Sun-Thur, Aug 8-12th Severe T'Storm Event Update #9

(9:00PM - 8/11/21) Several disturbances will continue to move through the region through Thursday, bringing daily severe t'storm potential to portions of the state, through Thursday night.

Summary...
Several disturbances will continue to move across the Plains, Midwest and Great Lakes through Thursday. These disturbances will bring severe t'storm potential to portions of the state, through Thursday night. With this update we have updated tonight's forecast based on current trends, as well as upgraded portions of the state to a level 2 severe t'storm risk for Thursday.

Forecast...
Tonight, Aug 11th...
While a few isolated to scattered showers and t'storms have developed and pushed across northern Illinois this evening, with even a severe t'storm, things have been overall fairly quiet due to a cap in place aloft. However, with a frontal boundary sliding southward across the northern half of the state tonight and a strong low level jet in place, isolated to scatter showers and t'storms will continue to be possible through the night across portions of Northern and Central Illinois. An environment will be in place supportive of a severe t'storm risk with this activity. This environment will feature high instability of 3,000-5,000J/KG, dew points in the mid 70's to low 80's, good shear, good forcing, and high lapse rates of 7.0-8.0C. This environment will be supportive of upwards of an isolated to sporadic severe t'storm risk (levels 1-2) across Northern and Central Illinois. Damaging winds, hail and an isolated tornado will be the severe weather threats.

Thursday Morning - Thursday Night, Aug 12th...
Areas of rain and t'storms may be ongoing across portions of Northern and central Illinois Thursday morning. In the wake of this activity some clearing and destabilization should occur across the state. With additional disturbances moving through and a frontal boundary moving southward into and across the state, development of scattered showers and t'storms is expected Thursday afternoon across Northern and Central Illinois, and Iowa. This activity will likely congeal into multiple clusters or a loose line, and will then spread southeastward across much of the state, Thursday afternoon through Thursday night. An environment will be in place supportive of a severe t'storm risk with this activity. This environment will feature high instability of 2,500-4,500J/KG, dew points in the upper 60's to upper 70's, good shear, good forcing, and good lapse rates of 6.0-7.5C. This environment will be supportive of upwards of an isolated to sporadic severe t'storm risk (levels 1-2) across much of the state. Damaging winds, hail and an isolated tornado threat will be the severe weather threats.

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

​Recap...
Sunday Afternoon - Sunday Night, Aug 8th...
A large complex of t'storms that originated across Missouri spread northeastward across a large portion of the state, Sunday afternoon into Sunday night. Isolated to sporadic t'storms were severe with this complex, producing damaging winds. A few additional clusters of rain and t'storms moved across portions of the state Sunday night into early Monday morning, however none of this activity was severe.

Monday Morning - Monday Night, Aug 9th...
A large complex of t'storms that originated across Iowa on Sunday night, spread eastward across Northern Illinois Monday morning. No severe weather occurred with this activity. Additionally, a complex of rain and t'storms developed across Central and Southern Illinois Sunday night, which pushed across Central and Southern Illinois through Monday morning. No severe weather occurred with this activity. The main focus was Monday afternoon into early Monday night, as several supercell t'storms developed and moved southeastward across Northern Illinois. Scattered activity was severe, producing several tornadoes, and a few instances of damaging winds and hail.

Tuesday Morning - Tuesday Night, Aug 10th...
A large complex of severe t'storms developed across Southwest Wisconsin and Eastern Iowa Tuesday afternoon. This complex of severe t'storms then quickly moved eastward across Southern Wisconsin and Northern Illinois Monday, later Tuesday afternoon into early Tuesday night. This complex produced scattered severe t'storms with widespread damaging winds, causing widespread tree damage and power outages across Northern Illinois.

JP