Thur-Sat, June 17-19th Severe T'Storm Event Update #1

(9:30PM - 6/16/21) Multiple disturbances will move through the region Thursday and Friday, bringing the risk for severe t'storms to much of the state, Thursday evening through Friday night.

Summary...
Multiple disturbances will eject out of the Plains, and push eastward across the Midwest and Great Lakes on Thursday and Friday. These disturbances will bring a severe t'storm risk to much of the state, Thursday evening through Friday 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.

​Forecast...
Thursday Evening-Friday Morning...
At least one or two disturbances are expected to eject out of the Plains and into the Midwest on Thursday. This will lead to the development of severe t'storms Thursday afternoon, from Southern Minnesota down into Iowa. This activity is likely to grow upscale into at least one complex, which will then push east-southeast Thursday evening through Friday morning. This complex(s) is then expected to push across Northern Illinois, late Thursday evening through early Friday morning. 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 at least an isolated to widely scattered severe t'storm risk (level 1-2) 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 Friday afternoon, allowing for clearing and destabilization to occur. With another disturbance 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 across Central Illinois. This activity will then push southeastward Friday evening into Friday night, affecting portions of Central and Southern Illinois. Across Central and Southern Illinois, 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 at least an isolated to widely scattered severe t'storm risk (level 1-2) across Central and Southern Illinois during this time. Damaging winds and hail will be the main severe weather threats.

​Below is the severe t'storm forecasts for this event.

JP