Tue-Wed, Dec 29-30th Winter Storm Update #3

(12:00PM - 12/29/20) A storm system moving through the region today into Wednesday will bring accumulating snow to much of Northern Illinois, and a wintry mix to portions of Northern and Central Illinois...This afternoon through Wednesday morning.

Summary...
A weak and loosely organized storm system is ejecting out from the Plains today, and will track northeastward into the Great Lakes by Wednesday. With cold air initially in place, snow will generally be favored across far Northern Illinois, with more of a wintry mix likely across other portions of Northern Illinois and also portions of Central Illinois for a time. Model guidance continues to be in decent agreement overall regarding the scenario expected to unfold, with the biggest question being timing of the transition from snow to a wintry mix across Northern Illinois...which will determine final snow/sleet and ice accumulations. Observational trends will continue to be monitored through the event, and updates will be provided as needed.

​Forecast...
A large area of precipitation will spread across the state, this afternoon through Wednesday afternoon. Precipitation, in the form of snow, has already pushed into Northwest and Western Illinois early this afternoon. Precipitation will quickly spread further across the remainder of Northern and Central Illinois the remainder of this afternoon, with much of it falling as snow across Northern Illinois and a wintry mix across Central Illinois. As warm air advection increase this evening, snow will turn to a wintry mix (snow/sleet/freezing rain) across Northern Illinois, with the wintry mix turining to 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.

A swath of snowfall totals up to 6-9" is expected in Northwest Illinois, with amounts gradually tapering with southward extent across Northern Illinois. An axis of ice accumulation of 0.10-0.25" is also expected across portions of Western and Northern Illinois. Additionally, some sleet accumulation is likely across Northern Illinois as well.

​Below are the snowfall and ice forecasts for this event.

JP