(11:00AM - 6/17/21) Multiple disturbances will move through the region today through Saturday, bringing periods of severe t'storm potential to portions of the state, this evening through Saturday night.
Multiple disturbances will eject out of the Plains, and push eastward across the Midwest and Great Lakes, today through Saturday. These disturbances will bring periods of severe t'storm potential to portions of the state, this evening through Saturday night. Model guidance has been showing potential during this time frame for a few days now, and continues to be in fairly good agreement regarding the expected evolution. Only minor changes were needed with this update.
Thursday Evening-Friday Morning...
At least one or two disturbances are expected to eject out of the Plains and into the Midwest on today. This will lead to the development of severe t'storms this afternoon, across Western Wisconsin, Southern Minnesota and Northern Iowa. This activity is likely to grow upscale into at least one complex, which will then push east-southeast this evening through Friday morning. This complex(s) is expected to push across Northern Illinois overnight tonight. Ahead of this activity, an environment supportive of a severe t'storm threat will be advecting in. This environment will feature moderate instability of 2,000-4,000J/KG, dew points well into the 60's, good shear, good forcing, and high lapse rates of 7.5-8.5C. This environment will be supportive of upwards of a widely scattered to scattered severe t'storm risk (level 2-3) across Northern Illinois during this time. Damaging winds and hail will be the main severe weather threats.
Friday Afternoon-Friday Night...
The complex(s) of t'storms from Thursday night/Friday morning is expected to clear the state by later Friday morning, allowing for clearing and destabilization to occur. With another disturbance or two expected to move through the area and a frontal boundary expected to be draped across the heart of the state, a new round of showers and t'storms is expected to develop later Friday afternoon and evening across portions of Northern and Central Illinois. This activity will then push southeastward Friday evening into Friday night, affecting the heart of the state. An environment supportive of a severe t'storm threat will be in place. This environment will feature moderate to high instability of 3,000-5,000J/KG, dew points in the mid 60's to low 70's, good shear, good forcing, and high lapse rates of 7.0-8.0C. This environment will be supportive of upwards of a widely scattered to scattered severe t'storm risk (level 2-3) across the heart of the state. Damaging winds and hail will be the main severe weather threats, though an isolated tornado cannot be ruled out.
Saturday Afternoon-Saturday Night...
With a frontal boundary expected to be draped across Central and Southern Illinois and another disturbance set to move through, isolated to scattered showers and t'storms are likely to develop Saturday afternoon. This activity will then affect portions of Central and Southern Illinois into Saturday night. Some of this activity could pose a severe threat, and will be addressed in future updates.
Below is the severe t'storm forecasts for this event.