Wed-Thur, Feb 16-17th Winter Storm Update #5

​(9:00AM Thursday - 2/17/22) A winter storm will continue to impact the region and state, this evening. This winter storm will produce a swath of accumulating snow/sleet/ice, heavy rainfall with localized to scattered flooding potential, and an isolated severe t'storm risk across the region and state during this time.

Summary...
A winter storm continues to affect the state and region today. Even as this winter storm is unfolding and an overall consensus solution had been in place within model guidance, there still has and continues to be some disagreement on how things will continue to unfold today regarding this winter storm. With that said, the overall going forecast is on track with some minor adjustments needed based on real time observations. These real time observations support the overall forecast, and consensus solution on hi-res/short term model guidance.

​A cold front that moved through the region Wednesday and Wednesday night associated with a storm system moving through Southern Canada stalled out near the Ohio Valley in the region and Southern Illinois. A storm system developed in the Southern Plains Wednesday night, and will be tracking through the Ohio Valley today, and eventually into the Northeast on Friday. This storm system is bringing a renewed push of precipitation and main impacts of this period across the region and state, this morning through this evening.

​Wintry (Snow/Sleet/Ice) Aspect Forecast...
This Morning - This Evening, Feb 17th ~ Main Winter Storm Event:
​As the main storm system is moving through the region today, an associated renewed push of precipitation is also moving across the state and region with the main impacts expected, this morning through this evening. This renewed push of precipitation, in the form of snow/sleet/freezing rain/rain has been spreading into West-Central and Southwestern Illinois this morning. This area of precipitation will continue to spread across portions of Northern and all of Central Illinois through late this afternoon, before ending this evening. A transition zone has set up and will be in place much of the day today across portions of Central Illinois, generally near and 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 this evening. North of this transition zone across affected areas of Northern and Central Illinois (Near/north of I-72), most precipitation will fall as snow. Periods of moderate to heavy snow is likely at times, with snowfall rates of 1-2" an hour likely at times. Additionally, windy conditions are expected this morning into this 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 and near blizzard conditions at times. 

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

​Severe T'Storm Risk/Heavy Rain/Flooding Aspect Forecast...
This Morning - This Afternoon, Feb 17th ~ Severe T'Storm Event:
​The main risk for an isolated severe t'storm risk will exist across far Southern Illinois, this morning through this afternoon. Areas of rain and isolated to scattered t'storms have been ongoing this 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 today, an arc of rain and t'storms will accompany the low pressure and cold front that sweeps across Southern Illinois, this morning through this 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 low 50's to around 60, 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. It should eb stressed that this is a very low and very isolated severe t'storm risk. Damaging winds, hail and an isolated tornado will be the severe weather threats.

Wed Afternoon - This Evening, Feb 16-17th ~ Heavy Rain/Flooding Event:
Persistent periods of rainfall have been occurring across the southern half of the state since yesterday afternoon, with additional periods of rainfall expected to continue through later this afternoon. This activity is 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. Rainfall totals of 1-3" have already occurred across the southern half of the state, with some reports of localized flooding. Including additional rainfall expected, widespread final rainfall totals of 1-4" 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, localized to scattered flooding is likely across the southern half of the state. Further north across Northern and Central Illinois, rainfall totals of 0.50-1.50" occurred Wednesday afternoon through early this morning, which lead to some instances of localized/minor flooding, 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 possible. Snowfall amounts will taper north and south of this main axis.
-Ice accumulations of a glaze (Up to 0.10") across a large portion of the state, with an axis of localized 0.10"+ ice accumulation across the heart of the state.
​-An isolated severe t'storm threat across Southern Illinois, this morning through this afternoon.
-Widespread heavy rainfall across the southern half of the state, with widespread rainfall totals of 1-4" expected. These rainfall totals will cause localized to scattered flooding potential for affected areas.
-Widespread travel impacts likely across much of the state, through this evening.

JP