Weekly Weather Event -Week of August 10thAugust 14, 2020
On the evening of August 10th, a derecho impacted large portions of the Midwest in a line stretching through Iowa, Illinois, and Indiana. Straight-line winds reached over 100 miles per hour in some reports, making this storm have the equivalent winds of a Category 2 hurricane. The National Weather Service reported 7 tornadoes in the Chicago area, and the damage to corn fields in Iowa could be seen from space. More than a million homes and business lost power on Monday evening, and as of August 13th, approximately 250,000 people are still without power. Estimates of agricultural losses alone are expected to be in the billions.
The storm system traveled a total of 770 miles over 14 hours, beginning in southeastern South Dakota and tapering out by the time it reached Ohio. While the brunt of the damage was felt in Iowa, Illinois, and Indiana, parts of Omaha, Nebraska and Wisconsin also saw the impacts of strong winds.
As explained in our July 17th article, derechos are strong thunderstorm systems associated with squall lines and powerful sustained winds. They also tend to be difficult to predict. While the atmospheric conditions needed to fuel a derecho are common during the summer, these storms remain relatively rare. This is because derechos are especially fierce thunderstorms that require several conditions to be properly met; most Iowa was only under a marginal or slight risk for most of August 10th. It wasn’t until the storms began that the Storm Prediction Center upgraded the storm outlook to a moderate risk, the second highest risk category for thunderstorms.