ACUS48 KWNS 300846
SWOD48
SPC AC 300844

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0344 AM CDT Sat Aug 30 2025

Valid 021200Z - 071200Z

...DISCUSSION...
A mid-level trough is poised to rapidly amplify while traversing the
eastern U.S. from around mid-week into next weekend, encouraging a
surface cold front to sweep across the northern Plains to the East
Coast Days 4-7 (Tuesday-Friday). Around Day 6 (Thursday), the
surface cold front should encounter richer low-level moisture while
impinging on the Appalachians. Surface dewpoints well into the 60s F
may support MUCAPE around 1000 J/kg. However, much of the stronger
vertical wind shear and associated upper support may potentially lag
the surface cold front. As such, uncertainties remain regarding
severe potential, with no probabilities introduced this outlook.
Nonetheless, it is plausible that a broken band or line of storms
with at least scattered gusty conditions (perhaps damaging winds)
may organize to the immediate lee of the Appalachians on Thursday.
By the weekend, medium-range guidance hints at the possibility of
moisture return to the southern Plains, along with instability,
which may foster isolated severe potential.

..Squitieri.. 08/30/2025

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ACUS48 KWNS 310851
SWOD48
SPC AC 310849

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0349 AM CDT Sun Aug 31 2025

Valid 031200Z - 081200Z

...DISCUSSION...
A surface cold front will surge east-southeastward across the Plains
states and the MS Valley Day 4 (Wednesday) before impinging on the
East Coast by Days 5-6 (Thursday-Friday) as a mid-level trough
amplifies over the Great Lakes. Adequate low-level moisture will
precede the cold front, supporting potentially strong thunderstorms
over the southern Plains on Wednesday given favorable overlapping shear/instability. Thereafter, potentially strong thunderstorms may
develop ahead of the cold front over the central/northern
Appalachians into the Hudson River Valley Thursday and Friday as the
cold front encounters progressively richer moisture. The main
limiting factor for a clearer severe threat is the potential for
deep-layer ascent/shear potentially lagging behind the cold front.
Nonetheless, convergence along the surface cold front may still
support enough of a severe threat to warrant probabilities by the
Days 1-3 time frame. Medium-range guidance depicts some moisture
return across the southern Plains by the end of the week into next
weekend, as a second mid-level impulse pivots around the broader
cyclonic flow enveloping the eastern U.S. Should this occur, enough
favorable overlapping buoyancy and shear may support an isolated
severe risk.

..Squitieri.. 08/31/2025

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ACUS48 KWNS 010817
SWOD48
SPC AC 010816

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0316 AM CDT Mon Sep 01 2025

Valid 041200Z - 091200Z

...DISCUSSION...
A pronounced mid-level trough will gradually advance eastward across
the eastern U.S. through the remainder of the week into this
weekend, with multiple embedded mid-level perturbations expected to
pivot around the upper trough. The upper trough and associated
impulses will reinforce surface high pressure and cooler air across
much of the U.S. between the Mississippi River and Appalachians
through the extended forecast period. The surface cold front will
encounter seasonably rich low-level moisture while encroaching on
the Eastern Seaboard, prompting the development of at least
scattered thunderstorms. At the moment, the best chance for strong
storms, perhaps accompanied by an isolated severe threat, will be
along the central and northern Appalachians into the Mid Atlantic
within the Days 4-6 (Thursday-Saturday) time frame.

Meanwhile, as surface high pressure builds over the OH/TN Valley
regions, and the Interior West, seasonal moisture return is expected
across parts of the southern Plains due to surface lee troughing.
The aforementioned impulses pivoting around the broader scale upper
trough may graze the southern Plains, perhaps promoting enough
vertical wind shear atop a moist low-level airmass to support
isolated severe thunderstorms Days 4-6 (Thursday-Saturday).

..Squitieri.. 09/01/2025

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ACUS48 KWNS 020835
SWOD48
SPC AC 020834

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0334 AM CDT Tue Sep 02 2025

Valid 051200Z - 101200Z

...DISCUSSION...
A pronounced mid-level trough will progress across the Northeast
late this week, ejecting into the Atlantic by the end of the
weekend. Thereafter, a more progressive pattern will ensue, with
multiple mid-level shortwave troughs poised to traverse the CONUS
early into the middle of next week. Despite differences among
medium-range guidance members, there is general agreement that a
surface cold front will encounter seasonal low-level moisture across
the eastern U.S. Days 4-5 (Friday-Saturday), promoting thunderstorm
potential (some of which may be strong). However, any severe threat accompanying these storms is expected to be localized and isolated.
Surface high pressure will then become established from the MS River
Valley eastward, allowing for moisture return across the Plains
states by next week. Nonetheless, overall forcing for ascent, along
with buoyancy, are expected to be weak over the Plains next week,
with severe potential currently appearing low.

