(11:45AM - 3/17/21) A storm system will be moving through the region today through Thursday, bringing a low end and isolated severe t'storm threat to the southern half of the state and high winds to Northern and Central Illinois.
A storm system will move from the Plains today on into the Ohio Valley on Thursday. The northern side of a larger and more significant severe t'storm risk to the south will reach into the southern half of the state, with a low end and isolated severe t'storm threat expected this afternoon through tonight. Additionally, a period of high winds are expected across Northern and Central Illinois, this evening through Thursday night.
Areas of rain and t'storms have been spreading across the state this morning. A warm front will be lifting northward through Southern Illinois this afternoon. In the wake of the early activity and with the warm front lifting northward, a marginal environment will develop. This marginal environment will feature low instability, modest moisture and great shear. Scattered showers and t'storms that develop along a cold front across Missouri and Arkansas during the afternoon, will spread across the southern half of the state later this afternoon through early Thursday morning. Given the aforementioned marginal environment in place, a low end severe t'storm threat will exist with this activity, with isolated severe t'storms being possible. Hail, damaging winds and an isolated tornado will be possible with any severe t'storm. It should be stressed that this will be an isolated overall risk, with a much higher and more significant severe t'storm event expected to the south, across MO/AR/TN/LA/MS/AL.
In addition the the severe t'storm potential, windy conditions are expected this evening through Thursday night across Northern and Central Illinois. High winds aloft, characterized by a low level jet of 50-70KT, will be in place. With ample mixing depth int he atmosphere, a corridor of high winds are expected. The jet aloft and mixing level will support northeasterly wind gusts upwards of 35-55MPH in a corridor across Northern and Central Illinois, this evening through Thursday evening...Which locally higher wind gusts in excess of 55MPH being possible. This period of highest winds will be from tonight through Thursday morning.
Below is the severe t'storm and wind forecasts for this event.