Late season winter storm update

1:00pm Update: Dry air remains in place across northern Illinois and southern Wisconsin so the leading edge of warm air that produced snow in Iowa earlier this morning fizzled a little, however, there have been some reports of light snow reaching the surface across Illinois.  Accumulations will remain minor through tonight with the main snow event still arriving after midnight tonight.

 

A Winter Storm Warning remains in effect for all of Southern Wisconsin and Northern Illinois beginning late tonight and lasting through Tuesday night.  Low pressure currently in the Plains will continue to dive southeast into Iowa tonight and south of the Stateline Tuesday.  Snow will begin to fall after midnight tonight (closer to dawn Tuesday for some) and continue through Tuesday night.  Heavy snow looks to begin mid to late morning Tuesday and last through the afternoon/evening commute with the evening commute becoming heavily impacted once the snow begins.  Snowfall amounts between 6"-8" with isolated amounts near 10" still look possible once the snow ends by Wednesday morning; especially if snowfall rates of 1" per hour or more occur.  Winds will increase from the north by Tuesday afternoon with blowing and drifting snow becoming a concern through Tuesday night and even a little Wednesday morning.  Travel by Tuesday afternoon will become very difficult with whiteout and blizzard conditions expected.

 

 

 

 

Dry air in place across northern Illinois and southern Wisconsin will slow the eastward progression of the light snow currently in Iowa.  Temperatures right now are in the low 20s under cloudy skies.  The snow will move in from west to east later this morning and through early afternoon.  Accumulations will remain minor with roughly 1"-2" falling from this initial band.  Looking at this first band as it moves east does show the snow decreasing in coverage some.

Winter Storm Warnings have been issued for all of northern Illinois and southern Wisconsin and these will go into effect late tonight and last throughout the day Tuesday.   Looks like we'll get two rounds of snowfall between now and Wednesday morning.  The first with what's coming today and the second with the main low pressure system.  A strong clipper system will continue to dive southeast out of the Plains this afternoon into Iowa by this evening and just south of the Stateline by Tuesday afternoon.  Snow after midnight tonight will increase in coverage and intensity through Tuesday morning with the heaviest of the snow falling during Tuesday afternoon.  Right now the track of the low places the heaviest snow band across the area from Madison, WI to Rochelle, IL where two day storm totals could reach close to 10".  It's important to note that there's still time for a slight shift in this track, but most should receive close to 6" of snowfall when all said and done.  Also, if there are any showers or storms that develop downstate this will block the Gulf moisture supply feeding into this storm which would cut back on snow totals.

The snow that will initially fall will be a little heavy and wet with low snow to liquid ratios but as colder air wraps into the storm by Tuesday afternoon the snow to liquid ratios will increase and with an increase in wind the snow will begin to blow around and drift over roads through Tuesday night.  Once the snow begins road conditions will quickly deteriorate as heavy snow (snowfall rates near 1"/hr) will be likely.  Morning model runs will come out between 9am and 11am and I'll have another complete analysis on here later today.