..Squitieri.. 09/02/2025

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ACUS48 KWNS 030818
SWOD48
SPC AC 030817

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0317 AM CDT Wed Sep 03 2025

Valid 061200Z - 111200Z

...DISCUSSION...
The western North American midlevel ridge of the previous days will
slowly move east into the central continent by the end of the
forecast period and in its place an amplified longwave trough will
take hold across the western US.

... Saturday/Day-4 ...
Before this transition happens, a seasonably strong cold front will
push east into the Atlantic and south into the northern Gulf states
as an expansive surface high will move into the central US on
Saturday/Day-4. Guidance disagrees to the degree instability will
materialize along and ahead of the front from the Mid-Atlantic
region into New England. However, pattern recognition would support
scattered strong thunderstorms along the front across this region.
Midlevel flow will be sufficiently strong to support at least some
damaging wind potential should thunderstorms develop.

... Sunday/Day-5 through Wednesday/Day-8 ...

A seasonably cool, dry continental airmass will be in place across
much of the eastern two-thirds of the contiguous US, resulting in
low potential of organized severe thunderstorms on Sunday/Day-5.
That said, as the western trough takes hold, lee troughing will
develop across the High Plains. This will result in return flow
drawing low-level northward by early next week. Weak shortwave troughs/vorticity maxima embedded in the increasingly southwesterly
flow may yield thunderstorms across the High Plains during the late
afternoon into the overnight hours. Depending on the quality of the
resulting low-level moisture return and the strength of any of these
shortwave troughs, the potential for organized severe thunderstorms
may develop, especially later in the forecast period. However,
predictability of these features at this time scale is too low to
warrant unconditional probabilities at this time.

..Marsh.. 09/03/2025

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ACUS48 KWNS 040848
SWOD48
SPC AC 040846

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0346 AM CDT Thu Sep 04 2025

Valid 071200Z - 121200Z

...DISCUSSION...
A seasonally cool and dry continental airmass will be in place
across much of the eastern US at the start of the forecast period,
resulting in low severe potential. By Monday/Day-5, the surface high
pressure responsible for this airmass will have begun to move east
allowing return flow to become established across the Plains. At the
same time, lee troughing in response to a western US longwave trough
will reinforce the return flow regime.

As the moisture is drawn northward into the Plains, steep lapse
rates will advect out into the Plains from the higher elevations to
the west. This combination of moistening low-levels and steep
midlevel lapse rates will support increasing buoyancy profiles
through the week.

Any subtle shortwave trough that ejects out of the western trough
and emerges into the central and northern Plains will have an
opportunity to tap into this moist, buoyant atmosphere. The result
would be at least some potential for thunderstorms, some of which
could be severe. However predictability of these kinds of subtle
features is too poor at these lead times to attempt to highlight
favored days or corridors, thus predictability remains too low for unconditional probabilities.

..Marsh.. 09/04/2025

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ACUS48 KWNS 050855
SWOD48
SPC AC 050854

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0354 AM CDT Fri Sep 05 2025

Valid 081200Z - 131200Z

...DISCUSSION...
Upper-level ridging within the West will slowly shift into the
Plains this weekend and into perhaps the middle of next week. Modest
to moderate mid-level flow will generally continue across the Midwest/Northeast. In the West, current guidance shows a trough
slowly making progress east next week. Model guidance has shown a
high degree of variability with regard to how this western trough
will evolve through time. Expansive surface high pressure will be
present in parts of the Plains and points eastward. With time, this
high will move east and promote southerly return flow across the
Plains. This process will accelerate as the western trough
approaches. While some strong to severe storms will be possible as
moisture returns northward, the timing and location of this
potential largely depends on where surface boundaries set up and
where smaller scale perturbations will eject into the Plains. The predictability of these features remains low at this time.

..Wendt.. 09/05/2025

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ACUS48 KWNS 060900
SWOD48
SPC AC 060859

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0359 AM CDT Sat Sep 06 2025

Valid 091200Z - 141200Z

...DISCUSSION...
Medium range guidance shows good agreement on the upper-level
pattern from next Tuesday into late next week. A western trough will
remain within the Great Basin and Northwest while a ridge across the
Plains will make very slow eastward progress. The overall pattern
will favor at least a narrow zone of moisture return northward into
parts of the Plains. Where models differ is when stronger mid-level
winds will spread into the Plains. The GFS suggests this could
happen late this coming week while the ECMWF shows the trough
ejecting more towards next weekend. Even with these differences,
some severe risk could develop within the High Plains/Plains near
surface boundaries or where small scale perturbations provide
additional ascent. Give the low predictability of these key
features, severe probabilities will continue to be withheld.

