The above is the mean of all Short Range Ensemble members for snowfall (inches). You can see they are showing 5-6" in the Chicago area! Do we believe this? No, but we cannot dismiss it entirely. A 2-4" snowfall is much more likely in this region because the band will be weakening and the thermal profiles are not that favorable.
A band of very heavy snow will enter the Chicago area around 10-11PM tonight and last into the morning hours. Very strong low to mid level frontogenetic forcing will overspread the region with elevated instability. The combination will lead to intense banding with thundersnow. To be more exact it might be thundergraupel/sleet in some cases with the significant riming of the snowflake. This is when the snowflake falls into a deep saturated layer of supercooled droplets allowing the supercooled droplets to freeze to the snowflake. This lowers ratios to below 6-8:1. However the charge separation with the graupel will enhance the threat for thundersnow/graupel.