Back to back 50 degree days - Accumulating snow by the weekend

Another beautiful December afternoon in the books for much of northern Illinois and southern Wisconsin Thursday. High temperatures warmed once again into the low to mid 50s, with Rockford officially reaching 57 degrees. This tied the previous daily high temperature record of 57 degrees for December 10th which was set back in 1911 and 2015.

Temperatures Friday won't be quite as warm. In fact, our temperatures will be about 10-15 degrees colder as a cold front comes through Thursday night. That front will come through dry, bringing with it a mostly cloudy sky. Friday morning temperatures will start out in the low to mid 30s, warming into the mid 40s for the afternoon. Winds are expected to increase from the Northeast, gusting at times to 25 mph.  

The low pressure system that was located off the southwest coast of California earlier in the week has now moved onshore and is currently in the Southwest. This low will lift to the north and east through the day Friday, moving near St. Louis, MO Friday evening and then towards Chicago Saturday morning. Ideally this would be a favorable storm track for a significant amount of snow for northern Illinois and southern Wisconsin, but this storm event will be a little different. 

Moisture will surge northward ahead of the low during the day on Friday. As it does, temperatures will warm above freezing and remain above freezing for much of the afternoon. This will allow precipitation to mostly fall as rain beginning mid to late morning, and continuing into the afternoon. Temperatures to the north during the day Friday will cool into the mid 30s, with the cooler air mass reaching the state line by Friday evening. This cooler air will likely allow some of the rain to mix with, or even change over to, snow through much of the evening and overnight. Further south, rain showers will likely dominate through early Saturday morning.

As the low passes south of Chicago Saturday morning colder air will begin to wrap in to the Stateline, bringing temperatures down into the 30s by late morning. This will allow a full transition over to snow during the day Saturday before coming to an end Saturday evening. Winds will also turn blustery, gusting in from the Northeast around 30-35 mph.

As the current track of the low looks right now, the

more favored area for some of the higher snow totals looks to be across Iowa, northwest Illinois, far northern Illinois and south-central Wisconsin. There, snow totals over three to four inches are possible. Further to the south and southeast snow totals will likely drop off rather quickly for areas that only receive rainfall. Rainfall totals could also be quite significant, between half an inch to an inch. Further south across central Illinois and towards Chicago rainfall totals could reach over one inch.  

The track of the low will likely change between now and Saturday, and has over the last few days. Given the warm days leading up to the event and the lack of snow cover on the ground across the Midwest, a shift to the north may be more likely than a big shift to the south.