179
ACUS01 KWNS 211258
SWODY1
SPC AC 211257

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0757 AM CDT Tue Jul 21 2026

Valid 211300Z - 221200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE OHIO VALLEY TO MID-ATLANTIC STATES...

...SUMMARY...
Numerous severe thunderstorms are expected across a broad region
from the Ohio Valley to the Mid-Atlantic and Northeast States today
into tonight. Swaths of damaging wind gusts are expected to be the
most common impact, but some tornadoes are possible as well.

...Ohio Valley into the Mid-Atlantic and Northeast...
A broad area of 40-50-kt mid-level west-southwesterly flow will
overspread the Ohio Valley into the Mid-Atlantic/Northeast as a
large-scale trough amplifies and shifts across the northeastern
CONUS. Scattered to numerous thunderstorms are expected to develop
ahead of an eastward-moving cold front across the Ohio Valley and
along a pre-frontal trough over the Mid-Atlantic. In the base of the
trough, a convectively augmented mid-level impulse moving from the
lower Ohio Valley into the Mid-Atlantic may also serve as a focus
for convective development. Severe thunderstorm potential could
increase relatively early today across parts of Ohio into
Pennsylvania and western New York.

Diurnal heating within cloud breaks, combined with upper 60s to
lower 70s F dewpoints, will support at least 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 Ohio 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 initial/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. This supercell related-tornado potential may
focus along the warm front into parts of the Northeast, and with
semi-discrete development later today focusing along the lee
trough/edge of higher terrain, although low-level shear/SRH will be
moderate in most of the open warm sector as well.

...Mid-South and the Tennessee Valley...
Greater instability is expected southwestward into portions of the
Mid-South and Tennessee Valley, although somewhat weaker deep-layer
shear (around 30-40 kt of effective shear) may temper storm
organization compared to areas 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 into evening.

...Gulf Coast...
Tropical Storm Bertha is expected to continue to drift northwest
then westward over the northern Gulf tonight from off the coast of
the Florida Panhandle toward the southern Mississippi coast and
coastal southeast Louisiana. Reference the National Hurricane Center
for the latest details. A strong low-level wind field will approach
these coastal areas later today and tonight. However, forecast SRH
should remain relatively modest inland with marginal thermodynamic
profiles aside from the rich boundary layer moisture. Any
Bertha-related mini-supercell potential is expected to focus
offshore in the open Gulf waters.

..Guyer/Broyles.. 07/21/2026

$$