This is Weather Explained, talking about the Greenland Blocking Pattern. The below image is from the NWS.
The Greenland Blocking Pattern is when a high pressure sets up over Greenland with mild air in that area. This makes the jet stream collapse down south, providing cold air into the areas affected as seen above.
This jet stream set-up is a particularly good conductor for snowstorms in cities such as Chicago, Rockford, and sometimes Springfield Illinois. Madison, Milwaukee Wisconsin can be affected as well.
So this will continue for the next few days, then milder temps, then some colder temps again.