All in a day: Heavy snow to tornadoes

From blizzard-like conditions to potential tornadoes, Thursday's weather will be anything but lacking.  Let's first start with today - strong south winds will give temperatures today a boost close to 40 degrees, but keep blowing and drifting snow issues on east/west roads.  A weak cool front settles south tonight only bringing with it a few extra clouds.  Temperatures behind the front won't be quite as warm Wednesday, but we'll still manage to climb into the middle 30's.  The warmer air, and especially the warmer south winds - will allow for some snow melt today and Wednesday ahead of Thursday's system.

Thursday's system is going to pack quite a punch over the lower 48.  Strong dynamics within the atmosphere will allow low pressure to quickly intensify during the day Thursday producing unseasonably warm air further downstate with a severe weather threat from central Illinois through Indiana and further south, to heavy snow and blizzard conditions across parts of Iowa and Minnesota.  Somewhere in the middle is where northern Illinois and southern Wisconsin will lie leaving us with a potentially messy and slick day.

A couple of questions need to be answered as we get closer to Thursday to help us determine just exactly how warm we'll get and what type of weather we'll actually experience.  First: How quickly and how much of the current snow pack will we melt off by then?  Second: What will the track of the surface low pressure be?  Third: How strong will the warm air advection be and will it be strong enough to actually get us into the low 40's? 

As a warm front lifts into northern Illinois by daybreak Thursday, a mixture of freezing rain and cold rain will be likely.  It's also possible that a few elevated thunderstorms may be heard late Wednesday night and Thursday morning.  Any freezing rain threat will quickly turn to rain south of Rockford as temperatures climb into 40's.  Dew points will also rise during this time into the upper 30's to low 40's which could speed up the process of how quickly the snow melts.  If we combine that with heavy rain, flooding will become a big concern not only with the snow melt but also with ice jams on local rivers.  However, if temperatures remain in the middle 30's then there is a greater risk for freezing rain.  By Thursday evening a strong cold front will move in allowing cold air to quickly spill into northwest Illinois by Friday night with temperatures falling back below freezing.  Either way, Thursday is shaping up to be a very messy day, especially if we receive significant rain.  We'll continue to track this storm over the next 36 hours with further updates to follow.