Heavy wet 6 to 8-inch snowfall is forecast to hit the Chicago area tonight and Wednesday forenoon. A combination of a Winter Storm Warning and a Winter Storm Advisory valid from 10PM CDT this evening until 1PM CDT Wednesday has been issued by the Chicago National Weather Service Forecast Office.
The Winter Storm Warning for 6 to 8 inches (locally up to 10-inches possible in thunder-snow) covers much of the Chicago area, while the Advisory covers areas to the north, with lightest amounts in the 1 to 3-inch range anticipated to the far northwest at the Illinois-Wisconsin border along the northern fringe of the snow system. Embedded thunderstorms, especially in southern areas will cause temporary locally heavy, white-out conditions.
A low pressure system is forecast to track out of the central plains up the Ohio River Valley tonight and Wednesday, spreading first rain across the area and then as colder air feeds into the system on the wings of the strengthening northeast flow, the rain will change to sleet and then heavy wet snow later this evening and overnight. Blowing and drifting caused by 25 to 40 mile-per-hour northeast winds will cause near-zero visibility at times and create treacherous travel/driving conditions. The snow will be ending from west to east across the area Wednesday forenoon, but the morning commute will most likely be severely impacted, especially closer in to the city and south.
The map below shows the Chicago area with the Winter Storm Warning in pink, the Winter Weather Advisory in purple, and a Winter Storm Watch (that will probably soon be updated to a Warning or Advisory) in dark green. Winter Storm Warnings/Advisories/Watches have been or will be issued farther east through Ohio and Pennsylvania.
Larger picture of Winter Warnings/Advisories/Watches