Rain is expected to spread across northern Illinois and southern Wisconsin into northwest Indiana and southern Lake Michigan Thursday night into Friday.
Rain is expected to change over to freezing rain in the northernmost Chicago area counties closest to the Illinois-Wisconsin state line – this includes Ogle, Winnebago, Boone and McHenry Counties and the cities of Rockford, Belvidere, Woodstock and Oregon, where a Freezing Rain Advisory has been issued from that area from midnight Thursday to noon Friday.
The Freezing Rain Advisory extends back to the immediate counties in northwestern Illinois and north into southern Wisconsin.
A cold front slowly sinking south through the Chicago area Thursday is expected to orient more east-west and become stationary south of Interstate 80. Then a center of low pressure will ripple east along the front triggering the development of rain north of and along the frontal boundary later tonight into Friday. Colder air will slide south out of Wisconsin dropping temperatures below freezing north of Chicago, allowing the rain to freeze on contact creating a layer of glaze that will make conditions extremely slick in the aforementioned areas under the Freezing Rain Advisory.
The situation will have to be monitored closely, as a slight movement of the colder air farther south, would mean more of the Chicago area could be impacted by the freezing rain conditions.
Story by Paul Dailey, Chicago Weather Center blogger