NASA - National Aeronautics and Space Administration

A tornado is the strongest and roughest of all storms. A tornado is also called a twister. It is made up of a huge, cone-shaped tube of air that twists and swirls very fast over land. A tornado over a large body of water is called a waterspout.

Image to left: A tornado forms under a large, anvil-shaped thundercloud. First, a dark wall cloud forms underneath the thundercloud. Then a twisting, funnel-shaped cloud comes down from the wall cloud and touches the ground. Rain and hail often fall from the thundercloud. The arrows show how the tornado spins. Credit: World Book illustration by Bruce Kerr

Tornadoes form under thunderclouds. First a dark wall cloud builds up underneath the thundercloud. Then a twisting funnel cloud comes down from the wall cloud and touches the ground.

Tornado winds swirl at speeds up to 300 miles (480 kilometers) per hour. A powerful tornado can lift cattle, cars, and even mobile homes into the air. And it can destroy almost everything in its path.

Only a few tornadoes cause major damage. The powerful ones can last longer than an hour, but most tornadoes last only a few minutes. Tornadoes strike most often during the spring and early summer in the late afternoon and early evening.

The United States has more tornadoes than any other country in the world. Most of these storms happen in an area known as Tornado Alley. This area stretches across the Midwestern and Southern states, especially Texas, Oklahoma, Kansas, Nebraska, and Iowa.

Tornadoes can strike in other parts of the world, too. Australia is second to the United States in number of tornadoes. Bangladesh also gets many tornadoes.

Scientists who study weather can tell that bad weather may happen 14 to 48 hours in advance. They use computers and radar to help determine that a tornado may happen. In the United States, the National Weather Service puts out a tornado watch when its scientists think a tornado could happen. If there is a tornado watch in the area, people should watch for bad weather and listen to the radio or television for more information. If the National Weather Service thinks a tornado is forming, or if it gets a report of a funnel cloud, it will put out a tornado warning. When there is a tornado warning, people should take cover right away by going in a basement or some other underground shelter.

How to cite this article: To cite this article, World Book recommends the following format: "Tornado." The World Book Student Discovery Encyclopedia. Chicago: World Book, Inc., 2005.

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