The last two tornado seasons have been the deadliest in a decade,

with 206 deaths. Everyone from the insurance industry to Al Gore worry 【M1】__________

that global warming may be causing more tornado activity. But there’s

no baseline for comparison. That’s why we have no accurate record of 【M2】__________

tornadoes before the 1950s, back when it was possible for these brief,

freakish funnels of air to blow over the unpopulated areas without a 【M3】__________

notice.

Tornado warnings have improved over the years; forecasters can

now issue warnings about 18 minutes after touchdown for 75 percent of 【M4】__________

twisters. As longer-term forecasts, the science isn’t there yet, 【M5】__________

despite that you hear on the nightly news. “Television forecasters cater 【M6】__________

with the public’s curiosity about extreme weather,” says Michael H. 【M7】__________

Glantz, a professor at the University of Colorado at Boulder. Their

goal, of course, is to be first with a forecast of trouble ahead.

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 for storm frequency or severity. Experts say 【M8】__________

things like terrain, population density, and the number of mobile homes

play a role. And the biggest factor might be timing: “In the Plains,” 【M9】__________

explains Schaefer, “we have much more clearly defined period of 【M10】_________

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

(倾向) 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.

【M9】