Even though confidence is slowly increasing for a swath of significant snow accumulations somewhere across portions of or most of northern Illinois, this remains a tricky and fickle setup with the main wave still offshore the west coast and coming ashore later tonight, as you'll see below. An update on this potential winter storm follows below....
Area National Weather Service offices across portions of the Midwest, including across portions of northern Illinois have issued Winter Storm Watches (for the counties in blue below) the threat of significant snow accumulations. These are subject to change, potentially being upgraded to Winter Weather Advisories or Winter Storm Warnings, along with other counties being added on the southeast side.
Below is a long animation from late this afternoon through late Wednesday night, showing the main moving pieces and upper level systems as they progress through the region. The first upper level low will move into the state tomorrow and tomorrow night with mostly rain chances and some snow on the north end. The main system is coming ashore the Pacific Northwest tonight and will dig southeast across the Rockies and eventually through the plains and into the Midwest by Tuesday afternoon and evening. This northern stream upper level low will then strengthen as it phases with a system digging southeast across southern Canada during the day on Wednesday.
Below is another long animation from tomorrow evening through late Wednesday night, showing the entire evolution of what looks to be a potential scenario as things look now.
1. Snow will be possible across the northern portions of the state Monday night into Tuesday morning with accumulations of maybe an inch or two possible by Tuesday morning.
2. There could be a lull in activity before the upper level low digs into the region, leading to an increase in widespread snowfall by Tuesday afternoon and evening across portions of northern Illinois, including in and around the Chicago metro area. It is from mid-late Tuesday afternoon through Wednesday afternoon where the brunt of accumulating snow would take place, potentially falling at a heavy clip for a time Tuesday night into Wednesday morning. There is even the potential for thunderstorm which would lead to impressive snowfall rates of 1-2"/hr if that were to occur. Model guidance continues snow into the heart of Wednesday afternoon before eventually waning from west to east across the area.
This continues to remain a tricky forecast as previously stated and fore that reason we are waiting till tomorrow morning to issued our first TAM/expected snowfall totals map so tuned for continued updates. We still expect the heaviest snowfall amounts to be across northern Illinois.
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