A challenging forecast for Chicago, but one that brings plenty of great news to the snow drought.  The latest models all agree on amounts ranging from 5" upwards to 10" possible.  The threat for more is certainly possible as we will get into.  But the snow will begin at 6am and the thermal profiles looks like this:

The start time will feature a snow and sleet mix, but overall most of the precip will be evaporating before hitting the ground.  This will allow melting induced cooling/evaporational cooling to take place helping to cool the low to mid levels.  

By game time for this event we see this:

The heavy snow this time around will have a slighlty better envvironment.  The convectively unstable layer around 600mb willl be released and produce some good snow rates as the lifting makes it into the dendritic snow growth zone.  MUCAPE values of 60-70J/Kg is pretty significant and could lead to snow rates around 1-1.5"/hr.  Could be more if we can extend this more into the whole snow growth zone instead of the lower half of it.

The storm never wants to end! As the storm pulls away it phases with another disturbance coming in from the west:

Notice how the upper level low redevelops to the west and places Chicago in an extended period of precip in the deformation zone/lake enhancement with fetch off Lake Michigan.  As this is happening the low level lapse rates become steeper adding a little dynamic element into the the mix.  

Summary:

Start Time: 6-8AM CST

Heaviest Snow: Noon-midnight

End- 6PM Wednesday with Lake enhancement

Total Snow Accumulation: 5-10" could see more if this works out as planned with the phase.