UPDATE: Winter Storm Watch has been posted for the entire Stateline beginning 3pm Saturday until Monday morning.
Well....today would be a good day to make sure that snow blower is ready to go! We have not one round of accumulating snow this weekend...but two!
A strong low pressure system will bring two waves of snow over a 48 hour period of time this weekend. The low is currently in moving onshore in the Pacific Northwest and will quickly track across the Rockies and into the plains today into early Saturday. Ahead of strong warm air advection and lift from the low, snow will develop in western Iowa and move east into northern Illinois and southern Wisconsin. A second wave will bring the second round of snow on Sunday. With warm air being drawn up with this system, just south of I-80 is where there looks to be less snow on Sunday and more of a mix.
TIMING: Because the snow moves is tied to individual waves of energy timing can be a bit tricky to nail down, but models have now started to get into better agreement. Northern Illinois and southern Wisconsin will remain dry Friday and most of Saturday, before snow arrives Saturday afternoon. It will move in from eastern Iowa around 3pm and head east over the area. Snow will be light to moderate, but it its becoming increasingly clear that a narrow band of heavy snow will develop as well. Snow will continue Saturday night into early Sunday morning. In the first round 3-6 inches looks like a good bet, but local higher amounts(not area wide) will be likely in that heavy band.
We get a break Sunday morning into the early afternoon to clear out the first round of snow before the second arrives. The second snow fall arrives with a second shortwave trough/energy wave for Sunday afternoon. Again this snow will continue into the evening and overnight hours before winding down Monday morning. This will make it a slick and slow commute Monday as crews work to clear snow.
HOW MUCH? : The low pressure is finally moving onshore, and so going forward today we will get an increasingly better idea on how much snow we will see. However, models are merging a bit more on a consensus on a track and a range in snow totals. The liquid to snow ratio for the first round is hoovering around 13:1 to 17:1. What this means for you is that it will be a drier and fluffier snow, in which it accumulates faster. Right now 3-6" looks like a good bet for the first wave of snow. While it is a bit too soon for snow totals Sunday, it is looking about the same as Saturday. This would bring a preliminary TWO DAY total to 8-12" for the area. But as mentioned before where narrow bands develop we will want to watch for a few locations to see locally higher amounts.
As you all know, this forecast will continue to be fine tuned up until the event, as we continue to collect more data on this system. But overall you can count on using your shovel and snow blower multiple times this weekend.