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Five years after the 2020 derecho, are the storms becoming more common?
Scientists are working to understand more about the storms, and technology could eventually help forecasters provide more warning that one is coming
Aug. 10, 2025 5:30 am, Updated: Aug. 11, 2025 9:20 am
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Five years ago, destructive prolonged wind gusts of up to 140 mph blew through Iowa, felling trees, flattening crops, ripping down power lines and tearing away building walls and roofs. It was the most costly thunderstorm in U.S. history.
Many Eastern Iowans didn’t know what a “derecho” was prior to the storm on Aug. 10, 2020, but there were similar storms before 2020 and there will be more in the coming years.
With a changing climate that continues to warm, forensic meteorologist Kaj O’Mara said derechos could become more common in Iowa. And, thanks to advances in technology, our ability to detect them also could increase the number of confirmed derechos.
Still, William Gallus, a professor in the Earth, Atmosphere and Climate Department at Iowa State University, said derechos remain relatively uncommon.
“The trick with derechos is they are rare events, so many years you won't even have one affect Iowa,” Gallus said. “It's difficult to look at the ratios that have been happening and say anything about trends, because they're so few and far between.”
What is a derecho?
To understand how a derecho is formed, O’Mara compared it to a rowing team.
“If the entire rowing team is in sync, that boat is going to fly down the river,” O’Mara said. “The ingredients for derechos are present almost every summer afternoon around the Midwest, all the ingredients are there. You just need to have thunderstorms to act on it.”
He said derechos typically start as a small cluster of thunderstorms that “organize” in a line due to high wind speeds. The storms then form a backward “C,” or kidney bean shape, due to the winds.
“From there, if the environment is conducive, it can continue to expand,” said O’Mara, who previously was a meteorologist with KCRG-TV9 in Cedar Rapids. “It can continue to intensify, and several 100 miles later, you can classify it as a derecho.”
For a storm to be classified as a derecho, it must meet several requirements.
The storm must have wind gusts of at least 58 mph along the length of the storm, and the wind damage swath must extend at least 250 miles. The storm must last at least three hours, according to the National Weather Service.
The 2020 derecho started in northern Nebraska and southeast South Dakota around 8 a.m. on Aug. 10, speeding east across Iowa. By the time it hit Des Moines and Marshalltown, the wind gusts were already about 100 mph, causing extensive damage.
When the storm hit Cedar Rapids, the wind gusts were estimated to be about 140 mph, on par with an EF3 tornado.
The storm continued into Illinois, Wisconsin, Indiana and Michigan.
Two types of derechos
When it comes to classifying a derecho, O’Mara said the storm can be one of two types.
One derecho type is called a “progressive derecho,” while the other is called a “serial derecho.”
Progressive derechos rely on heat and humidity to drive their formation. O’Mara said heat and humidity helps the storm become “more organized” so it can start moving at a greater speed.
“What happens is (progressive derechos) lift the warm and humid air up over the front, and then it drags down cold air behind it,” O’Mara said. “As that process continues to survive, as long as the environment is there to keep it going, it's actually driven by some of the cold air down near the ground.”
O’Mara said midlevel winds are strong with progressive derechos, which can help the weather system move fast from west to east. He said the August 2020 storm was a progressive derecho.
The other type, serial derechos, are driven by a low-pressure system, rather than by heat and humidity. They typically move from south to north.
A confirmed derecho on Dec. 15, 2021 was a serial derecho.
“It wasn't driven by daytime heat and humidity, because you just don't have that during the holiday season,” O’Mara said.
The storm packed wind speeds of 60-80 mph, far less than the August 2020 derecho.
“I would argue that progressive ones are more destructive because they're faster and they tend to have stronger peak winds as well,” O’Mara said.
2020 storm had ‘the worst possible wind swath’
According to the Iowa Department of Homeland Security and Emergency Management, derechos occur in Iowa every one to two years, on average. But a derecho with wind speeds beyond 85 mph is “quite unusual.”
While the 2020 derecho spanned hundreds of miles across the Midwest, O’Mara said the storm hit Cedar Rapids and Marion with “the worst possible wind swath.”
“There is essentially nothing to stop it,” he said.
O’Mara said that even if the storm had “a little bit more wiggle room” with the wind speeds toward Cedar Rapids, it would have made for “far less economic damage.”
“With a lot of these weather events that are so destructive, you tend to remember small details,” O’Mara said. “It was quite hot leading up to that. It was about a 12:30 (p.m.) impact at Cedar Rapids, but it got very warm. I recall my home weather station in the low 90s, and that’s fairly early in the day to have that happen.”
The problem with derechos, O’Mara said, is historically, they’ve been difficult to anticipate.
