UPDATE 10:00PM - Observing a slight northward trend in recent radar imagery and models runs. Heavy snow banding showing up in southern WI.
UPDATE 8:15 PM - Everything is on track and going as forecasted tonight through Friday morning. Will have to clean up the message for Friday PM to Sunday which has been tough.
10AM THURS - A low pressure system riding along a stationary boundary will bring heavy snow to southern Wisconsin, northern Illinois, and eastern Iowa tonight into Friday morning. Snow will start tonight at 6PM (9PM southeast) ending by 6PM Friday. Some models end snow Friday morning, others keep it around into the late afternoon in the southeast. There is another chance for snow in southern Wisconsin Saturday night & Sunday. Nonetheless travel will be heavily impacted Friday morning in the regions highlighted below.Impacts
- 8-12" of heavy snow is expected along and south of the WI/IL border. Locations include Beloit, Kenosha, and Dubuque. Locally higher amounts from Rockford to Chicago.
- 6-8" for the southern-most counties in Wisconsin. Locations include Platteville, Janesville, and Racine.
- 3-6" along and north of I-94 for locations such as Prairie du Chein, Madison, and Milwaukee
- 1-3" for La crosse, Wisconsin Dells, Fond du Lac, and Sheybogan. An inch or less expected in central Wisconsin.
- lake effect Snow is possible Friday as low level winds turn easterly, boosting totals (+1-2") along the Lake Michigan shoreline in southeast Wisconsin. The snow map reflects this impact.
- Snowfall rates may approach 1-2" per hour early Friday morning. The National Weather Service has issued a Winter Storm Watch for the southern-most counties and Snow Advisories north of that.
Another chance for snow will come on Saturday/Sunday as the stationary front tightens up and another system passes well to the south. It's still a bit early to get too specific but additional accumulations of 2-5" south of the WI/IL border (1-2" far southern Wisconsin?) are likely to overlap the Thurs PM-Fri event, contributing to potential three-day totals of 12-18" in northern Illinois!
Confidence is high in predicted snow totals. This is a classic, yearly occurrence for this part of the Great Lakes. I took a blend of 12GFS overall QPF and the 12ZNAM snow banding, de-emphasizing southern Wisconsin and focusing on northern Illinois. All models focus QPF over Chicago. Heavy snow banding will be a mesoscale feature that can be hard to pin down, therefore will wait for short range models to come in. Left northern IL in a good place to add a 12"+ zone should confidence or intensity increase. Models haven't been consistent on snow ending times.
The three-day totals could push 18" in northern Illinois. This is possible with snow banding that usually contains 20:1 - 22:1 SLR ratios with this type of event. I'm less confident in Saturday-Sunday and don't want to blindly assume the two events will overlap. The system from last weekend came together in the last minute so with that fresh in my mind I won't start knee-jerking yet.