Instability is forecast to be on the high end, not surprising for 100 degree heat. The Storm Prediction Center does mention the potential for 4000-5000 j/kg of instability, which is indeed very high. The NAM indicates a small area of enhanced rotation potential over northern Illinois, slanted more towards the area south of Chicago, IL going into extreme northwest Indiana. Over the general lower Great Lakes region, there could be a widespread weak capping inversion, which would likely be crushed by at least 3000 j/kg of instability currently being projected by the NAM.
The GFS is bullish on instability, placing over 5000 j/kg of potential energy over northern Illinois, whereas the NAM centers the instability into the Upper Midwest. Additionally, the GFS disintegrates capping potential in Northern Illinois, opting to place any inversion to the south of a line roughly following Interstate 80. There looks to be some shearing in southern Wisconsin and areas west, igniting potentials for some supercellular structures of which the Storm Prediction Center does find plausible. Precipitation values off the GFS at roughly 7:00 PM CDT tomorrow do indicate what could be a small cluster of storms, or an area of cells in northern Illinois. These could reach severe limits and will have to be watched in future forecasts.