Update 4PM CDT…
The Winter Storm Warning for 4 to 8-inches of snow or even more in a few locations associated with thunder-snow has been extended south and east into central Illinois and across the northern half of Indiana – valid from 10PM CDT this evening until 1PM CDT Wednesday. Northeast winds gusting to 40 miles per hour will cause considerable blowing and drifting and cut visibility to near zero at times. Below is the latest Chicago-area Winter Storm Warning (pink-shaded area) and Winter Weather Advisory 3 to 6-inches of snow in purple-shaded counties.
The center of lowest pressure is “winding up” in southeastern Kansas – set to move east through central Missouri this evening. A warm front extends east out of the low center through central Missouri and Illinois into Indiana and northwest Ohio.
A huge temperature differential exists across the warm front with readings in the 70s along and to the south of the front (Springfield and Decatur were around 70-degree at 4PM), while to the north temperatures drop off quickly into the 50s – resting in the 40s across the Chicago area. Strengthening northeast winds (already gusting over 25 miles per hour) pulling cold air off the ice-covered, 30-degree waters of Lake Michigan – will eventually force our temperatures into the 30s.
Rain is still forecast to spread across the Chicago area this evening – quickly turning over to sleet and then accumulating snow. Travel will quickly become hazardous later this evening as the snow builds up, roads become slush-covered and icy and strong winds cause blowing and drifting as well as cutting visibility.
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