May 22 (Bloomberg) -- Residents of Moore had about 36 minutes to prepare for a mile-wide tornado that flattened the Oklahoma City suburb, killing two dozen people, according to the National Weather Service.
The federal agency issued its first warning for residents to seek shelter at 2:40 p.m. local time on May 20, 16 minutes before the tornado touched down about 10 miles (16 kilometers) west of the city, said David Andra, a National Weather Service meteorologist in Norman, Oklahoma. The twister reached Moore at 3:16 p.m., he said, topping the service’s scale for tornadoes with winds of more than 200 miles per hour.
“A 36-minute time period is pretty substantial,” Andra said in an interview. The average lead time for tornado warnings is 14 minutes, according to the National Oceanic and Atmospheric Administration.
Tornadoes are nature’s most violent storms and can develop so rapidly that little, if any, advance warning is possible, according to the Federal Emergency Management Agency. Government officials and researchers credit early warnings with saving lives by giving people time to get to shelters.
“Advanced notice is very important,” said John Trostel, director of the Severe Storms Research Center at the Georgia Tech Research Institute in Atlanta. “That is why, even with such a massive scale of destruction, we are seeing tens of casualties instead of hundreds.”
The National Weather Service said in its May 20 warning that people in the affected area should “take cover now in a storm shelter or an interior room of a sturdy building. Stay away from doors and windows.”
Moore doesn’t maintain any community storm shelters and instead instructs residents to shelter in place in a resilient structure, calling that the best way to stay safe from a fast-approaching tornado, according to the city’s website.
It’s up to Oklahoma cities to activate alert systems once the National Weather Service issues a tornado warning, said Terri Watkins, a spokeswoman for the state Emergency Management Department.
Moore sounded its 36 tornado sirens three times before the twister hit, according to its Facebook page. In three postings on the page, the city warned residents that the sirens were sounding and said to take shelter and follow precautions.
Moore didn’t activate its “code red” mass notification system, said Jayme Shelton, a spokesman for the city. The system dials phone numbers, plays a recorded message and sends e-mail and text messages, according to an emergency operations plan published in September.
Asked why the city didn’t use the phone and e-mail system, Shelton said the sirens are more effective.
Moore was among the first cities certified as “StormReady” by the National Weather Service in 2001. The designation, which Moore renewed last year, requires a government to have multiple ways to alert residents.
In addition to the city’s warnings, forecasters, private groups and individuals sent alerts on the Internet.
The American Red Cross sent warnings through a new smartphone application that tells users of approaching tornadoes, according to Melanie Pipkin, a spokeswoman for the Washington-based group.
In a posting on the social-media service Twitter, the National Weather Service wrote: “The tornado is so large you may not realize it’s a tornado. If you are in Moore, go to shelter NOW!” The message was resent by users about 150 times.
The average lead time for tornado warnings was 5 minutes in the early 1990s, said Lans Rothfusz, deputy chief of warning research and development at the National Severe Storms Laboratory in Norman. Advances in radar have helped forecasters by showing how rapidly air is rotating and whether debris is being carried in a storm, both indicators of a tornado, he said.
Computer forecasting models a decade away from deployment may provide as much as an hour’s notice, Rothfusz said. Instead of relying on radar to spot a storm, the models would predict tornadoes based on weather patterns.
“There is room to grow,” Rothfusz said. “We’re taking baby steps.”
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