What Is a Tornado and How Does It Form?
A tornado, or twister, is a violently rotating column of air that extends between the Earth’s surface and a cloud, usually a cumulonimbus cloud.
A tornado begins as a funnel cloud with spinning columns of air that drop down from a severe thunderstorm. When they reach the ground they become tornadoes.
Tornadoes are between 300 and 2,000 feet wide and travel at speeds of 20 to 45 miles per hour. They usually only last a few minutes, but their spinning winds, up to 300 miles per hour, can lift houses into the air and rip trees from the ground.
The more common tornadoes have wind speeds of less than 110 miles (177 kilometers) per hour, are about 250 feet (76 meters) across, and travel only a few miles before they dissipate. Tornadoes kill an average of 60 people a year in the U.S., mostly from flying or falling debris.
Tornadoes are truly a mystery. Basically, they start as a horizontal column of air that rotates. For some reason, some of these turn vertical. Meteorologists are still unsure why this is. Once they turn vertical, they turn into a funnel cloud. As soon as they touch the ground, they become a tornado.