Mesoscale Discussion 1688
NWS Storm Prediction Center Norman OK
1115 AM CDT Tue Jul 21 2026

Areas affected...northeast Kentucky...northern West Virginia...and
southern Ohio

Concerning...Severe potential...Watch likely 

Valid 211615Z - 211815Z

Probability of Watch Issuance...80 percent

SUMMARY...The severe weather threat will increase this afternoon
across southern Ohio and northern Kentucky into West Virginia.

DISCUSSION...A cluster of storms in southeast Ohio will likely
continue east-southeast into a more unstable airmass along a
differential heating zone developing across northern West Virginia.
Damaging winds will likely be the primary threat with this cluster.
Additional storms are expected to strengthen farther southwest
through the afternoon with sufficient shear for some supercell
structures. Damaging winds will likely be the main threat with this
activity with some large hail potential. In addition, a tornado or
two is also possible, especially as the low-level jet strengthens
this afternoon/evening. 

A watch will likely be needed within the next 1 to 2 hours to
address the threat from the ongoing activity and any additional
storms which develop.

..Bentley/Mosier.. 07/21/2026

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...CTP...LWX...RNK...PBZ...RLX...JKL...ILN...LMK...

LAT...LON   39598231 39898072 39777895 39337864 38837871 38137954
            38018075 37938266 38338420 39078413 39598231 

MOST PROBABLE PEAK TORNADO INTENSITY...85-110 MPH
MOST PROBABLE PEAK WIND GUST...55-70 MPH
MOST PROBABLE PEAK HAIL SIZE...1.00-1.75 IN

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

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1118 AM CDT Tue Jul 21 2026

Valid 211630Z - 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 Tennessee and Ohio Valleys 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.

...Tennessee/Ohio Valley into the Mid-Atlantic and Northeast...
Recent satellite imagery reveals a shortwave trough moving quickly
southeastward across the Upper Great Lakes region, embedded within
the upper troughing that covers much of eastern Canada and extends
down into the Ohio Valley. Moderate mid-level flow accompanies this
shortwave, with wind speeds greater than 50 kt sampled around 500 mb
on the 12Z ILX, DTX, ILN, and PIT soundings. The strongest flow was
sampled at ILX and DTX, and the expectation is for this stronger
flow to spread eastward today, moving in tandem with the progressive
shortwave. 

Showers and thunderstorms are already ongoing downstream of this
shortwave, with the highest coverage along and near the pre-frontal
trough in Ohio. Recent surface analysis reveals a somewhat complex
boundary structure, with a wavy warm front, a diffuse pre-frontal
trough, and a cold front. Primary warm front appears to extend
west-to-east from southeast Ohio across southern Pennsylvania and
into northern New Jersey, far southern New York, and extreme
southwest Connecticut. The cold front arcs southwestward from
northern Lower Michigan through central Illinois and central
Michigan. 

Highest overall coverage is anticipated along and ahead of the cold
front this afternoon through this evening, with additional
development expected farther east (from central Pennsylvania into
central Virginia) along the lee trough as well. Highest buoyancy is
expected along the western periphery of the cold front from central 
into western Kentucky, where mid to upper 70s dewpoints are
anticipated amid temperatures in the upper 80s/low 90s. Strong
buoyancy is still anticipated across Ohio as well. Robust
thunderstorm development is expected along the front. Vertical shear
is robust enough for supercells, but linear forcing along the front
and strong downdraft production will likely lead to quick upscale
growth. In either convective mode, damaging gusts (with speeds from
55 to 70 mph) will be the primary risk, with brief tornadoes as a
secondary threat, and large hail tertiary.  

Farther east, a similar convective environment exists, although with
slightly less buoyancy and deep-layer vertical shear. A more
outflow-dominant multicell mode is anticipated across the central
Virginia vicinity, with a trend towards a more organized mode
possible with northern extent. Primary risk will be damaging gusts,
including a few around 65 to 70 mph. A somewhat confined corridor of
greater tornado potential exists from the Hudson Valley vicinity
into western Massachusetts/Connecticut as the warm front lifts
northward. Here, enhanced vorticity along the boundary coupled with
stronger low-level southerly flow could support a few brief
tornadoes.

...Great Basin...
Scattered to numerous thunderstorms are expected across the Great
Basin today, supported by strong diurnal heating/mixing and moderate
mid-level moisture along the western periphery of the upper ridging
centered over the central Rockies. A few strong updrafts/downdrafts
are possible, with an attendant risk for strong to severe (i.e. 50
to 65 mph) wind gusts. 

...Gulf Coast...
Tropical Storm Bertha is expected to continue to drift
west-northwestward over the northern Gulf tonight from off the coast
of the Florida Panhandle toward the southern Mississippi/southern
Alabama coast. 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, as is typical for a westward
moving tropical cyclone, forecast SRH should remain relatively
modest inland. Given the marginal thermodynamic profiles (aside from
the rich boundary layer moisture) and limited SRH over land, any
Bertha-related mini-supercell potential is expected remain offshore.

..Mosier/Chalmers.. 07/21/2026

Day 1 Fire Weather Outlook  
NWS Storm Prediction Center Norman OK
1030 AM CDT Tue Jul 21 2026

Valid 211700Z - 221200Z

Minor modifications were made to the IsoDryT area based on the
latest observations and forecast guidance. Portions of the IsoDryT
area may see more high-based showers with little to no lightning,
while a mix of wet/dry storms remains expected. Additionally, a few
storms may linger overnight in Oregon. Otherwise, the forecast is on
track, and please see the previous discussion for more details.

..Nauslar.. 07/21/2026

.PREV DISCUSSION... /ISSUED 1245 AM CDT Tue Jul 21 2026/

...Synopsis...
...Northern California and west/central Oregon...
Along the northwestern periphery of a large-scale ridge encompassing
much of the central and western CONUS, ample mid-level moisture will
be in place atop a warm and dry airmass across parts of northern CA
into OR. Forecast soundings depict inverted-V profiles with weak
(albeit sufficient) buoyancy for high-based thunderstorms across the
area during the afternoon and evening hours. Cloud cover, smoke, and
warmer temperatures aloft will help limit thunderstorm
development/coverage across the IsoDryT area, but isolated
thunderstorms remain possible. While 0.8 to 1.2 inch PWATs may
promote a mix of wet/dry storms, relatively fast storm motions and
the dry boundary layer should limit precipitation efficiency. As a
result, isolated lightning-induced ignitions will be possible within
a very dry fuelscape. 

...South Carolina...
Progressive upper-level troughing will continue across the
northeastern U.S. as a closed low traverses northern Ontario,
sending a cold front through the Ohio Valley. Enhanced 850 mb
southwesterly flow ahead of the front will encourage gusty surface
winds amid minimum RH values of 30-40% in portions of South
Carolina. Locally elevated fire weather conditions are likely, as
ERCs generally range from the 80th-95th percentile across this area.

...Please see www.spc.noaa.gov/fire for graphic product...