and into the Great Lakes
as another trough moves into the Rockies. Although thunderstorm
development will be possible ahead of this system in parts of the
Texas Coastal Plain and lower Mississippi Valley, weak instability
is again expected to keep any severe threat marginal. Predictability
is quite low during the mid week time-frame.

..Broyles.. 11/06/2020
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ACUS48 KWNS 070952
SWOD48
SPC AC 070951

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0351 AM CST Sat Nov 07 2020

Valid 101200Z - 151200Z

...DISCUSSION...
...Tuesday/Day 4 and Wednesday/Day 5...
An upper-level trough is forecast to quickly move northeastward from
the southern and central Plains into the Upper Midwest on Tuesday.
Thunderstorm development will be possible along a front from the
southern Plains north-northeastward into the upper Mississippi
Valley from Tuesday afternoon into the overnight period. Instability
is forecast to be weak along most of the front, suggesting any
severe threat will remain isolated. Surface dewpoints could reach
the lower 60s F in parts of the southern Plains where the severe
threat could be greater. However, the severe potential remains
highly uncertain due to instability concerns.

On Wednesday, the models move the upper-level trough into
southeastern Canada and maintain southwest mid-level flow across the
central and eastern United States. A moist airmass is forecast along
the Eastern Seaboard where thunderstorm development will be possible
Wednesday afternoon and evening. Although an isolated severe threat
can not be ruled out, weak instability is expected to keep any
threat marginal Wednesday afternoon.

...Thursday/Day 6 to Saturday/Day 8...
From Thursday to Saturday, the models move an upper-level trough
from the Great Plains into the northeastern U.S. Moisture return
ahead of this system is forecast to be minimal. Thunderstorms could
develop Thursday afternoon in parts of the southern Plains and along
the coast of the Carolinas during the day on Friday. But instability
in these two areas should be weak, minimizing any severe potential.
No severe threat is expected on Saturday due to limited moisture
return in the southern U.S., but predictability is quite low at the
extended ranges.

..Broyles.. 11/07/2020
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ACUS48 KWNS 080957
SWOD48
SPC AC 080955

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0355 AM CST Sun Nov 08 2020

Valid 111200Z - 161200Z

...DISCUSSION...
...Wednesday/Day 4 and Thursday/Day 5...
An upper-level trough is forecast to move quickly eastward across
the Great Plains on Wednesday as southwest mid-level flow remains
over much of the eastern half of the United States. At the surface,
a cold front is forecast to move southeastward across the
Appalachian Mountains. A moist airmass should be in place along much
of the Eastern Seaboard, where thunderstorm development will be
possible from parts of southeastern New York southward into the
Carolinas. In spite of the moisture, instability is forecast to
remain weak ahead of the front. Although a few marginally severe
storms may develop, the weak instability should keep any severe
threat very isolated.

On Thursday, the front is forecast to move to the coast of the
Carolinas. Low-level moisture will be in place ahead of the front
across parts of the Carolinas and southeastern Georgia. Although
instability should remain weak ahead of the front, a marginal severe
threat can not be ruled out along the immediate coast from Georgia northeastward to eastern North Carolina.

...Friday/Day 6 to Sunday/Day 8...
On Friday, the medium-range models move a shortwave trough across
the southern Rockies and suggest moisture will return on the Texas
Coastal Plain. Thunderstorms could develop Friday afternoon along
the western edge of this moist airmass in the Texas Hill Country.
Convective coverage may expand northeastward across parts of the
southern Plains as moisture return takes place Friday night.
However, instability along the moist axis is expected to remain
weak, keeping any severe threat marginal.

On Saturday and Sunday, model solutions sharply diverge. Some
solutions move an upper-level trough into the southern Plains while
others move an upper-level trough northeastward into the Great Lakes
region. The models do suggest a moist airmass will be in place from
parts of east Texas eastward across much of the Southeast.
Thunderstorms that form each day across this moist airmass should
have a potential for a isolated severe threat. However, weak
instability is again expected to keep any severe threat marginal.

..Broyles.. 11/08/2020
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ACUS48 KWNS 090958
SWOD48
SPC AC 090956

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0356 AM CST Mon Nov 09 2020

Valid 121200Z - 171200Z

...DISCUSSION...
...Thursday/Day 4 and Friday/Day 5...
On Thursday and Friday, the medium-range models move an upper-level
trough from the High Plains east-northeastward into the Northeast. A
cold front is forecast to move to the southern Eastern Seaboard and
central Gulf Coast. Further west, moisture return may take place in
the parts of the southern Plains on Friday as a surface low deepens
in the central High Plains. Thunderstorms will be possible during
the late afternoon near the moist axis across west Texas and western
Oklahoma. A shortwave trough approaching the southern Plains Friday
evening may support continued thunderstorm development in the
overnight period. Although instability is forecast to be weak Friday
and Friday night, an isolated severe threat will be possible.

...Saturday/Day 6 to Monday/Day 8...
On Saturday, the models move the shortwave trough into the Ozarks.
Ahead of the trough, low-level moisture is forecast to advect
northward into the lower and mid Mississippi Valley. This combined
with strong deep-layer shear, may support an isolated severe threat
from eastern Oklahoma eastward into Arkansas Saturday afternoon and
evening.

On Sunday and Monday, the shortwave trough is forecast to move
quickly eastward into the western Atlantic as a large upper-level
trough moves into the central states. Although there is a large
amount of uncertainty, thunderstorms will be possible ahead of the
trough in parts of the Southeast on Sunday, and along the Eastern
Seaboard on Monday. Instability is forecast to be weak ahead of the
trough both days, suggesting that any severe threat will be
marginal.

..Broyles.. 11/09/2020
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ACUS48 KWNS 100841
SWOD48
SPC AC 100839

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0239 AM CST Tue Nov 10 2020

Valid 131200Z - 181200Z

...DISCUSSION...
An upper trough is forecast to amplify over the West on D4,
traveling across northern Mexico and toward the MS Valley by Sat/D5.
Ahead of this trough, temperatures aloft will be warm over much of
the Southeast, but low-level moisture will increase across the lower
MS and TN Valleys, aided by the residual trajectories from Eta. Weak
low pressure is forecast to develop across the OH Valley on Sat/D5,
with a cold front trailing southwestward into AR/MS/LA. At this
time, it appears instability will remain weak, with minimal severe
threat. The ECMWF is more amplified with the upper trough than the
GFS, and may hold marginal severe potential.

While model differences still exist on Sun/D6, the general consensus
is for an 80 kt elongated midlevel speed max to nose into the
central Plains on Sat/D5, with a deepening upper trough into the OH
Valley, Great Lakes and Northeast. Given the progressive nature of
this trough, high pressure is likely to spread rapidly east from the
Plains across the Gulf of Mexico and Southeast by Mon/D7 morning,
pushing low-level moisture and any instability offshore. While
low-end severe potential may eventually materialize over parts of
the Southeast or Mid Atlantic given increasing winds aloft,
predictability is currently too low.

..Jewell.. 11/10/2020
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ACUS48 KWNS 110929
SWOD48
SPC AC 110927

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0327 AM CST Wed Nov 11 2020

Valid 141200Z - 191200Z

...DISCUSSION...
A mid/upper level trough over the Plains on Day 4/Sat will intensify
as it tracks across the Midwest and eastern U.S. through Day 5/Sun.
At the surface, low pressure will develop over the northern Plains
and deepen as it tracks eastward across the Upper Midwest on Day
4/Sat, and into Quebec by early Day 6/Mon. A trailing cold front
attendant to the low will sweep eastward across the Plains to the
Atlantic and Gulf coasts by Monday morning. Ahead of the cold front,
modest moisture will return northward through the lower MS Valley to
the lower OH and TN Valleys on Day 5/Sun, and thunderstorms will be
possible across parts of the Midwest and Mid-South vicinity. At this
time, it appears instability will be limited, and higher-quality
moisture displaces to the south of better forcing and stronger shear
profiles closer to the surface low and midlevel trough. Thus, severe
potential appears low.

The upper trough will continue to shift east across the eastern
CONUS through Day 7/Tue, while an amplified upper ridge develops
across the western and central U.S. Strong surface high pressure
will develop from the Rockies eastward behind the weekend cold
frontal passage, and persist through much of the rest of the period,
precluding severe potential through early/middle of next week.

..Leitman.. 11/11/2020
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ACUS48 KWNS 120920
SWOD48
SPC AC 120919

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0319 AM CST Thu Nov 12 2020

Valid 151200Z - 201200Z

...DISCUSSION...
An amplified yet progressive large-scale pattern will exist late
this weekend through much of next week based on latest-available
guidance. On Day 4/Sunday, an upper trough is likely to continue an east-northeastward transition over the Great Lakes/Northeast States
and Ontario/Quebec. Some thunderstorms will be possible across the
eastern third of the CONUS. While a few strong fast-moving storms
could occur, organized severe thunderstorms do not appear overly
likely at this juncture. Pre-cold-frontal moisture/buoyancy will
tend to be very limited in conjunction for the more appreciable
forcing for ascent and stronger shear.

Thereafter, the severe-weather risk should be very low through the
early/middle part of next week including Days 5-8. Appreciable
low-level moisture will be shunted southward across the Gulf of
Mexico/Florida Straits with a cold front, with high pressure and
stable conditions otherwise prevailing east of the Rockies.

..Guyer.. 11/12/2020
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ACUS48 KWNS 130909
SWOD48
SPC AC 130907

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0307 AM CST Fri Nov 13 2020

Valid 161200Z - 211200Z

...DISCUSSION...
Severe-weather potential is expected to be virtually nil for much of
the Day 4-8 time frame (Monday-Friday). An amplified yet
semi-progressive large-scale pattern will exist through much of next
week based on latest available guidance. Appreciable low-level
moisture will be shunted southward across the Gulf of Mexico/Florida
Straits in the wake of a Day 3/Sunday cold frontal passage across
the Eastern Seaboard. High pressure and stable conditions are
otherwise likely to prevail east of the Rockies for much of next
week. Low-level moisture may develop northward across the southern
Plains by late in the week (around Day 8/Friday), but considerable
guidance variability exists at this juncture.

..Guyer.. 11/13/2020
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ACUS48 KWNS 140925
SWOD48
SPC AC 140924

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0324 AM CST Sat Nov 14 2020

Valid 171200Z - 221200Z

...DISCUSSION...
Severe thunderstorm potential appears low during the Day 4-8 period.
An amplified mid/upper level pattern, with a ridge in the west and a
trough in the east, will de-amplify with time. The western upper
ridge will shift eastward, weakening over the Great Lakes and New
England through Day 6/Thu. In the wake of this feature, the upper
flow regime will become more quasi-zonal. Surface high pressure is
expected to persist over much of the eastern half of the CONUS,
resulting in dry and quiescent conditions for much of the weak. Some
weak Gulf return flow is possible across parts of the south-central
states around Days 7-8/Fri-Sat. Forecast guidance suggests at least
a weak shortwave mid/upper trough may eject across the Rockies and
into the northern/central Plains during that time, resulting in a
lee surface low and southerly low level return flow ahead of another
cold front. Details in timing and location of this feature vary, but
some shower or thunderstorm activity could return to parts of the
south-central U.S. by next weekend.

..Leitman.. 11/14/2020
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ACUS48 KWNS 150910
SWOD48
SPC AC 150908

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0308 AM CST Sun Nov 15 2020

Valid 181200Z - 231200Z

...DISCUSSION...
The risk for severe thunderstorms is expected to remain low through
the middle/late part of the week, largely owing to the initial
prevalence of high pressure east of the Rockies and associated
dry/stable conditions. An amplified large-scale flow regime will
tend to de-amplify by late in the week as the pattern trends
increasingly quasi-zonal. As this occurs, airmass modification is
expected across the south-central CONUS with a gradual northward
return of modest low-level moisture through Days 6-8 Friday-Sunday.
Regardless, the potential for organized severe storms is currently
expected to remain limited into next weekend.

..Guyer.. 11/15/2020
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ACUS48 KWNS 160927
SWOD48
SPC AC 160925

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0325 AM CST Mon Nov 16 2020

Valid 191200Z - 241200Z

...DISCUSSION...
The period will begin with a positively tilted trough over the
U.S./Canadian West Coast -- a degraded remnant of the substantial
cyclone now over the northeastern Pacific. Downstream and in low
levels, a slow-moving cold front will extend from the Great Lakes to
the southern High Plains days 4-5/22nd-23rd, largely parallel to and
south of the faster flow aloft. Strong low-level ridging over the
Southeast and Gulf Coast will be slow to retreat, precluding robust
moisture return into this regime, with organized severe potential
too low for an outlook area days 4-6.

Though details differ some at shortwave scales, operational
GFS/ECMWF/CMC, and available ensemble guidance, generally agree that
the positively tilted synoptic trough will cross the western/central
CONUS and amplifying days 5-6, with the front sagging southeastward
through the Appalachians and western Gulf Coast States.
Considerable spread occurs at mid/upper levels from day 6 onward.
Still, the general pattern of front-parallel flow aloft suggests
weak lapse rates and abundant clouds/precip near the front that
should keep severe potential generally marginal and conditional.

One exception may be near the end of the period (days 7-8/23rd-24th)
in the upper Ohio Valley to Mid-Atlantic/Northeast, if a more
intensely amplified northern-stream cyclone, as forecast by
operational ECMWF (but not deterministic GFS/CMC nor several EC
ensemble members), verifies over the southern ON/lower Great Lakes
region. Such a scenario would strengthen frontal forcing under
intense flow aloft for potential low-topped convective band(s).
However, at such a long time range, predictability is very low for
such a solution.

..Edwards.. 11/16/2020
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ACUS48 KWNS 170953
SWOD48
SPC AC 170952

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0352 AM CST Tue Nov 17 2020

Valid 201200Z - 251200Z

...DISCUSSION...
Quasi-zonal upper level pattern on Day 4/Fri will give way to a
somewhat more amplified and progressive pattern beginning Days
5-6/Sat-Sun. During this time, a series of mid/upper shortwave
troughs will migrate eastward from the western U.S. and into the
Plains. Strong surface high pressure will persist across much of the
U.S. east of the Rockies, resulting in dry, stable conditions.
However, a weak lee trough over the southern High Plains will allow
southerly low level flow to transport modest Gulf moisture northward
across the southern Plains ahead of a stalled front draped across KS
and into the lower MS/OH Valley vicinity. Surface dewpoints in the
50s to low 60s F could reside across parts of KS/OK/TX, but
cloudiness and heavy rain showers will limit instability. While
thunderstorm activity is possible for portions of the southern
Plains region during the weekend, severe potential appears limited.

Quite a bit of spread exists in forecast guidance beyond Day 6/Sun.
There is general agreement that another larger-scale trough will
eject eastward across the Rockies and into the Plains/Central U.S.
early next week. However, too much uncertainty remains at this time
scale given large spread in forecast guidance to ascertain severe
potential across parts of the southern U.S. around Days 7-8/Mon-Tue.

