(11:45AM - 12/28/20) A storm system will move through the region Tuesday and Wednesday, bringing accumulating snow to much of Northern Illinois and a wintry mix to portions of Northern and Central Illinois, Tuesday afternoon through Wednesday afternoon.
A weak and loosely organized storm system is expected to eject out from the Plains on Tuesday, tracking northeastward, and into the Great Lakes on Wednesday. With cold air initially in place, snow will generally be favored across far northern portions of Northern Illinois, with more of a wintry mix likely across other portions of Northern Illinois and also portions of Central Illinois for a time, as warm air advection occurs. There has been a select few within model guidance that have been consistent with many aspects of this event, showing a further south event across the region. Meanwhile, other model guidance has been further north with placement, but has been trending southward with time. The main change with this update was to slightly adjust the snowfall axis based on trends, as well as increase expected snowfall amounts in the heart of the snowfall axis.
A large area of precipitation is expected to spread across the state, from Tuesday afternoon through Wednesday afternoon. Precipitation will first push into Northwest and Western Illinois Tuesday afternoon and evening, in the form of snow across Northwest Illinois and a wintry mix (snow/sleet/freezing rain/rain) across Western Illinois. As precipitation spreads further across Northern and Central Illinois Tuesday night, much of it will fall as snow across a good portion of Northern Illinois and a wintry mix quickly changing rain across Central Illinois. By Wednesday morning as warm air advection continues, Central Illinois will have all rain, and snow across portions of Northern Illinois will have turned to a wintry mix (snow/sleet/freezing rain). Only far Northern Illinois along the Illinois/Wisconsin border may remain as all snow. By later Wednesday morning and afternoon, precipitation across Northern and Central Illinois will end from west to east.
Final snowfall totals will generally range from 2-5" in the swath of snowfall, with a higher corridor of 4-7" totals likely. Snowfall totals will rapidly lower along the southern end of the axis. Ice accumulation of a glaze to 0.10"+ will be likely across portions of Western and Northern Illinois. Additionally, some sleet accumulation is possible across Northern Illinois as well.
Below is the snowfall forecast for this event.