ACUS01 KWNS 211246
SWODY1
SPC AC 211245

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0745 AM CDT Sun Sep 21 2025

Valid 211300Z - 221200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
NORTH TEXAS AND SOUTHERN OKLAHOMA...

...SUMMARY...
Large hail may occur with supercells that develop this afternoon
across parts of north Texas and southern Oklahoma. Isolated strong
to severe thunderstorms are possible this afternoon and evening
across a broad portion of the southern Plains into the Ozarks, mid
Mississippi Valley, Ohio Valley, and Great Lakes, and also from the
mid Missouri Valley into southern Minnesota and northern Iowa.

...Southern Plains into the Ozarks and Mid Mississippi Valley...
Showers and thunderstorms are ongoing this morning across parts of
western/central OK and western north TX in association with a weak
MCV and modest low-level warm/moist advection. Convectively
reinforced outflow from this morning activity should be draped
along/near the Red River this afternoon, with a rich low-level
moisture present to its south. Northwesterly mid/upper-level flow
should gradually strengthen through the day across north TX/southern
OK as a weak mid-level perturbation moves southeastward from the
southern/central High Plains. A favorable combination of moderate
instability aided by modestly steepened mid-level lapse rates and
daytime heating, along with 35-45 kt of deep-layer shear, will
likely prove favorable for thunderstorm organization. Most guidance
suggests multiple thunderstorms will develop and become
supercellular this afternoon across parts of north TX and southern
OK. Scattered severe hail should be the main threat with this
convection as it spreads southeastward through the early evening.
Strengthening MLCIN with time this evening should result in a
weakening trend as this activity approaches the DFW metroplex, but
isolated large hail and gusty winds will remain possible until
convection dissipates. Given increased confidence in supercells
developing, have added a focused Slight Risk for large hail with
this update.

Weak mid-level troughing with multiple embedded perturbations will
move eastward today across the central Plains into the Ozarks and
mid MS Valley. One notable MCV with ongoing convection is also noted
this morning across central KS. Filtered diurnal heating should aid
in the development of weak to locally moderate instability this
afternoon along/south of a front that should be draped across
northern KS/MO. As modest large-scale ascent overspreads the warm
sector, at least scattered thunderstorms are forecast to develop
this afternoon in a weakly sheared environment, with modest
enhancement provided by the eastward-moving MCV across MO. Isolated
hail and damaging winds may occur with the stronger cores, with some
potential for eventual clustering towards the MS River by early
evening.

...Midwest/Great Lakes...
A broad zone of modest (20-30 kt) west-southwesterly mid-level flow
will be maintained today over much of the Midwest/Great Lakes, on
the southeast periphery of weak upper troughing over the Upper
Midwest. Recent visible satellite imagery across these regions show
generally widespread cloudiness, which may hinder diurnal
destabilization to some extent. Mid-level lapse rates are also
expected to remain rather poor (reference ILX/ILN/DTX observed 12Z
soundings). Even with these thermodynamic limitations, it still
appears possible that isolated damaging winds could occur with any
thunderstorms that can develop this afternoon and spread generally
east-northeastward. This activity should quickly weaken this evening
with the loss of daytime heating.

...Mid Missouri Valley into Southern Minnesota/Northern Iowa...
A compact mid/upper-level low will move southeastward from eastern
ND into MN today. This low and attendant shortwave trough may aid in
the development of isolated to widely scattered storms by early
evening from southwest MN into adjacent southeast SD, northeast NE,
and northwest IA, in the vicinity of a weak surface boundary. Cool
temperatures aloft, weak to moderate instability, and effective bulk
shear around 25-35 kt should support multicells and perhaps a couple
splitting supercells. Hail is expected to the primary severe hazard
with any thunderstorms that can be sustained, but confidence in this
occurring before this evening is low.

..Gleason/Grams.. 09/21/2025

$$
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