..Leitman.. 11/17/2020
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ACUS48 KWNS 180928
SWOD48
SPC AC 180927

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0327 AM CST Wed Nov 18 2020

Valid 211200Z - 261200Z

...DISCUSSION...
A more progressive and active weather pattern will emerge over the
CONUS during the Day 4-8 time period. A series of mid/upper troughs
will migrate from west to east across the country, bringing chances
for thunderstorm activity to parts of the southern/central Plains
eastward to the Mid-Atlantic. The first trough will shift eastward
from the Plains to the Atlantic coast Day 4/Sat through Day 7/Tue.
The second trough will dig across the western states beginning late
Day 5/Sun and emerge over the Plains on Day 7/Tue. Strong surface
high pressure over the eastern U.S. initially will preclude much in
the way of strong Gulf return flow over the south-central and
southeast states. Given limited moisture and a pattern more typical
of anafrontal precipitation, severe thunderstorms are not expected,
though some isolated thunderstorm activity could be embedded in
periods of moderate to heavy rain from the central/southern Plains
to the Midwest through Day 5/Sun and into the Northeast on Day
6/Mon.

Another round of rain and thunderstorms is expected to develop over
the central/southern Plains as the second upper trough ejects
eastward across the Rockies around Day 7/Tue. Forecast guidance
varies in the timing and intensity of this system, so confidence is
low in the later parts of the forecast period, though some
thunderstorm potential is expected to spread eastward across much of
the eastern portions of the CONUS. Depending on low level moisture
and degree of destabilization that could occur, some low-end strong
to severe thunderstorm potential could unfold across the Southeast
by the middle of next week, but uncertainty is too great to include probabilities at this time.

..Leitman.. 11/18/2020
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ACUS48 KWNS 190939
SWOD48
SPC AC 190937

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0337 AM CST Thu Nov 19 2020

Valid 221200Z - 271200Z

...DISCUSSION...
A progressive upper level pattern is expected during the Day 4-8
period. An upper trough over the Plains on Day 4/Sun will shift
eastward to the Atlantic coast through Day 5/Mon. At the same time,
a surface cold front will sweep east/southeast from the southern
Plains through the Midwest and eastern U.S., moving well offshore
the Atlantic coast by Day 6/Tue. Showers, and perhaps isolated
thunderstorms, are expected to accompany the frontal passage, but
mostly stable boundary-layer conditions will preclude severe
thunderstorm concerns through Day 5/Mon.

As this initial upper trough shifts east of the MS River on Day
5/Mon, an upper ridge will briefly amplify over the Plains.
Meanwhile, a western upper trough will deepen and shift eastward
toward the southern Rockies on Monday, and the central/southern
Plains on Day 6/Tue. Strong deep layer southwesterly flow will
overspread the southern Plains vicinity, and height falls will
result in strengthening lee cyclogenesis developing eastward across
the central/southern Plains Monday night through Tuesday. Increasing
southerly low level flow will transport somewhat modest Gulf
moisture northward. However, medium range guidance is in fairly good
agreement that surface dewpoints as high as the low to mid 60s F are
possible as far north as southern OK. How much destabilization will
ultimately occur remains somewhat uncertain, as the cold frontal
passage on Sunday/Monday could cut-off Gulf return flow more than
guidance currently indicates. Additionally, cloudiness and showers
in a strong warm advection regime could limit destabilization ahead
of the surface low/front. Nevertheless, overall pattern favors at
least some concern for isolated strong/severe thunderstorm potential
across the southern Plains vicinity on Day 6/Tue, but uncertainty
remains too high at this time to introduce probabilities.

Beyond Tuesday, spread among various guidance increases
dramatically, and predictability is low.

..Leitman.. 11/19/2020
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ACUS48 KWNS 200950
SWOD48
SPC AC 200948

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0348 AM CST Fri Nov 20 2020

Valid 231200Z - 281200Z

...DISCUSSION...
Organized severe thunderstorm potential appears low across the CONUS
on Day 4/Monday as a large-scale upper trough shifts eastward from
the western states to the Plains. Lee cyclogenesis should occur over
the central Plains ahead of the amplifying upper trough, with some
low-level moisture return occurring over the southern Plains. As the
southern portion of the upper trough consolidates and ejects
eastward across the southern Plains into the lower MS Valley and
Southeast from Day 5/Tuesday into Day 6/Wednesday, some severe
thunderstorm potential could materialize across parts of these
regions. At this point, instability appears fairly limited, which
should keep any severe threat isolated/marginal.

The upper trough may outpace the limited low-level moisture by Day
7/Thursday across parts of the eastern states, which suggests that
the severe risk will probably be lower compared to prior days. By
the end of next week, large differences emerge in medium-range
guidance regarding the evolution of another upper trough over the western/central CONUS. Depending on this trough's amplification and
the degree of low-level moisture return, it appears possible that a
severe threat could develop across parts of the southern Plains
around Day 8/Friday. Regardless, predictability remains very low at
this extended time frame.

..Gleason.. 11/20/2020
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ACUS48 KWNS 210946
SWOD48
SPC AC 210945

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0345 AM CST Sat Nov 21 2020

Valid 241200Z - 291200Z

...DISCUSSION...
At least an isolated/marginal severe threat should exist on Day
4/Tuesday across parts of the southern Plains into the Ozarks and
lower MS Valley as an upper trough/low ejects eastward over these
regions. Low-level moisture return ahead of a surface low and
related cold front may be sufficient to support surface-based storms
from Tuesday afternoon onward. Deep-layer shear appears more than
sufficient for organized severe storms, but some uncertainty exists
regarding how much instability will ultimately develop. Given this
uncertainty, will hold off for now on including a 15% severe area on
Day 4/Tuesday across any portion of the southern Plains vicinity,
but will reevaluate this possibility in future outlooks.

As the upper trough/low continues east-northeastward across the
central/eastern CONUS on Day 5/Wednesday, a low-end/marginal severe
threat may continue across parts of the lower MS Valley and
Southeast. However, medium-range guidance begins to diverge in the
placement and amplitude of the upper trough/low by Wednesday
evening. It also appears possible that any storms ongoing Wednesday
morning across the lower MS Valley/Mid-South may outpace the
low-level moisture return across the Southeast through the day.
Given these large-scale pattern predictability issues and concerns
about sufficient instability across the warm sector, a 15% severe
area has not been included across the lower MS Valley into the
Southeast for Day 5/Wednesday.

Substantial differences in the synoptic-scale pattern across the
CONUS continue from Day 6/Thursday through the end of the forecast
period. Even so, there appears to be some signal for another
large-scale upper trough to move from the western CONUS to the
Plains in the Day 7/Friday to Day 8/Saturday time frame. Depending
on the evolution of this upper trough/low and how much low-level
moisture return occurs ahead of it, there may be an increase in
severe potential across portions of the southern Plains and lower MS
Valley from Day 7/Friday into Day 8/Saturday. Regardless,
predictability remains far too low to delineate any severe areas at
this extended time frame.

..Gleason.. 11/21/2020
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ACUS48 KWNS 220928
SWOD48
SPC AC 220926

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0326 AM CST Sun Nov 22 2020

Valid 251200Z - 301200Z

...DISCUSSION...
As an upper trough/low moves across the central/eastern CONUS on Day 4/Wednesday, an isolated/marginal severe risk may continue across
parts of the lower MS Valley, TN Valley, and Southeast. Limited
low-level moisture and weak instability forecast across these
regions should temper the overall severe risk. Another large-scale
upper trough is forecast to develop eastward across the
western/central CONUS late this upcoming week. Medium-range guidance
is in general agreement with this scenario, although details in
surface low placement across the southern Plains and the northward
extent of the warm sector ahead of the upper trough remain rather
unclear. An organized severe thunderstorm risk appears possible in
association with this ejecting upper trough/low from Day 6/Friday
through Day 8/Sunday over some portion of the southern Plains, lower
MS Valley, and Southeast. Regardless, the timing/amplitude of this
feature and amount of instability that may be present remain too
uncertain to include 15% severe probabilities at this extended time
frame.

..Gleason.. 11/22/2020
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ACUS48 KWNS 230938
SWOD48
SPC AC 230936

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0336 AM CST Mon Nov 23 2020

Valid 261200Z - 011200Z

...DISCUSSION...
A positively tilted large-scale upper trough should develop eastward
across the western/central states on Day 4/Thursday. In the wake of
a prior frontal intrusion, low-level moisture may return northward
across parts of TX and the lower MS Valley from Day 4/Thursday into
Day 5/Friday. Depending on the evolution of this upper trough and
whether it closes off over the Southwest, it appears possible that
at least an isolated/marginal severe threat may develop across parts
of the southern Plains, lower MS Valley, and Southeast, mainly from
Day 5/Friday into the upcoming weekend. Regardless, too much
uncertainty currently exists regarding the placement/amplitude of
the upper trough/low and related surface features to include any 15%
severe probabilities at this time.

..Gleason.. 11/23/2020
--- SBBSecho 3.11-Linux
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ACUS48 KWNS 240953
SWOD48
SPC AC 240952

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0352 AM CST Tue Nov 24 2020

Valid 271200Z - 021200Z

...DISCUSSION...
The evolution of a positively tilted upper trough across the
western/central CONUS remains uncertain from Day 4/Friday into the
upcoming weekend. Some medium-range guidance indicates that the
southern portion of the upper trough will close off over the Four
Corners vicinity on Day 4/Friday, and then move slowly eastward
across the southern Plains and lower MS Valley through the weekend.
Other guidance suggests that the upper trough will not close off,
and will instead progress eastward more rapidly. Regardless of which
scenario occurs, some severe threat may exist across parts of
central and coastal TX on Day 4/Friday, the lower MS
Valley/Southeast on Day 5/Saturday and Day 6/Sunday, and perhaps a
portion of the East Coast on Day 7/Monday. However, far too much
uncertainty exists in the synoptic-scale pattern over the
central/eastern CONUS to include 15% severe probabilities at this
time.

..Gleason.. 11/24/2020
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ACUS48 KWNS 260902
SWOD48
SPC AC 260900

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0300 AM CST Thu Nov 26 2020

Valid 291200Z - 041200Z

...DISCUSSION...
It appears increasingly probable that a closed upper low over the
southern Plains will merge with a northern-stream upper trough over
the eastern CONUS on Day 4/Sunday, likely forming a highly amplified
upper trough/low by Day 5/Monday. Medium-range guidance is in
reasonably good agreement in depicting a deepening surface low
developing from coastal LA Sunday morning northeastward to the
Mid-Atlantic vicinity by Day 5/Monday.

As greater low-level Gulf moisture advances inland across parts of
the Southeast and Mid-Atlantic in tandem with the deepening surface
low, weak instability may develop across the warm sector of this
cyclone. Rapidly strengthening low and mid-level wind fields suggest
that organized severe storms capable of producing at least isolated
damaging winds may occur over parts of the Deep South into the
Carolinas on Day 4/Sunday, and from the Carolinas into eastern
portions of the Mid-Atlantic on Day 5/Monday.

At this point, it remains very uncertain how much surface-based
instability will ultimately develop across these regions, which will
have a large impact on overall severe potential. This uncertainty
precludes the introduction of 15% severe probabilities for now.
However, the severe potential for this system will be reevaluated in
later outlook updates. Once the cold front associated with this
cyclone clears the East Coast, severe thunderstorm potential appears
minimal across the CONUS on Day 6/Tuesday and Day 7/Wednesday.

..Gleason.. 11/26/2020
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ACUS48 KWNS 270946
SWOD48
SPC AC 270945

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0345 AM CST Fri Nov 27 2020

Valid 301200Z - 051200Z

...DISCUSSION...
A continued isolated/marginal severe threat may continue across
mainly eastern parts of the Carolinas and Mid-Atlantic as a
large-scale upper trough/low moves slowly across the eastern CONUS
on Day 4/Monday. Strong low/mid-level flow is forecast to be present
over these regions ahead of a cold front, but instability should
remain weak across the warm sector owing to fairly limited low-level
moisture. Confidence in a more substantial severe threat on Day
4/Monday remains too low to include 15% severe probabilities at this
time. Minimal potential for organized severe thunderstorms is
anticipated across the CONUS for Day 5/Tuesday and Day 6/Wednesday,
as offshore low-level trajectories should be maintained over much of
the Gulf of Mexico and western Atlantic. Predictability of the
synoptic-scale pattern in medium-range guidance appears low by late
next week, with any low-end severe potential remaining confined to
parts of the central/eastern Gulf Coast vicinity and possibly FL.

..Gleason.. 11/27/2020
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ACUS48 KWNS 010858
SWOD48
SPC AC 010857

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0257 AM CST Tue Dec 01 2020

Valid 041200Z - 091200Z

...DISCUSSION...
Most recent guidance from several deterministic models suggests some
severe potential may materialize across the Southeast D4/Friday and Mid-Atlantic on D5/Saturday. These models forecast a maturing
mid-latitude cyclone moving through those regions. However, previous
runs do not show a mature system, with most favoring a weaker, more
progressive evolution. Additionally, the ECMWF, which has shown more
run-to-run consistency, is forecasting mature low over the
Southwest/northern Mexico which slowly drifts eastward toward the
southern Plains during the weekend. All of these factor lead to a
low forecast confidence for the weekend. Even with these
differences, mostly stable conditions appear likely beginning
D6/Sunday and continuing through early next week.

..Mosier.. 12/01/2020
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ACUS48 KWNS 020949
SWOD48
SPC AC 020947

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0347 AM CST Wed Dec 02 2020

Valid 051200Z - 101200Z

...DISCUSSION...
Severe potential appears minimal this weekend through at least the
middle of next week. Shortwave trough over the northern Mid-Atlantic
States early D4/Saturday is expected to continue progressing
northeastward off the Northeast coast. Another shortwave trough is
expected to drop from the northern Plains/Upper MS Valley into the
Mid MS/Lower OH Valley on D5/Sunday and D6/Monday, with another
shortwave likely following. This series of shortwave troughs coupled
with persistent upper ridging across the western CONUS will help
maintain a dry, stable air mass east of the Rockies through at least D8/Wednesday.

The only severe potential appears to be early on D4/Saturday from
the Carolina coast into the Delmarva. Some of the guidance has
trended less progressive with a shortwave trough and its attendant
surface low, resulting in modest low-level moisture ahead of an
approaching cold front. Variability within the guidance curtails predictability, but even the less progressive solution yields only
limited overall severe potential.

..Mosier.. 12/02/2020
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ACUS48 KWNS 030948
SWOD48
SPC AC 030946

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0346 AM CST Thu Dec 03 2020

Valid 061200Z - 111200Z

...DISCUSSION...
A shortwave trough is expected to drop from the northern
Plains/Upper MS Valley into the Mid MS/Lower OH Valley on D4/Sunday,
continuing eastward through the TN Valley and into Mid-Atlantic on
D5/Monday. Upper ridging is anticipated across the central and
eastern CONUS in the wake of this shortwave from D6/Tuesday through D8/Thursday. As a result, stable conditions are anticipated across
the eastern CONUS for the entire period.

Farther west, an upper low is forecast to develop on D4/Sunday or
D5/Monday across the Great Basin before moving southward off the
southern CA/Baja coast. Some severe could be possible when/if this
low ejects northeastward across Mexico into the southern Plains late
next week. However, the overall evolution of this low remains
uncertain and forecast confidence past D7/Wednesday is low.

..Mosier.. 12/03/2020
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ACUS48 KWNS 040918
SWOD48
SPC AC 040917

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0317 AM CST Fri Dec 04 2020

Valid 071200Z - 121200Z

...DISCUSSION...
Severe potential appears low during the Day 4-8 period. A mean
trough will persist across the eastern U.S. through Day 5/Tue.
During this time, an upper ridge will spread eastward from portions
of the western U.S. to the Plains. Meanwhile, a mid/upper low over
CA will become cut-off and migrate southwest over the Pacific
offshore from southern CA/northern Baja through Day 6/Wed. By Day
7/Thu, medium range guidance develops the CA/Baja upper low eastward
across northern Mexico/southern AZ/NM, with an open wave upper
trough ejecting into the southern Plains on Day 8/Fri. Overall,
surface high pressure across much of the CONUS and dearth of
boundary layer moisture will preclude severe thunderstorm potential
through at least Day 6/Wed. Thunderstorm activity may increase late
in the period as southwesterly deep layer flow increases ahead of
the southwestern U.S./northern Mexico upper low/trough. However,
severe storms appear unlikely at this time given poor northward
return of Gulf moisture in advance of this system, likely leading to
poor thermodynamics.

