Sun-Wed, Aug 8-11th Severe T'Storm Event Update #6

(11:45AM - 8/10/21) Several disturbances will continue to move through the region through Wednesday, bringing daily severe t'storm potential to portions of the state, through Wednesday night.

Summary...
Several disturbances will continue to move across the Plains, Midwest and Great Lakes through Wednesday. These disturbances will bring severe t'storm potential to portions of the state, through Wednesday night. With this update no significant changes were needed for today's forecast, and we have introduced the first severe t'storm forecast for Wednesday.

Forecast...
This Afternoon - Tonight, Aug 10th...
A few isolated to scattered showers and t'storms have occurred across portions of Eastern and Southern Illinois this morning. In the wake of this early activity, ample clearing and destabilization will occur across the state through the day. As another disturbance approaches, widespread development of showers and t'storms is expected this afternoon across portions of Wisconsin, Iowa and Missouri. This activity will congeal into multiple clusters, and will then spread eastward across much of the state, this afternoon through tonight. An environment will be in place supportive of a severe t'storm risk with this activity. This environment will feature high instability of 4,000-6,000J/KG, high dew points in the mid 70's to low 80's, modest shear, modest forcing, and high lapse rates of 6.5-8.0C. This environment will be supportive of upwards of a sporadic severe t'storm risk (level 2) across a large portion of the state. Damaging winds will be the main severe weather threat, with hail and an isolated tornado being secondary threats.

Wednesday Morning - Wednesday Night, Aug 11th...
Area of rain and t'storms will be ongoing Wednesday morning across portions of the state. This activity will gradually clear the state by midday, allowing for clearing and destabilization to occur across the state. With additional disturbances moving through and a frontal boundary in place, widespread development of showers and t'storms is expected Wednesday afternoon across Wisconsin, Iowa, Northwest Illinois and Missouri. This activity will likely congeal into multiple clusters, and will then spread eastward across much of the state, Wednesday afternoon through Wednesday night. An environment will be in place supportive of a severe t'storm risk with this activity. This environment will feature high instability of 3,500-5,500J/KG, dew points in the low to upper 70's, good shear, good forcing, and high lapse rates of 6.5-8.0C. This environment will be supportive of upwards of an isolated to sporadic severe t'storm risk (levels 1-2) across a large portion 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.

JP