A Winter Weather Advisory is in effect for primarily the southern half of the Chicago area Sunday (purple-shaded area on the highlighted map above). An accumulating snow will likely spread from west to east across the Chicago area Sunday, beginning in western portions before sunrise and ending from the west later Sunday afternoon. Heaviest snow on the order of 3 to 5-inches looks to occur along and south of Interstate-80 with lesser accumulations of 1 to 3-inches farther north.
Eastward-moving low pressure will pass far to our south Sunday, but an associated upper-air disturbance will track farther north over our area triggering an accumulating snow that will spread across central and northern Illinois beginning in western portions not long after midnight tonight, across the Chicago area by Sunday forenoon – then ending from the west later in the day. Northerly winds on the back-side of the departing low pressure could cause additional lake-enhanced snowfall in southernmost Cook County and Will County in Illinois as well as the northwest Indiana counties later Sunday afternoon/evening.