ACUS48 KWNS 150808
SWOD48
SPC AC 150806

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0306 AM CDT Mon Sep 15 2025

Valid 181200Z - 231200Z

...DISCUSSION...
An upper low/shortwave trough will persist over the north-central
U.S. for much of the period. This system is not forecast to deepen,
resulting in little surface cyclogenesis, with mainly weak surface
troughing persisting over the Plains. Southerly low-level flow will
maintain a seasonally moist airmass, and periods of showers and
thunderstorms are expected each day across parts of the Plains to
the MS Valley. Modest vertical shear and airmass modification from
daily rounds of convection will likely limit overall severe
potential.

Medium range guidance suggests by late in the period, around Day
8/Mon, a stronger surface cold front may sweep across portions of
the Plains as a deepening, more progressive upper trough moves from
the Rockies into the Plains.

..Leitman.. 09/15/2025

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ACUS48 KWNS 160810
SWOD48
SPC AC 160809

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0309 AM CDT Tue Sep 16 2025

Valid 191200Z - 241200Z

...DISCUSSION...
Severe thunderstorm potential is expected to remain low through at
least Day 6/Sun. A shortwave upper trough over the north-central
U.S. will slowly migrate east across the Great Lakes region through
the weekend. Weak deep layer flow and limited large-scale ascent
will preclude severe thunderstorms. By the end of the period, around
Days 7-8/Mon-Tue, medium range guidance suggests a more substantial
upper trough will eject from the northern Rockies and deepen over
the Plains/Midwest as a stronger surface cold front moves through
the central portions of the CONUS. This could support some
increasing severe thunderstorm potential, but large spread remains
across various forecast guidance regarding timing and evolution of
this feature as it develops east of the Rockies early next week.

..Leitman.. 09/16/2025

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ACUS48 KWNS 170800
SWOD48
SPC AC 170759

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0259 AM CDT Wed Sep 17 2025

Valid 201200Z - 251200Z

...DISCUSSION...
Medium-range guidance generally indicates low-amplitude/weak upper
troughing will persist across portions of the central U.S. through
the weekend. By early next week, large spread exists between the
control members of the GFS and ECMWF and how these models handle the
evolution of a deepening upper trough moving out of the Rockies and
into the Plains/Midwest around Days 6-8/Mon-Wed. Ensemble mean 500
mb forecasts are in better alignment, indicating a stronger
large-scale trough will emerge over the Plains and MS Valley late in
the period, bringing a stronger autumn cold front south/southeast
across much of the central U.S. This could bring some increasing
severe potential to portions of the Plains MS Valley during the
second half of the forecast period, but given aforementioned
uncertainty/large spread, it is unclear which days/locations may
experience any increasing risk.

..Leitman.. 09/17/2025

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ACUS48 KWNS 180750
SWOD48
SPC AC 180749

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0249 AM CDT Thu Sep 18 2025

Valid 211200Z - 261200Z

...DISCUSSION...
An upper shortwave trough is forecast to move across the northern
Rockies on Day 4/Sun while low-amplitude, broad upper troughing
persists across the central portion of the CONUS. By Day 5/Mon, the
northern Rockies upper trough is expected to rapidly deepen as it
overspread the plains. Rich boundary layer moisture if forecast to
be in place across portions of the southern/central Plains into the
MS Valley as a strong cold front moves across parts of the Plains.
While the timing of the upper trough ejecting into the Plains is
uncertain, some severe potential could develop on Day 5/Mon across
the southern/central Plains toward the Mid/Lower MO Valley.
Uncertainty remains too high to include 15 percent probabilities at
this time however.

Beyond Day 5/Mon, uncertainty increases as large spread among model
guidance persists with regard to the evolution of a developing upper
low somewhere over the mid-section of the CONUS into Day 8/Thu.
Severe potential is uncertain, and the overall pattern may favor
heavy rain over organized severe heading into Day 6/Tue, but model
trends will continue to be monitored.

