A major storm system will be developing over the next 48 hours as it travels and intensifies from North Dakota Monday morning to off the Virginia coast Wednesday. This may become a major Nor'easter Thursday and Friday. The storm will be a combination of low pressure centers over North Dakota and Oklahoma Monday afternoon to a deepening low over extreme western Kentucky by Tuesday morning. This looks to be the last in a series of storms that have come in from the Pacific and moved over the country the last two weeks with very heavy bands of snow.
For the Chicago metro area, mainly the central and southern sections, this will be the heaviest snowfall of the season. Far northern sections over Lake county received from 10-11 inches last week. However, for the city and south the largest snowfall so far this winter has only been in the 4-5 inch range. For the metro area the snow will be a product of the deepening strong upper level trough over North Dakota moving to southern Illinois Tuesday evening as a closed upper level low.
Contrary to all the forecast challenges from the storm last week, this system looks a lot easier to diagnose. All the upper level lows (850, 700, 500mb) will move south of the area, surface temperatures will be just below freezing, there will be some frontogenesis aloft with slant wise instability, very strong Q-vector convergence aloft, and a 100mb deep snow dendritic growth zone. In other words, a lot of dynamics aloft working to produce a heavy snow over the area. The graphic shows the GFS model forecast Tuesday at 3:00 p.m. CST.
There will be a few flakes this evening and little light snow late tonight, but the main snow looks to begin over the metro area just after the morning rush. Moderate to heavy snow will fall from mid-morning to evening. Snow will taper off after dark and be mostly done by around midnight. There will be times from late morning to evening where snowfall rates will be 1+ inches. I am looking for a general 8-10 inches, with some local 12 inch amounts possible due to possible banding from the frontogenesis aloft. Most likely areas to see the heaviest snow would be the south part of the metro area for a change.
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