603
ACUS01 KWNS 182000
SWODY1
SPC AC 181959

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0259 PM CDT Mon Aug 18 2025

Valid 182000Z - 191200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF
NORTHERN ILLINOIS AND PARTS OF THE CENTRAL AND NORTHERN PLAINS...

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

...20Z Update...
The primary change to the current Day 1 Outlook was to trim severe
probabilities across portions of southern Wisconsin, where the
passage of an MCS has resulted in low-level stabilization.
Otherwise, only minor changes was made to severe/thunder
probabilities to reflect the latest guidance and observations.

..Squitieri.. 08/18/2025

.PREV DISCUSSION... /ISSUED 1129 AM CDT Mon Aug 18 2025/

...Mid MS Valley...
Extensive outflow from last night`s MCS currently extends from
extreme southwest WI southwestward through eastern IA and
north-central MO into eastern KS. This outflow has been moving
quickly eastward/southeastward this morning, and this trend is
expected to continue, although some slowing of its progression speed
is possible over time. The downstream airmass across from southern
WI and IL is characterized by dewpoints in the low to mid 70s.
Mid-level lapse rates are generally poor across the region, but
heating of this very moist airmass will still result in strong to
very strong buoyancy (i.e. MLCAPE around 3000 J/kg) by late
afternoon.

Strong to severe storms are possible along this outflow as it
impinges on this moist and buoyant airmass. Current trends suggest
the greatest severe potential will exist this afternoon across
southern WI and northern IL, where slightly stronger mid-level flow,
backed surface winds, and an east-west baroclinic zone exists.
Recently issued MCD 1983 addresses the short-term severe potential
for this area.

...Central High Plains into the northern/central Plains...
Strong heating and ample low/mid level moisture will promote the
development of scattered thunderstorms by mid-afternoon over the
foothills and plains of central/eastern CO. Additional isolated
storms are possible farther north across western NE into the Black
Hills region. Much of this area is within a corridor of modest
mid-level flow on the northern periphery of the upper ridging
covering the southern CONUS. Resulting modest shear may be enough
for hail production with the initial development before these
high-based storms trend towards outflow-dominant structures with
time. These storms may persist into the evening, with an attendant
threat for strong to severe gusts progressing into central NE before
weakening.

...MO/AR...
Clear skies and strong diurnal heating are expected across
central/southern MO and much of AR. Temperatures in the upper 90s
are expected, with dewpoints remaining in the mid 60s despite strong
mixing. These hot and humid conditions will result in strong
buoyancy this afternoon, with most guidance suggesting MLCAPE around
2000 J/kg. Shear will be weak, yielding mostly disorganized
multicells, but the strongest storms will be capable of locally
damaging wind gusts.

$$