Significant Winter Storm Impacting The State Fri-Sat, Jan 17-18th Update #10

(2:00PM - 1/17/20) A storm system will move through the region today through 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 large portion of the state. Additionally, high winds will be of a concern as well tonight through Saturday, along with a low flood threat across the heart of the state.

Synopsis...
A storm system cutting generally west to east across the Midwest is underway, with accumulating snow/sleet/ice occurring and expected across a large portion of the region.

​**As was mentioned in previous updates, model guidance has trended a higher with snow and ice accumulations across portions of the state the past few cycles, namely across Northern Illinois. After watching the storm system unfold across states to the west this morning and early afternoon with real-time data/observations, have indeed elected to raise snow/sleet and ice accumulations a bit from our previous updates, once again namely across Northern Illinois. We are not going as high as some model guidance would suggest, holding on the side of caution towards the lower end of guidance...due to some continued concern over how quickly a change over in precipitation types occurs. Will continue to monitor real-time data/observations should any significant changes look needed, otherwise it will be short term/impact updates from here on out for the duration of the event.**

This morning-tonight...
Precipitation has entered Northwest and Western Illinois as snow early this afternoon, with a mix of snow/sleet/freezing rain entering Southwest Illinois. Precipitation is expected to steadily overspread the rest of the state the next several hours. A several hour period of snow to sleet to freezing rain will occur across much of the state, with the exception being Southern Illinois, which may see mostly rain. This wintry mix will continue through this afternoon and into this evening across a good portion of the state, before precipitation transitions to rain from south to north across the state tonight. Snow/sleet accumulation during this period will range from 2-6" across Northern Illinois and a dusting to 3" across portions of Central Illinois. Ice accumulation of 0.10-0.25"+ is likely across a good portion of the heart of the state.

Friday night-Saturday afternoon...
A wintry mix of snow/sleet/freezing rain will transition to rain across Central Illinois earl to mid tonight, with the wintry mix expected to continue across Northern Illinois well into the night. By very late tonight and early Saturday morning, precipitation will have fully changed over to rain across just about the entire state, the exception being far Northern Illinois. 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 snows/sleet accumulation of a dusting to 2" and ice accumulation of a glaze to 0.20" will be possible across Northern Illinois during this time. It should be noted that a period of high winds is likely across the state from tonight through early Saturday night. Wind gusts across the state during this time will likely be in the 25-50MPH range.

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

Final snow/sleet totals over much of Northern Illinois will range from 2-6", with locally higher amounts possible. Snow/sleet totals of a dusting to 3" will be likely across Central Illinois. Ice totals will likely range from 0.15-0.30"+" across much of the heart of the state, though locally higher amounts possible within this axis. The combination of snow/ice/high winds may lead to some power outages and tree damage across portions of Northern and Central Illinois. Additionally, precipitation totals of liquid value of 1-2"+ are likely up through the heat of the state. These high precipitation totals, combined with the heavy rainfall from the storm system last weekend, will lead to a low end flood threat. 

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

JP

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