..Leitman.. 09/18/2025

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ACUS48 KWNS 181410
SWOD48
SPC AC 181409

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0909 AM CDT Thu Sep 18 2025

Valid 211200Z - 261200Z

...DISCUSSION...
An upper shortwave trough is forecast to move across the northern
Rockies on Day 4/Sun while low-amplitude, broad upper troughing
persists across the central portion of the CONUS. By Day 5/Mon, the
northern Rockies upper trough is expected to rapidly deepen as it
overspread the plains. Rich boundary layer moisture if forecast to
be in place across portions of the southern/central Plains into the
MS Valley as a strong cold front moves across parts of the Plains.
While the timing of the upper trough ejecting into the Plains is
uncertain, some severe potential could develop on Day 5/Mon across
the southern/central Plains toward the Mid/Lower MO Valley.
Uncertainty remains too high to include 15 percent probabilities at
this time however.

Beyond Day 5/Mon, uncertainty increases as large spread among model
guidance persists with regard to the evolution of a developing upper
low somewhere over the mid-section of the CONUS into Day 8/Thu.
Severe potential is uncertain, and the overall pattern may favor
heavy rain over organized severe heading into Day 6/Tue, but model
trends will continue to be monitored.

..Leitman.. 09/18/2025

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ACUS48 KWNS 190852
SWOD48
SPC AC 190850

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0350 AM CDT Fri Sep 19 2025

Valid 221200Z - 271200Z

...DISCUSSION...
A complex, split-flow, low-predictability upper pattern will exist
early next week and eventually evolve into a closed upper low across
the Midwest by the end of the week. The operational ECMWF and GFS
have significantly different evolution of the upper pattern.
However, the GEFS and EPS ensemble mean look very similar through
much of the extended forecast. Therefore, the operational GFS will
be treated as an outlier for this outlook cycle with an implied
preference for the ECMWF/EPS/GEFS.

...Day 4/Monday - TX/OK Panhandles into western Kansas and western
Oklahoma...
ECMWF forecast soundings on Monday show a favorable environment
featuring moderate to strong instability and moderate to strong
shear as a 40+ knot mid-level jet ejects across the TX Panhandle and
into Oklahoma. The primary trough will remain across the central
Rockies with only weak height falls across the Plains. However, a
strengthening low-level jet ahead of this trough may support
thunderstorm potential within this favorable zone. Relatively weak
synoptic support and lower predictability within the split-flow
regime precludes 15% probabilities at this time, but probabilities
may need to be included later, particularly if confidence in the
location and coverage of storms across portions of OK/KS and the TX
Panhandle increases.

...Day 5 and Beyond...
If a closed upper-low develops (as forecast by the GEFS and EPS
mean), some marginal severe weather concern will likely accompany
the low as it drifts east. No specific periods of greater severe
weather threat are apparent at this time, and given the slow forward
speed of the closed low, any severe weather threat will likely
remain marginal.

..Bentley.. 09/19/2025

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ACUS48 KWNS 200848
SWOD48
SPC AC 200846

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0346 AM CDT Sat Sep 20 2025

Valid 231200Z - 281200Z

...DISCUSSION...
A complex, low-predictability upper pattern will exist next week and
should eventually evolve into a closed upper low somewhere across
the eastern CONUS by the end of the week. The operational ECMWF and
GFS have significantly different evolution of the upper pattern,
almost switching places from the solution each showed 24 hours ago.
The ECMWF is now more progressive with a large cutoff low from the
GFS by Wed/D5 and Thu/D6. Even the EPS and GEFS (which showed
similar 500mb solutions 24 hours ago) have diverged and have lead to
increasing predictability concerns. Therefore, beyond Day 4, some
severe weather chances are possible within the warm sector ahead of
a surface front. However, significant differences in timing and
evolution of the pattern cast uncertainty on the overall threat.

