Appears to be the most costly thunderstorm event in US history.
Iowa derecho in August was most costly thunderstorm disaster in U.S. history
NOAA estimates damage at $7.5 billion, higher than many hurricanes.
By Bob Henson
Oct. 17, 2020 at 8:04 a.m. CDT
No single thunderstorm event in modern times — not even a tornado — has wrought as much economic devastation as the derecho that slammed the nation’s Corn Belt on Aug. 10, based on analyses from the public and private sectors.
The storm complex, blamed for four deaths, hit Cedar Rapids, Iowa, particularly hard, cutting power to almost the entire city of 133,000 people, and damaging most of its businesses and homes.
In an October update to its database of billion-dollar weather disasters, the National Oceanic and Atmospheric Administration estimated damages from the August derecho, which raced from Iowa to Indiana, at $7.5 billion. This includes agricultural impacts that are still being analyzed, so the total may be revised, said Adam Smith, who manages the database.
The derecho’s financial toll exceeds that of nine of this year’s record 10 landfalling U.S. hurricanes and tropical storms. The exception is Hurricane Laura, which struck Louisiana in late August and caused an estimated $14 billion in damage.
Including the derecho, the U.S. has been hit by a record-tying 16 billion-dollar weather disasters this year through September.
A derecho is a fast-moving, violent wind event associated with a thunderstorm complex. One common definition specifies that it must produce “continuous or intermittent” damage along a path at least 60 miles wide and 400 miles long, with frequent gusts of at least 58 mph and several well-separated gusts of at least 75 mph.
The Aug. 10 event more than qualified. Striking with unanticipated ferocity, the derecho brought winds gusting to more than 70 mph for the better part of an hour over a large swath of central and eastern Iowa and northwest Illinois. Numerous locations clocked gusts over 110 mph. The winds laid waste to millions of acres of crops, severely damaged or destroyed hundreds of homes, and brought down many thousands of trees. “One could make a strong case that this is the most destructive individual thunderstorm cluster on record in terms of damage cost,” said Steve Bowen, head of catastrophe insight at the insurance broker Aon, in an email. Aon released an initial damage estimate of $5 billion for the derecho, not yet including agricultural impacts.
Hourly composite of radar reflectivity for the thunderstorm complex that produced the Aug. 10 derecho. Shown in Central time. (NWS)
The derecho’s top winds ripped along the south edge of a mesoscale convective vortex, a low-pressure center embedded within the thunderstorm complex. “The vortex was one of the most distinctive ones of that size that I have ever seen,” said Stephen Corfidi, a meteorologist at the University of Oklahoma and derecho expert, in an email.
The peak wind gust observed in the derecho was 126 mph at Atkins, Iowa. The highest estimated gust, based on the partial destruction of an apartment complex in Cedar Rapids, was 140 mph. Gusts that strong are comparable to the peak that one would expect in an EF3 tornado or major hurricane.
Parts of five Iowa counties were struck by wind gusts estimated at 110 to 140 mph.
“To have a Midwest city endure [such] wind speeds, and also see such a devastating impact to a large volume of regional crops, is almost unbelievable,” Bowen said. “I don’t think most of the country truly realizes how severe the event ended up being.”
Iowa is as prone to destructive derechos as Florida is to hurricanes
Derecho winds typically last about 10 to 20 minutes at any one spot. In contrast, the 30- to 60-minute duration of severe gusts in the hardest-hit areas Aug. 10 was much more comparable to the passage of a hurricane eyewall than a tornado, whose winds typically last only a few seconds to a minute or two.
At North Liberty, Iowa, just north of Iowa City, gusts varied from roughly 70 to 98 mph for nearly an hour during the Aug. 10 derecho. (Johnson County Emergency Management Agency via NWS)
An immense toll on trees and crops
In Cedar Rapids alone, more than 1,000 housing units were deemed unlivable in the week after the storm, according to the Gazette. Hundreds of other homes were damaged.
Standard home and business insurance policies should cover much of the wind-related structural damage. Some of the hits to agriculture may fall through the cracks of insurance programs, though. For example, many huge grain-storage units were demolished by the derecho, with an estimated $300 million in structural losses alone. Any grain that can’t be salvaged from these destroyed bins wouldn’t be covered by standard crop insurance, according to the U.S. Department of Agriculture.
Debris from a destroyed silo that damaged crops Aug. 10 when it was blown across a field east of Cedar Rapids, Iowa, is shown on Aug. 21. (Rebecca F. Miller/The Gazette via AP)
Iowa state climatologist Justin Glisan highlighted the scope of agricultural impacts in a September webinar. According to initial estimates, more than 3.5 million acres of corn and 2.5 million acres of soybeans were affected in Iowa, or about 20 percent of the state’s total farmland.
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Along with the wind itself, crops were thrashed by small hail — pea to penny size — that was propelled “like machine-gun fire,” Glisan said.
“You’d be hard-pressed to draw a more efficient path across the Corn Belt to create a storm that has such a significant impact on agriculture at a sensitive time of the year,” Glisan added.
A cornfield damaged in the derecho is seen on the Rod Pierce farm near Woodward, Iowa, on Aug. 21. (Charlie Neibergall/AP)
The derecho ripped huge holes in the tree canopy above a number of Iowa towns and cities, according to Emma Hanigan, an urban forester with the state’s Department of Natural Resources. At least half of the trees in Cedar Rapids were destroyed or heavily damaged. The toll will only worsen over the coming months, as the wounds left by torn limbs allow pests and pathogens such as oak wilt to infect damaged trees.
“It takes so long to regain that tree cover,” said Hannigan in an interview. “We’re going to see impacts 30 years from now from this storm.”
