Afternoon Weather Update

A heavier band of precipitation is lifting north near the Illinois/Wisconsin state line.  Within this band, heavier wet snow or a mix of rain and wet snow has been occuring.  Where the heavy snow has fallen the flakes have been very large!  This mixture of rain/snow will continue before completely changing over to all snow by this evening.  Minor accumulations are likely where the snow falls this afternoon.  This will keep roads wet and slushy.

WINTER WEATHER ADVISORY FOR NORTHERN ILLINOIS COUNTIES, ROCK AND WALWORTH COUNTIES BEGINNING AT 6PM THIS EVENING.

Light rain mixed with snow is now beginning to lift north of I-88 late this morning and will continue northward through the afternoon.  There is a very warm layer a few thousand feet above the surface which should support the rain going through the afternoon, however, right above the warm layer colder temperatures are found.  These colder temperatures will eventually begin to trickle down allowing some snow to mix with the rain.  As the low begins to move closer this evening a complete change over to snow will occur; this appears to be somewhere during the 6pm to 8pm time frame.  Right after the complete change over to snow is the greatest potential for thundersnow to occur.  If thundersnow were to happen, totals would likely be increased due to higher snowfall rates. These rates could exceed an inch per hour.

Right along the I-88 corridor holds the greatest potential on totals possible exceeding six inches.  This puts Lee, Ogle, DeKalb and maybe even southern McHenry counties in the bullseye.  Further north snow totals will likely range from 3" to 6" and further south totals will be a little less.  

The dynamics of this storm are that of what we would typically see in spring in terms of instability, hence the potential for thundersnow.  Temperatures will range from 31° to about 36° as the change over to snow occurs and will slowly fall overnight.  With temperatures in the lower 30s the snow that does fall will be heavy and wet in nature.  Winds will begin to pick up tonight, but hopefully there shouldn't be too many concerns with blowing and drifting just because the snow will have some weight to it.  The reason an advisory has been issued for all is because the heaviest of the snow will fall later this evening and overnight when there won't be a lot of traffic on the roads.  The snow should be winding down by daybreak Friday.