Mon-Tue, Feb 21-22nd Winter Storm Update #1

​​(9:45PM - 2/21/22) A winter storm is set to impact the region and state, tonight through Tuesday afternoon. This winter storm is expected to produce a swath of accumulating freezing rain/ice, heavy rainfall with localized to scattered flooding potential, and an isolated to sporadic severe t'storm risk across the region and state during this time.

Summary...
Model guidance continues to be in good agreement regarding this winter storm, thus making for a high confidence forecast. With this update we have upgraded severe t'storm probabilities across Southern Illinois, as well as increased flood probabilities across Southern Illinois...As confidence in the given forecast scenario grows based on real time observations today/tonight.

​A storm system will develop across the Plains tonight, with it then tracking across Illinois and through the Midwest and Great Lakes on Tuesday, and eventually into the Northeast by Wednesday morning. This winter storm is expected to produce a swath of accumulating freezing rain/ice, heavy rainfall with localized to scattered flooding potential, and an isolated to sporadic severe t'storm risk across the region and state during this time.

​Wintry (Snow/Sleet/Ice) Aspect Forecast...
Tonight - Tuesday Afternoon, Feb 21-22nd ~ Freezing Rain/Ice Event:
The area low pressure with this storm system is expected to move across Northern Illinois early Tuesday morning through Tuesday afternoon. This will limit the wintry side of the storm system to far Northern Illinois, near the Illinois/Wisconsin border. Across this area, temperatures will be colder at the surface, with a northerly flow on the north side of the storm system. As several periods of precipitation develop and move across this area tonight through Tuesday afternoon, freezing rain is possible for areas closer to the Illinois/Wisconsin border. An isolated t'storm can't be ruled out either, in which case it would be an instance of thunder-freezing rain. It is also possible that if an isolated t'storm occurs, that some sleet would be possible for a time due to convective processes. 

​Below is the ice forecast for this winter storm.

​Severe T'Storm Risk/Heavy Rain/Flooding Aspect Forecast...
Tonight - Tuesday afternoon, Feb 21-22nd ~ Severe T'Storm Event:
​The main risk for an isolated to sporadic severe t'storm risk will exist across Southern Illinois, tonight through Tuesday afternoon. A complex of rain and t'storms has developed this evening and early tonight across portions of Oklahoma and Texas. This complex is expected to grow upscale as it pushes northeastward, eventually moving across Southern Illinois later tonight through Tuesday 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 low instability of up to 1,500J/KG, dew points in the mid 50's to low 60's, good shear, good forcing, and good lapse rates of 5.5-8.0C. This environment will be supportive of upwards of an isolated to sporadic severe t'storm risk (levels 1-2) across Southern Illinois. Damaging winds, hail and an isolated tornado will be the severe weather threats.

Tonight - Tuesday Afternoon, Feb 21-22nd ~ Heavy Rain/Flooding Event:
The same complex of rain and t'storms that is expected to move across Southern Illinois tonight through Tuesday afternoon producing a severe t'storm threat, will also bring a heavy rain/flooding threat to the same areas. This complex is expected to produce heavy rainfall, with widespread rainfall totals of 1-3" in a corridor across Southern Illinois during this period of time, with locally higher amounts possible. Due to the combination of recent heavy rainfall/flooding and the expected rainfall, localized flooding is expected.

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

​Impacts...
-Ice accumulations of a glaze (Up to 0.10") across far Northern Illinois near the IL/WI border, with an axis of 0.10"+ ice accumulation across far Northwest Illinois.
​-An isolated to sporadic severe t'storm threat across Southern Illinois, later tonight through Tuesday afternoon.
-Widespread heavy rainfall across Southern Illinois, with a corridor of widespread rainfall totals of 1-3"+ expected. These rainfall totals could cause localized to scattered flooding potential for affected areas.
-Travel impacts likely both for far Northern Illinois due to the freezing rain and across Southern Illinois due to the heavy rain/flood potential.

JP