Major Winter Storm With Snow, Sleet, Ice And High Winds This Weekend (Fri-Sat, Jan 10-11th) Update #7

(11:45AM - 1/10/20) A complex scenario is unfolding across the region in the coming days, with a few disturbances and then a main storm system expected to push across the region. During this period all of the following will be possible across the state... Snow, sleet, ice, heavy rain, flooding, high winds and severe t'storms. This post will be directed towards the snow, sleet, ice and high wind aspect. For information regarding the heavy rain, flooding, high wind and severe t'storm aspect...please read the update at the following link: https://www.illinoisstormchasers.com/forecasts/major-winter-storm-with-heavy-rain-flooding-high-winds-and-severe-tstorms-late-weekweekend-thur-sat-jan-9-11th-update-5

​**With this update...Based on model guidance and observations from last night and this morning, we have shifted ice axis a bit northwestward, and have increased snowfall accumulation across portions of Northern Illinois due to a more favorable setup for snow Saturday afternoon-night.

Why the changes? Quite simply...Model guidance has significantly struggled with trying to resolve the wintry side of this event. We believe (Hope) guidance is finally honing in on a solution, but will continue to monitor both guidance and observations as the event gets going, and will fine-tune the forecast if needed.**

Friday evening-Saturday afternoon...
​As a large area of rain spreads northward across the state today, colder air will be filtering in southward behind a cold front that will have stalled across Central Illinois. This will allow the rain that pushes northward to eventually change over to a mix of snow, sleet and freezing rain across first Northwest Illinois between 9PM-1AM, then Western and North-Central Illinois between 11PM-4AM. A change-over to mixed precip will not occur across Northeast Illinois until 4AM-9AM. A lengthy period of freezing rain and sleet is likely in an axis across the aforementioned areas, from the mentioned change-over times through Saturday afternoon. The northern portion of this axis may also receive snow for a period of time as well. Ice totals during this period will likely range from 0.10-0.50" across the main axis, with locally higher amounts possible. Snow/sleet accumulation upward of 1-3" will be possible as well for the aforementioned areas. In addition to the mixed precipitation, high winds are expected as well, with wind gusts of 25-45mph being possible across much of the state during this time-frame, with isolated higher wind gust sin excess of 45mph being possible. Tree damage and power outages will be possible, due the combination of ice accumulation and high winds. 


**It should be noted that the forecast during this time-frame (Fri Eve-Sat Aftn) is very tricky. Slight changes in surface and atmospheric temperatures, by even 1 degree or so, could me more/less ice accumulation or more/less sleet accumulation. In other words, instead of being a low/moderate amount of both sleet and ice...there is some potential this could turn into either a major sleet or major ice storm. Trends in model guidance and observations as the event unfolds will monitored closely for this potential.**

Saturday afternoon-Saturday night...
As the main storm system strengthens and lifts northeastward through the region, a large area of snow will move across Northern and Central Illinois Saturday afternoon through Saturday night. A period of heavy snow will be likely in the vicinity of Saturday evening for some of these areas, with 1-2"/hr snowfall rates and thundersnow being possible. Snowfall totals across portions of Northern Illinois will range between 3-6", with amounts tapering east/southeast across Western and Northeast Illinois. In addition to the snow, high winds will continue to be possible, with 25-45mph winds gusts likely, and isolated higher wind gusts in excess of 45mph being possible. This will likely create blowing and drifting snow for aforementioned areas.

Final event snowfall totals will greatly range across Western, Northwest and North-Central Illinois...From 3-7" in the main axis across Northern, tapering eastward with a gradient across Western and Northeast Illinois.

Final event sleet totals of a coating to 1.5” will be possible across Western, Northwest and North-Central Illinois.

Final event ice totals will range from upwards of 0.10-0.50" across Northern and Western Illinois, with isolated higher amounts being possible.

Below are the TAM snowfall, ice and high wind forecasts for this period.

JP

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