Mon-Wed, Feb. 11-13th Winter Storm Update #1

(12:30AM - 2/11/19) A winter storm will be affecting the state in many ways, starting this morning (Monday morning) into late Tuesday night or early Wednesday morning...

An area of rain ongoing at this time across Southern Illinois will begin to lift northward Monday morning. With colder surface temperatures in place, some of this may fall as freezing rain for a time across portions of Southern and Central Illinois Monday morning. as temps rise, this will turn to plain rain for these areas. Only a glaze of ice is expected.

​Precip will then push northward into Northern Illinois during the afternoon. All precip types will be likely across Northern Illinois during this event, including snow, sleet, freezing rain and rain. Model guidance is at a decent disagreement on exactly how things unfold across Northern Illinois, even less than 12 hours away from the storm beginning. At this time we will run with a blend of model guidance, which paints this picture... The aforementioned precip that moves northward from Central and Southern Illinois will make it into Northern Illinois during the afternoon. This will fall as snow across far Northwest Illinois, with a mix of snow/sleet/freeing rain elsewhere, with some plain rain mixing in for a time for areas south of I-80. This activity will continue into into Tuesday morning, before colder air wraps in and precip changes to snow for all areas, before finally ending by early Wednesday morning. As mentioned, this is a very complex scenario with a good amount of disagreement in model guidance. Small shifts in the storm track or small changes in warmer/cooler surface/aloft temps may lead to more or less of any given precip type. At this time we expected a north-south gradient of high/lower snow/sleet totals, from around 6" near the Illinois/Wisconsin border, to less than 1" south of I-80. An axis of 0.10-0.25" will run west-east across Northern Illinois as well, in the vicinity of I-80.

Across Southern Illinois, periods of heavy rain during the period will produce rainfall totals of 1-3" (Locally higher) across Southern Illinois. This new rainfall, combined with recent heavy rains, will lead to widespread flooding potential. An upgrade to higher heavy rain/flood risk is likely on our TAM.

Below are our updated TAM snowfall, ice and flood forecasts for the state for this event. As noted, the forecast across Northern Illinois is low-medium confidence, given the spread in model guidance. Further updates are likely as the situation becomes more clear.

​JP

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