J-Money:

For much of the afternoon, so far, scattered to numerous storms in central/southern IL have been non-severe in nature, with occasional small hail.  Prob Severe values have been correspondingly low, with meager flash rates, and poor growth rates.

However, just before 22z, a storm intensified in the far northeast part of the ILX CWA.  Prob Severe values rose quickly into the 70s and 80s, as flash rates and MESH values increased.  A warning was issued, based on the environment of cold air aloft, and seemingly more favorable storm-scale parameters for hail, as shown by Prob Severe.

A loop of refectivity at the -20C level, with Prob Severe overlayed, is shown here.  It well correlates with the above descriptions.