The calendar may say late April but Mother Nature has plans of her own bringing heavy snow to parts of the Stateline Saturday afternoon and evening.
Winter Storm Warnings have been issued for Green, Rock and Walworth counties in southern Wisconsin and for Winnebago, Boone and McHenry counties in northern Illinois. Winter Storm Watches have been issued for Jo Daviess, Stephenson, Carroll, Ogle and DeKalb counties. Both of those winter headlines go into effect late Saturday morning.
Low pressure moving out of the northern Rockies early Saturday will quickly strengthen as it moves across Nebraska and Iowa by Saturday afternoon. Temperatures for most Saturday morning will start off in the low to mid 40s. As moisture increases ahead of the low during the morning precipitation will initially begin as rain. As the low moves through southern Iowa into central Illinois temperatures will actually cool through a process called ‘dynamic cooling’. This will cause surface temperatures to fall into the low to mid 30s during the afternoon. The cooling effect in the atmosphere will allow what is falling as rain to mix with, or transition over to, mostly snow by Saturday afternoon and evening.
Initially the snow will melt due to relatively warm road and surface temperatures. However, a narrow band of snow will develop just north of the low track. This narrow band looks to be between roughly I-88 and southern Wisconsin. Within that band, snowfall rates of one to two inches per hour are possible with the potential for thundersnow!
There will be a sharp cut-off from where a heavy, wet snow occurs to where very little snow falls at all. It may even be as sharp of a cut-off as one part of a county experiences 4-6 inches of snow, while another part of the county only receives an inch. Because of this trying to forecast exact snowfall totals with this system have been very difficult.
There will be impacts to the roads where the heavier snow falls as snowfall rates will be able to overcome the warm surface temperatures. Visibility will also fall due to the heavier snow, but also because of the gusty East/Northeast wind. At times, wind gusts could exceed 35 mph. With a little more foliage on tree branches it’s possible sporadic power outages could occur.
The good news is this is a quick moving storm system and will be out of here by Saturday night. The bad news, temperatures will drop rather quickly Sunday morning with most falling into the upper 20s.
It’s important to also note that this storm track is NOT set in stone and could very well shift north or south by Saturday morning. Even a shift of 15-20 miles would make a big difference on who receives what Saturday.