WASHINGTON - Wind, humidity and rainfall combined to create the killer tornado in Moore, Okla. And when they did, the amount of energy released over the city dwarfed the power of the atomic bomb that leveled Hiroshima.
On Tuesday afternoon, the National Weather Service gave it the top-of-thescale rating of EF-5 for wind speed, breadth and severity of damage. Wind speeds were estimated at between 200 and 210 mph.
Several meteorologists used real-time measurements to calculate the energy released during the storm’s life span of almost an hour. Their estimates ranged from 8 times to more than 600 times the power of the Hiroshima bomb, with more experts at the high end.
The tornado at some points was 1.3 miles wide, and its path went on for17 miles and 40 minutes. That’s long for a regular tornado but not unusual for such a violent one, said research meteorologist Harold Brooks of the National Severe Storms Laboratory in Norman, Okla. Less than 1 percent of all U.S. tornadoesare this violent - only about 10 a year, he said.
With a third strong storm hitting Moore in 14 years, some people were wondering why. It’s a combination of geography, meteorology and a lot of bad luck, experts said.
A look at the climate history of tornadoes in May shows that they cluster in a spot - maybe 100 miles wide - in central Oklahoma, “and there’s good reason for it,” said Adam Houston, meteorology professor at the University of Nebraska, Lincoln. That’s the spot where the weather conditions of warm, moist air and strong wind shear needed for tornadoes combine in just the right balance.
The hot spot is bigger than just the city of Moore. Several meteorologists offer the same explanation for why that suburb seemed to be hit repeatedly by violent tornadoes: bad luck.
Scientists know the key ingredients that go into a devastating tornado. But they are struggling to figure out why they develop in some big storms and not others. They also are still trying to determine what effects, if any, global warming has on tornadoes.
Front Section, Pages 4 on 05/22/2013