Satellite imagery early Monday morning shows little contamination from cloud cover or thunderstorm outflow.
With ample sunshine and tropical air in place, as well as an amplifying upper-level disturbance approaching from the NW, the atmosphere is forecast to become extremely unstable this afternoon. Given the degree of instability and little inhibition for t-storm growth, strong to severe storms may erupt earlier than usual, perhaps as soon as early afternoon. The cluster of storms over western Iowa noted in the satellite imagery above may also come into play since it may not undergo the usual late-morning decay.
Given this scenario, the Storm Prediction Center has elevated the northern third of Illinois and part of NW Indiana to an Enhanced Risk of severe thunderstorms. The greatest threat appears to focus on the 3 to 8 PM time frame. Though damaging wind will be the primary threat, localized large hail is also likely. In addition, given increasing low-mid level wind shear a few tornadoes cannot be ruled out.