..Leitman.. 12/04/2020
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ACUS48 KWNS 050812
SWOD48
SPC AC 050810

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0210 AM CST Sat Dec 05 2020

Valid 081200Z - 131200Z

...DISCUSSION...
Severe potential is not expected for much of the Day 4-8 period. Dry
and stable conditions will prevail beneath an upper ridge developing
eastward from the western U.S. into the central and eastern U.S.
through Day 5/Wed. In the wake of the upper ridge, a shortwave
trough will dig across the Pacific Northwest and northern Rockies on
Day 6/Thu, and a persistent closed low off the southern CA/northern
Baja coast will eject eastward along the northern
Mexico/southwestern U.S. border. As the upper trough ejects eastward
toward the southern Rockies, at least weak lee cyclogenesis is
forecast. This should allow some degree of Gulf return flow ahead of
a southeastward-advancing cold front late Thursday into Days
7-8/Fri-Sat across TX into the northern Gulf Coast region. Medium
range guidance varies in the northward extent of moisture return and
the exact track of the associated surface low. While increasing
potential for thunderstorms appears likely Days 7-8, severe
potential is still uncertain.

..Leitman.. 12/05/2020
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ACUS48 KWNS 060854
SWOD48
SPC AC 060853

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0253 AM CST Sun Dec 06 2020

Valid 091200Z - 141200Z

...DISCUSSION...
An upper ridge will spread eastward across the Plains toward the MS
River on Day 4/Wed as a shortwave trough digs south and east across
the Pacific Northwest and northern Rockies. At the same time, the
persistent cut-off upper low off the southern CA/northern Baja coast
will develop eastward along the international border. This will
bring increasing chances for rain and perhaps a few thunderstorms to
portions of the southwestern U.S. Wednesday and Thursday.

By Day 5/Thu, the northern Rockies trough and the southwestern upper
low will merge into a larger-scale trough, and eject eastward from
the Rockies into the Plains by early Day 6/Fri. In response, lee
cyclogenesis is forecast over the southern/central Plains. Strong
southwesterly deep layer flow will overspread the southern Plains
into the mid MS Valley late Thursday, and southerly Gulf return flow
will develop across the south-central U.S. As this system shifts
eastward through Day 6/Fri and Day 7/Sat, thunderstorm potential
will increase across portions of the southern Plains into the lower
MS Valley, and perhaps as far north as the mid-MS/lower OH Valleys.
However, severe potential is uncertain. The quality of low level
moisture return could be limited to a small portion of the Sabine
and lower MS Valleys, and may be ill-timed with the passage of the
upper trough and surface cold front. Additionally, medium range
guidance varies in the intensity of the developing surface cyclone,
and in timing of the eastward-advancing cold front from the Plains
into the Midwest. As such, predictability is too low to include any
severe probabilities.

..Leitman.. 12/06/2020
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ACUS48 KWNS 070933
SWOD48
SPC AC 070931

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0331 AM CST Mon Dec 07 2020

Valid 101200Z - 151200Z

...DISCUSSION...
An upper trough over the western states will shift eastward into the
Plains through Day 5/Fri. In response to height falls, lee
cyclogenesis is expected, and a surface low will develop eastward
across the central/southern Plains vicinity on Thursday into early
Friday. Southerly low level flow ahead of the surface low and
attendant cold front will bring modest Gulf moisture northward
across east TX into the Ark-La-Miss on Friday. This system will
continue to develop eastward across the Midwest and Southeast on Day
6/Sat and early Day 7/Sun.

Isolated thunderstorm potential will increase across parts of the
southern Plains late Thursday night in a strong warm advection
regime associated with the deepening surface low and advancing
mid/upper trough. By Friday, some low-end severe potential could
exist across parts of east TX and persist eastward into the lower MS Valley/Gulf Coast vicinity through Saturday. However, this will
largely depend on the quality of Gulf moisture return, which will
influence instability in an otherwise strongly-sheared environment.
As such, confidence remains low concerning organized severe
potential on Days 5-6/Fri-Sat, though probabilities could become
necessary in subsequent outlooks.

..Leitman.. 12/07/2020
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ACUS48 KWNS 080948
SWOD48
SPC AC 080947

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0347 AM CST Tue Dec 08 2020

Valid 111200Z - 161200Z

...DISCUSSION...
A large-scale upper trough with several embedded shortwave troughs
will slowly migrate across the Plains and central U.S. Days
4-5/Fri-Sat. Strong southwesterly flow amid height falls will result
in a strengthening surface low developing northeast from the
southern Plains early on Friday to the lower Great Lakes vicinity by
Day 6/Sun morning. Low level Gulf return flow will spread moisture
northward ahead of a cold front attendant to the low. Better-quality
moisture will be confined to the TX Gulf Coast eastward to the lower
MS Valley and thunderstorms are likely to increase by Friday
afternoon along the front. Some low-end severe threat could develop
from east TX into the lower MS Valley through Saturday, but
uncertainty remains regarding how much destabilization will be able
to occur whether moisture return will be ill-timed with the frontal passage/strongest forcing.

Beyond Day 5/Sat, medium range guidance varies greatly in the
evolution of the larger-scale trough over the central U.S. and
predictability is low.

..Leitman.. 12/08/2020
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ACUS48 KWNS 130908
SWOD48
SPC AC 130907

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0307 AM CST Sun Dec 13 2020

Valid 161200Z - 211200Z

...DISCUSSION...
A significant, remnant short wave perturbation, accelerating out of
the southern Great Plains by Tuesday, may reach the southern Mid
Atlantic coast by Wednesday evening. As it approaches the coast,
medium-range models indicate that it will support substantive
further deepening of a frontal wave initially developing off the
South Carolina coast by daybreak Wednesday. It might not be
entirely out of the question that a moistening and destabilizing
warm sector boundary layer could spread across parts of the North
Carolina Outer and Inner Banks vicinity Wednesday afternoon or
evening. However, at this point, this seems a low probability, and
it is not clear that this would support more than a low severe
thunderstorm risk.

Otherwise, mid/upper flow is forecast to become more zonal across
Canada later this week through next weekend, with much of the U.S.
remaining under the influence of branching westerlies emanating from
the mid-latitude Pacific. It appears that this may include a number
of relatively fast moving short wave perturbations. While the
potential for significant surface cyclogenesis appears low, even if
one of these is able to support at least modest cyclogenesis near
Gulf coastal areas, it is not clear that the Gulf boundary layer
will be able to modify sufficiently to support a substantive inland
return flow of moisture.

..Kerr.. 12/13/2020
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ACUS48 KWNS 140923
SWOD48
SPC AC 140922

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0322 AM CST Mon Dec 14 2020

Valid 171200Z - 221200Z

...DISCUSSION...
Medium-range models suggest that branching flow downstream of a
strong western/central mid-latitude Pacific jet may become more
amplified early next week. Until then, it appears there will be
little change, with much of the U.S. remaining under the influence
of one prominent belt, with a number of progressive embedded short
waves. Guidance indicates that potential for strong surface
cyclogenesis to the east of the U.S. Rockies is low during this
period, and there appears little opportunity for deep boundary-layer
moistening over the northern Gulf of Mexico. As a result, stable
conditions are expected to generally persist with low convective
potential.

..Kerr.. 12/14/2020
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ACUS48 KWNS 160901
SWOD48
SPC AC 160900

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0300 AM CST Wed Dec 16 2020

Valid 191200Z - 241200Z

...DISCUSSION...
Based on the latest model output, low pattern predictability appears
an increasing concern through this period. Short wave developments,
within branching flow downstream of a strong mid/upper jet across
the southern mid-latitude/subtropical Pacific, are becoming more
unclear. In general, though, guidance continues to suggest that
there will be increasing amplification within the flow, probably
including a prominent building mid-level ridge near the Pacific
coast by early next week. It appears that this may be followed by
downstream large-scale upper trough amplification across the central
and eastern U.S., perhaps accompanied by strong surface cyclogenesis
east of the middle Missouri Valley through the Great Lakes region by
the middle of next week.

If this occurs, large-scale forcing for ascent and strengthening
deep-layer wind fields and shear within the evolving warm sector
probably will become at least conditionally supportive of increasing
severe weather potential, somewhere east of the Mississippi Valley
into the Appalachians. It does still seem unlikely that there will
be opportunity for deep boundary-layer moistening over the Gulf of
Mexico, and substantive inland return flow to the warm sector, by
this time. While this may tend to minimize severe weather potential
with vigorous, deep convective development, it is possible that the
environment could still become conducive to damaging surface gust
potential enhanced by an evolving pre-cold frontal low-topped
convective line.

..Kerr.. 12/16/2020
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ACUS48 KWNS 170935
SWOD48
SPC AC 170933

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0333 AM CST Thu Dec 17 2020

Valid 201200Z - 251200Z

...DISCUSSION...
Models indicate that an initially intense, zonal mid/upper jet
across western and central portions of the southern mid-latitude
Pacific will undergo considerable amplification through the extended
period. This is expected to lead to amplification within the
branching downstream flow, with guidance indicating greatest
certainty concerning the evolution of a prominent ridge across the
northeastern Pacific into the northern U.S./Canadian Pacific coast
early next week. It appears that this ridge will build as far north
as the Arctic latitudes of Alaska/northwestern Canada, before
large-scale downstream mid/upper trough amplification proceeds, from
the lee of the Canadian/northern U.S. Rockies through much of the
eastern U.S. by early Christmas Day.

There is sizable spread concerning the short wave perturbations
contributing to this large-scale trough evolution. However, model
output has been indicating the potential for strong cyclogenesis,
either with an initial low developing east-northeast of the middle
Missouri Valley though the Great Lakes region by mid week, or with a
secondary low developing to its southeast by late week.

Associated strengthening of deep-layer wind fields within the
evolving warm sectors will pose a conditional risk for increasing
severe weather potential, given sufficient instability. However,
moisture to contribute to appreciable destabilization remains
unclear, as deep Gulf of Mexico boundary-layer moistening to support
a substantive inland return flow remains hampered, particularly with
another mid-level perturbation forecast to pivot across the
Southeast early this week.

Still, there may be at least some potential for one or two
low-topped convective lines to evolve, which could be accompanied by
an enhancement of risk for damaging wind gusts, across parts of the
Ohio Valley on Wednesday, and parts of the eastern Gulf/south
Atlantic Coast states on Christmas Eve.

..Kerr.. 12/17/2020
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ACUS48 KWNS 180928
SWOD48
SPC AC 180927

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0327 AM CST Fri Dec 18 2020

Valid 211200Z - 261200Z

...DISCUSSION...
Latest medium-range guidance is in relatively good agreement that
upper ridging over the western CONUS on D4/Monday will move eastward
across the central and eastern CONUS on D5/Tuesday and D6/Wednesday.
Deep upper troughing is expected to develop across the Plains on
D6/Wednesday in the wake of the upper ridging. Further deepening is
anticipated as this upper trough continues eastward over the eastern
CONUS on D7/Thursday.

A strong cold front is forecast to accompany this upper trough. This
front is currently expected to move through much of the Plains on
D5/Tuesday, the MS, TN, and OH Valleys on D6/Wednesday, and off the
East Coast D7/Thursday. Moisture return ahead of the upper trough
and attendant cold front is currently expected to be modest and
confined to central/east TX and the Lower MS Valley. This limited
moisture return will temper severe potential. However, subtle change
in timing could result in higher potential, particularly given the
anticipated strength of the system.

..Mosier.. 12/18/2020
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ACUS48 KWNS 190953
SWOD48
SPC AC 190951

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0351 AM CST Sat Dec 19 2020

Valid 221200Z - 271200Z

...DISCUSSION...
Medium-range guidance continues to forecast significant
amplification of a shortwave trough moving out of the Pacific
Northwest D4/Tuesday. Forecast guidance suggests this shortwave
deepens as it moves over the Plains on D5/Wednesday and continues
maturing over the eastern CONUS on D6/Thursday. Very strong
mid-level flow will develop around this upper trough, with a very
deep surface low and strong cold front also anticipated.

Main uncertainties are the speed of the system's eastward
progression and the quality of the moisture return ahead of the cold
front. Current guidance would suggest some low-probability severe
potential does exist on D5/Wednesday and D6/Thursday, but limited
moisture return is forecast to limit a more widespread severe
threat.

..Mosier.. 12/19/2020
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ACUS48 KWNS 200945
SWOD48
SPC AC 200944

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0344 AM CST Sun Dec 20 2020

Valid 231200Z - 281200Z

...DISCUSSION...
Deep upper troughing is expected to be in place over the western and
central CONUS early D4/Wednesday. This upper troughing is then
expected to progress eastward as an embedded shortwave trough moves
across the central Plains. Another shortwave is forecast to follow
quickly in the wake of the first, moving across the southern Plains D4/Wednesday night.

By early D5/Thursday, a deep upper trough will likely extend from
Ontario southward into the southern Plains, with strong flow aloft
surrounding it. Continue eastward motion is expected into D6/Friday,
with further deepening/maturing of the system.

Some severe potential appears possible across central/east TX into
the Lower MS Valley on D4/Wednesday as the cold front moves through,
and the Carolinas/southern VA late D5/Thursday or early D6/Friday.
However, in both cases, instability is expected to be modest, which
will limit coverage. Additionally, differences in timing within the
guidance results in uncertainty regarding location. These factors
limit predictability. Stable conditions are currently forecast after
D6/Friday.

..Mosier.. 12/20/2020
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ACUS48 KWNS 210950
SWOD48
SPC AC 210949

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0349 AM CST Mon Dec 21 2020

Valid 241200Z - 291200Z

...DISCUSSION...
A deep and mature upper trough is expected to cover much of the
central and eastern CONUS early D4/Thursday. Primary low associated
with this system will likely be occluded over Ontario but secondary cyclogenesis is anticipated over the Southeast, with the resulting
low then moving quickly northeastward along the lee of the
Appalachians into the northern Mid-Atlantic. Some severe potential
may develop ahead of this low and its attendant cold front as it
moves quickly eastward. However, differences within the guidance
regarding frontal timing as well as uncertainty regarding antecedent
moisture return currently limit predictability.

High pressure will likely build across the central CONUS in the wake
of the upper trough on D5/Friday and across the eastern CONUS on
D6/Saturday. A shortwave is currently expected to move across the
Intermountain West on D6/Saturday and across the Plains D7/Sunday.
Moisture return ahead of this system will likely remain confined to central/east TX and the Lower MS Valley. Instability will be limited
even within this corridor of return flow and severe potential
currently appears very limited.

..Mosier.. 12/21/2020
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ACUS48 KWNS 220950
SWOD48
SPC AC 220948

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0348 AM CST Tue Dec 22 2020

Valid 251200Z - 301200Z

...DISCUSSION...
Medium-range guidance is in good agreement that a deep upper trough
will cover the eastern CONUS early D4/Friday. Surface low associated
with this trough will likely be over Ontario, with its attendant
cold front likely offshore. This system will continue
eastward/northeastward off the East Coast on D4/Friday. Another
shortwave will likely progress through southern Plains on
D5/Saturday, with another shortwave in its wake over the
central/southern Plains on D6/Sunday.

