Combination of factors contribute to US deadliest tornado

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In the wake of the deadliest tornado outbreak in the United States since the Great Depression, a U.S. meteorologist said Friday a combination of factors contributed to the tornadoes' devastation that killed more than 300.

Jim Stefkovich, meteorologist in charge at National Weather Service's office in Birmingham, Alabama, told Xinhua in an interview that to produce an extremely violent tornado, there must be very warm moisture near the ground, and at 10,000 to 20,000 feet above ground, when wind start to change, "circulations" are formed.

"Just like ice skaters skating on ice, as they bring their arms in together, they spring faster," he said. "So the storm is rotating for a depth of 3 or 4 miles within a thunderstorm. It gets narrower towards the ground, and spins faster."

He said tornadoes are typically not very wide, and are about 100 yards. But in the case of the tornado that struck Wednesday night at Tuscaloosa, the worst hit Alabama town in this outbreak, it was about half a mile wide, and that's why it caused so much damage to the small town.

Stefkovich said tornadoes in the United States almost all occur east of the Rocky Mountains at the so-called tornado alley, which includes the Midwest and eastern United States.

He said the Midwest is very flat and it is easy to see tornadoes. That is why a lot of storm chasers go there to watch or study the tornadoes.

He said southeastern states such as Alabama get just as many tornadoes as the Midwest, but because of the hilly terrain and dense vegetation, it is harder to see them.

"Unfortunately, this time, we here at Alabama were under the gun here instead of the Midwest," said Stefkovich.

Alabama took the hardest hit in Wednesday's tornado outbreak. All across the United States, the death toll from the storms reached 329 in seven states, and Alabama alone accounted for 238 of them, making it the deadliest tornado outbreak since March 1932, when another Alabama storm killed 332 people.

"It's just all the ingredients both near the ground and in the upper levels of the atmosphere. They had to come all together at one location for this severe weather to occur," said Stefkovich. "Unfortunately, everything came together at the exact spot in Alabama."

When such violent tornadoes were formed, Stefkovich said there're not many choices for people, and to remain safe, they must go underground. He said the National Weather Service put out warnings 48 hours ahead of the tornadoes struck, and local news channels have been broadcasting the events and warnings nonstop, but still big casualty numbers occur.

At Rosedale, one of Tuskaloosa's leveled neighborhoods, Robert Gordon, who is with the University of Alabama, said that despite the warning, some of the people just didn't believe the tornado will come their way.

"A lot of the kids walk around like they are invincible," said Gordon.

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