477
ACUS01 KWNS 212003
SWODY1
SPC AC 212001

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0301 PM CDT Tue Jul 21 2026

Valid 212000Z - 221200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM PORTIONS
OF THE NORTHEAST AND MID ATLANTIC TO THE OHIO VALLEY...

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

...20z Update Mid Atlantic and New England...
A complicated convective situation continues across the area with
numerous cluster of strong to severe storms ongoing from southern
NY/CT/MA to the DelMarVA. A diffuse warm frontal zone from the
Hudson valley to Long Island and the Atlantic coast has supported a
few instances of stronger rotating supercells and QLCS structures.
This focus may continue as additional more discrete storms approach
from northern NJ and eastern PA. Otherwise, clustering of storms
ahead of the cold front and across VA will pose a risk for damaging
gusts through this evening. The primary update to the outlook was to
lower probabilities behind the ongoing convection over NY and
northeast OH where the air mass has been partially overturned.
Isolated damaging gusts and some hail remain possible tonight.

...OH Valley...
A broken band of storms ahead of a cold front, extending into WV and
southwest PA should continue to track east/southeast through this
afternoon and into the evening hours. Strong northwesterly flow
aloft is supporting moderate deep-layer shear and a mixed mode of
supercells and clusters across southern IN/OH and into northern KY.
A primary risk for damaging winds is expected given  upscale growth
as storm coverage increases. However, the large buoyancy (MLCAPE
3000-4000 J/kg) and some supercell structures could support large
hail.  Some tornado potential will also exist with the semi-discreet
supercells and QLCS structures. This appears most likely near a
convective modified boundary from astern OH into WV and southwest
PA.

Storm coverage should continue to increase this afternoon across
western KY and the lower OH Valley. With a predominately linear
storm mode expected along the cold front, damaging winds are the
most likely hazard. The primary change to the probabilities was to
trim behind the front over OH/IN. See the prior outlook for more
information.

..Lyons.. 07/21/2026

.PREV DISCUSSION... /ISSUED 1118 AM CDT Tue Jul 21 2026/

...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.

$$