The air mass over northern Illinois and adjacent states has become quite unstable. Severe thunderstorms over Iowa will continue developing into SW Wisconsin during the late afternoon. Isolated, to scattered t-storms may pop up quickly across the metro area late this afternoon as well, but these are not part of the organized, severe system to our northwest.
The Iowa/Wisconsin storm complex may develop southeastward across northern Illinois during the evening, posing a damaging wind threat.
Mesoscale Discussion 1159 NWS Storm Prediction Center Norman OK 0251 PM CDT Thu Jul 09 2020 Areas affected...eastern Iowa...southern Wisconsin...northern Illinois Concerning...Severe Thunderstorm Watch 348... Valid 091951Z - 092145Z The severe weather threat for Severe Thunderstorm Watch 348 continues. SUMMARY...A threat of severe wind gusts and marginal hail continues across watch 348, and may spread east into southern Wisconsin and northern Illinois, necessitating another watch. DISCUSSION...An impressive flourish of storms near the meso-low/MCV has produced several measured severe gusts over IA. The primary low is now intersecting the east-west oriented outflow boundary over southern WI and far southeast MN, with cooler air to the north likely reducing wind potential. That said, this outflow boundary may stall and mix out, with a resurgence of larger SBCAPE northward into WI this evening. While the MCV is moving relatively slowly east, there still may be potential for at least isolated severe wind/hail across the warm sector over IL and southern WI where the air mass is clearly uncapped. Only subtle lift will be required to initiate storms in this air mass. The combination of storms along the MCV and any additional lead storms may necessitate a severe thunderstorm watch later this afternoon.