Despite this active and progressive upper pattern, stable conditions
are anticipated in the wake of the eastern CONUS upper trough and
the short duration between all the shortwaves will limit moisture
return. As such, severe potential appears low through at least early
next week.

..Mosier.. 12/22/2020
--- SBBSecho 3.11-Linux
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ACUS48 KWNS 230931
SWOD48
SPC AC 230930

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0330 AM CST Wed Dec 23 2020

Valid 261200Z - 311200Z

...DISCUSSION...
A relatively active upper pattern is anticipated from this weekend
through the middle of next week. A shortwave trough will likely
progress through southern Plains on D5/Saturday, with another
shortwave in its wake over the central/southern Plains on D6/Sunday.
Dry and stable conditions ahead of these shortwaves will keep severe
potential very low.

A third, potentially stronger system is expected to move from
central/southern CA eastward across the Four Corners region and into
the central/southern Plains early next week. Medium-range guidance
has varying solutions for the evolution of this system, but some
severe potential appears possible if enough moisture return occurs
ahead of it.

..Mosier.. 12/23/2020
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ACUS48 KWNS 270958
SWOD48
SPC AC 270957

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0357 AM CST Sun Dec 27 2020

Valid 301200Z - 041200Z

...DISCUSSION...
...Wednesday/Day 4 and Thursday/Day 5...
The medium-range models move an upper-level trough across the
southern Rockies and central High Plains on Wednesday. At the
surface, a cold front is forecast to advance southeastward into the
mid Mississippi Valley and Arklatex. Thunderstorms appear likely to
develop along and ahead of the front during the day due to weak
destabilization and strong large-scale ascent. Moisture advection is
forecast to continue during the day across the lower Mississippi
Valley in the presence of a pronounced low-level jet. In spite of
weak instability, very strong wind profiles associated with the low
to mid-level jet structure, could enable thunderstorms that obtain a
severe threat. Cells that initiate well to the east of the front
across the moist sector will have potential to become supercells.
The main threat would be for a few tornadoes and isolated wind
damage. The potential appears great enough to add a 15 percent
contour for parts of the lower Mississippi Valley.

On Thursday, an upper-level low is forecast to develop in the
southern Plains. In response, the low-level jet in the central Gulf
Coast states is forecast to strengthen. Thunderstorms will be
possible in the Tennessee Valley and central Gulf Coast states along
the axis of the low-level jet and further to the west, along the
cold front. Instability is forecast to remain weak from Wednesday
into Thursday. However, strong wind profiles should offset this
limitation, with the possibility of a severe threat continuing into
Thursday. The main severe weather potential would be for an isolated
tornado and wind damage threat with clusters that organize during
the day. The wind damage threat could become more widespread if a
squall-line can develop across the region. A 15 percent contour has
been added to parts of the central Gulf Coast for Thursday to
account for this possibility.

...Friday/Day 6 to Sunday/Day 8...
Southwest mid-level flow is forecast to be maintained from the
Southeast to the Eastern Seaboard on Friday. A cold front is
forecast to move eastward across the eastern Gulf Coast States and
Carolinas. Thunderstorm development will be possible along and ahead
of the front. Surface dewpoints in the 60s F along with weak
instability and strong deep-layer shear could be enough for an
isolated severe threat.

On Saturday and Sunday, the system is forecast to move eastward to
the Eastern Seaboard as surface high pressure dominates across much
of the continental United States. For this reason, thunderstorm
potential is expected to be minimal over the weekend in most areas.

..Broyles.. 12/27/2020
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ACUS48 KWNS 281001
SWOD48
SPC AC 280959

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0359 AM CST Mon Dec 28 2020

Valid 311200Z - 051200Z

...DISCUSSION...
...Thursday/Day 4 and Friday/Day 5...
An upper-level low is forecast to move northeastward across the
southern Plains on Thursday as an associated cold front advances
eastward into the lower Mississippi Valley. Moisture advection
appears likely to continue ahead of the front across the central
Gulf Coast states where surface dewpoints should be in the 60s F.
Thunderstorms may develop during the day along the front with
additional convection forming further east across the moist sector.
Model forecasts suggest that a low-level jet will increase in
strength, moving north-northeastward across Alabama during the late
afternoon. Convective development may be favored on the nose of the
low-level jet during the late afternoon and early evening.
Additional storms may develop further to the west across the lower
Mississippi Valley. Low-level and deep-layer shear profiles should
be favorable for severe storms across those two areas. The main
threats would be for tornadoes and wind damage. At this point, there
is some uncertainty concerning how far the quality moisture can
advect northward. For this outlook, have drawn the 15 percent
contour across central Alabama, where there appears to be a good
chance surface dewpoints will reach the lower to mid 60s F.

On Friday, the upper-level low is forecast to move
north-northeastward into the mid Mississippi Valley as southwest
mid-level flow remains entrenched across the eastern Seaboard.
Thunderstorm development will be possible along and ahead of a cold
front as a low-level jet moves northward across the Carolinas.
Low-level and deep-layer shear profiles are forecast to be favorable
for severe storms with the main threats being tornado and wind
damage. Have placed the 15 percent contour in the area where the
chance for quality moisture and convective potential is maximized,
according the latest ECMWF solution.

...Saturday/Day 6 to Monday/Day 8...
On Saturday, an upper-level trough is forecast to move eastward
across the southern Plains and mid Mississippi Valley as southwest
flow remains over much of the Southeast. The upper-level trough is
forecast to move across the Southeast on Sunday as a cold front
advances southward across the Florida Peninsula. Severe storms can
not be ruled out during the day on Sunday in central Florida but
uncertainty concerning the model solutions is substantial at this
time. On Monday, surface high pressure across much of the eastern
third of the nation should limit thunderstorm potential.

..Broyles.. 12/28/2020
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ACUS48 KWNS 290957
SWOD48
SPC AC 290955

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0355 AM CST Tue Dec 29 2020

Valid 011200Z - 061200Z

...DISCUSSION...
...Friday/Day 4 and Saturday/Day 5...
An upper-level trough is forecast to move northeastward across the
mid Mississippi Valley on Friday as southwest mid-level flow remains
in place along the Eastern Seaboard. The moist sector should be
located across much of Georgia and South Carolina. Thunderstorms may
develop in Georgia Friday afternoon ahead of the upper-level trough
with this convection spreading east-northeastward across South
Carolina and into southern North Carolina. Due to strong low-level
shear, a tornado threat could exist with this activity, in addition
to having a wind damage potential.

On Saturday, southwest mid-level flow is forecast to remain in place
across the Southeast as an upper-level low moves through the Ozarks.
At the surface, a cold front is forecast to advance southeastward
toward southern sections of the Atlantic Seaboard. Thunderstorm
development will be possible along the front during the day.
Although a severe threat is not expected due to weak instability,
isolated strong thunderstorms can not be ruled out in areas that
heat up sufficiently.

...Sunday/Day 6 to Tuesday/Day 8...
An upper-level low is forecast to move northeastward across the
central Appalachians on Sunday as a cold front advances southward
across the Florida Peninsula. Thunderstorm development could occur
Sunday afternoon in central Florida along or just ahead of the
front. An isolated severe threat would be possible if enough
instability can develop.

On Monday and Tuesday, surface high pressure over the central and
eastern U.S. should minimize thunderstorm potential in most of the
continental United States.

..Broyles.. 12/29/2020
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ACUS48 KWNS 300827
SWOD48
SPC AC 300826

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0226 AM CST Wed Dec 30 2020

Valid 021200Z - 071200Z

...DISCUSSION...
...Saturday/Day 4 to Sunday/Day 5...
An upper-level low is forecast to move across the mid Mississippi
Valley on Saturday as southwest mid-level flow remains over much of
the Southeast. At the surface, a cold front is forecast to move
across the eastern Gulf Coast States. Thunderstorm development will
be possible ahead of the front during the day from northern Florida
into southeastern Georgia and South Carolina. Although surface
dewpoints should be in the 60s F ahead of the front, instability is
forecast to be very weak suggesting that any severe threat should be
marginal.

On Sunday, an upper-level trough is forecast to move through the
central Appalachians as another upper-level trough moves into the
Ozarks and Arklatex. At the surface, a cold front is forecast to
advance southward across the Florida Peninsula. Marginally severe
storms will be possible along and ahead of the front in southern
Florida Sunday afternoon.

...Monday/Day 6 to Wednesday/Day 8...
On Monday and Tuesday, surface high pressure is forecast to be in
place across the eastern third of the nation, which should limit
thunderstorm potential. On Wednesday, the models suggest an
upper-level trough will move eastward across the southern U.S. The
models have large spread concerning the timing of the upper-level
trough. Some moisture return could occur ahead of the trough in the
western part of the Gulf Coast, where marginally severe storms can
not be ruled out. However, uncertainty is substantial at this range
in the forecast period.

..Broyles.. 12/30/2020
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ACUS48 KWNS 310945
SWOD48
SPC AC 310944

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0344 AM CST Thu Dec 31 2020

Valid 031200Z - 081200Z

...DISCUSSION...
...Sunday/Day 3 to Monday/Day 5...
An upper-level trough is forecast to move northeastward across the
central Appalachians on Sunday and across New England on Monday. A
cold front is forecast to move southward across the Florida
Peninsula on Sunday, along which thunderstorm development may take
place during the day. Behind the front, surface high pressure is
forecast to settle in across much of the southern half of the
nation. As a result, thunderstorm activity is expected to be
minimized from Sunday night into Monday.

...Tuesday/Day 6 to Thursday/Day 8...
On Tuesday, the medium-range models are in good agreement, moving an upper-level trough quickly eastward into the southern Rockies. Under
that scenario, moisture advection would increase across the Texas
Coastal Plain. Marginally severe storms can not be ruled out over
south-central Texas as the upper-level trough approaches the
southern Plains Tuesday night.

On Wednesday and Thursday, the upper-level trough is forecast to
progress quickly eastward across the Gulf Coast States. At this
time, moisture return is forecast to remain weak ahead of the
trough. That would limit the potential for severe storms to coastal
areas from Louisiana to the Florida Panhandle. The current thinking
is that any severe threat with this system will remain isolated.
However, uncertainty is substantial at this range in the forecast
period.

..Broyles.. 12/31/2020
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ACUS48 KWNS 010908
SWOD48
SPC AC 010907

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0307 AM CST Fri Jan 01 2021

Valid 041200Z - 091200Z

...DISCUSSION...
Various models such as the ECMWF and GFS are in relatively good
agreement with the large-scale pattern through the period, depicting
little chance of thunderstorms on Monday/D4 and Tuesday/D5 as an
upper trough departs the East with high pressure at the surface.

By Wednesday/D6, an amplified upper trough is forecast to progress
across the Plains, with height falls strongest over the central and
southern Plains. By this time, the antecedent surface ridge will
have moved to the East Coast, with southerly surface winds bringing
mid 50s F dewpoints as far north as the Arklatex. Even so, forecast
MUCAPE is only on the order of a few hundred J/kg, and the
instability plume is to be quite narrow, resulting in low
predictability.

This trough is expected evolve into a cut-off low on Thursday/D7
over the OH/TN Valleys, with strong westerly winds aloft across the
Southeast. It appears moisture quality will be a concern across this
region, thus predictability remains low despite strong shear.

By Friday/D8, any remaining moisture and instability over the
Southeast is forecast to be shunted offshore as the pattern remains progressive.

..Jewell.. 01/01/2021
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ACUS48 KWNS 011946
SWOD48
SPC AC 011945

Day 4-8 Convective Outlook RESENT 1
NWS Storm Prediction Center Norman OK
0145 PM CST Fri Jan 01 2021

Valid 041200Z - 091200Z

...DISCUSSION...
Various models such as the ECMWF and GFS are in relatively good
agreement with the large-scale pattern through the period, depicting
little chance of thunderstorms on Monday/D4 and Tuesday/D5 as an
upper trough departs the East with high pressure at the surface.

By Wednesday/D6, an amplified upper trough is forecast to progress
across the Plains, with height falls strongest over the central and
southern Plains. By this time, the antecedent surface ridge will
have moved to the East Coast, with southerly surface winds bringing
mid 50s F dewpoints as far north as the Arklatex. Even so, forecast
MUCAPE is only on the order of a few hundred J/kg, and the
instability plume is to be quite narrow, resulting in low
predictability.

This trough is expected evolve into a cut-off low on Thursday/D7
over the OH/TN Valleys, with strong westerly winds aloft across the
Southeast. It appears moisture quality will be a concern across this
region, thus predictability remains low despite strong shear.

By Friday/D8, any remaining moisture and instability over the
Southeast is forecast to be shunted offshore as the pattern remains progressive.

..Jewell.. 01/01/2021
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ACUS48 KWNS 020851
SWOD48
SPC AC 020849

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0249 AM CST Sat Jan 02 2021

Valid 051200Z - 101200Z

...DISCUSSION...
On Tuesday/D4, a large upper trough is likely to be situated over
the East, with shortwave ridging over the MS Valley occurring in
advance of an amplifying Plains upper trough. Due to a prominent
surface ridge over the eastern states, thunderstorms are unlikely.

As the Plains trough develops eastward toward the Arklatex and lower
MS Valley on Wednesday/D5, a deepening cut-off low is forecast to
form, with a cold front moving across east TX and becoming occluded
into AR and LA. Instability is forecast to be weak (at or below 200
J/kg) by the ECMWF across OK and TX, and even less as the narrow
moist sector shrinks with the occlusion. In addition, capping will
be a concern for thunderstorms in general.

Severe potential does not appear to get any better as the trough
continues eastward across the Southeast into Thursday/D6 and
Friday/D7, with minimal moisture return the primary limiter.

..Jewell.. 01/02/2021
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ACUS48 KWNS 030750
SWOD48
SPC AC 030748

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0148 AM CST Sun Jan 03 2021

Valid 061200Z - 111200Z

...DISCUSSION...
A shortwave trough with closed low will be situated over the central
and southern Plains on Wednesday/D4 and will move across the lower
MS Valley on Thursday/D5. This system will continue east across the
remainder of the Southeast through Friday/D6, exiting the CONUS by
00Z Saturday/D7.

At the surface, a cold front is forecast to be situated over
eastern/coastal TX by 00Z Thursday/D5, and over southern MS by 12Z
Thursday. Ahead of this front, only meager low-level moisture return
is indicated, with minimal SBCAPE and a warm sector shrinking from
north to south due to occlusion. For the duration of this upper low
over land, it appears instability will be minimal, thus potential is
currently too low for any severe probabilities.

Another amplifying upper trough is shown by the models into the
southern Plains on Saturday/D7, then moving across the Deep South
and northern Gulf of Mexico on Sunday/D8. However, given the
progressive pattern, there will be little opportunity for sufficient
moisture return and destabilization, thus potential remains low for
severe storms through Sunday/D8.

..Jewell.. 01/03/2021
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ACUS48 KWNS 050816
SWOD48
SPC AC 050815

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0215 AM CST Tue Jan 05 2021

Valid 081200Z - 131200Z

...DISCUSSION...
Models are in good agreement for the Friday/D4 to Sunday/D6 period,
and show an upper trough exiting the Mid Atlantic Friday/D4. High
pressure will be in place from the Plains into the East behind this
wave, and in advance of the next upper trough. This second trough is
forecast to move from the Four Corners into the southern Plains
during the Saturday/D5 to Sunday/D6 period, and indications are that
there will be no appreciable low-level moisture return over land. As
a result, thunderstorm chances appear minimal through Sunday/D6.

