Well, I've had 24 hours to cool off from the epic snow storm model parameter induced widespread panic we faced Sunday afternoon. Going to lower my storm total from 20" down to about 15" total for DeKalb, IL. Looking at 1-3" tonight with the first wave of warm air advection snowfall. Tuesday late afternoon the first bands of snow start making their way into northern Illinois before things pick up in earnest by late evening. I originally wished I was a little further south near Interstate 80, but am becoming a little more content with my placement here. Once you get into central Illinois near Interstate 72 you reach the rain/snow cutoff line. This line will be bouncing around between a heavy wet snow, sleet, and perhaps some freezing rain. This will have a chance to dramatically cut down on snow totals near Interstate 72. In Champaign, I'm going with 8" total accumulation.
Totals should dramatically increase as you head northwest. My bullseye at this point for snow maxima is west central into north central Illinois. Anywhere from Quincy/Macomb to LaSalle, IL I'd give a shot of 14-18" with embedded higher amounts. I was initially worried about my location in DeKalb being too far north, and that very well may be the case. However, once you near Interstate 80, from LaSalle eastward toward Kankakee you start running the risk of being dry-slotted. The dry slot on these powerful systems has a habit of working it's way northward and choking off the precipitation. Whether this happens or not again remains to be seen, but it's another key element in how widespread the heavier snow totals wind up.
All that said, in the deformation zone north of the dry intrusion and surface low, a benefiting factor for higher snow totals will be the strength of the system as it rapidly deepens/occludes, strongly forced bands of at times convectively induced heavy snow bands. Thunder and snow fall rates nearing 3 inches per hour are possible in these areas, and the placement of these bands will be the main deciding factor in snow totals. At this time I believe the best chance for an extended period of these heightened snow fall rates / thundersnow should be along that aforementioned Quincy to LaSalle line.
This is fairly disorganized, but I don't pretend to be a big winter weather guy. To summarize I suppose, along Interstate 72 in central Illinois I believe the composite parameter projections of 20+ inches of snow are likely being overdone and will be hampered by transitions between heavy snow/sleet/freezing rain. 8" forecast stands for Champaign. Further north, periods of very heavy snow Tuesday evening into Wednesday morning with a band of 14-18" with embedded higher amounts from Quincy to LaSalle, IL. Further east, potential dry-slotting lowers totals from Pontiac to Kankakee and eastward. I'll go with 15" total for DeKalb, including the 1-3" forecast for tonight. I didn't even touch on the ice storm potential with this system, but the real story could easily become ice accumulations with very strong gradient winds exacerbating that problem on Wednesday. If ice accumulations near 0.5"-1" along Interstate 70, as the surface low pushes to the east and strong northerly winds near 30 mph with higher gusts, power failures could become the norm.
I'm not sure what I'll have in the way of documenting the storm as I don't plan on driving anywhere for the next 72+ hours, but I'll be updating periodically with whatever little bit I have to share from the home stead in DeKalb in north central Illinois.
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