Iowa derecho in August was most costly thunderstorm disaster in U.S. history
NOAA estimates damage at $7.5 billion, higher than many hurricanes.
By Bob Henson
Oct. 17, 2020 at 8:04 a.m. CDT
No single thunderstorm event in modern times — not even a tornado — has wrought as much economic devastation as the derecho that slammed the nation’s Corn Belt on Aug. 10, based on analyses from the public and private sectors.
The storm complex, blamed for four deaths, hit Cedar Rapids, Iowa, particularly hard, cutting power to almost the entire city of 133,000 people, and damaging most of its businesses and homes.
In an October update to its database of billion-dollar weather disasters, the National Oceanic and Atmospheric Administration estimated damages from the August derecho, which raced from Iowa to Indiana, at $7.5 billion. This includes agricultural impacts that are still being analyzed, so the total may be revised, said Adam Smith, who manages the database.
The derecho’s financial toll exceeds that of nine of this year’s record 10 landfalling U.S. hurricanes and tropical storms. The exception is Hurricane Laura, which struck Louisiana in late August and caused an estimated $14 billion in damage.
Including the derecho, the U.S. has been hit by a record-tying 16 billion-dollar weather disasters this year through September.
A derecho is a fast-moving, violent wind event associated with a thunderstorm complex. One common definition specifies that it must produce “continuous or intermittent” damage along a path at least 60 miles wide and 400 miles long, with frequent gusts of at least 58 mph and several well-separated gusts of at least 75 mph.
The Aug. 10 event more than qualified. Striking with unanticipated ferocity, the derecho brought winds gusting to more than 70 mph for the better part of an hour over a large swath of central and eastern Iowa and northwest Illinois. Numerous locations clocked gusts over 110 mph. The winds laid waste to millions of acres of crops, severely damaged or destroyed hundreds of homes, and brought down many thousands of trees. “One could make a strong case that this is the most destructive individual thunderstorm cluster on record in terms of damage cost,” said Steve Bowen, head of catastrophe insight at the insurance broker Aon, in an email. Aon released an initial damage estimate of $5 billion for the derecho, not yet including agricultural impacts.
Hourly composite of radar reflectivity for the thunderstorm complex that produced the Aug. 10 derecho. Shown in Central time. (NWS)
The derecho’s top winds ripped along the south edge of a mesoscale convective vortex, a low-pressure center embedded within the thunderstorm complex. “The vortex was one of the most distinctive ones of that size that I have ever seen,” said Stephen Corfidi, a meteorologist at the University of Oklahoma and derecho expert, in an email.
The peak wind gust observed in the derecho was 126 mph at Atkins, Iowa. The highest estimated gust, based on the partial destruction of an apartment complex in Cedar Rapids, was 140 mph. Gusts that strong are comparable to the peak that one would expect in an EF3 tornado or major hurricane.
Parts of five Iowa counties were struck by wind gusts estimated at 110 to 140 mph.
“To have a Midwest city endure [such] wind speeds, and also see such a devastating impact to a large volume of regional crops, is almost unbelievable,” Bowen said. “I don’t think most of the country truly realizes how severe the event ended up being.”
Iowa is as prone to destructive derechos as Florida is to hurricanes
Derecho winds typically last about 10 to 20 minutes at any one spot. In contrast, the 30- to 60-minute duration of severe gusts in the hardest-hit areas Aug. 10 was much more comparable to the passage of a hurricane eyewall than a tornado, whose winds typically last only a few seconds to a minute or two.
At North Liberty, Iowa, just north of Iowa City, gusts varied from roughly 70 to 98 mph for nearly an hour during the Aug. 10 derecho. (Johnson County Emergency Management Agency via NWS)
An immense toll on trees and crops
In Cedar Rapids alone, more than 1,000 housing units were deemed unlivable in the week after the storm, according to the Gazette. Hundreds of other homes were damaged.
Standard home and business insurance policies should cover much of the wind-related structural damage. Some of the hits to agriculture may fall through the cracks of insurance programs, though. For example, many huge grain-storage units were demolished by the derecho, with an estimated $300 million in structural losses alone. Any grain that can’t be salvaged from these destroyed bins wouldn’t be covered by standard crop insurance, according to the U.S. Department of Agriculture.
Debris from a destroyed silo that damaged crops Aug. 10 when it was blown across a field east of Cedar Rapids, Iowa, is shown on Aug. 21. (Rebecca F. Miller/The Gazette via AP)
Iowa state climatologist Justin Glisan highlighted the scope of agricultural impacts in a September webinar. According to initial estimates, more than 3.5 million acres of corn and 2.5 million acres of soybeans were affected in Iowa, or about 20 percent of the state’s total farmland.
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Along with the wind itself, crops were thrashed by small hail — pea to penny size — that was propelled “like machine-gun fire,” Glisan said.
“You’d be hard-pressed to draw a more efficient path across the Corn Belt to create a storm that has such a significant impact on agriculture at a sensitive time of the year,” Glisan added.
A cornfield damaged in the derecho is seen on the Rod Pierce farm near Woodward, Iowa, on Aug. 21. (Charlie Neibergall/AP)
The derecho ripped huge holes in the tree canopy above a number of Iowa towns and cities, according to Emma Hanigan, an urban forester with the state’s Department of Natural Resources. At least half of the trees in Cedar Rapids were destroyed or heavily damaged. The toll will only worsen over the coming months, as the wounds left by torn limbs allow pests and pathogens such as oak wilt to infect damaged trees.
“It takes so long to regain that tree cover,” said Hannigan in an interview. “We’re going to see impacts 30 years from now from this storm.”