“They're absolutely tough to predict,” he said.
Even though the technology to predict derechos is improving, O’Mara said they still can only be forecast about six to 18 hours ahead of time.
“That's just the way it is right now because, again, all the ingredients are in place all the time,” he said. “It's just, does that particular storm cell start to really get organized.”
However, O’Mara said meteorologists are working to extend that lead time to 24 hours ahead of storms.
“And that would be huge if we could ever get there,” he said.
Gallus, at Iowa State, is using climate model data to create computer simulations of derechos in an attempt to determine how the storms might be changing as the climate continues to warm. However, he said that the work still is “very new” and so far is showing “mixed results.”
Iowa has history of destructive derechos
Statistics say derechos should occur only once every one to two years, and Iowa has seen its share of storms.
Timothy Gunkel, a meteorologist with the National Weather Service’s Quad Cities Bureau, said there have been five derechos in Iowa in the five years since the 2020 storm.
Eastern Iowa had a confirmed derecho last month. A storm that swept across the Upper Plains and into the Midwest on July 29 brought 99 mph wind gusts to Eastern Iowa, according to reporting by the Associated Press. It included a confirmed derecho.
In addition to the December 2021 derecho, Gunkel said there was another derecho June 20, 2023, in far southeast Iowa.
There were two derechos in 2024. One, on May 24, 2024, went through most of Iowa, Gunkel said. The other was on July 15, 2024, and went through central and Eastern Iowa.
Gunkel said Eastern Iowa sees about one derecho per year, while the western part of the state sees one every two years.
Other notable derechos in Iowa prior to Aug. 10, 2020, include:
- June 30-July 1, 2014, 4 million people lost power and two people were killed by fallen trees. “Countless” acres of growing crops were flattened across the upper Midwest.
- July 10-11, 2011, the storm’s 100 mph wind gusts blew through nearly all of Iowa and traveled all the way to the east coast.
- June 29, 1998, the derecho’s strong winds traveling southeast caused a train in Iowa City to flip off its tracks
- May 30-31, 1998, storm started in far northeast Iowa and traveled east through Michigan.
- July 7-8, 1991, the storm traveled through far northern Iowa and into Wisconsin. One woman was killed near the Mason City Airport.
- July 29, 1989, from Iowa’s Western to eastern border.
- July 10-11, 1989, heavy damage in Tama and Benton counties, destroying 75 percent of Vinton’s trees; the derecho’s path ran from the Plains to the mid-Atlantic states.
- July 28, 1986, in northwest Iowa and Des Moines.
- July 4-5, 1980, 67 people were injured by a derecho as it blew through southern Iowa and into Illinois and Indiana.
- May 26, 1965, in Cedar Rapids, the “worst windstorm in the city’s history,” The Gazette reported. Seventeen people were injured.
Officials advise Iowans to have a plan for severe weather
B.J. Dvorak is coordinator of Linn County Emergency Management. He said the agency communicates derecho warnings and extreme weather threats with the same criteria for any time the outdoor warning sirens are activated.
The outdoor sirens are used to create “situational awareness” across the county. If a siren sounds — and it’s not a test — that means a hazardous situation that could impact public safety is occurring or will occur shortly.
If Iowans hear the sirens, they should go inside and seek more information about the alert and monitor emergency alerts.
“We also want to stress the importance of having multiple ways to receive severe weather alerts,” Dvorak told The Gazette in an email. “These include having a (National Oceanic and Atmospheric Administration) weather radio, having Wireless Emergency Alerts (WEA) on your cellphone and tuning in to local news broadcasts and mobile weather apps.”
Dvorak said Linn County uses Alert Iowa, the state’s official emergency notification system. Through Alert Iowa, state and local officials can use a single, statewide system that allows them to control how and when to disseminate emergency and public safety messages to residents.
“It is a free app provided by Linn County and the State of Iowa that allows you to get emergency or severe weather alerts sent via voice, text, and email,” Dvorak said.
In August 2020, Gallus said the only warnings in place were severe thunderstorm warnings.
“But most everybody has experienced dozens of severe thunderstorm warnings in their life where they don't really see much of anything happen,” Gallus said. “A severe thunderstorm warning, if there's wind happening, just means the winds are going to at least get up to 58 miles per hour. And usually, it's only 58 miles per hour for like, a minute.”
Olivia Cohen covers energy and environment for The Gazette and is a corps member with Report for America, a national service program that places journalists in local newsrooms to report on under-covered issues. She is also a contributing writer for the Ag and Water Desk, an independent journalism collaborative focusing on the Mississippi River Basin.
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Comments: olivia.cohen@thegazette.com
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