..Wendt.. 09/06/2025

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ACUS48 KWNS 070900
SWOD48
SPC AC 070858

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0358 AM CDT Sun Sep 07 2025

Valid 101200Z - 151200Z

...DISCUSSION...
The mid-level flow pattern across the US is forecast to become more
stagnant into the extended-range forecast period as the western US
upper low deepens and shortwave ridging over the Plains moves slowly
eastward. Broad troughing over the East should gradually
consolidate, slowing eastward progress of the upper ridge. As the
western trough slowly approaches the Rockies, a lee trough should
sharpen each afternoon with a narrow zone of moisture return along
and east into parts of the High Plains. Sufficient destabilization
is expected to support isolated thunderstorms, and perhaps some
severe risk, near the lee trough as smaller embedded perturbations
eject eastward periodically. However, with only slow movement of the
upper ridge expected, forcing for ascent should remain modest until
early next weekend. Somewhat greater severe potential may develop
D6/Friday or D7/Saturday as the primary upper trough begins to
emerge over the Plains. However, given the uncertainties associated
with the smaller scale features, and the timing of the main trough,
limited confidence exists regarding severe potential in the extended
forecast.

..Lyons.. 09/07/2025

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ACUS48 KWNS 080902
SWOD48
SPC AC 080900

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0400 AM CDT Mon Sep 08 2025

Valid 111200Z - 161200Z

...DISCUSSION...
The primary focus for isolated severe potential for the next several
days will be the upper low over the western US. The upper low is
forecast to slowly deepen late this week as it drifts eastward.
Shortwave ridging over the Plains is also forecast to move eastward,
gradually breaking down into this weekend. Surface high pressure
over the eastern US will allow modest return flow into the western
Plains along a lee trough and weak surface low over the Dakotas.
Sufficient destabilization is expected to support isolated
thunderstorms, and perhaps some severe risk, near the surface trough
as several shortwave perturbations within the southwesterly flow
ahead of the primary upper low move over the Plains. Somewhat
greater severe potential may develop this weekend as the upper low
ejects over the Plains and more robust moisture. However,the upper
trough may begin to weaken with the stronger flow aloft being
displaced north of the best moisture and buoyancy. While isolated
severe potential may exist each afternoon over the central and
northern Plains into early next week, confidence in widespread
severe potential remains too low for probabilities at this time.

..Lyons.. 09/08/2025

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ACUS48 KWNS 090901
SWOD48
SPC AC 090859

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0359 AM CDT Tue Sep 09 2025

Valid 121200Z - 171200Z

...DISCUSSION...
As shortwave ridging begins to breakdown into this weekend, the
upper trough and enhanced southwesterly flow over the Rockies will
finally begin to overspread the Plains D4/Friday and D5/Saturday.
Continued east/southeasterly low-level flow is likely over the
northern Plains and Upper Midwest, allowing for the return of richer
surface moisture. A stalled front extending eastward from the lee
low over the Dakotas into the western Great Lakes may serve as a
focus for storm development across the Dakotas and MN. However,
models vary on the degree of moisture and resulting buoyancy near
the low/front, which casts significant uncertainty on severe
potential. Enhanced southwesterly flow aloft could support some
organized severe threat, but confidence in specifics remains too low
for 15% probabilities.

Farther south, sufficient destabilization is expected to support
isolated thunderstorms each afternoon into the central and southern
Plains. While the main upper trough should begin to weaken later
into the weekend, lingering mid-level flow could support some severe
risk within a hot and unstable air mass along a surface trough. By
early next week, mid-level ridging is expected to rebuild over the
central CONUS keeping stronger flow aloft and severe potential
limited for the remainder of the extended forecast period.

..Lyons.. 09/09/2025

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ACUS48 KWNS 100857
SWOD48
SPC AC 100856

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0356 AM CDT Wed Sep 10 2025

Valid 131200Z - 181200Z

...DISCUSSION...
Severe potential in the extended forecast period will be tied to a
shortwave trough and stronger southwesterly flow aloft emanating
from the Rockies over the central US. Flow aloft will increase
D4/Saturday as the upper trough begins to overspread the central US.
Ascent from the trough will maintain a weak surface low and
stationary front over the northern Plains and Upper Midwest. At the
same time, a weak cold front will move eastward over the High Plains
serving as a focus for thunderstorm development from the Dakotas and
MN to the southern Plains each afternoon. Some isolated severe
potential is apparent near the surface low/stalled front over the
northern Plains and along the cold front farther south through the
remainder of the weekend. However, model guidance varies widely on
available moisture/buoyancy and the overlap with more robust
vertical shear. This continues to cast significant uncertainty on
severe probabilities through the first half of the extended forecast
period.

By early next week, mid-level ridging is expected to strengthen,
forcing stronger flow aloft northward as the primary western trough
begins to weaken. A second trough will stall over the West as the
ridge continues to build. This should favor drier surface conditions
while also limiting the overlap of buoyancy with stronger flow
aloft. Severe potential appears limited beyond this weekend and into
the first half of next week.

