(10:30AM - 6/20/21) A storm system will move through the region today, bringing a severe t'storm risk to a large portion of the state from this afternoon through tonight.
A storm system moved through the Plains last night into this morning, and will move through the Midwest and Great Lakes today, and eventually into the Northeast by Monday. This storm system will bring a severe t'storm risk to a large portion of the state this afternoon through tonight. Model guidance continues to be in overall agreement regarding this event, with real time observations now supporting as well. Little change was needed with this update, as the going forecast is on track.
Two lead disturbances are moving across Iowa and Missouri this morning, and will move across Illinois this afternoon, and then into Michigan and Indiana by this evening. The regeneration and development of showers and t'storms associated with these disturbances is likely across portions of Northern and Central Illinois this afternoon. This activity will then spread eastward across portions of Northern and Central Illinois this afternoon.
Further west along the cold front and along any potential outflow boundary from early activity, additional showers and t'storms will develop this afternoon across Iowa, Missouri and Northwest/Western Illinois. This activity will spread eastward across a large portion of the state, late this afternoon through tonight.
For both aforementioned waves of severe weather potential... An environment supportive of a severe t'storm threat will be in place. This environment will feature moderate to high instability of 2,500-4,000J/KG, dew points in the mid 60's to mid 70's, high shear and strong forcing. This environment will be supportive of upwards of a widely scattered to scattered severe t'storm risk (level 2-3) across much of Northern and Central Illinois. Damaging winds, large hail and a few tornadoes will be the main severe weather threats.
Below is the severe t'storm forecasts for this event.