While model spread increases significantly beyond Sunday/D6, the
existing pattern does not appear to support severe thunderstorms
with the potential for several reinforcing surface highs and
fast-moving shortwave troughs.

..Jewell.. 01/05/2021
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ACUS48 KWNS 060756
SWOD48
SPC AC 060754

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0154 AM CST Wed Jan 06 2021

Valid 091200Z - 141200Z

...DISCUSSION...
In the wake of an upper trough departing the Mid Atlantic, another
shortwave trough will dive southward across the Four Corners on
Saturday/D4, and into TX on Sunday/D5. A large surface ridge will be
in place during this period, with pressure centers over the Great
Basin and Northern Plains. Given the low latitude of this shortwave
trough, low pressure is forecast to form over the western Gulf of
Mexico on Sunday/D5. Low-level moisture return will be minimal over
land due to poor trajectories around the surface ridge, but low 60s
F dewpoints are possible near Brownsville TX before a cold front
surges east. Only minimal elevated instability is forecast over
southern TX.

From Monday/D6 through Wednesday/D8, little thunderstorm activity is anticipated. As the aforementioned shortwave trough continues across
the Gulf of Mexico, another wave is forecast to move into the
central Plains or Great Lakes, depending on the model. In either
case, reinforcing surface highs are expected, minimizing potential
for destabilization.

..Jewell.. 01/06/2021
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ACUS48 KWNS 070850
SWOD48
SPC AC 070849

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0249 AM CST Thu Jan 07 2021

Valid 101200Z - 151200Z

...DISCUSSION...
Models are in relatively good agreement with the large-scale pattern
through most of the D4-D8 period, beginning with a shortwave trough
over TX on Sunday/D4. This wave will proceed across the southeastern
and Mid Atlantic through Tuesday/D6, with northwest flow developing
over the Plains beyond Tuesday/D6. Further upper trough
amplification is hinted at across the Plains toward Thursday/D8.

Regardless of the precise timing of these waves, models agree the
limiting factor will continue to be the lack of instability and
low-level moisture over land. As the pattern remains progressive,
there will be little time in between waves for sufficient
destabilization. Thus, potential is likely to remain too low through
the period.

..Jewell.. 01/07/2021
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ACUS48 KWNS 080757
SWOD48
SPC AC 080756

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0156 AM CST Fri Jan 08 2021

Valid 111200Z - 161200Z

...DISCUSSION...
A weakening shortwave trough will move from TX across the Southeast
during the Monday/D4 to Tuesday/D5 period, with a weak surface low
moving from the northern Gulf Coast at 12Z Monday/D4 to just off the
Outer Banks of NC by 00Z Wednesday/D6. Given the cool/dry air mass
in place ahead of this system, little if any surface-based
instability is forecast to develop.

For the remainder of the period Wednesday/D6 to Friday/D8, models
show a stable pattern will continue with several days of offshore
flow across the Gulf of Mexico and East Coast. While models disagree
on whether there will be a closed upper low or a large upper trough
over the eastern CONUS, very low heights and strong northwest flow
over the Plains will aid in prolonging the cool and stable pattern.

..Jewell.. 01/08/2021
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ACUS48 KWNS 090854
SWOD48
SPC AC 090853

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0253 AM CST Sat Jan 09 2021

Valid 121200Z - 171200Z

...DISCUSSION...
While model solutions show disagreement with upper-level features
across the northern Plains on Tuesday/D4, they are in general
agreement with the presence of a dry, stable air mass over much of
the central and eastern states as a midlevel speed max exits the Mid
Atlantic. This will result in little if any thunderstorm activity,
regardless. The ECMWF and GFS actually come into better agreement
into the Thursday/D6 to Saturday/D8 period, showing a large-scale
upper trough over the East. If this pattern verifies, it will ensure
a continued lack of severe-weather potential through the period.

..Jewell.. 01/09/2021
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ACUS48 KWNS 100722
SWOD48
SPC AC 100720

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0120 AM CST Sun Jan 10 2021

Valid 131200Z - 181200Z

...DISCUSSION...
On Wednesday/D4, models are in agreement showing a de-amplifying
shortwave trough moving quickly across the Southeast, where a dry
air mass will remain at the surface. As such, very little elevated
instability is expected to support thunderstorms.

On Thursday/D5, a major trough amplification is forecast to occur as
powerful northwest flow aloft dives southeastward into the Plains,
resulting in a large-scale upper trough over the East with upper low
over the Great Lakes. Given the antecedent dry air across the Gulf
of Mexico, a brief window of southwest surface flow over the
southern Plains and lower MS Valley is unlikely to be enough for any
CAPE to develop.

Beyond Thursday/D5, thunderstorm chances will remain nearly zero as
a large surface ridge moves from the Plains across the Southeast and
over the Gulf of Mexico. Additional trough amplifications are
possible across the midsection of the country with a mean upper
ridge over the West Coast, maintaining the dry surface pattern.

..Jewell.. 01/10/2021
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ACUS48 KWNS 110755
SWOD48
SPC AC 110754

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0154 AM CST Mon Jan 11 2021

Valid 141200Z - 191200Z

...DISCUSSION...
An inactive convective pattern is likely to persist through
Monday/D8, with a large upper trough developing over the central and
eastern states during the Thursday/D4 to Saturday/D6 period. Little
low-level moisture return is forecast over land ahead of the initial
cold front, which will be near the TX Coast at 00Z Friday.

Additional surges of high pressure are forecast to occur over the
central and eastern states from Sunday/D7 to Monday/D8, as models
indicate another upper trough amplification over the Plains and
Great Lakes region. As such, severe weather is quite unlikely, with
little thunderstorm potential in general.

..Jewell.. 01/11/2021
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ACUS48 KWNS 130931
SWOD48
SPC AC 130930

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0330 AM CST Wed Jan 13 2021

Valid 161200Z - 211200Z

...DISCUSSION...
Model consensus is that a synoptic upper trough will move through
the eastern U.S. day 4 (Saturday) followed closely by an upstream
trough on day 5. This pattern will be accompanied by offshore winds
over the Gulf, maintaining stable conditions inland. A pattern
transition is forecast to occur by day 6 (Monday) as an upper trough
amplifies across the Great Basin region. Modifying Gulf moisture
should return through south TX, but instability will remain
insufficient for a severe threat. Moisture return should be more
substantial across south and southeast TX and possibly into southern
LA by day 7 with potential for greater destabilization. However, by
this time frame. predictability diminishes due to uncertainty
regarding the trajectory of the Great Basin upper trough.

..Dial.. 01/13/2021
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ACUS48 KWNS 140904
SWOD48
SPC AC 140903

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0303 AM CST Thu Jan 14 2021

Valid 171200Z - 221200Z

...DISCUSSION...
Day 4 (Sunday) offshore flow over the Gulf will maintain stable
conditions inland. By day 5 (Monday), winds will return to southerly
over the western Gulf resulting in the advection of a modifying Gulf
boundary layer supporting dewpoints in the 50s F across south
through eastern TX. A few showers may develop in the pre-frontal
warm advection regime late Monday night from northeast TX into OK
but instability will remain too marginal for severe storms. An upper
low will settle into the southwest U.S. by day 6 (Tuesday) with
downstream weak upper ridging across TX in vicinity of a cold front
that will move slowly south. While showers and a few thunderstorms
may develop along the front and possibly farther south in the warm
sector across southeast TX, no severe weather is expected due to the
very weak thermodynamic environment. By day 7 the cutoff upper low
is forecast to settle into northern Mexico, but models remain
inconsistent regarding the timing and future trajectory of this
feature, resulting in low predictability.

..Dial.. 01/14/2021
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ACUS48 KWNS 150855
SWOD48
SPC AC 150853

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0253 AM CST Fri Jan 15 2021

Valid 181200Z - 231200Z

...DISCUSSION...
Day 4 (Monday), southerly winds will return to the western Gulf and
south TX resulting in the northward advection of a modifying Gulf
boundary layer through south and east TX. A few showers may develop
along a southward-advancing cold front and in the pre-frontal warm
advection regime late Monday night from OK into northeast TX, but
very little instability will exist to support thunderstorms. Upper
low is forecast to be situated over southern CA by day 5 (Tuesday)
with downstream weak upper ridging across TX in vicinity of a cold
front that will move slowly south. While showers and thunderstorms
may develop along the front and possibly farther south in the warm
sector across southeast TX, no severe weather is expected due to the anticipated very weak thermodynamic environment. By day 6
(Wednesday) model consensus is that the cutoff upper low will settle
into the Baja area with a downstream upper ridge across the Southern
Plains. Showers and a few thunderstorms may persist in vicinity of
the stalled and weakening front from central TX into the lower MS
Valley, but the expected parameter space does not appear conducive
for severe storms.

..Dial.. 01/15/2021
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ACUS48 KWNS 160928
SWOD48
SPC AC 160927

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0327 AM CST Sat Jan 16 2021

Valid 191200Z - 241200Z

...DISCUSSION...
...Tuesday/Day 4 and Wednesday/Day 5...
Zonal mid-level flow is forecast to be in place form the southern
Plains eastward to the Eastern Seaboard on Tuesday and Wednesday. At
the surface, high pressure is forecast to be dominate across much of
the continental United States on Tuesday. The associated surface
high is forecast to move across the Southeast on Wednesday. This
will keep a dry airmass in place over much of the nation limiting
thunderstorm development through mid week.

...Thursday/Day 6 to Saturday/Day 8...
The medium-range models are forecasting an upper-level trough to
move from the Desert Southwest to the southern Plains from Thursday
into Friday. Moisture return is expected to take place ahead of the
system in parts of the southern Plains. Thunderstorm development
will be possible from Thursday night into Friday along northern
parts of the moist airmass, most likely from central Texas eastward
into the lower Mississippi Valley. However, instability is expected
to remain very weak which should limit any severe potential. On
Saturday, model forecasts develop a low-amplitude upper-level ridge
across the central U.S. At this time, instability is expected to be
minimal across most of the nation helping to limit thunderstorm
development.

..Broyles.. 01/16/2021
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ACUS48 KWNS 170949
SWOD48
SPC AC 170948

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0348 AM CST Sun Jan 17 2021

Valid 201200Z - 251200Z

...DISCUSSION...
...Wednesday/Day 4 and Thursday/Day 5...
The medium range models maintain west-northwesterly mid-level flow
across much of the U.S. on Wednesday as an upper-level low remains
south of the southern California coast. The low is forecast to
weaken and move northeastward across the Desert Southwest on
Thursday. Ahead of this system, an upper-level ridge is forecast to
be in place across the southern Plains with a moist airmass located
across the western Gulf Coast region. Thunderstorm development will
be possible along the northwestern edge of the moist airmass on
Wednesday and Thursday, mainly from the Texas Hill Country and Texas
Coastal Plain east-northeastward into the Arklatex and lower
Mississippi Valley. Instability is expected to be very weak limiting
any severe potential.

...Friday/Day 6 to Sunday/Day 8...
The upper-level trough is forecast dampen and move quickly
east-northeastward across the southern U.S. on Friday. Thunderstorm
development will be possible ahead of the trough from parts of the
southern Plains eastward into the central Gulf Coast region.
Instability is expected to be weak on Friday minimizing any severe
potential. Low-level moisture is forecast to gradually increase in
parts of Texas from Saturday into Sunday, where the models suggest
scattered thunderstorms will be possible. The greatest potential for
an isolated severe threat Saturday and Sunday would be from central
Texas northeastward into the Arklatex. However, uncertainty is
substantial at this extended range in the forecast period.

..Broyles.. 01/17/2021
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ACUS48 KWNS 180951
SWOD48
SPC AC 180950

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0350 AM CST Mon Jan 18 2021

Valid 211200Z - 261200Z

...DISCUSSION...
...Thursday/Day 4 and Friday/Day 5...
The medium-range models move a shortwave trough across the Desert
Southwest on Thursday as zonal mid-level flow remains from the
southern Plains to the Eastern Seaboard. Thunderstorm development
will be possible on Thursday across parts of the western and central
Gulf Coast region along the northern edge of a moist airmass.
Instability is expected to be too weak for severe thunderstorm
development. The shortwave trough is forecast to move into the Gulf
Coast States on Friday. Thunderstorms will again be possible in the
northern part of the moist airmass which should be located from the
Texas Coastal Plain eastward to the Florida Panhandle. Instability
is again forecast to be weak suggesting severe thunderstorm
potential will be minimal.

...Saturday/Day 6 to Monday/Day 8...
On Saturday, the medium-range models move an upper-level ridge
across the Mississippi Valley as southwest mid-level flow becomes
established from the Four Corners region eastward into the Great
Plains. The models are in reasonable agreement on Sunday moving an
upper-level trough across the Intermountain West. Moisture return is
forecast to take place ahead of this system in parts of the southern
Plains. Thunderstorm development will be possible during the day on
Sunday from Texas northward into Oklahoma along an axis of
instability. Although a severe threat can not be ruled out,
predictability remains low for Sunday. On Monday, the upper-level
trough is forecast to move into the Great Plains as a cold front
advances into the Arklatex. Thunderstorm development will be
possible along and ahead of the front across the lower to mid
Mississippi Valley during the day on Monday. If the forecasts
verify, a severe threat would be possible in areas that can heat up sufficiently ahead of the front. However, predictability is low this
far out in the forecast period.

..Broyles.. 01/18/2021
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ACUS48 KWNS 200932
SWOD48
SPC AC 200930

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0330 AM CST Wed Jan 20 2021

Valid 231200Z - 281200Z

...DISCUSSION...
Medium-range models are in reasonably good agreement with respect to
the synoptic-scale features across the U.S. through roughly Day 5
(Sunday). Beyond that, increasing divergence in solutions suggests insufficient predictability to make any meaningful assessment of
convective potential.

Within the Day 4-5 time frame, the primary feature of interest will
be the large trough situated over the West at the start of the
period. More specifically, a short-wave feature moving through the broader-scale cyclonic flow -- which is progged to lie near the
central California coast at the start of Day 4 -- will substantially
influence convective potential in the medium range.

Day 4 (Saturday), this short-wave feature is forecast to shift
southeastward, moving into the southwestern U.S./northern Baja
during the overnight hours. As this occurs, an increase in
southerly low-level flow is progged over the southern Plains. This
trend will continue into Day 5, as the upper system shifts eastward
and crosses northern Mexico/Arizona/New Mexico -- but while
weakening steadily as it progresses eastward. In response, rather
ill-defined cyclogenesis is expected to occur over the Texas
vicinity. As ascent increases and low-level moisture advection
continues, an increase in convective potential will occur across the
southern Plains and into the lower Mississippi Valley. However,
despite favorable shear that would otherwise support severe
potential, some likelihood for persistent/weak boundary layer
stability beneath low-level capping is a concern. Still, some
severe potential could evolve, possibly focused along a weak
east-to-west warm frontal zone across east Texas and the Arklatex
region later Sunday and into Monday. However, degree of risk
remains questionable at this time, such that an outlook area will
not be introduced at this time.

