Twisters Most Common in United States

Tornado season is upon us. The whirlwinds that rank among nature's most destructive phenomena occur most often during the spring in the United States. Violent tornadoes, huge funnels of furiously rotating air, may pack winds of 300 miles per hour, the strongest ever seen on the Earth's surface. Even a “weak” one may carry winds stronger than a hurricane. Most tornadoes last for only a few minutes, and none survives for more than several hours. But in their short lifetimes, these fearsome storms can kill people, level towns and toss automobiles—even train cars—around like toys.

The word “tornado” derives from the Spanish words “tornar” (to turn) and “tronada” (thunderstorm). The most common nicknames for tornado are “twister” and “cyclone.” More tornadoes form in the United States than anywhere else on Earth. Between 750 and 1,000 are reported each year. The country's vast expanse of flatland—particularly the Great Plains area between the Rockies and the Appalachians—is the perfect arena for clashes of cold and warm air that create severe thunderstorms which, in turn, spawn tornadoes. Many of them occur in open spaces and do not harm inhabited areas. Tornadoes are rare in the Pacific Coast and Northeast states.

Scientists have theories on how tornadoes are formed but so far have been unable to prove them. No instrument that can measure wind speed and air pressure within a storm funnel has ever survived a direct hit by a tornado. Systematic efforts by “storm-chasers” to photograph and measure tornadoes have been undertaken only since the early 1970s.