Our winter storm continues to inch closer to us as we are now about 24 hours away from it starting across portions of the state with then deteriorating conditions by tomorrow evening for some, favoring the northern half of the state. Get the latest information below including how much snow and ice to expect across your area.
Our winter storm is coming ashore California this afternoon and will continue in a eastward direction for the most part over the next 24 hours or so as it crosses the Rockies and ejects out into the plains. This will then induce that strong period of warm air advection we've been talking about and what will be the big generator of precipitation later tonight into tomorrow morning to our southwest.
Widespread wintry precipitation will gradually work its way northeast through the day tomorrow, reaching western Illinois first before continuing northeast. It will begin as snow for much of central and northern Illinois while downstate Illinois sees a mix or just plain rain for this event. Snow will then continue for several hours, especially across the northern portion of the state with potentially a period of heavy snow as well. This could lead to a pretty rough evening commute where snow is falling, pending on when exactly snow begins and starts to accumulate. It will be fighting some dry air at the surface which is making it a bit tougher to pin down start times across the area. It will be a fight against the warm air aloft which should eventually with out and change snow to a mix of sleet and freezing rain overnight and then potentially all rain by early Saturday morning. The loop below runs till midnight tomorrow night and you can see more mixed precipitation working into northern Illinois by that time. There is some model guidance that says it will stay snow longer and that will have to be watched in real time tomorrow afternoon and evening. After the changeover to a mix and some rain even across the northern portions of the state, colder air will eventually advect back in on the backside, changing leftover precipitation back to snow with some light accumulations possible Saturday morning and afternoon.
Winds will also be apart of the story by tomorrow night and overnight with the potential for gusts exceeding 30mph across a large area. Further north where snow is falling, this will only make travel more difficult, reducing visibility even further. The image below is valid at 8pm tomorrow night.
Another way to visualize where the heaviest snow is falling is looking at a surface visibility product. The lower the visibility is, the harder it is snowing. In the loop below, you can see a fairly large area of visibility less than a mile moving into much of northern Illinois during the evening and early overnight hours. The loop below runs from noon tomorrow till midnight tomorrow night.
Below is our latest thinking on snowfall and ice amounts across the state. Stay tuned those as these are still subject to change as we get closer to the start of the winter storm.