(11:30PM – Saturday, January 4th, 2025) Saturday night update on a winter storm that will bring significant winter weather impacts to the state from tonight through Monday evening.
Timing…
•Tonight – Monday evening, January 4-6th.
Location…
•Much of Illinois.
Impacts…
•Snowfall accumulation widely ranging from a dusting to 8-11” is expected across portions of Northeastern, Central, and Southern Illinois, with locally higher amounts likely.
•Freezing rain/ice accumulation will range from a glaze to 0.50-0.75” across portions of Southern Illinois.
•Snowfall and ice accumulation will lead to widespread snow and ice covered roads, leading to travel issues, likely significant in some areas.
•Power outages and tree damage will be likely across Southern Illinois, due to expected ice accumulation, which will be significant for a large area areas.
•Moderate to heavy snow will be likely at times between Sunday morning and Monday morning across roughly the heart of Illinois, where snow will be favored for much of the event.
•Wind gusts of 25-40MPH will be likely across Central and Southern Illinois from later Sunday morning through midday Monday.
Update…
•With this update, we have made slight boundary adjustments to snowfall accumulation ranges. Otherwise, the going forecast is on track.
•With this update, we have made slight boundary adjustments to ice accumulation ranges. Otherwise, the going forecast is on track.
Discussion…
•As a winter storm moves through the region, multiple types of precipitation will accompany it. Snow, sleet, and freezing rain will be the precipitation types most favored across affected areas for this event, with significant accumulations of each precipitation type expected.
•Across Central Illinois, a majority of precipitation will fall as snow, as temperatures from the surface up through the atmospheric column will stay cold enough for an all snow event.
•Across Southern Illinois, with warm air advection on the frontside of the winter storm, dynamic cooling during the event, and cold air advection on the backside of the storm system, multiple precipitation types are likely. Precipitation may initially start as snow/sleet, before transitioning to freezing rain and sleet will be favor during the middle 2/4th of the event, before ending as snow for the final 1/4th of the event.
•Across Northeastern Illinois, lake effect snow will be likely. While the significance of this potential is still in question, lake effect parameters are on the lowered, which would favor a lower end outcome. Thus, we have hedged in this direction.
•Even at “zero hour”, there are still some discrepancies within weather model guidance regarding exact amounts of each wintry precipitation type and exact placement of each precipitation type. This is nothing unusual, but as always, it is leading to a non-100% confidence level forecast.
