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Tornado season off to violent start

Tornado season off to violent start

Tornado season arrived early this year with unusually active and violent weather that has resulted in up to $2 billion in insured losses, but next year could be entirely different due to several factors, catastrophe modelers and other experts say.

The factors include incomplete data regarding past tornado activity and the fact that decades may be required to determine whether global climate change has any impact on tornado activity, experts say.

Although the peak of tornado activity usually doesn't happen until May, this year's season has begun early and destructively.

According to Oakland, Calif.-based EQECAT Inc., more than 150 tornadoes touched down in two distinct systems between Feb. 28 and March 3. Total activity for the year through March 4 was 272 tornadoes, more than double the 2005-2011 average of 123 per year through the same period.

Alabama, Indiana, Illinois, Kentucky and Tennessee bore the brunt of the damage, according to EQECAT, which estimated that insured damage from the events could reach up to $2 billion.

For individual states, Texas leads the pack with an average of 155 tornadoes a year (see chart, page 20).

The tornadoes stemmed from a collision of warm, humid air from the Gulf of Mexico and colder, drier air from the west.

“It wasn't like a big heat wave going on,” said Tim Doggett, principal scientist at Boston-based catastrophe modeler AIR Worldwide.

The early March outbreak, which spawned more than 100 tornadoes, was caused by “a late winter jet stream pattern that gave us the right conditions for the thunderstorms to develop rotations,” he said. “Because the jet stream was so strong, when the storms formed, they traveled very quickly and so they had very long tracks.”

Some tornadoes in the recent outbreak had tracks 30 miles long.

“For this year and even last year, La Niña was partly to blame,” said Matt Nielsen, senior product manager at modeler Risk Management Solutions Inc. in Newark, Calif. “What we've seen even going back to 2008 is an increase in the amount of moisture coming up from the Gulf and the interaction with the storm systems increasing.”

But “I don't think we really can read very much into the timing of this particular outbreak,” said AIR's Mr. Doggett. “In 2006, we had a very similar strong start, but May and June were very quiet, so we actually ended that season below normal,” he said.

“2010 was very slow until May and June, and it ended up being very normal despite the slow start,” he said.

Tony Del Genio, research physical scientist at the National Aeronautic and Space Administration's Goddard Institute for Space Studies in New York, which is part of the National Aeronautic and Space Administration, cautioned against linking tornado activity with potential climate change. He said that predicting tornadoes is more difficult than predicting other forms of severe weather.

“The problem with climate change and tornadoes is we don't know enough about them to make those projections,” said Mr. Del Genio.

“It's tempting to look at some unusual, severe early season weather and wonder if it had something to do with climate change, but we wouldn't have enough data,” he said. “There's no way to say” whether this is just luck of the draw or whether it's part of something larger.

“There isn't an increase in tornado activity that's been scientifically proven, said Jose Miranda, EQECAT's Hackensack, N.J-based director of client advocacy. “Scientifically, there has not been an increase in tornadoes over 60 years.”

Instead, “bad luck of the draw” with tornadoes hitting metropolitan areas has occurred, with increased insured damage and loss of life, he said. He added that information about tornado activity has improved as well. Fifty years ago, there were not as many storm spotters and technology was less advanced, he said.

RMS' Mr. Nielsen pointed out that as activity shifted east in the recent outbreak, losses were higher than would have been the case in “Tornado Alley” farther west because of higher population density to the east.