By Day 6 (Monday), the weakening upper system is progged by the GFS
to essentially dampen out with time, as it crosses Oklahoma and
Kansas, and shifts into Missouri. Meanwhile, the ECMWF maintains a
much more well-defined feature, that moves quickly across the Ozarks
and Mid Mississippi Valley by evening, and then into/across the
Carolinas and Virginia by the end of the period. Along with this
more pronounced upper feature, a corresponding/well-developed
surface cyclone is also progged to cross the southeastern quarter of
the country Monday, suggestive of at least some severe potential
spreading eastward across this region should the pattern evolve more
similar to the ECMWF solution.

At this time however, given the increasing model differences beyond
Day 5/Sunday, no severe-weather assessment will be attempted through
the remainder of the medium-range period.

..Goss.. 01/20/2021
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ACUS48 KWNS 210921
SWOD48
SPC AC 210919

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0319 AM CST Thu Jan 21 2021

Valid 241200Z - 291200Z

...DISCUSSION...
Medium-range models are exhibiting reasonable agreement Day 4
(Sunday) and into Day 5 (Monday), after which divergence in
solutions begins to increase markedly.

On Day 4 (Sunday), the western U.S. trough is progged to begin
ejecting -- and deamplifying as it does -- across the Desert
Southwest and southern Rockies, and finally into the southern
Plains, as it acquires negative tilt through latter stages of the
period.

As this occurs, height falls will overspread northern and central
Texas and Oklahoma, atop southerly low-level flow providing theta-e
advection into the region. While a capping inversion -- remnants of
prior anticyclonic flow/subsidence aloft -- will likely hinder
potential for surface-based convection through much of the day,
isolated to scattered storms may evolve by early evening across
parts of central and northern Texas, and possibly into southeastern
Oklahoma. While questions persist with this scenario, including
degree of surface-based instability which may be present, shear
profiles will be quite supportive of organized/rotating storms.
Therefore, though details remain sketchy, enough consistency exists
within tonight's model runs, and those from prior days, to warrant
inclusion of a conditional 15% risk area for severe storms.

By Monday, differences begin to become apparent with
evolution/progression of the weakening mid-level system as it shifts
eastward toward/into the Midwest/Ohio Valley. Likewise, similar
differences are manifest in the strength/advance of the associated
surface low. This uncertainty, combined with likelihood for weaker
instability with eastward extent, suggests lesser/decreasing severe
potential, and diminishing confidence -- both therefore mitigating
against risk area inclusion at this time.

Beyond Day 5, model differences -- suggestive of an inherent lack of predictability -- preclude any assessment of convective potential
through the remainder of the medium-range period.

..Goss.. 01/21/2021
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ACUS48 KWNS 221004
SWOD48
SPC AC 221002

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0402 AM CST Fri Jan 22 2021

Valid 251200Z - 301200Z

...DISCUSSION...
Medium-range models appear to be in reasonably good large-scale
agreement through most of the period. Of primary interest from a
convective perspective, will be two short-wave troughs expected to
move out of the southwestern U.S. and quickly across the south
central and then southeastern portions of the country.

The first of these features -- initially progged to lie over the
Oklahoma vicinity at the start of the Day 4 period (Monday morning)
will move quickly east northeastward into/across the lower
Missouri/mid Mississippi/Ohio Valleys into Day 5. An accompanying
surface low will likewise shift eastward across this same general
region, but at this time, it appears that available instability will
be quite limited, due to weak lapse rates in the surface to roughly
700mb layer. As such, any potential for severe weather appears low
-- below the 15% threshold for areal inclusion.

As this system weakens and shifts off the East Coast Day 5
(Tuesday), a second short-wave trough crossing the southwestern U.S.
is expected to reach the into the central and southern Plains late Tuesday/early Wednesday (Day 6). The system is then progged to
continue eastward to the Tennessee Valley late Day 6/early Day 7,
before moving off the Atlantic Coast prior to the start of Day 8.

However, a cool/stable boundary layer is forecast to spread
southward into the south central and southeastern U.S. in advance of
this feature, and thus -- with the primary surface baroclinic zone
progged to lie over the northern Gulf of Mexico, only a muted
surface response is expected in association with the advance of this
system. As such, conditions will likely remain thermodynamically
unfavorable for any appreciable severe weather risk through the
middle and latter stages of the period.

..Goss.. 01/22/2021
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ACUS48 KWNS 230944
SWOD48
SPC AC 230942

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0342 AM CST Sat Jan 23 2021

Valid 261200Z - 311200Z

...DISCUSSION...
Medium-range models are in reasonable agreement with respect to
evolution of large-scale features through Day 6, after which
divergence in solutions increases through the end of the period.

Even early on in the period, however, differences at smaller scales
-- particularly with an upper short-wave trough ejecting from the
Southwest across the southern tier of the U.S. during the first half
of the period -- complicate assessment of convective potential.

Models generally agree in the maintenance of persistent western U.S.
upper troughing, with the aforementioned short-wave feature progged
to eject eastward, crossing the Four Corners states and eventually
emerging into the central/southern Plains Day 4 (Tuesday). By Day 5 (Wednesday), as the feature shifts across the Mid and lower
Mississippi Valley and then the Mid South and central Gulf Coast
states, surface cyclogenesis is expected to occur. With the GFS stronger/sharper with the upper feature, stronger surface
cyclogenesis is depicted, with a deepening low over the Tennessee
Valley area by Wednesday evening, while the weaker ECMWF solution
places a much weaker low over the southern Alabama/southern Georgia
vicinity. In either case however, it appears likely that the
boundary layer will remain stable, as a strong baroclinic zone over
the northern Gulf of Mexico just ahead of this system will likely be
slow to retreat northward. Thus, severe weather is not expected
with this system.

As the system moves offshore Day 6 (Thursday), large-scale ridging
will prevail over much of the country, ahead of re-establishment of
western U.S. troughing. Therefore, severe weather is not expected
Thursday, and then beyond which pattern predictability diminishes
steadily through the end of the period.

..Goss.. 01/23/2021
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ACUS48 KWNS 241146
SWOD48
SPC AC 241144

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0544 AM CST Sun Jan 24 2021

Valid 271200Z - 011200Z

...DISCUSSION...
Latest runs of the medium-range models show fair model-to-model
agreement with respect to large-scale features into Day 6 (Friday
Jan. 29), though even larger-scale similarities between models fade
further into the second half of the period. This increasing
large-scale disagreement centers around timing of the ejection of a
short-wave trough across the southwestern U.S. Day 6, and then
into/across the central U.S. Day 7. Depending upon evolution of
this feature, convective potential could increase over the south
central and later the southeastern U.S. during the second half of
the period. However, predictability concerns in this time frame
preclude any further assessment of convective potential.

Prior to this, through the first half of the period, a short-wave
trough is forecast to move from the central/southern Plains region
at the beginning of the period (Wednesday Jan. 27), to the East
Coast states by the start of Day 5. Slight differences in the
strength of this feature between the GFS and ECMWF result in more
notable deviations in depiction of associated surface low intensity,
with the GFS more aggressive in terms of surface cyclone development
over the southern Appalachians area, and thus more bullish with
respect to convective potential. With the ECMWF showing a much more
muted frontal wave much farther south -- shifting from the Gulf
Coast to the southeast Georgia coast -- confidence remains too low
to render a more thorough assessment.

As this upper feature moves offshore Day 5, strong cyclogenesis is
progged over the Gulf Stream/western Atlantic, with cold high
pressure building southward in its wake, across the eastern half of
the country -- in tandem with large-scale ridging/anticyclonic flow
across most of the CONUS.

..Goss.. 01/24/2021
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ACUS48 KWNS 250947
SWOD48
SPC AC 250946

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0346 AM CST Mon Jan 25 2021

Valid 281200Z - 021200Z

...DISCUSSION...
Latest runs of the medium-range models exhibit fair agreement
through the medium-range period, though differences in strength and
timing of the advance of smaller-scale features is evident
throughout the period.

In general however, the period will be characterized primarily by
the slow evolution/migration of a trough -- initially just off the
West Coast -- that is progged to traverse the entire U.S. and reside
near the East Coast at the end of Day 8.

As this system progresses, an associated surface cyclone/frontal
system is forecast to emerge into the Plains by Day 6 (Saturday),
and then shift steadily eastward until moving off the East Coast
late Day 7/Day 8.

Preceding the advance of the surface system however, strong surface cyclogenesis off the East Coast Day 4 (Thursday) will be followed by
a surge of cold continental air across the eastern U.S. and through
the Gulf of Mexico. This will likely lead to only a very
incompletely modified return of low-level air ahead of the advancing
surface system, and thus likelihood for very minimal instability.
As such, risk for severe weather appears low, through the period.

..Goss.. 01/25/2021
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ACUS48 KWNS 260956
SWOD48
SPC AC 260954

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0354 AM CST Tue Jan 26 2021

Valid 291200Z - 031200Z

...DISCUSSION...
Medium-range models are again exhibiting fair model-to-model
agreement through most of the medium range, in terms of larger-scale
features. The overall scenario remains that a trough over the
western U.S. at the start of the period will gradually evolve while
shifting slowly but steadily eastward, finally reaching/moving off
the East Coast late Day 7 into Day 8 (early next week).

This system will be accompanied by a fairly well developed surface
low/frontal system, first emerging into the Plains late Day 4/early
Day 5 (Saturday morning). While southerly low-level flow within the
warm sector of this cyclone will permit theta-e advection to occur
into the south-central U.S., the prior intrusion of cold continental
air through the Gulf of Mexico will be incompletely modified in
advance of this system. Thus, minimal instability is anticipated,
and thus, only weak -- and largely elevated -- convection is
expected. As the system progresses through the rest of the period,
an increasingly stable airmass with eastward extent will likely
preclude any severe risk through the period.

..Goss.. 01/26/2021
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ACUS48 KWNS 270943
SWOD48
SPC AC 270941

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0341 AM CST Wed Jan 27 2021

Valid 301200Z - 041200Z

...DISCUSSION...
Medium-range models continue to exhibit reasonable large-scale
agreement with respect to evolution of the upper pattern, through
roughly Day 7. Beyond that, differences quickly arise with handling
of a large trough crossing the West late in the period.

Prior to then, the pattern aloft will be characterized by the
progression of a trough -- initially situated over the southern
Rockies/central and southern High Plains. As this feature
evolves/shifts eastward with time, it will be accompanied by a
well-developed surface low/frontal system, that models suggest will
move from the High Plains early Day 4 (Saturday), to near/off the
East Coast by the end of Day 6 (Tuesday morning).

Despite the well-developed nature of this surface system, its warm
sector will likely remain notably lacking in instability, due to the
antecedent cP airmass intrusion through the Gulf of Mexico, and
persistence of ridging aloft across the western Atlantic and into
the Gulf. As such, though precipitation -- including
weak/low-topped convection -- will accompany passage of the system,
severe weather is not expected.

..Goss.. 01/27/2021
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ACUS48 KWNS 280952
SWOD48
SPC AC 280951

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0351 AM CST Thu Jan 28 2021

Valid 311200Z - 051200Z

...DISCUSSION...
Agreement/similarity in solutions amongst medium-range models only
appears reasonable through Day 5 (Monday), in the most recent runs,
as models continue to differ rather markedly with the
evolution/advance of an eastern Pacific trough forecast to move
onshore over the West late Day 5/early Day 6. These continued
differences suggest ongoing lack of predictability within this
evolving pattern, rendering any convective assessment largely
meaningless beyond Day 5.

Early in the period, an eastern U.S. upper trough will advance
slowly toward the Appalachians Day 4 (Sunday), and then across the
mountains early Monday, possibly then evolving into a closed low and subsequently drifting up the Northeast U.S. coastal vicinity.

At the surface, a low-pressure system will take a similar eastward
path across the eastern U.S., with a cold front -- trailing from an
Ohio Valley low -- forecast to cross the Appalachians Day 4, before
shifting offshore Day 5. However, a lack of warm-sector instability
is expected, due to an insufficiently warm/moist boundary layer.
Therefore, severe weather is not expected through Day 5.

..Goss.. 01/28/2021
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ACUS48 KWNS 290851
SWOD48
SPC AC 290849

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0249 AM CST Fri Jan 29 2021

Valid 011200Z - 061200Z

...DISCUSSION...
A deep upper trough is forecast to exit the East Coast on D4/Monday,
with upper ridging (and associated stable conditions) moving across
the Plains and eastern CONUS in its wake. Consequently,
thunderstorms potential will be very low.

A strong shortwave trough is expected to move over the West Coast
late D5/Tuesday or early D6/Wednesday. Guidance varies on the
evolution of this system, but some severe potential could manifest
if a slower, more southerly track is realized. However, model
differences and forecast range currently limit predictability,
leading to low forecast confidence.

..Mosier.. 01/29/2021
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ACUS48 KWNS 300911
SWOD48
SPC AC 300909

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0309 AM CST Sat Jan 30 2021

Valid 021200Z - 071200Z

...DISCUSSION...
Upper ridging is forecast to traverse the central CONUS on
D4/Tuesday, leading to continued stable conditions east of the
Rockies. Thereafter, a deep upper trough is expected to move across
the western CONUS and into the Plains. Overall evolution of this
upper trough remains uncertain although it does appear increasingly
likely that a series of shortwave troughs will move through the
larger upper trough, contributing to severe potential as well as
ushering in a very cold air mass.

Current guidance suggests any severe potential would be linked to
the lead shortwave trough, which will likely eject out across the
southern Plains late D6/Thursday and into the MS Valley on
D7/Friday. Currently, modest moisture return, minimal buoyancy, and
deep southwesterly (i.e. boundary-parallel) flow all suggest limited
severe potential. Even so, very strong forcing for ascent and
vertical shear will accompany this shortwave, and some severe storms
may materialize if mesoscale details (which are difficult to
ascertain at this forecast range) align.

..Mosier.. 01/30/2021
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ACUS48 KWNS 310950
SWOD48
SPC AC 310949

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0349 AM CST Sun Jan 31 2021

Valid 031200Z - 081200Z

...DISCUSSION...
Medium-range guidance is in relatively good agreement on the overall progression of the upper pattern into the weekend, but continues to
show variance of embedded shortwave troughs.

Expectation is for a deep upper trough to begin the period extended
from western Canada to off the southern CA coast. Several shortwaves
will likely be embedded within this larger trough, with guidance
offering various solutions of their evolution. The southernmost
shortwave is forecast to move across the Southwest/northern Mexico
on D5/Thursday and across the southern Plains on D6/Friday. Previous
model runs suggested this shortwave had the potential to interact
with modest moisture return across the southern Plains. However,
most recent runs have trended faster with a cold front on
D5/Thursday, which pushes through before the shortwave arrives.

Another shortwave trough is expected to follow quickly in the wake
of the first, rotating through the parent upper trough and across
the southern Plains across on D6/Friday or D7/Saturday.

Main forecast uncertainty is whether or not either one of these
shortwaves will be able to interact with any low-level moisture.
Recent runs trended away from more vigorous interaction, but, given
the strength of these systems, some severe potential could still
manifest and guidance will be monitored closely for upcoming
outlooks.

..Mosier.. 01/31/2021
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ACUS48 KWNS 010919
SWOD48
SPC AC 010917

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0317 AM CST Mon Feb 01 2021

Valid 041200Z - 091200Z

...DISCUSSION...
Recent medium-range guidance is showing better consistency into the
weekend. Current expectation is for an upper trough to extend from
the Canadian Prairie Provinces to off the southern CA coast early
D4/Thursday. This upper trough is forecast to move eastward on
D4/Thursday and D5/Friday. The northern and central portions of the
trough will be more progressive than the southern portion, which may
lead to bifurcation and the development of a upper low off the
northern
+ coast of the Baja Peninsula.