...Day 4/Tuesday...
As the stronger mid-level trough emerges across the Plains Monday
night, a low-level jet will strengthen across Oklahoma. Therefore, a
MCS will likely be ongoing at 12Z Tuesday in the Oklahoma vicinity.
Moderate destabilization is forecast to the south of the remnant
MCS/outflow boundary on Tuesday. This region will likely be the
focus for some severe weather threat. It is unclear how the
Monday/D3 convection will evolve and how that may impact Tuesday,
but there is some potential for severe storms Tuesday
afternoon/evening. Once the evolution of the mid-level trough and
location of Monday night convection becomes more clear, severe
weather probabilities may be needed.

..Bentley.. 09/20/2025

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ACUS48 KWNS 210741
SWOD48
SPC AC 210740

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0240 AM CDT Sun Sep 21 2025

Valid 241200Z - 291200Z

...DISCUSSION...
A mid-level trough will amplify across the eastern CONUS on
Wednesday and Thursday with differing model solutions of the trough
evolution by next weekend and beyond. Regardless of the exact
solution, severe weather chances should be low from Saturday and
beyond as high pressure builds into the eastern CONUS and pushes
moisture offshore into the Atlantic and Gulf. Some severe weather is
possible across portions of the Southeast on Day 4/Wed to Day 6/Fri
as moisture remains onshore ahead of the mid-level trough.

...D4/Wed - Lower Mississippi River Valley...
Upper 60s to low 70s dewpoints are anticipated within the Lower
Mississippi River Valley on Wednesday. A zone of moderate
instability may develop within this moisture plume from Louisiana
into Arkansas and Mississippi. Guidance varies greatly on the
evolution of the mid-level trough as it advances east on Wednesday.
This will have a significant impact on the specific location and
intensity of any severe weather threat on Wednesday. However, even
if a less amplified, more subdued mid-level pattern evolves, some
severe weather could exist across the Lower Mississippi Valley as
moderate mid-level flow overspreads moderate instability within the
region.

..Bentley.. 09/21/2025

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ACUS48 KWNS 220835
SWOD48
SPC AC 220833

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0333 AM CDT Mon Sep 22 2025

Valid 251200Z - 301200Z

...DISCUSSION...
A positively tilted mid-level trough around the Great Lakes on
Thu/D4 will move across the Northeast by Fri/D5. A weak surface low
will move through the eastern Great Lakes on Thursday with a cold
front extending southwest from that low. Upper 60s to low 70s
dewpoints ahead of the cold front will support some instability, but
it will remain mostly weak amid weak lapse rates. Moderate mid-level southwesterly flow will provide ample shear for storm organization
if pockets of greater instability can develop. At this time, it
appears a few isolated strong to severe storms may be possible from
the Carolinas to the Mid-Atlantic, but a more organized severe
threat is not anticipated.

On D5/Friday the remnant cold front will likely reside somewhere
near the Southeast coast. A few stronger storms will be possible
along this front on Friday before it pushes into the Atlantic on
Friday night.

In the wake of this cold front, high pressure will build into much
of the eastern CONUS. This will result in low severe weather
probabilities amid a dry, continental airmass. Rich low-level
moisture will remain offshore into the early part of next week and
keep severe weather potential low.

..Bentley.. 09/22/2025

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ACUS48 KWNS 230845
SWOD48
SPC AC 230843

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0343 AM CDT Tue Sep 23 2025

Valid 261200Z - 011200Z

...DISCUSSION...
A frontal zone will linger along the Southeast coast on Friday. A
few strong storms are possible along this front given the moist
airmass in the region. High pressure and a continental airmass will
build into the eastern CONUS in the wake of this front. This should
result in minimal severe weather potential across much of the CONUS
this weekend and into next week. Operational and ensemble guidance
shows a closed low developing across the Southeast this weekend and
lingering through the middle of next week. Richer moisture may
advect inland to the east and north of this low, and spread
thunderstorms inland, but severe weather chances should still remain
low given weak lapse rates and instability and relatively weak
shear.

