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'Very unusual' start to tornado season

Residents salvaged what they could after several tornadoes touched down near Dallas on Tuesday, flattening houses. More than 600 homes were damaged, but remarkably nobody died. NBC's Lester Holt reports.

Tornado season is only just beginning, but already this year has seen dozens of destructive twisters from Illinois to Texas, where up to 18 might have touched town on Tuesday alone in the Dallas-Fort Worth area.

"We're at just the beginning of a very unusual" tornado season, NBC weather anchor Al Roker said on TODAY. 

The numbers show just how unusual: March saw 223 twisters, up from an average of 80 from 1991-2010, according to the National Weather Service. February saw 63, compared to an average of 29; and January saw 97, compared to an average of 35.

So what's behind the outbreak?

"We've had record heat," weather.com meteorologist Greg Forbes told TODAY, and "that warmth is a big ingredient that provides the instability for the storms."

Last year started off slowly but then saw a record 758 tornadoes in April 2011, noted Roker. "Hopefully we're not on track for that this year."

U.S. forecasters have predicted a warmer than normal spring in the central part of the country, which could increase tornado threats. But countering that is the fact the cyclical La Nina weather pattern, which can help fuel twisters, is waning.

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Before Tuesday, the last big twister outbreak was on March 23, when tornadoes touched down in six states -- Alabama, Georgia, Illinois, Indiana, Kentucky and Missouri -- killing one person, injuring dozens and damaging hundreds of structures.

So far this year, tornadoes have caused 55 deaths, most on Feb. 29 and March 2 during outbreaks across the Midwest and the South. Through March of 2011, only 2 deaths were attributed to tornadoes.

The peak months for tornadoes are usually April, May and June, so this season is really just beginning.

Tuesday's outbreak suggests "we're on pace to be above normal," the Associated Press quoted National Weather Service meteorologist Matt Bishop as saying.

Some climate scientists expect more extreme weather if global temperatures continue to rise, while others say the science is not strong enough to make that conclusion about single events or even a single season.

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