ACUS01 KWNS 201230
SWODY1
SPC AC 201228

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0728 AM CDT Sun Jul 20 2025

Valid 201300Z - 211200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PARTS OF THE
NORTHEAST...MIDWEST...OHIO VALLEY...AND NORTHERN PLAINS...

...SUMMARY...
Strong to severe storms appear most likely later today into this
evening across parts of the Northeast, Midwest and Ohio Valley, and
northern Plains.

...Synopsis...
A mid-level trough will amplify across the Northeast today with
increasing mid-level flow ahead of an approaching jet streak. A
low-amplitude ridge will build somewhat across the Upper Midwest.
Farther west, mid-level flow will strengthen across the northern
Rockies into the northern Plains as a trough amplifies on the
Pacific Northwest coast.

As of 12Z, an elongated frontal zone exists from the Northeast to
the Ohio Valley/southern Great Lakes and into the northern Plains.
Ongoing thunderstorms are present across the eastern Great Lakes,
the Midwest, and the northern Plains. This is correlated with the
stronger ascent and the areas with the greatest severe weather
potential today.

...Northeast...
Weak to moderate instability is forecast to develop across the
Northeast today as temperatures warm into the 80s with dewpoints in
the upper 60s, and as mid-level temperatures gradually cool through
the day. As the cold front advances east into this uncapped airmass,
scattered thunderstorms should develop. Shear of 30 to 35 knots and
relatively long/straight hodographs will support the potential for
supercells. Weak mid-level lapse rates will be the primary limiting
factor for large hail, but the overall favorable shear with strong
venting aloft and potential supercells may support some isolated
large hail.

Damaging wind gusts will be the primary threat, both from initial
cells and also from any clusters which develop. Any stronger
clusters with bowing segments could support a better organized
damaging wind swath. The greatest wind damage threat will likely
exist from western Massachusetts to far southern Maine.

...Ohio Valley...
A large mass of thunderstorms continues east across eastern Iowa and
northern Illinois this morning. Heating is anticipated south and
east of this activity which should result in an increasing severe
weather threat by late morning to early afternoon. It remains
unclear whether the afternoon severe threat may materialize out of
ongoing thunderstorm activity, or from additional storm development
along the front or the outflow boundary associated with these
storms. Nonetheless, 1000 to 1500 J/kg MLCAPE and effective shear of
35 to 40 knots will support an organized severe weather threat
including the potential for supercells. Despite the supercell mode,
the hail threat should remain minimal given the weak mid-level lapse
rates and warm mid-level temperatures with high freezing levels.
Damaging wind gusts will be the primary threat from these storms
with the greatest threat from central Indiana to southwest Ohio and
northern Kentucky.

...Northern Plains...
Weak lee troughing is forecast in the western Nebraska vicinity
today as moderate mid-level flow overspreads the northern Plains. A
dryline will extend southward from this surface low into the central
High Plains. Isolated storms are possible along this boundary this
afternoon/evening. Moderate destabilization is forecast across
central South Dakota and vicinity as low-level moisture is advected
westward to the north of the surface low.

Diurnal thunderstorm activity is forecast to be relatively isolated
along the dryline with perhaps slightly greater coverage across
eastern Minnesota amid cooler temperatures aloft. However, the
ongoing cluster of storms across North Dakota is forecast to linger
as isentropic ascent is maintained through the day. Eventual upscale
growth and a southeastward movement along the instability gradient
is anticipated. RAP forecast soundings show an environment favorable
for large hail initially with any supercells which develop. However,
the severe wind threat may increase by this evening as storms
congeal into a MCS with potential linear, bowing segments.

..Bentley/Gleason.. 07/20/2025

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