$7.5 billion and counting: August derecho that slammed Iowa was most costly thunderstorm in US history, data shows

It’s estimated that August’s multi-state derecho — which has left wide swathes of Iowa devastated — resulted in $7.5 billion in damages and counting, according to updated data from the National Oceanic and Atmospheric Administration.

The Aug. 10 storm, which hit Iowa the hardest and also impacted Illinois, Ohio, Minnesota and Indiana, was the most costly thunderstorm in U.S. history, the Washington Post says. Beyond that, NOAA’s data says it is the fourth-most expensive severe storm since 1980, and the second-costliest disaster so far in 2020.

Hurricane Laura, which slammed the Gulf Coast in late August, had resulted in $14 billion in damages, according to the report. Cost estimates for other disaster events, including the widespread wildfires along the West Coast, were not available in the NOAA research.

Iowans are still recovering from the damages the derecho’s straight-lined, hurricane-strength winds caused a little over two months ago. Half a million Iowans lost power in the aftermath of the August wind storm. In some areas, it took weeks for power to be restored. In the hard-hit city of Cedar Rapids, an Iowa record of 140 miles-per-hour wind gusts blasted the city and shattered its power grid.

Nearly the entire city lost power, and residents experienced widespread damages.

Across the state, unemployment claims spiked. Thousands of homes, trees, and powerlines were damaged and even destroyed in some cases. Millions of crop acres were also damaged or destroyed in an agricultural state.

And the derecho was deadly, taking at least four lives as it made its way across the Midwest. Three of the deaths reported were Iowans.

Heavy straight-line winds destroyed a grain elevator in Luther, Iowa. The storm, a derecho, ripped through central Iowa on August 10, 2020, taking down trees and leaving at least 480,000 Iowans without power.

Given all of the damage recorded so far, the $7.5 billion cost is not unexpected for experts.

Allan Curtis, a meteorologist for the National Weather Service of Des Moines, attributes the hefty cost to the size and longevity of the derecho and its destruction of crop acres.

In her derecho disaster declaration request to President Donald Trump, Iowa Gov. Kim Reynolds estimated that Iowa’s agriculture industry experienced about a $3.8 billion hit. 

The August derecho grew from a cluster of thunderstorms ranging from southeast South Dakota to Ohio. In its 14-hour span, it traveled east 770 miles across the Midwest, hitting Iowa the hardest with windspeeds of 100-plus miles per hour.

“It grew very quickly both in strength and area,” Curtis said. “As it moved east, it grew stronger along the way and ramped up in strength in Iowa.”

Curtis told the Register derechos are classified as severe weather, or thunderstorms, in the NOAA data. That’s because derecho winds are straight-lined and generally move in one direction. Hurricanes and tornadoes, on the other hand, are cyclonic.

Curtis says the cost of damages would have been significantly less if the derecho occurred in March or April, before crops were tall enough to be caught in the wind path. 

“They would have been much more resistant to wind damage closer to the ground,” he said, adding that in August corn stocks were mature and top-heavy. 

“If you were looking to exert the most damage on corn crops when it comes to thunderstorms and heavy winds, when the derecho rolled through in August, it was the perfect time to do it,” Curtis continued.

The scope of crop damage has been heartbreaking for Iowa farmers. About 850,000 Iowa crop acres were flattened and an estimated 57 million bushels of Iowa grain storage capacity were damaged or destroyed, heightening the struggle for farmers during a harvest unlike any other before. A total of at least 14 million crop acres were impacted from the derecho, and estimates of crop acres lost are expected to grow.

Andrea Sahouri covers breaking news for the Des Moines Register. She can be contacted at asahouri@registermedia.com, on Twitter @andreamsahouri, or by phone 515-284-8247.