..Lyons.. 09/10/2025

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ACUS48 KWNS 110855
SWOD48
SPC AC 110854

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0354 AM CDT Thu Sep 11 2025

Valid 141200Z - 191200Z

...DISCUSSION...
Model guidance is in fairly good agreement that the upper trough
over the central US will continue to lift northeastward into the
northern Plains and Upper Midwest through early next week. This will
drag a surface low and cold front slowly eastward with seasonably
high moisture in place. The low will begin to fill as it also lifts
into southern Canada. Scattered to numerous thunderstorms appear
likely over the Northern Plains and Upper Midwest, and along the
trailing front over the southern/central Plains each afternoon, as
increasingly meridional flow will parallel the slow moving cold
front. This will favor continued storm development/training along
the boundary with limited air mass destabilization/recovery.
Mid-level lapse rates should also weaken as the upper trough begins
to fill. While some marginal severe risk is evident over the
northern Plains near the low and front, mainly D4/Sunday,
significant uncertainty exists regarding boundary-layer
destabilization and its impacts on severe potential through
D5/Monday.

By D6/Tuesday, mid-level ridging behind the trough is forecast to
temporarily strengthen, weakening upper-level flow across the CONUS.
A second upper trough over the northern Rockies will begin to
approach behind the central US ridge, while a cutoff low develops
over the Southeast. This should limit broader overlap of instability
and stronger mid-level flow across much of the CONUS. Widespread
severe weather appears unlikely through next week.

..Lyons.. 09/11/2025

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ACUS48 KWNS 120759
SWOD48
SPC AC 120758

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0258 AM CDT Fri Sep 12 2025

Valid 151200Z - 201200Z

...DISCUSSION...
On Monday, a shortwave trough in the northern Plains will continue
to pivot northeast. The timing of this feature remains uncertain.
The ECMWF is the lone model that has a solution slow enough to have
some destabilization occur ahead of the trough. It is not clear how
much, if any, severe threat will exist in parts of central/northern
Minnesota.

On Tuesday, models indicate shortwave ridging will develop behind
the departing trough in the Upper Midwest. A secondary, broader
trough will be situated in the northern Rockies. Mid-level flow will
not be particularly strong, but embedded perturbations may provide
some enhancement. Depending on the quality of remaining moisture in
the Plains, some severe risk could develop along the surface trough
in the central High Plains. Uncertainty is high, however.

Through the remainder of the week, the upper-level pattern becomes
much more disorganized. Stronger flow may not return until the
weekend with a trough approaches the Northwest. Organized severe
potential appears to be low during this period.

..Wendt.. 09/12/2025

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ACUS48 KWNS 130756
SWOD48
SPC AC 130754

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0254 AM CDT Sat Sep 13 2025

Valid 161200Z - 211200Z

...DISCUSSION...
Weak mid/upper-level troughing should continue to move slowly
eastward from the northern Rockies/High Plains into the central
Plains and Upper Midwest from Day 4/Tuesday into Day 5/Wednesday.
Thunderstorms should develop across these regions both days as a
surface cold front likewise develops east-southeastward. While
moderate to locally strong instability may develop across the warm
sector each afternoon, mid-level flow and related deep-layer shear
are expected to remain rather modest. This should tend to limit
updraft organization and intensity to some extent, although
isolated/marginal severe potential may necessitate low severe
probabilities in later outlooks.

By late next week into the following weekend (Day 6/Thursday to Day 8/Saturday), medium-range guidance begins to diverge in its
depiction of the evolution of upper troughing across the Midwest/OH
Valley into the eastern CONUS. This lowers confidence in the
predictability of organized severe thunderstorms, but some potential
for strong thunderstorms may exist across portions of these regions
along/ahead of an advancing cold front.

..Gleason.. 09/13/2025

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ACUS48 KWNS 140739
SWOD48
SPC AC 140737

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0237 AM CDT Sun Sep 14 2025

Valid 171200Z - 221200Z

...DISCUSSION...
Organized severe thunderstorm potential appears low during the Day
4-8/Wed-Sun period. Medium range guidance is in fairly good
agreement that the upper shortwave trough over the northern/central
Plains Day 4 will develop an upper low as it meanders slowly east
toward the Mid/Upper MS Valley and the upper Great Lakes through
most of the forecast period. Some modest west/southwesterly
mid/upper flow ahead of the trough, in conjunction with a seasonally
moist boundary layer ahead of a southeastward-drifting cold front
could support sporadic strong storms across parts of the central
U.S. from the Ozarks to the Upper MS Valley mid to late in the week.
However, vertical shear is expected to remain poor, and the
slow-moving nature of the upper low and weakening surface front with time/eastward extent, will generally be unfavorable for a more
robust severe risk.

..Leitman.. 09/14/2025

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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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