Surface low associated to the primary trough is expected to move
from the central Plains northeastward across the MS Valley and upper
Great Lakes and into Ontario by D5/Friday. Attendant cold front will
sweep eastward/southeast across the southern Plains and mid/lower MS
Valley on D4/Thursday and remainder of the eastern CONUS on
D5/Friday. Modest low-level moisture will precede this front, but
relatively cool and cloudy antecedent conditions are currently
expected to limit thunderstorm coverage. Slight changes in the
thermodynamics would result in a more favorable environment and
trends will be monitored closely in subsequent outlooks.

Another shortwave trough and attendant surge of cold air is forecast
to follow quickly in the wake of the first system this weekend.
Short period between this surge and the lead wave is expected to
limit moisture return and thunderstorm potential.

..Mosier.. 02/01/2021
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ACUS48 KWNS 020957
SWOD48
SPC AC 020955

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0355 AM CST Tue Feb 02 2021

Valid 051200Z - 101200Z

...DISCUSSION...
An expansive upper trough is expected to persist across much of the
CONUS through the weekend before the flow then trends less
amplified/more zonal. Latest medium-range guidance forecasts a pair
of strong cold fronts, one on D5/Saturday and D6/Sunday and the
other on D7/Monday and D8/Tuesday, will likely keep conditions
stable across the majority of the CONUS. The only exception is from
the Gulf Coast into FL, where these fronts may interact with modest
low-level moisture to produce thunderstorms.

While the most recent run of the guidance suggests limited potential
throughout extended period, moderate run-to-run variability exists. Additionally, given the active/progressive nature of the pattern and
presence of strong dynamics, minor changes in system evolution could
result in more thermodynamically favorable environments. As such,
trends will be monitored closely in subsequent outlooks.

..Mosier.. 02/02/2021
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ACUS48 KWNS 030919
SWOD48
SPC AC 030917

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0317 AM CST Wed Feb 03 2021

Valid 061200Z - 111200Z

...DISCUSSION...
At least broadly cyclonic flow aloft is forecast to persist across
the CONUS until the middle of next week. A series of shortwave
troughs are expected to traverse this parent upper troughing, the
first on D4/Saturday, followed by another on D5/Sunday, and
potentially a third on D6/Monday or D7/Tuesday. The first two waves
will be accompanied by surges of cold, continental air, acting to
reinforce the stable conditions expected to be in place. This will
limit any low-level moisture return and associated buoyancy,
preventing thunderstorms.

The only exception is across FL, where enough low-level moisture may
remain for isolated storms ahead of each frontal passage. Enhanced
mid/upper level southwesterly flow will likely be in place over FL
from D4/Saturday through D5/Sunday, resulting in the potential for a
few stronger storms as the surface low and attendant front progress
across the peninsula. After D5/Sunday, the stronger flow aloft is
forecast to retreat northward, limiting severe potential with the
next frontal passage.

..Mosier.. 02/03/2021
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ACUS48 KWNS 040905
SWOD48
SPC AC 040904

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0304 AM CST Thu Feb 04 2021

Valid 071200Z - 121200Z

...DISCUSSION...
Broad upper trough is expected to persist into the middle of next
week as a series of shortwave troughs continued to reinforce the
prevailing pattern. Additionally, a cold, polar air mass is expected
to move into the northern/central Plains and Upper Midwest on
D4/Sunday before continuing southward/southeastward into the
southern Plains and MS and OH Valleys on D5/Monday. High surface
pressure associated with this cold air mass will then dominate
sensible weather across the majority of the CONUS for the remainder
of the period.

The only exception is across FL, where a few thunderstorms are
possible on late D5/Monday into early D6/Tuesday as a shortwave
trough glances the region.

..Mosier.. 02/04/2021
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ACUS48 KWNS 060926
SWOD48
SPC AC 060924

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0324 AM CST Sat Feb 06 2021

Valid 091200Z - 141200Z

...DISCUSSION...
Run-to-run model consistency continues to be an issue in the medium
to extended time range. In the mean, upper troughing will persist
across much of the CONUS, with a series of embedded shortwave
troughs ejecting from the Rockies eastward through the period.
Surface high pressure will generally be maintained over the northern
Plains and much of the Midwest, resulting in a cold and dry air mass
over those regions for the next week or so. Guidance has wavered
with regard to how far south this arctic air mass intrusion will
progress and the timing of such. Some guidance suggests that a cold
front will dive southeast across the southern Plains and into the
Southeast late in the week, potentially leading to thunderstorms and
a low-end severe threat across the Gulf Coast states around Day
5/Wed-Day 6/Thu. However, this signal has not been consistent. As
such, confidence is low in any severe potential during the Day 4-8
period.

..Leitman.. 02/06/2021
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ACUS48 KWNS 070928
SWOD48
SPC AC 070926

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0326 AM CST Sun Feb 07 2021

Valid 101200Z - 151200Z

...DISCUSSION...
A series of shortwave upper troughs are expected to migrate through larger-scale troughing across the CONUS during the Day 4-8 period.
Some strong to severe storm potential may develop from the ArkLaTex
vicinity into the lower MS Valley on Days 4-5/Wed-Thu as the initial
shortwave ejects eastward from the southwest U.S. to the
Mid-Atlantic during that time frame. Southerly flow ahead of the
trough will allow moisture to surge northward from southern and
eastern TX through the Gulf coast states ahead of an arctic cold
front. This warm advection regime ahead of the front would likely
result in elevated thunderstorm activity to the cool side of the
warm front over the Gulf coast region, or undercut by the advancing
cold front. Medium range guidance run-to-run consistency continues
to be poor, and the timing of these features varies, resulting in
low predictability of severe potential.

Beyond Day 5/Thu, guidance suggests several surges of arctic air
will overspread much of the CONUS, resulting in cold and stable
conditions and limiting thunderstorm activity through the weekend.

..Leitman.. 02/07/2021
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ACUS48 KWNS 080909
SWOD48
SPC AC 080908

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0308 AM CST Mon Feb 08 2021

Valid 111200Z - 161200Z

...DISCUSSION...
A progressive upper pattern is forecast during the Day 4-8 period,
with a series of troughs migrating across the CONUS. The first upper
trough in this series will spread eastward across the Plains and
toward the Atlantic coast on Day 4/Thu. At the surface, an arctic
air mass will percolate south and east behind a cold front,
extending from the coastal Carolinas to the central Gulf coast
vicinity by Day 5/Fri morning. Thunderstorm potential will exist
across parts of the Southeast in the vicinity of the front on
Thursday and Friday, though most of this activity is expected to
remain elevated/to the cool side of the boundary, limiting severe
potential in the absence of stronger surface cyclogenesis.

Strong surface high pressure will continue to build south/southeast
across the Plains and Midwest, as a second upper trough digs across
the western states and shifts eastward over the Plains and Midwest
during the weekend. This will reinforce a bitterly cold air mass
across much of the U.S. through the end of the period, precluding
severe thunderstorm potential.

..Leitman.. 02/08/2021
$$
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ACUS48 KWNS 090921
SWOD48
SPC AC 090919

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0319 AM CST Tue Feb 09 2021

Valid 121200Z - 171200Z

...DISCUSSION...
Severe potential will be low during the Day 4-8 period. Strong
surface high pressure and an arctic airmass will persist across much
of the CONUS through at least Day 7/Monday. Thunderstorms are
possible across parts of GA/FL on Day 4/Friday as a cold front sags
southward and stalls over northern FL. Severe storms are not
expected with this activity given poor lapse rates and weak forcing.
Given the persistent arctic airmass over the eastern two-thirds of
the CONUS, thunderstorm activity will remain limited.

..Leitman.. 02/09/2021
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ACUS48 KWNS 100914
SWOD48
SPC AC 100913

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0313 AM CST Wed Feb 10 2021

Valid 131200Z - 181200Z

...DISCUSSION...
An arctic airmass will envelop much of the CONUS through at least
Day 6/Mon. A series of upper troughs will allow reinforcing shots of
cold air to spread southeast across the Plains and Midwest. While a
cold and dry airmass will settle across the Southeast U.S.,
southwesterly deep-layer flow will prevail, maintaining weak warm
advection across the region with a surface boundary extending across
the northern Gulf of Mexico and northern FL for much of the period.
This will allow for periods of showers and thunderstorms across
parts of the Southeast, but severe potential appears low.

The exception may be around Day 6/Mon or Day 7/Tue when a shortwave
trough is forecast by some guidance to develop eastward across
northern/central Mexico and into the Gulf, before lifting northeast
toward the Mid-Atlantic by the end of the period. If this occurs,
surface cyclogenesis across the lower MS/TN Valley vicinity could
result in a favorable warm sector overlapping with strong shear and
upper forcing across parts of the Southeast ahead of another strong
cold front. Medium-range guidance currently differs in timing and
intensity of these features, resulting in low predictability, but
severe probabilities could be needed in future outlooks if
confidence in this scenario increases.

..Leitman.. 02/10/2021
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ACUS48 KWNS 120926
SWOD48
SPC AC 120925

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0325 AM CST Fri Feb 12 2021

Valid 151200Z - 201200Z

...DISCUSSION...
An upper trough is forecast to develop eastward across parts of the central/eastern CONUS from Day 4/Monday into Day 5/Tuesday.
Low-level moisture should return northward across parts of the Gulf
Coast states and the Carolinas ahead of a northeastward-developing
surface low. A severe risk may develop across parts of these
regions, mainly from late Monday into Tuesday. However, confidence
in sufficient destabilization to support surface-based storms is not
great enough to include 15% severe probabilities for now.

Medium-range guidance is in relatively good agreement that another
large-scale upper trough will move across the central/eastern states
around the Day 6/Wednesday to Day 7/Thursday time frame. Some severe
risk may once again materialize across parts of the central Gulf
Coast states and perhaps the Carolinas as low-level moisture returns
northward across these areas. Regardless, there is far too much
uncertainty in the prospect for substantial boundary-layer
destabilization to include any severe probabilities at this extended
time frame.

..Gleason.. 02/12/2021
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ACUS48 KWNS 130956
SWOD48
SPC AC 130954

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0354 AM CST Sat Feb 13 2021

Valid 161200Z - 211200Z

...DISCUSSION...
Some severe threat may exist on Day 4/Tuesday across parts of the
eastern Carolinas and the central/southern FL Peninsula ahead of a
cold front. Strong deep-layer shear associated with a
northeastward-ejecting shortwave trough should be present across
these regions. However, forecast instability appears marginal to
support organized severe storms. Have therefore not included any 15%
severe probabilities for Day 4/Tuesday.

In the wake of this lead system, medium-range guidance is in fairly
good agreement that another upper trough should develop eastward
across the central/eastern CONUS in the Day 5/Wednesday to Day
6/Thursday time frame. Sufficient low-level moisture may return
northward across parts of the Southeast ahead of the upper trough to
support surface-based storms, mainly late Wednesday into Thursday.
An associated severe risk appears possible based on forecast
instability and shear. However, the overall severe threat appears
too marginal and uncertain at this extended time frame to introduce
15% severe probabilities. By late next week into the following
weekend, meager low-level moisture behind another frontal passage
should greatly limit the severe potential across the CONUS.

..Gleason.. 02/13/2021
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ACUS48 KWNS 140937
SWOD48
SPC AC 140936

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0336 AM CST Sun Feb 14 2021

Valid 171200Z - 221200Z

...DISCUSSION...
A large-scale upper trough is forecast to amplify over the Plains on
Day 4/Wednesday while moving slowly eastward. Substantial low-level
moisture confined to the Gulf of Mexico and FL Peninsula ahead of
this feature should return northward across parts of the Southeast
Wednesday night into Day 5/Thursday. An organized severe threat
could develop over parts of the central Gulf Coast states if
low-level moisture sufficient to support surface-based storms can
advance far enough inland. At this point, there is too much
uncertainty regarding the quality of low-level moisture and related boundary-layer instability to include 15% severe probabilities for
any part of the Southeast for Wednesday night or Thursday. From Day
6/Friday through next weekend, organized severe potential appears
nil across the CONUS, as low-level moisture behind a cold front
passage should be very limited.

..Gleason.. 02/14/2021
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ACUS48 KWNS 150954
SWOD48
SPC AC 150952

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0352 AM CST Mon Feb 15 2021

Valid 181200Z - 231200Z

...DISCUSSION...
A highly amplified upper trough should continue moving eastward from
the Plains across much of the MS/OH/TN Valleys and Southeast on Day
4/Thursday. A related surface low is forecast to develop
northeastward across the central Gulf Coast states and towards the
vicinity of SC by Thursday evening. Greater low-level moisture and a
warm sector should likewise develop northward over portions of the
FL Panhandle, southeastern AL, and southern/central GA through the
day. Rather strong low- and mid-level flow appears likely to
overspread these areas, and deep-layer shear will easily support
organized severe convection. Strong to severe storms may be ongoing
Thursday morning across the western FL Panhandle/southern AL
vicinity near the surface low. Current expectations are for these
storms to move quickly east-northeastward on Thursday across the
developing warm sector.

Both damaging winds with a possible squall line and a couple
tornadoes with any supercells either ahead of or embedded within the
line may occur given a favorable veering/strengthening low-level
wind profile and sufficiently unstable airmass. With a consistent
signal in guidance depicting this scenario, have included a 15%
severe area for Day 4/Thursday where surface-based storms appear
probable. Some severe risk may extend northeastward into parts of
the Carolinas Thursday evening/night. However, too much uncertainty
currently exists regarding the degree of boundary-layer instability
to extend the 15% severe probabilities any farther northeastward.
Once the cold front associated with the surface low clears the East
Coast, potentially late Thursday night or early Day 5/Friday, then
the severe risk across the CONUS appears negligible through the
remainder of the extended forecast period.

..Gleason.. 02/15/2021
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ACUS48 KWNS 160946
SWOD48
SPC AC 160945

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0345 AM CST Tue Feb 16 2021

Valid 191200Z - 241200Z

...DISCUSSION...
A surface cold front should clear much of the East Coast early on
Day 4/Friday as a large-scale upper trough continues advancing
across the eastern CONUS. Any thunderstorm potential Friday will
likely be limited to parts of the central/southern FL Peninsula.
With enhanced southwesterly mid-level flow present over this region,
a few strong storms cannot be ruled out along the front as it
advances quickly southeastward through Friday evening. However, weak instability will probably limit an organized severe risk.
Thereafter, meager low-level moisture across the CONUS should
preclude any severe risk this upcoming weekend into early next week.

..Gleason.. 02/16/2021
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ACUS48 KWNS 170836
SWOD48
SPC AC 170834

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0234 AM CST Wed Feb 17 2021

Valid 201200Z - 251200Z

...DISCUSSION...
Multiple upper troughs should progress eastward across the CONUS
from this upcoming weekend into the middle of next week. Rich
low-level moisture is not expected to return northward from the Gulf
of Mexico ahead of any of these upper troughs. Therefore,
instability should remain minimal, and organized severe
thunderstorms are not expected.

..Gleason.. 02/17/2021
$$
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ACUS48 KWNS 180814
SWOD48
SPC AC 180812

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0212 AM CST Thu Feb 18 2021

Valid 211200Z - 261200Z

...DISCUSSION...
An upper trough should move across the central/eastern CONUS from
Day 4/Sunday into early next week. Low-level moisture ahead of this
system will likely remain insufficient for any organized severe
thunderstorm risk. There are some indications in medium-range
guidance that another upper trough may amplify over the western
CONUS around Day 6/Tuesday through the end of the period. If this
occurs, then low-level moisture return across the southern Plains
and lower MS Valley could potentially support a risk for organized
storms by Day 8/Thursday. However, there are large differences in
guidance regarding the timing and amplification of the potential
upper trough at this extended time frame, leading to low
predictability.

