A Winter Weather Advisory (purple-shaded counties on the map below) for possible icy conditions has been issued for Winnebago, Boone, McHenry and Ogle Counties for a brief period between 3AM and 9AM CST Saturday morning.
Lower and mid-level clouds accompanying by light rain are expected to spread into our area from the southwest later tonight well in advance of a deepening low pressure center approaching out of the Central Plains. Existing snow cover may keep temperatures below freezing in our northernmost counties close to the Illinois-Wisconsin state line, so if the rain occurs there, it could freeze upon contact, creating slick icy roads/streets and sidewalks and dangerous driving and outdoor conditions. Temperatures should rise above freezing my mid-morning.
The main thrust of a deepening low pressure system is forecast to bring locally heavy rains with embedded thunderstorms across the Chicago area later in the day Saturday, followed by strong northwest winds gusting over 50 miles per hour and falling temperatures later Saturday night into Sunday.