This article, first published Wednesday, was updated Thursday.

On Monday evening, a violent, fast-moving thunderstorm complex known as derecho tore a 700-mile path from Nebraska to Indiana. Winds over 70 mph battered Chicago, and as of Thursday afternoon, more than 300,000 people were still without power in northern Illinois as well as Iowa, the state hardest hit.

The destructive storms laid siege to more than 10 million acres of Iowa’s corn and soybean crop, devastating farmers and capping off what has already been a difficult few years of farming for many.

Up to 43 percent of the state’s corn and soybean crop has suffered damage from the storms, a severe blow to a $10 billion industry that’s central to the Hawkeye State’s economy. The magnitude of the battered vegetation was even visible on the same weather satellites used to track Monday’s violent thunderstorms.

Steve Bowen, a meteorologist and head of catastrophe insight for the reinsurer Aon, said the damage toll to agriculture alone is likely to reach the billions of dollars.

“This has all the makings of a billion-dollar agricultural impact in Iowa and Illinois,” he wrote in a Twitter message. “With that said, it will take some time for farmers to determine how much of the downed crop is salvageable for harvest. When combined with the rest of the physical property damage to homes, businesses, vehicles, and infrastructure, it is entirely plausible that the derecho was responsible for a multi-billion-dollar economic cost on its own.”

State officials were surveying the damage in hopes that some of the crop may be salvageable. Iowa Gov. Kim Reynolds (R) issued a disaster proclamation for 20 Iowa counties, freeing up state funding for disaster response and recovery. The state is also making grants available to low-income families who need to pay for food, repairs, or temporary housing in the wake of the disaster.

A derecho storm hit Chicago and parts of Iowa on Aug. 10, bringing heavy rain fall and violent winds. (The Washington Post)

“Although it will take days or weeks to know the full scope of [the] damage, initial reports are significant,” Reynolds said at a news conference on Tuesday. She noted that the state is working to frame its storm response while also managing the ongoing coronavirus pandemic.

Drive-up coronavirus testing sites in Cedar Rapids, Davenport and Marshalltown were closed Monday and Tuesday. “They are working to reopen those as quickly as possible,” Reynolds said.

In these Iowa communities, the derecho struck with the force of a hurricane. An article on the self-publishing website Medium Wednesday laid bare the scope of the damage in Cedar Rapids: “Nearly every home has damage. Most big trees in the city fell. Most local businesses are closed. Every business is damaged. Most roads are impassable,” wrote resident Ben Kaplan.

Satellite captures scenes of storm damage

Satellite imagery on Tuesday captured the scope of the agricultural destruction. At least two significant swaths of wind damage can be seen, particularly north of Interstate 80. Radar signatures indicate the core of 90 to 100 mph winds may have been between 30 and 50 miles wide at times.

Winds were clocked at 112 mph in Midway, Iowa, about 10 miles north of Cedar Rapids. A gust to 100 mph was recorded nearby in Hiawatha.

A personal weather station measured a gust of 106 mph in Marshalltown, a city of 27,000 people northeast of Des Moines. The airport gusted to 99 mph as the storms barreled through.

All told, more than 700 instances of damage or severe weather were reported to the National Weather Service following the passage of the derecho, which wrought havoc along a track some 700 miles long from Nebraska to Indiana.

Millions of bushels of corn damaged

Jan Dutton, chief executive of Prescient Weather, a private forecasting group specializing in predictions for agricultural interests, said between 180 and 270 million bushels of corn were expected to be affected. His technique employed his company’s corn production forecast, which predicts crop yields based on antecedent and ongoing conditions.

“I saw the satellite image, outlined the counties in Iowa that were affected by the derecho, and looked at what counties were inside the domain,” Dutton explained.

He said that figure causes a serious dent in yield for Iowa, but that other states could help soften the deficit.

“Total corn production for the U.S. is going to be 15.4 to 15.6 billion bushels,” Dutton said. “The amount impacted is like one purchase from China.”

Iowa is the number-one producer of corn in the United States, with 2.58 billion bushels harvested in 2019, accounting for roughly one-sixth of nationwide yields. The state has been the country’s top corn producer every year for the past 26 years.

Not all of the corn affected by the derecho was destroyed. It will take time for agronomists to assess the health of corn plants affected, said Keely Coppess, communications director for the Iowa Agriculture Department.

“A lot of the corn is in the later development stages,” said Coppess. “Some is at a 45-degree angle, but it may attempt to stand back up. But it’s really too soon to tell. We’ll know more in a week or so.”

Carl Jardon, the vice president of the Iowa Corn Growers Association (ICGA), said in a statement that the derecho affected the entire width of the state.

“Harvest will begin shortly and one-third of Iowa’s crop are flattened, it’s hard to tell at this point whether all the corn will recover and the impact of potential yield,” he said. “2020 has been a year of downfalls for the farmer. It has been one hit after another with trade disputes, low demand and attacks on ethanol and the Renewable Fuel Standard, on top of a global pandemic and the lowest corn prices in over a decade.”

Corn is typically harvested in Iowa between late September and mid-October.

Corn plays a significant role in Iowa’s climate. By releasing water into the atmosphere in a process called evapotranspiration, it has been shown to increase the dew point and subsequently the humidity. That can lead to higher heat indexes during heat waves, and it can also contribute to severe thunderstorms.

A serious storm system that came by surprise

The vicious windstorm came by surprise on a morning when most of Iowa was predicted to see very isolated severe weather. The National Weather Service Storm Prediction Center (SPC) had issued a level 1 out of 5 “marginal risk” of severe weather for most of Iowa just a few hours before winds began gusting upward of 90 mph in the central part of the state.

Only after the storms began their violent march to the east did SPC issue a dramatic upgrade in their storm outlook to a level 4 out of 5 “moderate risk” from central Iowa east to Chicago. In areas to the east of the Iowa cornfields, the forecast is considered a success.

Derechos are notoriously difficult to predict. The atmospheric ingredients for them are in place during much of the summer, yet those ingredients are rarely combined in the necessary way to generate such a fierce storm system.

“It was very bizarre. . . . It’s been a whirlwind,” said Brandi Snyder, a spokesperson for the ICGA. “I remember my husband telling me, ‘It will be cooler, like 75 [degrees.] . . . There won’t be much heat.’ ”

But when she awoke Monday morning, it was hot and humid — even by Iowa standards.

“I woke up and noticed all of our windows were fogged over,” she said. “You could just feel the extreme humidity. It was weird out.”

Jason Samenow and Andrew Freedman contributed to this article.