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By SUSAN F. LAVOY, a freelance writer in Philadelphia.

They struck while many slept. From the overnight hours of February 28 until March 3, as many as 77 confirmed tornadoes roared through 13 states, causing perhaps $2 billion in claims costs, killing dozens of people, and obliterating entire communities. The leap-day event alone saw 36 tornadoes make landfall with shocking force, including a particularly violent twister -- rated second highest (EF4) on the Enhanced Fujita Scale, with winds between 166 mph and 200 mph -- that effectively wiped out several small towns in Illinois and Indiana.

Forty-nine deaths have been attributed to tornadoes in 2012, according to EQECAT. But catastrophic risk modeling firms weren't exactly caught sleeping. They had 2011 to alert them.

Dubbed "Year of the Tornado" by weather wonks, 2011 was the second-deadliest tornado year (from 1950); 1,709 twisters caused 552 deaths, and an insured loss of around $20 billion.

Tornadoes are only one component of convective storms, which also produce large hail, straight-line winds and heavy rain.

Simply put, warmer-than-normal Gulf of Mexico waters supplied the humid, unstable air that energized this month's tornadoes by colliding with a cold front in the southern plains.

So do these near-record-breaking number of recent tornadoes represent the "new normal" in U.S. weather? And, if fluctuating ocean temperatures -- a major factor in tornado formation -- occurs in regular cycles, why so many tornadoes in just the past year?

Most modeling experts acknowledge a recent rise in tornado numbers, but believe that the statistics reflect increased reporting of weaker twisters in more-populated areas. "Clients are asking if there is a continuing upward trend," said Matthew Nielsen, model product manager at Risk Management Solutions. "While data is not robust enough to support that, tornado outbreaks have been farther east over the last four years, placing dangerous tornadoes in areas of higher population density than traditional Tornado Alley."

Jose Miranda, EQECAT's director of client advocacy, takes an historical view of tornado activity. "Over the last 60 years, the records don't show an increased trend. A tornado requires many ingredients, in the right place, in the right proportion, at the same time -- a very rare occurrence. Unfortunately, this convergence happened several times recently. But past tornado activity is not a predictor of future tornado activity."

Still, a perceived acceleration could shake a client's faith in accurate catastrophic risk modeling. Miranda, a meteorologist, asserts that, by explaining the science behind risk and engaging in ongoing "healthy dialogue," EQECAT can keep its clients' expectations realistic. "We advocate complete understanding of tornado risk, being informed of the entire range of possibilities out there."

Miranda believes that adjusting EQECAT's extremely complicated tornado risk model, accurately updated in 2007, is unnecessary. RMS's formula was designed to take into account anomalies like the 2011 season, Nielsen said.

"RMS built a solution that attempts to capture the true frequency of these damaging events, leveraging numerical modeling output and other methods.? RMS estimates that 2011 was a one-in-100-year aggregate loss event."

March 13, 2012

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