..Bentley.. 09/23/2025

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ACUS48 KWNS 240825
SWOD48
SPC AC 240824

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0324 AM CDT Wed Sep 24 2025

Valid 271200Z - 021200Z

...DISCUSSION...
Surface high pressure will dominate much of the eastern CONUS this
weekend and into early next week with dry conditions anticipated.
The only exception may be across the Southeast where tropical
moisture may move inland early next week with some rain and
thunderstorm chances.

Western CONUS mid-level troughing for much of the period will
support lee surface troughing across the northern and central High
Plains. Northerly flow across the Gulf of America should limit rich
moisture inland early next week. Therefore, some residual moisture
may result in weak instability across the central and northern High
Plains, but thunderstorm potential will likely be limited with even
lower severe weather potential.

..Bentley.. 09/24/2025

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ACUS48 KWNS 250909
SWOD48
SPC AC 250908

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0408 AM CDT Thu Sep 25 2025

Valid 281200Z - 031200Z

...DISCUSSION...
Ridging will dominate much of the eastern 2/3rds of the CONUS during
the extended forecast period which will limit thunderstorm activity.
The exception will be across the Southeast United States into the
Mid-Atlantic where a weak cut-off low is forecast to persist into
next week. Some tropical moisture may advect northwestward and bring
some thunderstorm activity to portions of the Southeast into the
Carolinas and Mid-Atlantic. However, instability and shear should
both remain weak and limit any severe weather potential.

A large-scale western CONUS trough will shift east across the
northern Rockies by the middle of next week. This may result in some thunderstorm activity along the lee trough. However, moisture (and
thus severe weather potential) should remain limited given continued
northerly flow across the Gulf of America and southern United
States.

..Bentley.. 09/25/2025

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ACUS48 KWNS 260833
SWOD48
SPC AC 260832

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0332 AM CDT Fri Sep 26 2025

Valid 291200Z - 041200Z

...DISCUSSION...
It appears that an amplification within the westerlies will quickly
translate inland of the North American Pacific coast, across Canada/
adjacent portions of the northern U.S into the northern Atlantic
through the early to middle portion of next week. In its wake,
medium-range guidance suggests a return to a more zonal regime, with
stronger flow confined to the northern mid-latitudes while troughing
is maintained within weaker flow across the Gulf Basin through
Southeast vicinity.

The risk for organized severe convection appears low through the
period, with perhaps the most notable conditional severe weather
potential accompanying a pair of tropical cyclones forming across
parts of the subtropical western Atlantic. While it currently
appears probable that Humberto will turn northeastward/eastward well
offshore of the Atlantic Seaboard, guidance continues to indicate at
least some possibility that a developing cyclone to its west could
approach or migrate inland of Atlantic coastal areas anywhere from
Florida to the Carolinas. However, even if this occurs, it is not
certain that this will be accompanied by the inland advection of a
sufficiently moist/buoyant boundary-layer air mass to support an
appreciable risk for tornadoes.

..Kerr.. 09/26/2025

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ACUS48 KWNS 270845
SWOD48
SPC AC 270843

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0343 AM CDT Sat Sep 27 2025

Valid 301200Z - 051200Z

...DISCUSSION...
Potential Tropical Cyclone Nine may approach coastal South Carolina
early in the period, before probably stalling near or offshore, then accelerating away from the coast into the western Atlantic. This is
likely to be influenced by some combination of a lingering frontal
zone near the Carolina coast, an initial increasing proximity of
Humberto to its east, and cool surface ridging building across the
Northeast through the lee of the Appalachians, in the wake of an
amplifying mid-level trough off the north Atlantic coast during the
early to middle portion of next week. However, even if it does
migrate inland at some point, as some model output indicates is at
least possible, probabilities for the inland advection of a
sufficiently moist and buoyant boundary layer to support an
appreciable risk for tornadoes still appears low.

