072
ACUS01 KWNS 140459
SWODY1
SPC AC 140457

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1157 PM CDT Wed Aug 13 2025

Valid 141200Z - 151200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE NORTHERN PLAINS AND UPPER MISSISSIPPI VALLEY...

...SUMMARY...
Storms with large hail and severe wind gusts are expected this
afternoon and evening across parts of the central and northern
Plains, into the upper Mississippi Valley. Hailstones of greater
than 2 inches in diameter will be possible.

...Central and Northern Plains/Upper Mississippi Valley...
A series of mid-level shortwave troughs will move across the
north-central U.S. today and tonight. The first shortwave trough
will move into the upper Mississippi Valley today. Near this
feature, isolated severe storms will be possible along the eastern
edge of a moist and unstable airmass this afternoon from eastern
Minnesota southward into northern Iowa. A second shortwave trough
will move through Saskatchewan today, and into Manitoba tonight.
Ahead of the trough, a cold front will advance eastward into the
eastern Dakotas this afternoon. A moist and unstable airmass will be
in place ahead of the front. Convective initiation should take place
near or just ahead of the front as low-level convergence increases
late this afternoon or early evening. The more aggressive model
solutions suggest that storms will develop in eastern North Dakota
late this afternoon, with additional storms forming during the
evening further south into parts of South Dakota and Nebraska. A
severe threat will likely develop with some of these storms.

Model forecasts along and near the instability axis early this
evening suggest the strongest deep-layer shear will be in
northeastern North Dakota near Grand Forks. RAP forecast soundings
for this location at 00Z have MLCAPE around 3500 J/kg, with 0-6 km
shear near 45 knots, and 700-500 mb lapse rates approaching 8 C/km.
This environment will likely support supercells with large hail, and
potentially hailstones greater than 2 inches in diameter with the
strongest of updrafts. A potential for severe wind gusts will also
be possible, especially if the favored storm mode transitions toward
linear during the evening. Although an isolated severe threat may
persist into the early overnight period, a capping inversion will
strengthen and result in mainly elevated storms.

Further south into southeastern North Dakota, the environment should
support severe storms during the evening, but convective initiation
is a bit less certain. Across much of South Dakota and central
Nebraska, weaker deep-layer shear will be in place, which should
help to marginalize any severe threat.

..Broyles/Moore.. 08/14/2025

$$