864
ACUS11 KWNS 180146
SWOMCD
SPC MCD 180145
NEZ000-SDZ000-180345-

Mesoscale Discussion 1981
NWS Storm Prediction Center Norman OK
0845 PM CDT Sun Aug 17 2025

Areas affected...northwest Nebraska and southern South Dakota

Concerning...Severe potential...Watch possible

Valid 180145Z - 180345Z

Probability of Watch Issuance...60 percent

SUMMARY...Thunderstorms capable of large hail and strong winds are
ongoing across portions of the area. These storms should continue
through the evening and perhaps increase in coverage/organization.
Trends will continue to be watched for a potential severe
thunderstorm watch.

DISCUSSION...Several clusters of discrete storms -- with at least
transient supercellular characteristics -- are ongoing across
portions of the area. These storms are embedded within a belt of
stronger upper-level winds stretching from Baja northeast into
northern Minnesota, and may have initiated in association with a
subtle vorticity maximum coming off the higher terrain of northern
Colorado.

These storms are on the western edge of the MUCAPE gradient, with
higher MUCAPE -- 3000+ J/kg -- to the east. Effective-layer shear is
variable between 30-40 knots which is likely contributing to the
supercellular structures, and these storms will continue to pose a
threat for damaging winds and large hail.

The evolution of these multi-cell/supercell clusters this evening is
unclear. Currently thinking is that given the environment in place,
these storms` outflows/cold pools should congeal into one or more
small MCS clusters, leading to an increased potential in severe
wind.

Trends across the region are being monitored for potential watch
issuance. If convective trends suggest upscale growth is imminent a
severe thunderstorm watch may become necessary.

..Marsh/Smith.. 08/18/2025

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...FSD...OAX...ABR...GID...LBF...UNR...CYS...

LAT...LON   41169723 41329857 41500023 41780132 42250254 43000348
            43660276 43690098 43699938 43729851 43419716 42609657
            41729654 41169723

MOST PROBABLE PEAK WIND GUST...65-80 MPH
MOST PROBABLE PEAK HAIL SIZE...1.50-2.50 IN