Tuesday's Wintry Weather Update

7:00pm Update: The entire Stateline will be under a Winter Weather Advisory from 3:00am until noon on Tuesday with snow, sleet, and freezing rain possible for the morning commute. Regardless of what we see tomorrow, leave yourself some extra time getting out the door. Roads look to be messy in many spots. Check out the video update below for more details.

11:45am Update: A Winter Weather Advisory has been issued for Winnebago, Boone, McHenry, Ogle, Lee and DeKalb counties in northern Illinois and for Green, Rock and Walworth counties in southern Wisconsin.



The calendar may have switched over to March, but Mother Nature will remind us that it's still winter until March 20th.  Even then, we still get occasional reminders.

The weather will get a little messy in 24 hours and have an impact on Tuesday morning's commute.  As Meteorologist Kristin Cwynar discussed over the weekend, the threat for snow, sleet, freezing rain and rain will be present throughout the day Tuesday - with the greatest impact coming through the morning.

All will be quiet through late tonight as high pressure slowly slides southeast of Rockford.  As we head into the overnight, moisture will lift north from the Gulf but with temperatures still below freezing (32 degrees), snow will fall.  This looks to be after Midnight with snow spreading north between Midnight and 3am.  Southwest winds and a strong low level jet will allow temperatures a few thousand feet above to rise very close to, if not slightly above, freezing.  Temperatures at the surface, however, will remain below freezing through Tuesday morning.  This means snow overnight will mix with sleet, or completely change over to sleet, early Tuesday morning.  As the temperature continues to rise above freezing during the morning, the snow and sleet could change over to, or mix, with freezing rain through the morning commute.  By the afternoon, surface temperatures should be above freezing.  However, a mixture of snow/drizzle will still be possible across southern Wisconsin.


In anticipation of the wintry weather, a Winter Weather Advisory has been issued for Green, Rock and Walworth counties in southern Wisconsin late tonight through Tuesday evening.

So, let's time this out:

Timing: A mixture of snow & sleet will develop between Midnight and 3am Monday night.  This will spread from north to south by Tuesday morning.  Accumulations are not expected to be much as the snow will have a little more weight with it.  The snow and sleet will mix with freezing rain across northern Illinois until late Tuesday morning.  If temperatures warm above 32 degrees, the threat for freezing rain will decrease.  Southern Wisconsin may hold on to the snow/sleet/freezing rain mixture a little longer with temperatures right near, or slightly below, freezing.  By the afternoon, surface temperatures will warm above 32 degrees which will bring more of a drizzle/rain threat.  However, drier air moving in during that time will cut back on the amount of moisture left in the atmosphere.

Amounts: Snow/sleet amounts won't be much, but accumulations of 1" to 2" will be possible through Tuesday morning - especially if the snow occurs at a heavy burst.  From roughly 6am through 11am, freezing rain will be possible, but again, total atmospheric moisture will remain low, so any ice accumulation should remain under a tenth of an inch.   After Noon, a mix of drizzle/light snow will be possible ahead of a cold front that will swing through by Tuesday evening.

Impacts: Any snow that does accumulate could cause roads to be slick during the overnight and early Tuesday morning.  If freezing rain does mix in, untreated roads will become slick with minor ice accumulation possible.  As temperatures warm above freezing, this will melt any ice or snow that may still be on the roads.

Snow will melt over the next 36 hours, but the threat for flooding will remain low - although run off from the melting snow and a slow rise in local rivers & streams will be possible as the frost depth is still pretty deep in the ground.