Otherwise, developments within the westerlies off the mid-latitude
Pacific into North America remain unclear through the latter portion
of the coming week into next weekend. Guidance now appears to
indicate a more amplified regime, including one or more short wave perturbations emerging from evolving large-scale troughing across
the West. However, a slow to develop moist return flow off the Gulf
into the interior U.S. may continue to preclude an appreciable risk
for organized severe thunderstorm development.

..Kerr.. 09/27/2025

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ACUS48 KWNS 280826
SWOD48
SPC AC 280825

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0325 AM CDT Sun Sep 28 2025

Valid 011200Z - 061200Z

...DISCUSSION...
Strong cyclogenesis within the westerlies near the Aleutians late
this week into next weekend may lead to the development of an
increasingly prominent blocking pattern over the eastern
mid-latitude Pacific into western North America. This may include
an evolving low near the California coast, to the southeast of
building mid/upper high over the northeastern Pacific by the end of
the period. In general, though, stronger westerlies are forecast to
remain confined to the northern mid-latitudes, with little potential
for substantive cyclogenesis to the lee of the Rockies, and moist
return flow off the Gulf Basin. This likely will maintain generally
low convective potential across the nation.

..Kerr.. 09/28/2025

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ACUS48 KWNS 290830
SWOD48
SPC AC 290828

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0328 AM CDT Mon Sep 29 2025

Valid 021200Z - 071200Z

...DISCUSSION...
Latest model output is not much different from prior runs concerning
the continuation of generally low convective potential across the
U.S. into and through the medium-range period. Guidance continues
to suggest that an increasingly amplified regime across the
mid-latitude eastern Pacific into western North America could lead
to the evolution of a prominent blocking pattern late this week into
next weekend. By early next week, this may include a building
mid-level high over the northeastern Pacific, near the British
Columbia/Pacific Northwest coast, flanked by a pair of evolving lows
at somewhat lower latitudes, including one over the U.S.
Intermountain West. Otherwise, the stronger westerlies may retreat
to somewhat higher latitudes, and mid/upper ridging may build in the
southern mid- to subtropical latitudes east of the Rockies and
Mexican Plateau. Significant surface cyclogenesis still appears
unlikely to the east of the U.S. Rockies, and low-level moisture
return off the Gulf Basin may be slow to develop.

..Kerr.. 09/29/2025

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ACUS48 KWNS 300823
SWOD48
SPC AC 300822

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0322 AM CDT Tue Sep 30 2025

Valid 031200Z - 081200Z

...DISCUSSION...
Late this work week through the weekend, medium-range models
continue to indicate mid/upper flow amplification across the
mid-latitude eastern Pacific into North America, which may lead to
the evolution of an increasingly prominent blocking high offshore of
the British Columbia/Pacific Northwest coast. This would probably
be flanked by persistent troughing at somewhat lower latitudes,
including California coastal areas into the Great Basin. However,
the spread within/among the model output is sizable concerning this
and subsequent developments through early next week.

Stronger and more progressive westerlies, and potential for
significant surface cyclogenesis, may remain confined to the higher
latitudes. However, there does appear a consensus within the
medium-range output of modestly deepening surface troughing across
parts of the central Great Plains into Upper Midwest (roughly along
an axis from the Front Range through Minnesota) by this weekend,
perhaps as one notable short wave perturbation accelerates
northeastward out of the Intermountain West. In the presence of
steep lower/mid-tropospheric lapse rates and strengthening flow,
this could provide a focus for strong thunderstorm development
Saturday and/or Sunday. However, due to the continuing lack of a
substantive moist return flow off the Gulf, the potential for
organized severe storms still appears low.

