Extremely hazardous driving/travel conditions will develop this evening and continue overnight through Saturday/Saturday night across the Chicago area of northeast Illinois into northwest Indiana.
As cold air sinks slowly across northern Illinois, a center of low pressure will track northeast out of Oklahoma through Arkansas today and tonight into Indiana and Ohio later Saturday. The combination of the colder air overhead and low pressure approaching and passing to our south will spread heavy rains, a combination of freezing rain and sleet, and eventually accumulating snow across portions of the Chicago area the next 24 to 36 hours.
A Winter Storm Warning (pink-shaded area on the headlined map) for first freezing rain and sleet later this evening and overnight into Saturday morning followed by accumulating snow up to 6-inches later Saturday is in effect for Winnebago, Boone, McHenry, Ogle, Lee and DeKalb Counties.
A Winter Weather Advisory (purple-shaded counties on the headlined map) for first freezing rain and sleet Saturday morning changing over to accumulating snow 2 to 4-inches later in the day into the overnight hours Saturday is in effect for Kane, DuPage, Kendall, LaSalle, Lake, and Cook Counties in Illinois. The Snow accumulation in Cook County could range from 1-inch or less in the extreme southern portion to nearly 4-inches in northernmost sections.
Lakeshore Flooding is also forecast for the Lake Michigan Shoreline in Lake and Cook Counties, Illinois as well as Lake and Porter Counties in Indiana later tonight through Saturday night with strong northeast winds at times gusting 45 to 50 mph building 15 to 20-foot and occasionally higher waves over the already high lake levels causing significant erosion and flooding.
A Flood Watch (green-shaded areas on the headlined map) is in effect – heavy rains of 2 to possibly 4-inches tonight and Saturday may not only cause localized flooding of low-lying areas and roads, but also cause rapid rises and eventual flooding of some rivers and streams over the remaining Illinois into northwest Indiana counties generally along and south of Interstate-80 (including Cook County).