Slippery conditions possible early Tuesday

11am Update:  The breaks in the high based cloud cover early this morning have allowed temperatures to rise into the upper 30s, so it's possible we may hit 40° this afternoon.  The difference between the temperature and dew point continue to increase so this will likely keep the fog development low for this afternoon.

Some drizzle or even a few light rain showers will be possible later this afternoon and evening as a cold front passes.  Temperatures today will range from the upper 30s/low 40s under mostly cloudy skies.

Once the front passes later this evening an area of low pressure will move in from the southwest overnight and pass just south of Chicago by daybreak Tuesday.  With temperatures in the upper 30s for the majority of the day any precip that does fall should remain in the liquid form.  Tonight, however, could be a different story.  Temperatures at the surface will likely fall into the upper 20s/low 30s overnight as winds shift around to the north/northeast.  Southerly winds will continue a few thousand feet above providing a relatively warm layer aloft so any precipitation that falls through that layer will remain liquid.  As it gets closer to surface it will be falling through a layer that is very close to 32°F (0°C) and this could cause the drizzle/light rain to freeze upon reaching the surface. 

This image is a forecast sounding from the National Weather Service's GFS for midnight tonight.  Notice how winds around 850mb and up remain from the southwest but then shift to the northeast below 850mb.  The northeasterly component to the wind will keep temperatures at the surface cooler than above allowing any precipitation that falls through that layer to potentially freeze upon reaching the surface.  One thing of note:  the atmosphere will remain fairly saturated in the lowest levels so should any freezing drizzle/rain form overnight it shouldn't last too long and we're not expecting major ice accumulation.  There could be a few slick spots, though, for your early morning commute.

Low pressure will slide just south of Chicago by daybreak Tuesday with cold air moving in behind it.  This will change over any mixed type of precipitation to all snow by Tuesday morning.  Depending on how quickly the snow falls and how fast the changeover is, there could be some accumulations by Tuesday evening.  As of right now it looks like anywhere between 1"-3" could fall area wide.  Winds will be gusty from the northwest and temperatures will go from the upper 20s in the morning down to the lower 20s by the afternoon.