SPC AC 201255
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0755 AM CDT Wed Oct 20 2021
Valid 201300Z - 211200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE UPPER
Thunderstorms with isolated severe hail are possible today across
northern Iowa and southern Minnesota, primarily this morning into
...Midwest including northern Iowa/southern Minnesota...
Immediately ahead of an eastward-moving upper low, early morning
convection has exhibited a modest uptick in coverage and intensity
in the pre-dawn hours across far northeast Nebraska and northwest
Iowa into far southwest Minnesota. For additional short-term
details, see Mesoscale Discussion 1877. Steep mid-level lapse rates
(12Z Omaha observed sounding) and sufficient elevated instability
(upwards of 1000 J/kg MUCAPE) may support some storms capable of
hail today as this activity spreads northeastward across northern
Farther south across the middle Mississippi Valley, substantial
convective inhibition will likely inhibit surface-based storms along
and ahead of the cold front, although moistening near 850 mb may
support some slightly elevated convection. The potential for
severe-caliber hail/wind is expected to remain very limited today.
...Lower Michigan and far northern Indiana/northwest Ohio...
Thunderstorms are expected to develop this evening into the
overnight, particularly across Lower Michigan. This convection will
be rooted atop a stable boundary, with modest elevated instability
(MUCAPE generally 500-750 J/kg) supportive of thunderstorms. This
could include some potential for hail, but current thinking is that
the risk for severe-caliber hailstones should remain low given the
modest overall 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, along the western periphery of a surface ridge
over the Southeast CONUS. As this occurs, moderate buoyancy will
support scattered thunderstorms near the coast this morning, with
convection expected to spread further inland with time by afternoon.
While weakly veering wind profiles may favor some organization with
the strongest storms, poor mid-level lapse rates and generally
modest low/mid-level flow should tend to limit the severe risk in
this area, although a few instances of small hail and gusty winds
cannot be ruled out.
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z