SPC AC 161723
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1223 PM CDT Thu Sep 16 2021
Valid 171200Z - 181200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
Organized severe thunderstorms appear unlikely across the contiguous
United States on Friday.
...Great Lakes through Midwest and central Plains...
Scattered thunderstorms will be in progress 12Z Friday along a cold
front and in association with a northern-stream shortwave trough
from the upper Great Lakes into the upper Midwest regions. The front
will continue east and southeast through the Great Lakes and central
Plains during the day. Weak to modest instability is expected in the
pre-frontal warm sector with near 500 J/kg MLCAPE over a portion of
the Great Lakes to 1500 J/kg across KS into northern MO and southern
IA, where a few strong storms with gusty winds and small hail will
be possible during the afternoon. Weak vertical shear should limit
the potential for an organized severe threat from KS to the Midwest.
Farther northeast across the Great Lakes, vertical wind profiles
accompanying a northern-stream shortwave trough will be more
favorable for severe storms, but weak instability should remain a
Gulf moisture will begin to return to a portion of southern Arizona
contributing to 500-1000 J/kg MLCAPE by late afternoon. Diabatic
warming will result in inverted-V profiles, and a few storms may
develop in this regime by late afternoon or early evening. A couple
of strong convective gusts cannot be ruled out, especially where
instability will be locally higher across far southern and southwest
AZ, but the overall threat appears too marginal to introduce severe
probabilities at this time.
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