A Wind Chill Advisory is in effect from midnight tonight until 10AM Friday morning for the northwest counties of the Chicago area including Winnebago, Boone, McHenry, Ogle, Lee, DeKalb involving the cities of Rockford, Belvidere, Woodstock, Oregon, Dixon and DeKalb. As Arctic high pressure pushes south into the Midwest and western Great Lakes, temperatures overnight willl drop below zero over much of northern Illinois and areas to the north (Wisconsin and Lower Michigan) and west (Iowa). These sub-zero temperatures combined with west to northwest winds 10 to 20 miles per hour will result in wind chills of -15 to -25 degrees later tonight well into Friday morning. In the closer-in Chicago metro area and suburbs wind chills of -5 to a -15 degrees will be common during this same time period.
The areas under Wind Chill Advisory are depicted in light blue on the map below. The darker blue/grey shaded areas in the Dakotas and Minnesota are under Wind Chill Warnings calling for wind chills of -25 to -45 degrees.