*****WINTER STORM WATCH HAS BEEN ISSUED FOR WINNEBAGO, BOONE AND MCHENRY COUNTIES FROM LATE TONIGHT UNTIL SUNDAY AFTERNOON****
*****WINTER STORM WATCH HAS BEEN ISSUED FOR GREEN, ROCK AND WALWORTH COUNTIES FROM SUNDAY MORNING UNTIL SUNDAY NIGHT****
An area of low pressure will begin to strengthen over the Plains later this evening and move across northern Illinois Sunday. As it does a warm front will lift northward and be the focus for precipitation, could be heavy, to develop starting late tonight. Initial indications are suggesting the precipitation will start off as snow and sleet, with some accumulations expected. Through the overnight and early Sunday morning warmer air is expected move into the upper levels of the atmosphere which would likely change the snow and sleet to freezing rain sometime Sunday morning and then possibly just rain during the afternoon.
The top image on the left is the GFS model at 6am Sunday morning. Notice the darker blues over southern Wisconsin and northern Illinois. This is indicating a heavy amount of precipiation over that area by Sunday morning. If surface temperatures were to stay right around freezing the chances of the freezing rain to switch over to rain would be less and we could be talking about a significant amount of ice accumulation Sunday. Further north into Wisconsin heavy snow is expected as temperatures will likely stay cold enough. The low will then move pretty much right over northern Illinois Sunday with a change over back to snow/sleet Sunday night.
This image shows the probability of seeing at least a tenth of an inch ice accumulation Sunday through Monday. All of the forecast area is under the 10% chance with portions of north-central/northeast Illinois and southeast Wisconsin under a 40% chance. We'll continue to track this system as it moves closer through the afternoon and evening. Sunday travel may become tricky, or even dangerous, if freezing rain continues throughout the day.
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