Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1130 AM CDT Sun Jul 20 2025
Valid 201630Z - 211200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF
THE NORTHERN AND CENTRAL PLAINS...OHIO VALLEY...AND PARTS OF THE
NORTHEAST...
...SUMMARY...
Severe thunderstorms appear most likely this afternoon into this
evening across parts of the Northeast, portions of the northern and
central Plains, and perhaps the Ohio Valley.
...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.
...Northeast...
Weak to moderate instability is forecast to develop across the
Northeast through mid afternoon as the airmass continues to
destabilize. Midday surface analysis indicates temperatures are
warming into the 80s with dewpoints in the upper 60s to lower 70s.
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.
...Southeast MT into the Dakotas and Central Plains...
Lee troughing is forecast to extend southward from eastern MT into
the central High Plains near and south of the westerlies confined to
the northern tier of states. Elevated weak thunderstorm activity
along the ND/SD border may continue but considerable uncertainty
exists whether these storms will intensify and pose a severe risk
this afternoon. Meanwhile, farther west, moist low levels arc from
southeast MT southeastward through west-central SD and south into
NE/northwest KS. Strong heating will contribute to a moderate to
very unstable airmass from the central Plains states into eastern
MT. Easterly low-level flow beneath 30-40 kt 500 mb flow in
southeast MT will support organized storms, including supercell
potential. Isolated to scattered storms are forecast to develop and
spread east into the Dakotas. Other isolated to widely scattered
storms are possible from SD southward into NE/CO/KS border vicinity
late this afternoon into the evening.
Large to very large hail will be possible with any supercells that
develop within this general region. However, the severe wind threat
may increase by this evening and become the main threat as storms
congeal into one or more clusters or MCS.
...Ohio Valley...
Visible-satellite/radar composite shows an elongated area of
showers/thunderstorms from northern MO east into western OH in
conjunction with an MCV moving east from IL into IN. Additional
storm development along the composite front/trailing outflow
boundary is expected, but timing of this storm activity remains
unclear. Nonetheless, differential heating along the baroclinic
zone will yield 2000 to 3000 J/kg MLCAPE amidst moderate effective
shear (25-35 kt). A few clusters are forecast to eventually evolve
later this afternoon into the evening with the stronger storms
capable primarily of a wind-damage threat.
..Smith/Halbert.. 07/20/2025
Read more CHECK UPDATE ZOOM GRAPHIC
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