National Geographic Tornadoes 101
A Tornado is a rapidly rotating column of air known as a vortex that has reached the ground. It is often associated with a funnel cloud, a funnel-shaped cloud that may appear near the ground in a thunderstorm. Tornado winds swirl at speeds that may exceed 300 miles (480 kilometers) per hour on rare occasions. Tornadoes are also sometimes called twisters.
Source: World Book Online, 2014.
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