Disorganized, non-severe storms have shown signs of developing in a zone of warm air transport aloft from NW Illinois into SE Wisconsin. Some of these cells may develop, producing an isolated severe hail threat. Heavy downpours are likely with larger storms.
Here is the discussion from the SPC:
Areas affected...Northern IL...Northern IN...Southern Lower MI Concerning...Severe Thunderstorm Watch 430... Valid 120406Z - 120530Z The severe weather threat for Severe Thunderstorm Watch 430 continues. SUMMARY...Additional thunderstorm development is possible overnight, but the magnitude and coverage of any severe risk remain quite uncertain. DISCUSSION...Thunderstorms which briefly intensified earlier across northern IL and produced a near-severe gust west of Chicago have recently dissipated, while other generally disorganized convection continues across southwest lower MI in the wake of an earlier thunderstorm cluster. The greatest thunderstorm coverage across WW 430 in the short term may continue to be across southwest MI, with the primary low-level jet expected to remain focused in this area. Further west, midlevel cumulus continues to be noted in IR imagery across northwest IL, and additional storm development remains possible into northern IL late tonight as a cold front moves into the region. While buoyancy remains rather large across the region, any additional development later tonight will likely become increasingly elevated with time as MLCINH increases, and effective shear for elevated parcels will likely remain rather weak due to marginal (at best) midlevel flow. Thus, any severe risk may remain isolated at best, and it is possible that portions of WW 430 will be cancelled early if no substantial redevelopment occurs by 05Z or sooner.