Friday morning concerns

Skies will remain sunny through the afternoon before clouds start to creep back in later this evening.  The next low/shortwave is already moving out of southwest Canada and will track southeast through Iowa and pretty much right over the Wisconsin/Illinois border.  This low is currently forecast to track just a bit further south than the one this morning and looks to have a bit more moisture with it.  There are a couple critical elements we need to look at in helping us determine just what type and how much precipitation will fall.  Temperatures tonight will likely fall into the low 30s ahead of another warm front that will move through northern Illinois.  Precipitation will begin to move in after midnight tonight and possibly fall as rain early on.  Forecast soundings, which are like a snapshot of the different layers of the atmosphere, indicate the temperature profile to be above freezing aloft, however near freezing at the surface.  Initially mixed with the rain could be another dose of light freezing rain or sleet.  There will likely be a mix or change over to a wet snow as the low moves closer towards daybreak Friday.  It's even possible that a slushy one to two inches of snow will be found across southern Wisconsin.  Another factor at play will be the dew points.  Typically, when you have a dew point that's below 30° your atmosphere is likely able to support what is known as 'evaporative cooling'.  The slightly dry air would allow the rain to evaporate and since evaporation is a cooling process, the surrounding air would cool allowing for a change over to wet snow.  There could be an additional rain/snow mix going into the early afternoon Friday.