Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0258 PM CDT Wed Sep 23 2026
Valid 232000Z - 241200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PATS OF
THE WESTERN DAKOTAS...
...SUMMARY...
Isolated severe thunderstorms are possible this afternoon across
parts of the western Dakotas.
...20Z Update...
The forecast for this afternoon remains largely on track. Isolated
damaging wind gusts and severe hail are possible late this afternoon
across portions of the Western Dakotas, where moisture pooling has
resulted in upper-50s to low-60s F dewpoints coincident with
clearing on visible satellite. Moderate deep-layer shear and modest
buoyancy will support organized storms and potentially transient
supercells. Given the potential for supercells, adequate buoyancy
and shear combinations, and cooler temperatures aloft, a CIG 1 area
was introduced to highlight the potential for isolated occurrences
of 2" hail, particularly with any stronger/more organized supercell
structures. See the previous discussion for more details.
..Halbert/Lyons.. 09/23/2026
.PREV DISCUSSION... /ISSUED 1122 AM CDT Wed Sep 23 2026/
...Western Dakotas...
Recent surface analysis placed a low over far southeast MT, with a
lee trough extending southward from this low across the High Plains
into far West TX. A plume of moderate low-level moisture exists just
east of this troughing, with upper 50s dewpoints currently reaching
into southwest SD and mid 50s into western ND. This lee trough will
help facilitate the maintenance of this moisture plume as the
shortwave trough currently moving through WY and eastern MT
continues northeastward into the region today and tonight.
Widely scattered thunderstorms are forecast to develop as convective
inhibition erodes in the vicinity of the lee trough and the Black
Hills this afternoon. Strengthening southwesterly flow aloft will
result in moderate deep-layer vertical shear (i.e. 30 to 40 kt from
0-6 km) amid 500 to 1000 J/kg of MLCAPE. This shear may aid in some
storm organization potential, with the stronger thunderstorms
perhaps yielding an isolated risk for marginally severe hail/gusts
through early evening.
...Southern Appalachians...
Recent visible satellite imagery shows widespread low stratus across
both the Mid-Atlantic/Carolinas and farther east over much of the TN
Valley. There is corridor between these regions from roughly
northwest GA across far eastern TN/far western NC into far western
VA where less low-level cloud cover is in place, replaced by more
vertically developed structures. Temperatures in this region range
from the upper 70s across northwest GA to the upper 60s/low 70s
across far western VA. There is also slightly greater low-level
moisture in this region (i.e. low 70s dewpoints), and these
thermodynamic conditions are supporting modest buoyancy. This
buoyancy explains the deeper clouds and recent lightning that has
been observed in eastern TN. Thunderstorm activity will likely
persist in this region throughout the day, supported by large-scale
ascent attendant to an approaching shortwave trough and mesoscale
convergence on an inverted surface trough that extends from southern
AL into the southern KY/VA border vicinity. Some increase in the
mid-level flow is anticipated as the shortwave moves through, but
modest buoyancy and a mostly cluster multicellular mode should keep
severe potential low. As such, removed the 5% wind probabilities
across the region.
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