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Mesoscale Discussion 1385 NWS Storm Prediction Center Norman OK 0628 PM CDT Fri Jul 21 2017 Areas affected...Eastern IA...Southern WI...Northern IL...Northwest IN Concerning...Severe Thunderstorm Watch 429... Valid 212328Z - 220100Z The severe weather threat for Severe Thunderstorm Watch 429 continues. SUMMARY...Severe threat continues across most of WW429. DISCUSSION...Remnants of long-lived MCS, that evolved over the central Plains before dawn, have progressed into the upper Great Lakes region. Considerable amount of redevelopment is occurring in proximity to the remnant center with the majority of strong updrafts evolving along the southwestern flank of the mid-level debris shield from eastern IA into extreme southwest WI. Early-day convection has contributed to a well-defined outflow boundary that is draped across the south side of the Chicago metro, westward into IA where a few supercells have evolved. This new development will likely continue to grow upscale with storm mergers likely contributing to another mature MCS over southern WI/northern IL later this evening. Large hail and damaging winds remain possible with most storms this evening and a tornado can not be ruled out with supercells that utilize more favorable shear near the outflow boundary.