Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0100 AM CDT Thu Aug 20 2026
Valid 201200Z - 211200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
THE MID ATLANTIC...THE MIDWEST AND CENTRAL PLAINS....
...SUMMARY...
Scattered severe storms are possible today and tonight across parts
of the Mid Atlantic, posing a risk for damaging wind gusts. Large
hail and isolated wind damage will be possible with severe storms
from Nebraska into northwest Wisconsin.
...Mid Atlantic and central Appalachians...
A shortwave trough embedded within broader northwesterly flow aloft
is forecast to move eastward from the OH valley into the Mid
Atlantic through today. Embedded within a broader upper trough over
the eastern Great Lakes, this shortwave perturbation will serve as a
focus for convective development across the Mid Atlantic and central
Appalachians this afternoon. As ascent overspreads the area, a warm
front is forecast to lift northward across southern PA, northern MD
into NJ and southern NY.
South of the front, a very moist air mass (dewpoints in the 70s F)
will lift northward. Despite poor low and mid-level lapse rates,
moderate buoyancy is expected south of the front and ahead of a
trailing lee trough into southern VA. Ongoing storms from a remnant
morning cluster may reintensify as they cross the Appalachians late
morning and early afternoon. Additional, possibly discrete,
development may occur east of the Blue Ridge and across the higher
terrain of southern PA and northern MD near the front by late
morning. 40-50 kt of deep-layer shear ahead of the front is forecast
to support a mix of supercells and line segments. Damaging winds and
isolated severe gusts appear probable. Enlarged low-level hodographs
near the front may also support a couple of tornadoes and marginally
severe hail with any more robust QLCS segments or supercells.
...Central Plains...
Strong northwesterly flow aloft will overspread a cold front moving
southward from the western Great Lakes into the central Plains.
Ahead of the front, warm temperatures and dewpoints in the mid to
upper 60s F will support moderate to large buoyancy by mid
afternoon. A shortwave impulse within the broader trough should
overspread the destabilizing air mass and aide in convective
development along the front across MN and SD, and farther south near
the front and surface trough intersection in central NE.
Forecast soundings show supercell wind profiles, with
elongated/straight hodographs aloft. Isolated to widely scattered
storms will develop by late afternoon/early evening, posing a risk
for large hail, severe wind gusts and perhaps a tornado. Some
significant hail (greater than 2 inch diameter) is possible across
the southern risk area given steeper mid-level lapse rates/cool
temperatures aloft and somewhat deeper low-level moisture. Some risk
for isolated damaging gusts may persist into the early overnight
across southern NE and northern KS if clustering can occur.
...Southeast...
South of the primary upper wave over parts of the Western Carolinas
and TN Valley, a surface trough in the lee of the Appalachians may
focus convective development during the afternoon. A few stronger
clusters with damaging gusts are possible, though weaker flow aloft
suggests more limited storm organization.
Additional scattered thunderstorms are expected again this afternoon
within a seasonably hot and humid air mass across the southeast and
lower MS Valley. Convective coverage is likely to focus along a
weakening cold front sagging southward across parts of AR/LA and
western MS and near a weak MCV across the central Gulf Coast. With
PWATs upwards of 2 inches, some potential for wet microbursts are
possible with the stronger storm clusters through early evening.
...AZ...
Strong heating beneath a prominent upper ridge will support another
round of scattered thunderstorms this afternoon and evening.
Seasonably rich monsoon moisture (dewpoints in the upper 50s to 60s
F) will support moderate destabilization amid modest easterly
mid-level flow. A few high-based clusters are possible, initially
over the higher terrain, before expanding west and south into the
lower elevations. This could support a few severe gusts given steep
lapse rates.
..Lyons/Thornton.. 08/20/2026
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