Wed-Thur, Feb 16-17th Winter Storm Update #4

(10:30PM Wednesday - 2/16/22) A winter storm will continue to impact the region and state, tonight through Thursday evening. This winter storm is expected to produce a swath of accumulating snow/sleet/ice, heavy rainfall with minor flooding potential, and an isolated severe t'storm risk across the region and state during this time.

Summary...
Over the past several days model guidance has been honing in on the potential for a winter storm to affect the region and state through Thursday. A large majority of model guidance has shown a consensus solution for the past day or so, and lingering outlier model guidance has finally come into agreement as well. Even so, as the winter storm continues to unfold some changes to the forecast are still possible. Stay tuned to updates over the next several days regarding this winter storm.

​A cold front has been moving through the region today and will continue to tonight, associated with a storm system moving through Southern Canada. This frontal boundary will become nearly stationary by Thursday morning, near the Ohio Valley in the region and Southern Illinois. Furthermore, a storm system will develop in the Southern Plains tonight, and will then track through the Ohio Valley on Thursday, and eventually into the Northeast on Friday. This storm system will bring a renewed push of precipitation and main impacts of this period across the region and state, Thursday morning through Thursday evening.

​Wintry (Snow/Sleet/Ice) Aspect Forecast...
Tonight - Thursday Morning, Feb 16-17th ~ Cold Front/Lead Wave Event:
A cold front has been moving through the region today and will continue to tonight, associated with a storm system moving through Southern Canada. This frontal boundary will then become nearly stationary by Thursday morning, near the Ohio Valley in the region and Southern Illinois. Precipitation in the form of rain developed ahead of the cold front, across portions of Missouri, Iowa, Northern/Central Illinois and Wisconsin this afternoon. This area of rain continued to expand as it further developed and pushed northeastward, spreading into other portions of Northern and Central Illinois this afternoon and evening. This activity will continue across Northern and Central Illinois tonight, and has also started to push into Southern Illinois as well early tonight with it expected to continue overnight tonight. Isolated to scattered t'storms will be possible with this activity across much of the state through tonight. Colder air has started to filter in behind the cold front across Northern and Western Illinois, with this expected colder air expected to continue to push southward behind the cold front overnight tonight. As this colder air filters in, rain will transition to a mix of rain/freezing rain/sleet/snow across portions of Northern and Western Illinois overnight tonight, and then continuing into Thursday morning. Some snow/sleet/ice accumulation will be possible across portions of affected areas of Northern and Western Illinois, tonight into Thursday morning. Windy conditions featuring wind gusts of 30-45MPH that had been in place much of the day across the state have subsided this evening, with winds remaining lighter overnight tonight.

Thursday Morning - Thursday Evening, Feb 17th ~ Main Winter Storm Event:
​As the main storm system moves through the region, an associated renewed push of precipitation will move across the state and region with the main impacts expected, Thursday morning through Thursday evening. This renewed push of precipitation, in the form of snow/sleet/ice, will move into Western Illinois by mid morning Thursday. This area of precipitation will then spread across portions of Northern and all of Central Illinois late Thursday morning through mid Thursday afternoon, before ending Thursday evening. A transition zone will set up much of the day on Thursday across portions of Central Illinois, generally between I-72 and I-70. Across this zone, precipitation types will from south to north will range from freezing rain to sleet to snow. This transition zone will eventually change over to snow for a time, before precipitation ends between mid Thursday afternoon into Thursday evening. North of this transition zone across affected areas of Northern and Central Illinois, most precipitation will fall as snow. Periods of moderate to heavy snow will be possible at times, with snowfall rates of 1"+ an hour likely at times. Additionally, windy conditions are expected Thursday morning into Thursday evening across a large portion of the state. During this time wind gusts upwards of 20-40MPH will be possible, which will cause some blowing and drifting snow for areas experiencing snow. 

​Below are the snowfall and ice forecasts for this winter storm.

​Severe T'Storm Risk/Heavy Rain/Flooding Aspect Forecast...
Thursday Morning - Thursday Evening, Feb 17th ~ Severe T'Storm Event:
​The main risk for an isolated severe t'storm risk will exist across far Southern Illinois, Thursday morning into Thursday afternoon. Areas of rain and isolated to scattered t'storms will be ongoing Thursday morning across Southern Illinois, in the vicinity of a nearly stationary frontal boundary in place. An isolated severe t'storm cannot be ruled out with this activity. As the main storm system moves through the region, an arc of rain and t'storms will accompany the low pressure and cold front that sweeps across Southern Illinois, Thursday morning into Thursday afternoon. Ahead of this activity, an environment will be in place supportive of some severe t'storm risk with this activity. This environment will feature marginal instability of up to 500J/KG, dew points in the mid 50's to low 60's, good shear, good forcing, and modest lapse rates of 5.0-7.0C. This environment will be supportive of upwards of an isolated severe t'storm risk (levels 1) across far Southern Illinois. Damaging winds, hail and an isolated tornado will be the severe weather threats.

This Afternoon - Thursday Evening, Feb 16-17th ~ Heavy Rain/Flooding Event:
Persistent periods of rainfall are expected across the southern half of the state tonight through Thursday afternoon, associated both with a frontal boundary becoming stationary across Southern Illinois and the main storm system moving through. During this period of time, periods of heavier rainfall will be possible. Widespread rainfall totals of 1-3" are expected across the southern half of the state during this period of time, with locally higher amounts possible. Due to the combination of frost depth/frozen ground and the expected rainfall, some localized/minor flooding will be possible for some areas. Further north across Northern and Central Illinois, rainfall totals of 0.50-2.00" through early Thursday morning could lead to some instances of localized/minor flooding potential, due to frozen ground not being able to absorb lingering snow melt and rainfall.

Below are the severe t'storm and heavy rain/flooding forecast for this winter storm.

​​Impacts...
-An axis of of snow/sleet accumulation of 2-5" to 4-7" across portions of Northern and Central Illinois, with locally higher amounts likely. Snowfall amounts will taper north and south of this main axis.
-Ice accumulations of a glaze (Up to 0.10") across much of the state, with an axis of 0.10-0.25"+ ice accumulation across the heart of the state.
​-An isolated severe t'storm threat across Southern Illinois, Thursday morning through Thursday afternoon.
-Widespread heavy rainfall across the southern half of the state, with widespread rainfall totals of 1-4" expected. These rainfall totals could cause localized/minor flooding potential for affected areas.
-Widespread travel impacts likely across much of the state, Wednesday night through Thursday evening.

JP