451
ACUS01 KWNS 180549
SWODY1
SPC AC 180548

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1248 AM CDT Mon Aug 18 2025

Valid 181200Z - 191200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
THE CENTRAL HIGH PLAINS...

...SUMMARY...
Strong to severe storms capable of damaging winds are possible in
parts of the Upper Midwest today. Isolated to widely scattered
storms with large hail and severe winds are possible in parts of the
central/northern Plains through tonight.

...Central High Plains...
A broad upper trough over the northern Plains will move east today
with an attendant surface low and cold front also moving east.
Behind the departing surface low, weak upslope flow is expected
across portions of western SD, northeastern WY. Strong heating and
steep mid-level lapse rates should allow for diurnal destabilization
with widely scattered thunderstorms expected along a lee trough by
the afternoon. Elongated hodographs, courtesy of 30-40 kt of
westerly flow aloft, will allow for some organized storms including
supercells or clusters. Steep mid-level lapse rates, and moderate
buoyancy will support a hail risk.

Farther south, stronger heating and mixing will limit low-level
moisture across southeastern WY and northeastern CO. Still, enough
CAPE should be present for scattered high-based storms near peak
heating. The steep low-level lapse rates and any clustering that
develops should support damaging winds as storms spread eastward
into northeast CO and western NE.

Some potential exists for a longer-lived cluster to spread eastward
into central/eastern NE and northern KS overnight. Should this
occur, damaging winds and some hail would be the primary concerns,
though this scenario remains highly uncertain given weaker forecast
low-level jet.

...Midwest...
One or more clusters of thunderstorms or an MCV is expected to be
ongoing at the start of the period in the vicinity of the warm front
across portions of IA/MN, casting significant uncertainty on the
overall convective evolution for the day. Filtered diurnal heating
and nebulous ascent from the broad trough over the northern Plains
could support continuation of these storms and additional
development into southern WI and northern IL this afternoon. While
complications abound, substantial buoyancy (3000-4000 J/kg of
MLCAPE) and dewpoints in the mid 70s F south of the composite
front/remnant outflow will be supportive of occasional vigorous
updrafts. Modest enhancement of the mid and upper-level flow could
support a few semi-organized clusters or transient supercells with
damaging wind potential. Given the potential for outflow or
thunderstorm clusters to significantly alter the environment,
confidence in higher wind probabilities is low.

...Southwest into central Montana...
Despite a strong ridge building into the northern Rockies,
sufficient moisture may promote thunderstorm development in the
higher terrain this afternoon. 20-30 kt of flow aloft will be
sufficient to support at least marginally organized storms. However,
strong mixing during the afternoon could limit buoyancy and storm
coverage. Occasional strong, gusty outflow winds are possible with
any high-based storms, but confidence in severe potential remains
low.

..Lyons/Kerr.. 08/18/2025

$$