Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1244 AM CDT Sat Sep 13 2025

Valid 131200Z - 141200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE
SOUTHWEST TO THE DAKOTAS AND IN A PART OF THE MIDWEST...

...SUMMARY...
Isolated severe wind and hail will be possible from the
Southwest/southern Rockies to the northern Great Plains and a
portion of the Midwest, mainly today into early tonight.

...Southwest/southern Rockies/High Plains...
The basal portion of the broad mid/upper trough from the northern
Rockies to the Lower CO Valley will progress more quickly east,
yielding an elongated trough enveloping the entire High Plains by
early Sunday. Widespread thunderstorm development is anticipated by
midday to early afternoon across western NM/CO as cooling mid-level
temperatures become favorably timed with moderate diurnal heating of
a seasonably moist airmass. Lower-level instability should be
tempered by remnants of early morning convection and the quick
redevelopment cycle by afternoon. Nevertheless, a broad belt of
moderate southwesterly speed shear should support transient
mid-level updraft rotation within the deepest updrafts. These should
tend to become focused across southern/eastern NM later in the
afternoon, but this region will be on the fringe of greater
mid-level cooling centered on the Four Corners. As such, mid-level
lapse rates will be weak where boundary-layer heating is more
pronounced. A broad swath of sporadic strong to marginally severe
hail/wind is anticipated before convection subsides after sunset. 

...NE/SD/ND...
Overall severe wind/hail potential appears low across multiple
regimes through the period, amid a persistent meridional mid-level
flow regime. Ongoing convection over the western Dakotas, tied to a
minor MCV, should progress north-northeast towards the Canadian
border this morning. Residual cloudiness/overturning should limit
the northern extent of more substantial diurnal destabilization in
ND. Late afternoon to evening storm development appears more likely
to emanate out of the central High Plains north-northeastward across
western/central NE within a modestly sheared and weakly buoyant
airmass. This activity may foster another MCV that drifts north into
SD, which could impinge on a confined corridor of recovered moderate
buoyancy and sustain a marginal severe wind/hail threat tonight.

...IL/IN/WI...
Low-probability severe hail/wind potential remains evident, but
seems likely to be rather isolated. An MCV over central WI will
drift south-southeast this morning. An increase in convective vigor
is possible towards sunrise along the MUCAPE gradient in southern WI
to northern IL. Within a belt of moderate mid-level northwesterlies,
transient/weak updraft rotation is possible in a cell or two.
Guidance differs greatly on the degree of boundary-layer heating
downstream of the morning elevated activity. The more aggressively
warm guidance suggests a conditional threat of diurnal
intensification with potential for locally strong gusts.

..Grams/Dean.. 09/13/2025

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1251 AM CDT Sat Sep 13 2025

Valid 141200Z - 151200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF
THE NORTHERN PLAINS...EXTENDING INTO THE SOUTHERN HIGH PLAINS...

...SUMMARY...
Isolated severe storms are possible across parts of the northern
Plains into the southern High Plains tomorrow (Sunday).

...Synopsis...
A negatively tilted upper trough will pivot northward across the
central/northern Plains, around broader cyclonic flow aloft, as a
second upper trough traverses the Pacific Northwest tomorrow
(Sunday). A surface low will develop and intensify while drifting
northward across the Dakotas through the forecast period.
Strengthening of the low will encourage the development of a
southerly low-level jet, which will result in both northward
moisture advection, and increased vertical wind shear, to support at
least isolated severe storms across the Plains.

...Great Plains States...
Widespread clouds and precipitation may be underway at the start of
the period (12Z Sunday) given the warm-air advection regime in place
ahead of the surface low. Through the day, some breaks in the cloud
cover will support adequate insolation to generate surface-based
buoyancy ahead of a confluence boundary. Surface temperatures may
rise into the 70s F, amid 60+ f dewpoints, yielding 1000-2000 J/kg
MLCAPE in spots. However, mid-level lapse rates are expected to be
modest at best (e.g. 6-7 C/km), with the aforementioned MLCAPE
constrained to tall, thin profiles. However, 20-40 kt southerly flow
at 850 mb (driven by the low-level jet), overspread by 40-50 kts of
south-southwesterly 500 mb flow, will yield elongated, mainly
straight hodographs across the central/northern Plains. Effective
bulk shear of 35-45 kts is possible from NE northward, with weaker
values, but relatively more curved hodographs possible farther south
into the southern High Plains.

By afternoon peak heating, the rejuvenation of warm-sector
convection ahead of the confluence band is likely, with scattered
multicells and perhaps supercells possible from the Dakotas to the
TX Panhandle. Storms will first develop across the northern Plains
by early afternoon, with gradual southward development likely by
early evening. Given modest lapse rates/thin CAPE profiles amid
straight hodographs, the severe threat appears relatively isolated,
with occasional severe gusts/hail the main threats. A tornado is
possible over the northern Plains if a supercell can become
sustained within the low-level jet axis and traverse a corridor of
locally stronger surface-based buoyancy. The severe threat should
gradually wane after dark, when surface-based buoyancy diminishes
with nocturnal cooling and increased MLCINH.

..Squitieri.. 09/13/2025

Day 3 Convective Outlook  
NWS Storm Prediction Center Norman OK
0200 AM CDT Sat Sep 13 2025

Valid 151200Z - 161200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Organized severe thunderstorm potential appears generally low on
Monday.

...Synopsis and Discussion...
A pair of upper troughs/lows should be in place over the northern
Rockies and northern Plains Monday morning. The lead wave is
forecast to advance northward from the Dakotas and MN into central
Canada through the day, while the trailing low gradually opens and
weakens as it moves slowly eastward over the northern Rockies/High
Plains. A weak surface low should develop northward from ND into
Manitoba by Monday evening, with a weak front extending southward
from this low across parts of the northern/central Plains. Organized
severe thunderstorm potential is currently expected to remain fairly
limited, with modestly enhanced but meridional/southerly
mid/upper-level flow across MN limiting deep-layer shear over the
moderately unstable warm sector. Better large-scale ascent is also
forecast to gradually shift northward into central Canada through
the day as well. Given these potential limiting factors, low severe
probabilities have not been included across northern MN and vicinity
at this time.

Elsewhere, general thunderstorms should occur beneath the upper low
across the northern Rockies/High Plains, but both instability and
deep-layer shear are forecast to remain weak across these regions.
Isolated convection may also develop Monday afternoon and evening
with southward extent along a surface lee trough across the
southern/central Plains, but weak forcing aloft should tend to limit
overall coverage. Other convection may also occur along a low-level
moist axis extending from parts of the Ozarks/Mid-South northward
into the Upper Midwest.

..Gleason.. 09/13/2025