Thur-Sat, June 17-19th Severe T'Storm Event Update #5

(10:30PM - 6/18/21) Multiple disturbances will continue to move through the region through Saturday, bringing periods of severe t'storm potential to portions of the state through Saturday night.

Summary...
Multiple disturbances will continue to eject out of the Plains, and push eastward across the Midwest and Great Lakes through Saturday. These disturbances will bring periods of severe t'storm potential to portions of the state, through Saturday night. With this update...Little to no change was needed for tonight's forecast, and for Saturday/Saturday night the biggest change was to increase severe probabilities to a level 2 severe t'storm risk across Southwest Illinois.​

Forecast...
Tonight-Early Saturday Morning...
While a few isolated severe t'storms have occurred this afternoon and evening across portions of Central Illinois, the main focus is tonight. With another disturbance moving through the area tonight and a frontal boundary expected to be draped across the heart of the state, new development of area of showers and t'storms are occurring early tonight across Southern Iowa, Northern Missouri and Central Illinois. Clusters of showers and t'storms are expected to push east-southeastward tonight into early Saturday morning, 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 large hail will be the main severe weather threats, though an isolated tornado cannot be ruled out.

Saturday Afternoon-Saturday Night...
A few lingering areas of showers and t'storms my be ongoing Saturday morning across Central and Southern Illinois, weakening and diminishing activity left over from Friday night. With a frontal boundary expected to be draped across the heart of the state and another disturbance or two set to move through, areas of showers and t'storms will develop Saturday afternoon across the heart of the state. This activity will spread east-southeastward across portions of Central and Southern Illinois, Saturday afternoon through late Saturday night. Of focus will be a corridor across Southwest and Southern Illinois, where a frontal boundary and outflow boundary may provide more of a focal point for slightly better potential. 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 6.0-7.5C. This environment will be supportive of upwards of a an isolated severe t'storm risk (level 1) across the heart of the state, and a widely scattered severe t'storm risk (level 2) across portions of Southwest and Southern Illinois.. Damaging winds and hail will be the main severe weather threats, though an isolated tornado cannot be ruled out.

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

Recap
Thursday Evening-Friday Morning...
As expected, a large complex of rain and t'storms developed across Western Wisconsin, Southern Minnesota and Northern Iowa Thursday evening. This complex featured numerous severe t'storms Thursday evening and early Thursday night across Western and Central Wisconsin and Southern Minnesota. This complex then pushed southeastward across Central and Southern Wisconsin, Northern Illinois, Northern Indiana and Southern Michigan, Thursday night into Friday early morning. While there were no severe t'storms that occurred while traversing Northern Illinois with this complex Thursday night and early Friday morning, some areas received strong non-severe winds of 45-55MPH, including across the Chicago metro area.

JP