The deadliest tornado in history was invisible. In 1925, the Tri-State Tornado ravaged a mile-wide path for 219 miles across Missouri, Illinois, and Indiana at 60 miles per hour—twice the forward speed of the average tornado. It lacked the classic funnel cloud, but the damage was catastrophic: nearly 2,000 people were injured, property losses totaled more than $16 million, and 689 people died.
The high death count in the Tri-State disaster is extremely unusual. The odds a person will be killed by a tornado in a year are 1 in 4,513,000. Over that same period, it is more likely a person will die from a fall off a cliff—1 in 4,101,000—or will be diagnosed with leprosy—1 in 2,930,000.
The spring 2009 tornado season saw US fatalities at their lowest level in three years. At the end of June 2009, 21 deaths were on record, compared with an unusually high 121 deaths at the same time in 2008, and 74 deaths at the same time in 2007.
There is no fixed relationship between the number of lives lost and the number of tornadoes that occur every year. Despite so few deaths, the US tornado count at the end of June 2009 was only slightly below the three-year average: 850 versus 935.
Tornadoes are measured on the Fujita Scale, named after a professor who started his career cataloging the damage in post-1945 Hiroshima and Nagasaki, Japan. The 6-category Fujita Scale classifies a tornado by the damage it causes. The majority of tornadoes rank low on the scale and leave a minimal mark. At F0, a tornado might do nothing more than break some tree branches. The odds a tornado will be an F0 are 1 in 2.32. A tornado that measures F3 has the wallop to uproot those trees. At F5, a storm can easily uproot houses, even those with a solid foundation. The odds a tornado will be categorized as an F5—Tri-State level—are 1 in 634.5.
No one knows why some thunderstorms form tornadoes and others do not. Last spring, more than 50 scientists embarked on the largest tornado research project to date. The “Verification of the Origins of Rotation in Tornadoes Experiment,” or VORTEX2, is an in-field observation initiative that will be concluded this spring. The research area spans nearly 900 miles of prairie land.
Tornados can occur almost anywhere, but VORTEX2 focuses on the central swath of the US, a region dubbed “Tornado Alley.” It encompasses parts of the High Plains, Midwest, and South. This area is the perfect breeding ground for intense storms because of the clash of warm, moist winds blowing northward from the Gulf of Mexico and cold, dry winds drifting east off the Rocky Mountains.
This geographic vulnerability puts Tornado Alley citizens at greater risk. The odds a tornado in Tennessee, Arkansas, and Kentucky will cause one or more deaths are 1 in 10.49, 1 in 15.16, and 1 in 15.44, respectively, while the same odds for a tornado in arid Colorado (ironically in the center of the Rockies) are 1 in 1,631. And the odds a tornado will cause at least $5,000,000 worth of damage are nearly 20 times greater in Ohio than in North Dakota (1 in 28.13 vs.1 in 553).
VORTEX2 hopes to minimize these losses by developing better forecasting strategies. But fighting unpredictability is predictably difficult. The project observed only one tornado during five weeks of observation in the spring of 2009 and missed more than 75 twisters that occurred within days of leaving the scene. Mother Nature likes to keep her secrets.
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