WASHINGTON (AP)—Everything had to come together just perfectly to create the killer tornado in Moore, Okla.: wind speed, moisture in the air, temperature and timing. And when they did, the awesome energy released over that city dwarfed the power of the atomic bomb that leveled Hiroshima.
On Tuesday, the National Weather Service gave it the top-of-the-scale rating of EF5 for wind speed and breadth, and severity of damage. Wind speeds were estimated at between 200 and 210 mph. The death count is 24 so far, including at least nine children. The United States averages about one EF5 a year, but this was the first in nearly two years.
To get such an uncommon storm to form is “a bit of a Goldilocks problem,” said Pennsylvania State University meteorology professor Paul Markowski. “Everything has to be just right.”
For example, there must be humidity for a tornado to form, but too much can cut the storm off. The same goes with the cold air in a downdraft: Too much can be a storm-killer.
But when the ideal conditions do occur, watch out. The power of nature beats out anything man can create.
“Everything was ready for explosive development yesterday,” said Colorado State University meteorology professor Russ Schumacher, who was in Oklahoma launching airborne devices that measured the energy, moisture and wind speeds on Monday. “It all just unleashed on that one area.”
Several meteorologists contacted by The Associated Press used real time measurements, some made by Schumacher, to calculate the energy released during the storm’s 40-minute life span. Their estimates ranged from 8 times to more than 600 times the power of the Hiroshima bomb, with more experts at the high end. Their calculations were based on energy measured in the air and then multiplied over the size and duration of the storm.
An EF5 tornado has the most violent winds on Earth, more powerful than a hurricane. The strongest winds ever measured were the 302 mph reading, measured by radar, during the EF5 tornado that struck Moore on May 3, 1999, according to Jeff Masters, meteorology director at the Weather Underground.
With the third strong storm hitting Moore in 14 years—and following roughly the same path as an EF5 that killed 40 people in 1999 and an EF4 that injured 45 others in 2003—some people are wondering why Moore?
It’s a combination of geography, meteorology and lots of bad luck, experts said.
If you look at the climate history of tornadoes in May, you will see they cluster in a spot, maybe 100 miles wide, in central Oklahoma, Houston said. That’s where the weather conditions of warm, moist air and strong wind shear needed for tornadoes combine, in just the right balance.
“Central Oklahoma is a hot spot and there’s a good reason for it,” Houston said. “There’s this perfect combination where the jet stream is strong, the instability is large and the typical position for this juxtaposition climatologically is central Oklahoma.”
Of the 60 EF5 tornadoes since 1950, Oklahoma and Alabama have been struck the most, seven times each. More than half of these top-of-the-scale twisters are in just five states: Oklahoma, Alabama, Texas, Kansas, and Iowa. Less than 1 percent of all .S. tornadoes are this violent—only about 10 a year.
The United States’ Great Plains is the “best place on Earth” for the formation of violent tornadoes because of geography, Markowski said. You need the low pressure systems coming down off the Rocky Mountains colliding with the warm moist unstable air coming north from the Gulf of Mexico.
Early research, much of it by Brooks, predicts that as the world warms, the moist energy—or instability—will increase, and the U.S. will have more thunderstorms. But at the same time, the needed wind shear—the difference between wind speed and direction at different altitudes—will likely decrease.
The two factors go in different directions and it’s hard to tell which will win out. Brooks and others think that eventually there may be more thunderstorms and fewer days with tornadoes, but more tornadoes on those days when twisters do strike.
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