snow update

A quick update as this storm comes together -- it's actually pretty impressive. 

No significant change to the outlook for the city and especially downtown. A couple of inches would be toward the high end. Warm pavement and the warming effect of the lake could keep precip more to the liquid side and/or limit accumulations. Rain will eventually shift to snow and it might look impressive at times, but it's not likely to pile up.

To the west, however, conditions look like to deteriorate more than previously expected. The center of the low continues to intensify and drive south. The axis of heaviest snow -- which has laid down more than a foot in Sioux Falls, SD and across portions of Iowa -- may now target northern Will County, DuPage, portions of Kane, and far W/NW Cook County. The same NEward gradient exists, as snow rates will fall as you travel to the SE (especially in areas within a few miles of the lake). Warm surface temps (near or just above 32F) also give me pause.  But there is growing confidence that very strong snowfall rates (well above 1" per hour) will overcome other factors. Many suburban areas could see 4-6" of snow. Some of the probabilistic models (see below) really like the odds for >6" in the darker oranger and reddish areas. 

No major change to timing. The rain will commence after sunset, with a transition to snow near midnight. The heaviest snow will fall between midnight and mid-morning, with the snow tapering after noon.