..Gleason.. 02/18/2021
$$
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ACUS48 KWNS 190922
SWOD48
SPC AC 190920

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0320 AM CST Fri Feb 19 2021

Valid 221200Z - 271200Z

...DISCUSSION...
Medium-range guidance indicates that initially suppressed mid-level
ridging, across the eastern mid-latitude Pacific into the U.S.
Pacific coast, may undergo considerable amplification next week,
roughly between 130-160 W longitude. It appears that this may build
toward the Alaskan Arctic Circle vicinity, as a deep mid-level low
(initially centered to the north of Alaska, Yukon and the Canadian
Northwest Territories) shifts a bit southward and eastward across
north central Canada. As this occurs, a mean west-northwesterly
mid-level flow regime, from the northeastern Pacific through the
U.S., may take on a much more substantive northerly component near
the Canadian/U.S. Pacific coast vicinity, into deepening troughing
across the Southwest by late next week.

Arctic surface air is expected to begin to surge southward to the
lee of the Canadian Rockies, but it may remain to the north of the
U.S. international border through at least this period. However,
models suggest that it will be preceded by a southward surge of more
modestly cold air across much of the central and eastern U.S. by mid
to late next week. With guidance indicating little potential for
significant surface cyclogenesis to the lee of the southern Rockies,
and boundary-layer moistening over the Gulf of Mexico slowed by
reinforcing subsidence and drying early next week, the risk for
severe thunderstorms appears low (i.e., less than 10 percent
probabilities) through at least next Friday.

..Kerr.. 02/19/2021
$$
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ACUS48 KWNS 200941
SWOD48
SPC AC 200940

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0340 AM CST Sat Feb 20 2021

Valid 231200Z - 281200Z

...DISCUSSION...
An elongated center of low mid-level heights over the Arctic, to the
north of Alaska, Yukon and the Canadian Northwest Territories by the
beginning of this period, is forecast to redevelop
east-southeastward into the northern Hudson Bay vicinity by late
next week. At the same time, it appears that mid-level ridging will
remain prominent over the mid-latitude eastern Pacific, with a
number of significant short wave troughs progressing within the
westerlies around its periphery, and inland of the Pacific coast.

It appears that this regime will contribute to the evolution of
broad mid-level troughing over much of interior North America this
coming work week, accompanied by at least gradual surface cooling
across much of the U.S. By late in the week, mid-level subtropical
ridging is also forecast to build across the Caribbean and
southeastern Gulf of Mexico into the Southeast, and associated
low-level warming may contribute to a strengthening low-level
baroclinic zone across parts of the Gulf into south Atlantic Coast
states.

This front could provide a focus for increasing thunderstorm
activity as early as Thursday, into next weekend. It is possible
that this may include some risk for severe weather. However, models
continue to suggest that any evolving waves along the front will
remain generally weak, and the extent of Gulf boundary-layer
moistening by this time remains unclear. Anything more than
relatively marginal and/or isolated severe weather potential
currently appears unlikely, but it is not out of the question that
this could change in subsequent outlooks for this period.

..Kerr.. 02/20/2021
$$
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ACUS48 KWNS 210939
SWOD48
SPC AC 210937

Day 4-8 Convective Outlook CORR 1
NWS Storm Prediction Center Norman OK
0337 AM CST Sun Feb 21 2021

Valid 241200Z - 011200Z

CORRECTED FOR TYPO

...DISCUSSION...
Medium-range model output suggests that blocking mid-level ridging
may become increasingly amplified across the mid-latitude Pacific
late this week and remain prominent through next weekend. At the
same time, it appears that a deep mid-level low at Arctic latitudes,
initially developing east-southeastward across far northern Canada,
may linger near or just north of Hudson Bay, while a subtropical
mid-level ridge builds across much of the Gulf of Mexico and
Southeast. Between these features, it appears that a branching
regime will gradually develop across the northeastern Pacific into
the western U.S. by late next weekend, with flow becoming
increasingly confluent across and east of the Great Plains.

Short wave developments within this regime are becoming more
unclear, and the pattern predictability appears to be decreasing.
It seems possible, though, that boundary-layer moistening over the
Gulf of Mexico could become increasingly supportive of severe
weather potential by late next weekend, pending short wave
developments across the southern Rockies into the southern Great
Plains.

..Kerr.. 02/21/2021
$$
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ACUS48 KWNS 220916
SWOD48
SPC AC 220915

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0315 AM CST Mon Feb 22 2021

Valid 251200Z - 021200Z

...DISCUSSION...
Blocking may linger within the large-scale pattern across the
southern mid-latitude and subtropical eastern Pacific late this week
into the beginning of next week. However, the latest medium-range
guidance indicates that prominent/amplified mid-level ridging,
forecast to evolve across the eastern Pacific during the middle to
latter portion of this week, will become increasingly suppressed by
a series of significant short wave perturbations emerging from the
upstream westerlies.

Mid-level flow inland of the Pacific coast appears likely to become increasingly split, with a number of embedded progressive short wave perturbations. The northern branch is currently forecast to
maintain a relatively low amplitude with a west-northwesterly
component, to the southwest of an elongated deep vortex centered
just north of Hudson Bay. Within the southern branch, it appears
that relatively amplified mean troughing will develop across the
Pacific Coast into the Great Plains.

At the same time, subtropical ridging may become increasingly
prominent across much of the Gulf of Mexico into the Southeast.

This regime may become increasingly conducive to significant surface cyclogenesis to the lee of the southern Rockies by next
Sunday/Monday, as boundary-layer moistening continues over the Gulf
of Mexico (particularly the southwestern Gulf). Associated
large-scale forcing for ascent and destabilization could support
increasing severe thunderstorm potential across parts of the
southern Great Plains into the middle/lower Mississippi Valley.
However, much will hinge on the shorter wavelength developments,
which are still fairly uncertain at this extended range. One
particular concern is the timing of the northern branch short waves,
and their associated southward surges of colder air to the lee of
the Rockies, relative to the emerging southern branch short waves,
which could displace and/or mitigate the risk for severe storms.

..Kerr.. 02/22/2021
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ACUS48 KWNS 230946
SWOD48
SPC AC 230945

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0345 AM CST Tue Feb 23 2021

Valid 261200Z - 031200Z

...DISCUSSION...
Medium-range models continue to suggest that, although blocking may
linger to some degree through much of this period, an initially
prominent mid-level high and amplified ridging across the eastern
Pacific will become suppressed by a series of short wave
perturbations emerging from the upstream Pacific. As this occurs,
it still appears that a more pronounced split flow will evolve
downstream, across much of the U.S. and southern Canada. This may
include mean mid-level troughing in the southern branch, across the
southern Pacific coast through the Southwest, from which one or two
significant perturbations may emerge late this weekend into early
next week. At the same time, subtropical ridging, centered over the
southern Gulf of Mexico, may undergo a period of amplification, and
a deep mid-level low near/north of Hudson Bay may maintain some
influence, before perhaps returning northward across the Arctic
Circle vicinity by the end of the period.

This pattern could include potential for significant surface
cyclogenesis to the lee of the southern Rockies and a substantive
return flow of moisture off the western Gulf of Mexico by early next
week, accompanied by at least some increase in risk for severe
weather. However, based on sizable differences evident among the
various models, and from run to run, the predictability of the short
wave developments throughout this period appears relatively low.

..Kerr.. 02/23/2021
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ACUS48 KWNS 240951
SWOD48
SPC AC 240950

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0350 AM CST Wed Feb 24 2021

Valid 271200Z - 041200Z

...DISCUSSION...
An initially prominent mid-level high and amplified ridging across
the eastern Pacific likely will become suppressed by a series of
short wave perturbations emerging from the upstream Pacific, late
this week into the weekend. This has been, perhaps, the main point
of consistency in the medium-range guidance over the past several
days. However, blocking may persist within the large-scale flow to
some degree, and the pattern predictability, in general, appears
relatively low. Short wave developments, in particular, have been
highly variable within the various model output.

For the period late this weekend into the middle of next week,
guidance appears to be trending toward a solution with decreasing
potential for significant surface cyclogenesis to the lee of the
southern Rockies. Low amplitude wave development might still be
possible along an evolving frontal zone across parts of the southern
Great Plains through the Gulf and south Atlantic Coast states, and
this could still be accompanied by at least some risk for severe
weather. However, the potential for the development of more than
relatively marginal conditions for severe thunderstorms currently
seems low.

..Kerr.. 02/24/2021
$$
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ACUS48 KWNS 250954
SWOD48
SPC AC 250953

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0353 AM CST Thu Feb 25 2021

Valid 281200Z - 051200Z

...DISCUSSION...
Blocking may persist to some degree within the evolving large-scale
pattern over the eastern Pacific late this weekend into early next
week, maintaining a split flow with embedded short wave developments characterized by a relatively low degree of predictability. In
general, though, by the middle of next week, it does appear that a
progression of short waves will contribute to the suppression of
fairly prominent initial subtropical ridging centered over the
southeastern Gulf of Mexico/northwestern Caribbean. There also
appears consensus that amplified large-scale troughing will evolve
across the eastern Pacific (mostly to the west of the Pacific
coast), with downstream large-scale ridging building inland of the
Pacific coast through the U.S. Great Plains and Canadian Prairies.

While developments east of the Rockies are more uncertain, a frontal
zone initially extending from near or south of the Texas Big Bend
into the Mid Atlantic Coast region may provide a focus for
continuing thunderstorm development, and perhaps at least some
severe weather potential. In the wake of a deepening surface
cyclone across the Great Lakes into Quebec on Sunday, this frontal
zone may shift southward into the south Atlantic and Gulf Coast
states by early next week. As it does, it is possible that
destabilization along and south of it could become sufficient to
support vigorous thunderstorms with the potential to produce
damaging wind gusts and perhaps a risk for tornadoes, in the
presence of strong deep-layer mean wind fields and shear.

As the frontal zone becomes quasi-stationary across the southern
tier of the U.S. during the early to middle portion of next week,
the extent of any continuing severe weather potential will largely
depend on the strength of subsequent surface wave development along
it. There has been, and continues to be, considerable variability
within medium range output concerning this.

..Kerr.. 02/25/2021
$$
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ACUS48 KWNS 260932
SWOD48
SPC AC 260930

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0330 AM CST Fri Feb 26 2021

Valid 011200Z - 061200Z

...DISCUSSION...
An upper low will become an open shortwave trough as it ejects
eastward from NM to the southern Plains and the Ohio Valley Days
4-5/Mon-Tue. A second upper shortwave will then migrate from the
southern Rockies and merge with a larger-scale upper trough over the
central U.S. on Day 6/Wed. These features will induce surface low
development over coastal TX late Mon/early Tue. The weak surface low
will lift east/northeast toward the Mid-South on Tuesday and the
Mid-Atlantic vicinity late Wednesday. This will bring a cold front southeastward across the southeastern states through Day 7 Thu. Some
low-end severe potential could develop near the cold front, mainly
Day 5/Tue into Day 7/Thu near the central Gulf Coast vicinity. Rich
Gulf moisture will be in place ahead of the front, and moderate
shear will exist as the shortwave troughs lift northeast of the
region. However, surface cyclogenesis will remain weak, and
widespread precipitation and cloudiness will likely inhibit
destabilization. At this time, the overall severe threat appears too low/uncertain to include probabilities.

..Leitman.. 02/26/2021
$$
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ACUS48 KWNS 270922
SWOD48
SPC AC 270920

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0320 AM CST Sat Feb 27 2021

Valid 021200Z - 071200Z

...DISCUSSION...
A series of upper shortwave troughs will migrate across the southern
tier of the U.S. during the Day 4-8 period. The first in this
series, located over the southern/central Plains on Day 4/Tue will
shift eastward to the Carolinas/Mid-Atlantic vicinity through Day
5/Wed. At the surface, a weak low will develop near coastal LA on
Tuesday, shifting east/northeast across the southern states and
offshore the Carolinas by Wednesday evening. This will bring a cold
front across the southeastern U.S. and widespread showers and
thunderstorms are expected. Much of this activity is expected to
remain elevated, with instability limited and shear relatively
modest. High pressure will settle across the eastern half of the
U.S. Day 6/Thu, with the surface cold front continuing southward
into the northern Gulf and FL Straits vicinity.

Late in the period, a second upper shortwave trough/closed low is
expected to develop eastward across the southern Plains and Gulf
coast vicinity around Day 7/Fri-Day 8/Sat. Guidance varies quite a
bit in the evolution of this system, with some medium range guidance
digging the trough fairly far south into the Gulf. This could limit
northward moisture return, keeping any severe potential offshore
from the central Gulf coast. However, this could bring an increase
in severe potential to the FL Peninsula over the weekend. Given
large spread, uncertainty is too great to include severe
probabilities at this time.

..Leitman.. 02/27/2021
$$
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ACUS48 KWNS 280928
SWOD48
SPC AC 280926

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0326 AM CST Sun Feb 28 2021

Valid 031200Z - 081200Z

...DISCUSSION...
Run-to-run consistency among medium-range guidance has been poor the
past day or two. In general, the lends to low confidence in any
given solution through the extended period. Forecast guidance
continues to show a couple of shortwave troughs migrating across the
southern tier of the CONUS during the period. One upper shortwave
trough over the southeastern states will quickly shift offshore on
Day 4/Wed, bringing a cold front across FL. Thereafter, high
pressure will persist east of the Rockies through at least Day
5/Thu. By the weekend, another shortwave is then forecast to track
eastward from the Plains to the southeastern U.S. At this time, poor
Gulf return flow ahead of this system is forecast to limit severe
potential.

..Leitman.. 02/28/2021
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ACUS48 KWNS 010933
SWOD48
SPC AC 010932

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0332 AM CST Mon Mar 01 2021

Valid 041200Z - 091200Z

...DISCUSSION...
Medium-range guidance is in somewhat better agreement compared to
the past couple of days. Overall, severe potential appears low
during the Day 4-8 period. A shortwave upper trough over the western
U.S. will migrate eastward to the southeastern states through Day
5/Fri. As this occurs, a weak surface low is forecast to develop
over central TX and weak Gulf return flow will overspread parts of
coastal TX. Some low-end severe potential could develop ahead of low
and attendant cold front, but moisture return will likely be shallow
and ill-timed with this system. After Friday, surface high pressure
will dominate east of the Rockies, limiting any northward moisture
return through the end of the period.

..Leitman.. 03/01/2021
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ACUS48 KWNS 020928
SWOD48
SPC AC 020926

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0326 AM CST Tue Mar 02 2021

Valid 051200Z - 101200Z

...DISCUSSION...
Severe potential will remain low for much of the Day 4-8 period.
Persistent surface high pressure east of the Rockies, and a cold
front dropping southward across the much of the Gulf of Mexico will
result in dry and stable conditions. Toward the end of the period,
an upper trough is forecast to develop southward along the Pacific
coast and shift eastward to the Plains. While forecast guidance
varies in the exact evolution and timing of this feature, associated
strong surface cyclogenesis could result in a deeper northward
transport of Gulf moisture and possible strong-to-severe
thunderstorm development around Day 8/Tue or just beyond the
forecast period from the southern Plains toward the MS Valley.

..Leitman.. 03/02/2021
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