Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1259 AM CDT Tue Jul 21 2026
Valid 211200Z - 221200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
OF THE UPPER OHIO VALLEY INTO THE MID-ATLANTIC...
...SUMMARY...
Numerous severe thunderstorms are expected across a broad region
from the Ohio Valley into the Mid-Atlantic and Northeast today. All
severe hazards are possible, but swaths of damaging wind gusts
should be the primary severe risk during the afternoon and early
evening hours.
...Ohio Valley into the Mid-Atlantic...
A broad area of 40-50-kt midlevel west-southwesterly flow will
overspread the OH Valley into the Mid-Atlantic as a large-scale
trough shifts across the northeastern CONUS. Scattered to numerous
thunderstorms are expected to develop ahead of an eastward-moving
cold front across the OH Valley and along a pre-frontal trough over
the Mid-Atlantic. In the base of the trough, a convectively
augmented midlevel impulse moving from the lower OH Valley into the
Mid-Atlantic may also serve as a focus for convective development.
Diurnal heating within cloud breaks, combined with upper 60s to
lower 70s dewpoints, will support moderate surface-based instability
across the broad pre-frontal warm sector. The most favorable overlap
of this instability and 40-50 kt of effective shear is expected from
the lower OH Valley into the Mid-Atlantic, where a mix of organized
clusters and supercells should evolve and spread eastward through
the day. Swaths of damaging wind gusts will be the primary severe
hazard, though severe hail will also be possible with any sustained
supercells. Additionally, a gradually strengthening and expanding
30-kt low-level jet will contribute to clockwise-curved low-level
hodographs, and a few tornadoes may occur.
...Mid-South into the Tennessee Valley...
Greater instability is expected southwestward into portions of the
Mid-South and TN Valley, although somewhat weaker deep-layer shear
(around 30-40 kt of effective shear) may temper storm organization
compared to ares farther northeast. Nevertheless, widely scattered
thunderstorms capable of organizing into multicell clusters and
occasional supercell structures will pose a risk of damaging wind
gusts and isolated severe hail ahead of the cold front during the
afternoon and early evening hours.
...Northeast...
Increasing midlevel height falls/forcing for ascent preceding the
upper trough will support scattered thunderstorm development near an
effective warm front moving northward across portions of the
Northeast. While poor midlevel lapse rates and weaker instability
should limit the overall severe risk compared to areas farther
south, around 40 kt of effective shear will still support organized
storm structures. Damaging wind gusts will be the primary concern,
though isolated severe hail and a tornado or two will also be
possible.
..Weinman/Jirak.. 07/21/2026
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