..Kerr.. 09/30/2025

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ACUS48 KWNS 010851
SWOD48
SPC AC 010850

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0350 AM CDT Wed Oct 01 2025

Valid 041200Z - 091200Z

...DISCUSSION...
Downstream of a building mid-level ridge, and perhaps evolving
embedded high over the northeastern Pacific, it appears that
large-scale troughing will be maintained across the Great
Basin/Southwest vicinity through this coming weekend and beyond.
However, an initially notable short wave trough, digging into the
Great Basin by late this week, is forecast to accelerate across and
northeast of the Rockies, through northern Ontario, Saturday into
early next Monday morning. The extent to which it maintains
strength as it eventually consolidates into mid-level troughing
shifting across and east of the Canadian Prairies, remains unclear.
But, latest medium-range output appears to be trending deeper with
developing surface troughing, and perhaps a relatively compact
evolving surface cyclone, northeast of the Front Range through the
northern Great Plains/Upper Midwest vicinity.

Preceded by a northeastward advecting plume of elevated mixed-layer
air, strengthening flow and shear could contribute to potential for
organized severe convection across parts of western/central Nebraska
through the eastern Dakotas/western Minnesota late Saturday into
Saturday evening, and perhaps farther east across the Upper
Midwest/adjacent Great Lakes vicinity on Sunday. However, this
threat still appears largely conditional. It will probably take
greater boundary-layer moistening than is currently suggested
possible by the medium-range output to support more than relatively
minor severe weather potential in the form of a few strong gusts, in
the presence of thermodynamic profiles characterized by a deeply
mixed boundary layer with sizable lower/mid-tropospheric dew point
spreads.

Into the early through middle portion of next week, the mid/upper
flow evolution becomes more unclear, but guidance continues to
indicate little potential for organized severe thunderstorms.

..Kerr.. 10/01/2025

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ACUS48 KWNS 020848
SWOD48
SPC AC 020847

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0347 AM CDT Thu Oct 02 2025

Valid 051200Z - 101200Z

...DISCUSSION...
Medium-range guidance indicates that blocking within the westerlies
across the mid-latitude eastern Pacific will remain prominent into
the middle to latter portion of next week. However, one mid-level
high forming off the Pacific coast this weekend may be relatively
short-lived, and subsequent developments off the Pacific into North
America remain unclear, based on rather large spread apparent in the
model output.

Early in the period, a still notable, but perhaps weakening,
mid-level short wave perturbation, and associated compact surface
cyclone, may quickly migrate from the eastern Dakotas through
northwestern Ontario during the day Sunday. In the presence of
seasonably strong and sheared lower/mid-tropospheric wind fields,
there appears at least some potential for renewed strong to severe
thunderstorm development, mainly across parts of north central
Minnesota through the western Lake Superior vicinity by Sunday
evening. However, mostly due to a continuing lack of better
low-level moisture return, potential for destabilization supportive
of more than a relatively isolated/marginal severe risk still seems
low or at least uncertain.

Elsewhere, there appears at least some signal for increasing
convective potential ahead of an amplifying short wave trough and
associated cold front advancing southeast of the lower Great Lakes
region, which could impact the Northeastern urban corridor by late
Wednesday. At this point, this appears most notable in ECMWF/ECENS
related output, compared to other model output, at a period of
increasing model spread and low predictability.

..Kerr.. 10/02/2025

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ACUS48 KWNS 030817
SWOD48
SPC AC 030816

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0316 AM CDT Fri Oct 03 2025

Valid 061200Z - 111200Z

...DISCUSSION...
A cold front is forecast to move east across much of the Midwest and Northeast/Mid-Atlantic vicinity through Day 6/Wed. This could result
in increasing thunderstorm potential ahead of this feature given a
moist prefrontal boundary layer. Most guidance suggests instability
will be limited however, likely due to a combination of weak lapse
rates and areas of cloudiness/showers ahead of the front. Severe
thunderstorm potential appears low.

Further west, the ECMWF suite of guidance suggests an upper
shortwave trough may eject across the central Rockies into the
central Plains around Day 6 or 7/Wed or Thu, with some southerly
return flow bringing Gulf moisture northward ahead of this feature.
However, the GFS suite of guidance is delayed with this feature
until near/after Day 8/Fri. Thunderstorm could increase across parts
of the Plains late in the forecast period, but uncertainty/model
spread is quite large.

..Leitman.. 10/03/2025

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