539
ACUS01 KWNS 211253
SWODY1
SPC AC 211251

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0751 AM CDT Thu Aug 21 2025

Valid 211300Z - 221200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE
NORTHERN PLAINS/UPPER MIDWEST AND SOUTHERN ARIZONA...

...SUMMARY...
Isolated severe thunderstorms are possible across portions of the
northern Plains and Upper Midwest this afternoon and evening, with
severe wind gusts and hail the primary concerns. A few strong to
severe storms could also occur across southern Arizona.

...Northern Plains/Minnesota...
Late-day height falls are expected regionally in relation to an
amplifying shortwave trough over the Canadian prairies. While the
primary large-scale forcing will be north of the international
border, high-level diffluent flow is expected across the eastern
Dakotas/Minnesota, coincident with the front that will be draped
across the region at peak heating. Short-term models (HRRR/RRFS) are
tending to limit late-afternoon/evening convective development,
while most global models and most HREF constituents are a bit more
aggressive, which is plausible and lends credence to the potential
for at isolated severe storms within a moderately to strongly
unstable environment near the front. Deep-layer should be sufficient
to potentially yield a few supercells. Increasing storm coverage
later into the evening/overnight will be supported by an increasing
low-level jet.

...North-central High Plains including eastern Wyoming...
Northeasterly low-level upslope flow evolving within the
post-frontal environment, and differential heating in vicinity of
higher terrain, are expected to influence widely scattered
thunderstorm development by late afternoon, particularly across
eastern Wyoming. While forecast buoyancy is not expected to be
particularly strong, adequate deep-layer shear will prove supportive
of organized updrafts that could generate hail/wind, including the
possibility that a couple of eastward-moving clusters could evolve
by early evening.

...Southern Arizona...
The upper ridge should shift slightly northward regionally, with a
modest enhancement to mid-level easterly flow late today
particularly across southeast Arizona. With isolated storm
development expected initially over the rim/mountains this
afternoon, storms should drift west-southwestward into a moist/very
hot boundary layer, with the potential for outflows/blowing dust to
reach the desert floor.

..Guyer/Marsh.. 08/21/2025

$$