Winter Storm To Impact The State Fri-Sat, Jan 17-18th Update #8

​(9:30PM - 1/16/20) A storm system will move through the region on Friday and Saturday, bringing with it a wide range of precipitation types across the state, including snow, sleet, ice and rain. Light to moderate accumulations of wintry precipitation are likely across a good portion of the state. Additionally, high winds will be of a concern as well.

Synopsis...
Model guidance has been and continues to be in decent agreement regarding this period. A storm system cutting generally west to east across the Midwest is expected, with accumulating snow/sleet/ice expected across a large portion of the region. Once again, there are minimal changes needed with this update. In case any one missed it, we did increase expected ice accumulation amounts across the heart of the state in the update this afternoon, due to high model guidance agreement and overall increasing confidence in higher ice totals coming to fruition.

It should also be mentioned that there continues to be a trend among some model guidance for precipitation to stay as snow for a longer period of time across portions of Northern Illinois. Should this trend continue and look more likely, then an increase in expected snowfall amounts would be needed across portions of Northern Illinois. Two significant points arguing against higher snowfall totals is overall short duration and dry air issues. For now we will not make changes and will stick with the going forecast, closely monitoring the situation.

Friday morning-Friday night...
Precipitation is likely to begin as snow as it enters Northwest, West and Southwest Illinois around midday Friday. As precipitation then spreads across the state Friday afternoon, a several hour period of snow to sleet to freezing rain will occur. This wintry mix will continue through the afternoon and into the evening, before precipitation transitions to rain from southwest to northeast across the state Friday night. Snow/sleet accumulation during this period will range from 1-4" across much of Northern and portions of Central Illinois, with locally higher amounts possible. Ice accumulation of 0.10-0.25"+ is likely across a good portion of the heart of the state.

Friday night-Saturday afternoon...
By later Friday night and early Saturday morning, precipitation will have fully changed over to rain across just about the entire state. Rain will then continue into Saturday afternoon across Central and Southern Illinois, before ending from west to east across the state. The exception will be across Northern Illinois, where rain will change back over to snow by mid Saturday morning, continuing into the afternoon, before coming to an end. Additional snow accumulation of a dusting to 1.5" will be possible across Northern Illinois during this time. It should be noted that a period of high winds is likely across the state early Saturday morning through early Saturday night. Wind gusts across the state during this time will likely be in the 25-45mph range.

Below are maps featuring estimated start times of wintry precipitation on Friday, and then estimated times of the change-over to rain Friday night. These visual representations will be much better than several sentences of text, which gets confusing.

Final snow/sleet totals over much of Northern and portions of Central Illinois will range from 1-4", with higher totals likely near the Illinois/Wisconsin border and far Northwest Illinois. Ice totals will likely range from 0.10-0.25"+" across much of the heart of the state, though locally higher amounts possible within this axis. Additionally, precipitation totals of liquid value of 1-2" are possible across Central Illinois. These high precip totals combined with the heavy rainfall from the storm system last weekend, will likely lead to a low end flood threat.

​Below are the TAM snow/sleet, ice and flood forecasts for this event.

JP

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