Winds Too Quick to Meter
Although tornadoes occur throughout the world, including India and Bangladesh, they are most intense and devastating in the United States. Tornadoes can strike at any time of day, but they are much more frequent in the afternoon and evening, after the heat of the day has produced the hot air that is a requirement of a tornadic thunderstorm (defined).

On average, the United States experiences 100,000 thunderstorms each year, causing about 1,000 tornadoes. The National Weather Service says an average of 42 people are killed by tornadoes annually.

Tornadoes are so common in Tornado Alley because of mountains to the west and the Gulf of Mexico to the south, explains Howard Bluestein, professor of meteorology at University of Oklahoma, and veteran storm chaser. In spring, he says, a strong westerly jet stream flows across the Alley, creating instability and a trough of low pressure that draws in warm, moist air from the Gulf. "Conditions for the supercells [large, powerful thunderstorms] that spawn tornadoes require strong vertical wind shear [changes in wind speed and direction with height] and lots of instability," he says. And that's exactly what happens in Tornado Alley.

The Fujita scale shows the range of violence of tornadoes. An F-5 tornado produces the most violent winds on earth, approaching speeds of 300 miles per hour. (In the Fujita scale, the wind speed is inferred by analyzing the damage, it's not measured directly.)

Tornadoes range in width (as measured by the damage path) from less than 150 feet to more than a mile.

Tornadoes can last from a few minutes to more than an hour.

A tornado can travel along the ground between a few hundred feet to more than 100 miles.

Tornadoes travel along the ground at between 0 and 60 mph.

Other peculiar winds
Tornadic thunderstorms produce a couple of other bizarre kinds of wind.

• A waterspout is a weak (usually) tornado over water. They are most common along the Gulf Coast and southeastern states. In the western United States, they occur with cold fall or late winter storms, when you would least expect a tornado to develop.
• A downburst is a downward blowing wind that sometimes comes blasting out of a thunderstorm. The damage looks like tornado damage, since the wind can be as strong as an F2 tornado (!), but debris is blown straight away from a point on the ground. It's not lofted into the air and transported downwind.

We haven't even talked about why twisters are so phenomenally powerful.