(1:15PM - 11/25/18) The expected major storm system is now pushing into the region, with precipitation ongoing across portions of Northern and Central Illinois this morning and early afternoon. The only real change this update is to tighten snowfall gradients on our likely final TAM snowfall map and the increased likelihood of blizzard conditions.
Most of the precip this morning has been in the form of rain. As colder air filters in and cooling occurs from heavy precip rates, precip is now slowly transitioning to snow across portions of Northern Illinois. Snow will continue across portions of Northern Illinois through this afternoon, before becoming more widespread to encompass just about all of Northern Illinois and portions of Central Illinois this evening and into Monday morning. During the height of the storm, snowfall rates will likely reach 1-3" per hour across portions of Northern and Central Illinois. Thundersnow will also be possible during the height of the storm as well for some areas.
Another major concern is windy conditions, with wind gusts of 30-50mph likely across portions of Northern and Central Illinois this afternoon into Monday morning. The combination of heavy snow and high winds will create blizzard conditions across a large area this afternoon into Monday morning. Additionally, given snow with this system will be of high water content, some tree and powerline damage may occur.
The main swath of snow will be across much of Northern and portions of Central Illinois. Within this main axis, a large corridor of 9-12" of snow is likely. It is also likely that there will be pockets of 12-15" within that corridor.