Mesoscale Discussion 1476
NWS Storm Prediction Center Norman OK
0952 AM CDT Wed Aug 11 2021
Areas affected...Portions of northeastern IL...northern
IN...southern Lower MI...and far northwestern OH
Concerning...Severe Thunderstorm Watch 422...
Valid 111452Z - 111615Z
The severe weather threat for Severe Thunderstorm Watch 422
SUMMARY...A damaging wind threat continues in the short term with
storms approaching Chicago. A downstream watch may be needed soon if
storms maintain their intensity this morning.
DISCUSSION...Multiple measured severe wind gusts up to 64 mph have
been observed with a small bowing cluster moving eastward across
northern IL this morning. Recent VWPs and velocity data from KLOT
show evidence of a rear-inflow jet, and the potential for 60-75 mph
wind gusts will likely continue in the short term as this cluster
approaches downtown Chicago within the next 30 minutes. With mostly
clear skies ahead of this convection across northern IN and southern
Lower MI, the already moist low-level airmass downstream should
continue to destabilize over the next couple of hours. The presence
of modestly enhanced mid-level flow should support 30-40 kt of
deep-layer shear, and 2000-3000 J/kg of MLCAPE will likely exist as
well. There is still some uncertainty if the ongoing cluster will be
able to maintain its intensity with eastward extent this morning.
Still, if current trends continue, then a downstream Severe
Thunderstorm Watch may need to be considered soon for parts of
northern IN, southern Lower MI, and vicinity given the current rapid
forward speed of the cluster.
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