SPC AC 291619
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1119 AM CDT Thu Sep 29 2022
Valid 291630Z - 301200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THIS
AFTERNOON/EVENING FROM NORTHERN UT INTO WESTERN MT...
A few strong to severe thunderstorms are possible from northern Utah
and western Wyoming into western Montana this afternoon and evening.
...Northern UT into MT this afternoon/evening...
A midlevel low will move slowly east-southeastward over the northern
Rockies, as midlevel height rises occur upstream over the northeast
Pacific. Ascent preceding the midlevel low/trough, and an
associated low-midlevel baroclinic zone, will provide an environment
to support thunderstorms this afternoon/evening from northern UT
into MT. Regional 12z soundings revealed modest low-midlevel
moisture and the potential for steep low-level lapse rates and weak
surface-based buoyancy with surface heating/mixing. Thus,
high-based thunderstorm development is expected this afternoon, with
the potential for isolated strong outflow gusts based on inverted-v
profiles and some downward momentum transfer. Isolated, marginally
severe hail may occur in MT, closer to the midlevel cold core.
...Southeast Atlantic Coast through early Friday...
The core of Tropical Storm Ian, which has some hybrid/baroclinic
characteristics, is moving off the east central FL coast and is
forecast to strengthen some while gradually turning more northward
toward the Carolinas on Friday (see latest NHC forecasts for
details). A cool/dry, continental air mass is entrenched across the
Carolinas now, with widespread rainfall offshore. It will take
until Friday during the day to bring richer moisture and
surface-based buoyancy inland across northeast SC and coastal NC, so
any severe/tornado threat should remain offshore until the day-2
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NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 2000Z