Sun-Tue, Aug 8-10th Severe T'Storm Event Update #4

(11:00AM - 8/9/21) Several disturbances moving through the region through Tuesday will continue to bring severe t'storm potential to portions of the state, through Tuesday night.

Summary...
Several disturbances will continue to move across the Plains, Midwest and Great Lakes through Tuesday. These disturbances will bring severe t'storm potential to portions of the state, through Tuesday night. With this update we have upgraded the severe t'storm threat across Northeast Illinois for today, and have introduced the first severe t'storm forecast for Tuesday.

​Forecast...
​Monday Morning - Monday Night, Aug 9th...
There will be two areas of focus for today...
Northern Illinois:
A complex of rain and t'storms has been moving across portions of Northern Illinois this morning, and will exit the area by early afternoon. In the wake of this activity, clearing and fairly quick destabilization will occur. As potent disturbance moves through the area, a new round of scattered showers and t'storms are expected to develop across portions of Northern Illinois this afternoon. This activity will likely begin in the form of supercells, before eventually congealing with time into a loose cluster as it spreads southeastward across portions of Northern and Central Illinois, 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 3,000-5,000J/KG, dew points in the upper 60's to upper 70's, decent shear, good forcing, and modest lapse rates of 5.5-6.0C. This environment is expected to be maximized this late this afternoon and evening across Northeast Illinois. This environment will be supportive of upwards of an isolated to scattered severe t'storm risk (levels 1-3) across portions of Northern and Central Illinois. Damaging winds, hail and a few tornadoes will be the severe weather threats.
​
Southern Illinois:
In the wake of a cluster of rain and t'storms moving across the area last night and into this morning, clearing and destabilization is expected to occur. A new round of scattered showers and t'storms will develop this afternoon across portions of Missouri, Southern Illinois, and Southern Indiana. This activity may congeal into a loose cluster or two, as it moves eastward, affecting Southern Illinois from 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 2,500-4,500J/KG, dew points in the upper 60's to upper 70's, modest shear, modest forcing, and modest lapse rates of 5.5-7.0C. This environment will be supportive of upwards of an isolated severe t'storm risk (level 1-) across portions Southern Illinois. Damaging winds will be the main threat, though a hail and isolated tornado threat cannot be ruled out.

Tuesday Morning - Tuesday Night, Aug 10th...
A few areas of scattered showers and t'storms will be ongoing across portions of Eastern and Southern Illinois Tuesday morning. In the wake of this activity, a new round of showers and t'storms will develop across Wisconsin, Iowa and Missouri during the afternoon.This activity will likely congeal into multiple clusters, and will then spread eastward across much of the state, Tuesday afternoon through Tuesday 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, modest shear, decent 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.

JP