(10:30PM - 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 morning.
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 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. Model guidance overall generally remains within a concentrated envelope of outcomes, with only minor adjustments occurring now. Little change was needed with this update, just generally minor noise level adjustments.
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, early to mid Tuesday afternoon, in the form of snow across Northwest Illinois and a wintry mix (snow/sleet/freezing rain/rain) across Western Illinois. Precipitation will quickly spread further across the remainder of Northern and Central Illinois Tuesday evening, with much of it falling as snow across a good portion of Northern Illinois and a wintry mix quickly changing rain across Central Illinois. As warm air advection increase Tuesday night, snow will turn to a wintry mix (snow/sleet/freezing rain) across Northern Illinois, with all rain across Central Illinois. By Wednesday morning as warm air advection continues, a wintry mix (snow/sleet/freezing rain/rain) will continue across Northern Illinois, with precipitation ending by afternoon. It continues to look possible that only far Northern Illinois along the Illinois/Wisconsin border may remain as all snow for the duration of this event.
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 likely across Northern Illinois as well.
Below is the snowfall and ice forecasts for this event.