SPC AC 201626
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1126 AM CDT Wed Oct 20 2021
Valid 201630Z - 211200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
THE UPPER MIDWEST...
Thunderstorms with isolated severe hail are possible today across
northern Iowa and southern Minnesota, primarily through
...Midwest including northern Iowa/southern Minnesota...
Upper-level low near the NE/SD border will lift east/northeast
towards the Great Lakes region through tonight. An associated
surface low and cold front will move east towards lower MI/OH Valley
as a warm front extends from southern MN/central WI/northern lower
MI. In advance of the cold front, lower-mid 50s dew points remain
prevalent and will contribute to modest buoyancy in the presence of
35-45 kts effective shear. A stronger storm or two within the
Marginal Risk area will have some potential for hail that could
approach severe thresholds through early/mid afternoon.
...Lower Michigan and far northern Indiana/northwest Ohio...
Thunderstorms are expected to develop this evening into the
overnight, primarily across Lower Michigan, aided by ascent within
the left exit region of an approaching 250-mb jet maximum. This
convection will be rooted atop a stable boundary layer, with modest
elevated instability (MUCAPE generally 500-750 J/kg) supportive of
thunderstorms. This may include some potential for hail, but current
thinking remains that the risk for severe-caliber hailstones should
remain low given the modest buoyancy.
...Middle Gulf Coast...
Relatively rich low-level moisture will stream northward into
portions of Louisiana and southern Mississippi/southwest Alabama
during the day today, supporting moderate buoyancy this afternoon.
Modestly veering wind profiles may favor some organization with
a few stronger storms developing within an environment with
negligible CINH, however poor mid-level lapse rates and generally
modest low/mid-level flow should tend to limit the severe risk in
this area. Still, a few instances of small hail and gusty winds
cannot be ruled out.
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NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 2000Z