After a day of unusually warm temperatures, a major storm system will bring a variety of weather concerns to the area tonight through Thursday, including heavy rain with the potential for flooding, possible ice accumulation and several inches of wet, heavy snow.
Wednesday evening thru early morning: Rain & mixed-precipitation event
Rain showers will begin along I-80 early this evening, eventually expanding coverage to most of the area by late evening. As temperatures fall, rain transitions into mixed precipitation around 2 am for areas nearest the IL-WI state line and between 3-4 am for the immediate Chicago area, before changing over to snow through 8 am. Some of the mixed precipitation may lead to ice accumulation as well.
Thursday: Main snow event
A lull in activity will follow the morning commute, providing a break in precipitation for a few hours before the main snow event begins. Snow is likely to start falling around 10 am southwest near La Salle County and spread northeast to blanket the entire Chicago area and Northwest Indiana by Noon.
Snowfall accumulation will favor southern sections, with rates up to 1″ per hour possible in the heaviest bands. Wind will also be a factor, gusting over 40 mph at times, which may lead to blizzard-like conditions of blowing and drifting of snow, especially along and south of I-80. Snow will wind down around 7 pm for most of the area and by 9 pm for Northwest Indiana.
A wide range of snow totals is expected, with the lightest totals of 1-2″ near Rockford and Lake County, IL; 2-4″ in Chicago and the western suburbs; and 3-7″ south and east of I-55. A swath of 8″+ totals is possible from Kankakee through Valparaiso in Northwest Indiana.
A Winter Storm Warning is in effect from 3 am to 9 pm Thursday for southern counties, including Will, Kendall, Grundy, Southern Cook, Lake (IN) and Porter Counties for difficult driving conditions expected, especially during the evening commute.