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Flash Points
- The last two tornado seasons have been the deadliest in a decade, with 206 deaths. Everyone from the insurance industry to Al Gore worries that global warming may be causing more tornado activity. But there's no baseline for comparison. That's because we have no accurate record of tornadoes before the 1950s, back when it was possible for these brief, freakish funnels of air to blow over then-unpopulated areas without notice.
- Tornado warnings have improved over the years; forecasters can now issue warnings about 18 minutes before touchdown for 75 percent of twisters. As for longer-term forecasts, the science isn't there yet, despite what you hear on the nightly news. "Television forecasters pander to the public's curiosity about extreme weather," says Michael H. Glantz, a professor at the University of Colorado at Boulder. Their goal, of course, is to be first with a forecast of trouble ahead. But beware those who insist on linking El Niño (the cyclical surface warming of the eastern Pacific Ocean) to tornado likelihood. The slight correlation is "not enough to be directly useful in forecasting," says Joe Schaefer, director of the Storm Prediction Center in Norman, Oklahoma.
- The number of deaths per tornado is greater in the South than in Tornado Alley (the Great Plains and part of the Midwest)—a disparity that can't be explained by storm frequency or severity. Experts say things like terrain, population density, and the number of mobile homes play a role. But the biggest factor might be timing: "In the Plains," explains Schaefer, "we have a much more clearly defined period of tornado activity, generally from March to late June. In the Southeast, tornadoes can happen all year long, so there may be less vigilance." Research also shows that the South may have a climatological propensity for nighttime storms, which catch people unawares—asleep in bed. Last year's two killer tornado outbreaks in North Carolina landed between 11:30 p.m. and 3:30 a.m.
From storm to major event: how havoc happens
1. Warm, moist air at the surface rises rapidly, creating an updraft.
2. Falling rain evaporates, cooling the air around it.
3. The wall cloud rotates as it's hit with winds from opposite directions.
4. As the rotation intensifies, a visible funnel drops out of the clouds.
5. A prominent overshooting top forms when the updraft is very strong.
6. Powerful updrafts give hail time to form.
7. A dust shroud is kicked up by the tornado's strong winds at ground level.
8. Central downdrafts appear in some tornadoes.
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