Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1233 AM CDT Tue Oct 21 2025
Valid 211200Z - 221200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
...SUMMARY...
Isolated thunderstorms are possible over the Great Lakes, South
Florida, and the northwest Gulf Coast regions. Organized severe
threat appears low today.
...Discussion...
Strong upper trough will dig into the central Great Lakes region by
late afternoon as 80+kt 500mb speed max translates across southern
IL into central KY. 180m 12hr height falls will overspread much of
the Great Lakes region with substantial falls expected as far south
as the TN Valley. Latest model guidance suggests notable
boundary-layer heating will occur across southern IL/IN into
southern Lower MI by mid day, just ahead of a surging cold front.
This will contribute to steep 0-3km lapse rates and weak instability
as convective temperatures are breached by 19z ahead of the wind
shift. Forecast soundings support this with a few hundred J/kg
SBCAPE by early afternoon as 500mb temperatures cool below -24C.
Isolated thunderstorms should develop within a strongly forced
environment then spread downstream ahead of the progressive trough.
With surface dew points expected to mix into the upper 30s there is
some concern this activity could generate gusty winds; however, mean
wind in the boundary layer should remain around 30kt and this may
prove too weak to warrant more than sub-severe mixing/downdrafts.
Isolated thunderstorms, a few possibly strong, are also expected
along the trailing boundary across the lower MS Valley. While
large-scale forcing will be limited at lower latitudes, instability
will be considerably greater, though deep-layer shear will not be
strong. Current thinking is convection should remain sub severe with
the possibility for gusty winds.
Elsewhere - scattered convection should once again develop across
the southern FL Peninsula today, and perhaps across southern New
England very late in the period as LLJ strengthens into this part of
the country.
..Darrow/Moore.. 10/21/2025
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