More than a week later, upward of 30,000 customers remain without power, down from 590,000, as residents continue the lengthy recovery process.
The storm’s ferocity caught many Iowans off-guard, but the Hawkeye State is surprisingly vulnerable to these violent tempests. While the storm’s intensity was on the high end of derechos, this wasn’t some freak event. Destructive derechos are as common in Iowa as hurricane strikes are in Florida.
The derecho damaged or destroyed 10 million acres of crops while many structures in communities such as Cedar Rapids, Marshalltown, Ankeny and Iowa City lay in shambles. The historical record indicates these violent, fast-moving storm complexes will continue to torment the state most years into the future.
Derecho unleashed 110 to 140 mph winds
President Trump traveled to Iowa on Tuesday to survey the damage, and he met with Iowa Gov. Kim Reynolds (R). She described the storm as “basically a 40-mile-wide tornado that went through.”
Alex Gibbs, a lead meteorologist at the National Weather Service in the Quad Cities, said that his office, which serves central and eastern Iowa and western Illinois, inspected and rated the storm’s intensity using damage indicators traditionally reserved for tornado surveys. His office found evidence of 110-to-140-mph winds.
In Atkins, Iowa, about 10 miles northwest of Cedar Rapids, a wind gust of 126 mph was measured. That’s near where the WMT Cedar Rapids transmitter tower was toppled.
A nearby tower’s antenna was snapped 340 feet above the ground. The tower had originally been rated to withstand 125 mph winds.
Rich Kinney, the warning coordination meteorologist for the Quad Cities office, said damage observed at an apartment complex, where the winds caused the removal of the roof, most exterior walls and some interior walls, led them “to come up with the 140 mph estimate for the max wind gusts.”
Few derechos produce catastrophic wind gusts of up to 140 mph but, by definition, they have significant wind gusts over 75 mph — rivaling the force of some hurricanes, which must have maximum sustained winds of at least 74 mph.
Gibbs said that, on average, his forecast areas see one derecho per year.
As common as hurricanes in Florida
The scope of the devastation had many comparing the damage to that of an “inland hurricane,” with wind gusts similar to those of a major Category 3 or 4 storm.
While the 140-mph gusts were extreme, they are not unprecedented in a part of the country some have labeled Derecho Alley.
A comparably strong derecho struck Iowa during the early morning hours of July 11, 2011. Vinton and Garrison, about 20 miles northwest of Cedar Rapids, saw wind gusts of up to 130 mph. That’s the same area that bore the brunt of the Aug. 10 storms. Marshall County, Iowa, gusted above 80 mph in 2011. Last week’s storms buffeted them with 100-mph gusts.
Weaker derecho events are even more common. Based on the distribution of observed wind gusts over time, the National Weather Service’s Storm Prediction Center has found that, in central Iowa, winds greater than 74 mph are likely to occur within 25 miles of any given point an average of once or more per year. Some weather stations in Iowa recorded 10 or more instances of 60 mph thunderstorm winds in six years’ time.
Considering these statistics, it becomes easy to see how the wind threat in Iowa from derechos may be just as great as in Florida from hurricanes.
Since 1850, the Sunshine State has been hit by 112 hurricanes, 38 of which were major (Category 3 or greater) storms with winds exceeding 111 mph. That’s an average of two hurricanes every three years or one major hurricane every four or five years.
It’s important to remember that the severe winds from derechos and hurricanes are localized in nature, so any given place in Florida or Iowa will see them far less frequently than once per year.
“[A]t least one piece of Iowa will end up in a derecho every year. But that is a different piece of info than the frequency at a point/city,” wrote Bill Gallus, an atmospheric scientist at Iowa State University in an email. “It is probably more like once every 10 years or more at any particular spot.”
He said winds of the magnitude of the most recent derecho, however, are unusual. “Winds above 85 mph which were common in this event, [are] very rare. Probably a first in most people’s lifetimes, and in the lifetimes of many cities and towns,” Gallus wrote.
Little time to prepare
A key difference between hurricanes and derechos is the amount of advanced notice people receive. Typically, forecasters track hurricanes for days as they traverse the oceans, alerting vulnerable coastal residents of the danger one to three days before landfall. This lead time offers the opportunity to prepare. But derechos often flare up suddenly, and the warning time can be under an hour when they first develop. Areas farther downwind may receive up to several hours of warning.
In the case of last week’s Iowa derecho, severe thunderstorm warnings were issued about 30 to 45 minutes before the winds struck central Iowa, but the derecho was otherwise largely unexpected. Predictions from the National Weather Service that morning called for a “marginal risk” of thunderstorms producing 60 mph wind gusts, a forecast that was ramped up throughout the day as the magnitude of the forming derecho became apparent.
But even with the warning provided for the derecho, many people were unaware when it was first organizing. That’s because the severe thunderstorm warning bulletins issued by the Weather Service did not activate wireless emergency alerts on mobile phones the same way that flash flood or tornado warnings do. Only those with a third-party weather application would have been notified on their phone unless they consulted the Weather Service website or local media.
The Weather Service has proposed configuring severe thunderstorm warnings to trigger wireless emergency alerts when winds are forecast to hit 80 mph, but that proposal has yet to be enacted. Several high-end windstorms such as a 90-mph squall line in Alabama on May 19 or an 85-mph derecho east of Philadelphia in early June would have been met with shrieking alerts on the phones of those impacted.
What it was like inside the storms
Clearly, it’s not only the coastline that needs to be ready for hurricane-force winds.
Denise Lehenbauer lives in Davenport, Iowa, and encountered last week’s derecho at full force.
She knew something was very wrong when she received a phone call from her daughter in Cedar Rapids.
“She said, ‘I’m just calling to warn you to say there’s a bad storm coming your way,' ” recounted Lehenbauer. “But then I heard her on the phone saying, 'there are trees going by my window.’ ”
Lehenbauer, who had been out with her husband running errands at the time, told her daughter to stay put. Then the pair quickly drove home.
By the time it was over, century-old trees in her neighbor’s yard had been knocked down like dominoes.
The winds were even more severe in Cedar Rapids, where Lisa Zwanziger was working at a hospital.
“I work on the third floor of the building,” Zwanziger said. “Finally when our floors started shaking, security came up and told us we had to evacuate the building.”
She and her colleagues relocated to an interior radiation laboratory on the lowest floor. When she finally left the building to head home, she was met with what she described as a “war zone.”
“Usually I have a 15-minute commute, but it took me two hours to get home,” Zwanziger said. “I never did make it home. I had to park my car in a nearby park and walk.”
She said that people were everywhere in the street trying to clear downed trees, but that fallen wires made it a dangerous task.
“I am [without power still],” Zwanziger said. “It’s day eight, and I’m without power. We’ve learned how to cook on a campfire.”