Violent Okla. System was a Derecho, Meteorologists Say

July 24, 2013






TULSA, Okla. — A violent storm system packing up to 80 mph winds and lightning that churned through the Tulsa area early Wednesday was later classified by meteorologists as a rare derecho because of the widespread wind damage it left throughout the city.
Meanwhile, nearly 70,000 homes and businesses in Tulsa County were still without electricity Wednesday afternoon — there were more than 100,000 at the storm's peak — and utility officials said it could be several days until all power is restored.
Authorities said one firefighter was injured while operating a chain saw to clean up debris, but the injuries weren't life-threatening. No other injuries were reported.
Late Tuesday, Gov. Mary Fallin declared a state of emergency for Tulsa County and 34 more counties due to the overnight storms, damaging winds and flooding. Her executive order paves the way for state agencies to make emergency purchases and is a first step in seeking federal assistance if necessary.
National Weather Service meteorologist Karen Hatfield said derechos are a special type of damaging storm event that have consistent reports of wind damage or measured wind gusts of 58 mph or over for at least 250 miles.
Hatfield said forecasters at the weather service only informally discussed the possibility of the weather event but did not use the term in forecasts, instead opting to use layman's terms language predicting a severe and damaging wind event.
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Adding to the difficulty of classifying a possible derecho ahead of time, the classification typically comes after extensive field work to survey the wind damage to estimate how widespread it was, she said.
"They are not common," she said in an interview. "Typically across the country, there are only a handful of derechos every year."
The storm snapped power lines and decades-old trees and left tens of thousands of homes and businesses without electricity.
"It was the most amazing sound I've heard in a long time," recounted resident Sherry Bruster, who's lived in her midtown home since 1981. "I thought the roof was going to go."
A new batch of potentially violent thunderstorms could hit the same area when they are forecast to clip eastern Oklahoma late Thursday and early Friday, according to the National Weather Service in Tulsa. The service predicts highs in the low 90s on Wednesday and Thursday.
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"This is one of the worst storms we've seen hit Tulsa," American Electric Power-Public Service Company of Oklahoma president Stuart Solomon said Wednesday at a news conference at City Hall, where he announced that extra crews from out of state were being tapped to help restore power. "There is widespread damage throughout the entire city."
The storms toppled trees, bent road signs and caused at least 10 house fires, the fire department reported. The city's 911 call center was inundated with thousands of calls, causing a near-overload of the system.
"We had 100 calls in the queue," said Scott Clark, deputy chief of support services for the fire department, who described a chaotic scene at the call center where supervisors were fielding some of the calls. "At one point last night (the fire department was) down to no resources."
The supercell storms originated over the Kansas plains and tracked southeast, holding together long enough to rake Tulsa. Brad McGavock, a meteorologist with the National Weather Service in Tulsa, said the type of storm was atypical for mid-July in the northeastern part of the state. The difference, he said, was that this storm hit a populated area.
"They happen, but they may not move into a populous area, even though the systems have the same damaging winds," he said.
On Wednesday, Bruster, the longtime Tulsa resident, and another neighbor, Julie Strauss, lamented the 80-year-old pecan tree that had landed partly on Bruster's front lawn. The scene was a familiar one throughout the heart of the city, as many properties appeared to have sustained some kind of damage to trees or property.
"I've never seen so many trees diagonal," Strauss marveled. "The trees would bend further and further. I thought it sounded like a hurricane."