Any tornado is a swirl of air that's rising into its parent cloud. Scientists are still trying to work out the details of what supplies the twisting motion. We have another index to the Vortex Project , a major tornado research effort. You could also go to our graphic on supercell thunderstorms , which are the source of the strongest tornadoes. The numbers are ratings of tornado wind speed.
Tornadoes can last from a few seconds to more than an hour.
They might remain on the ground for just a few yards or for more than 100 miles. On average, tornadoes move from the southwest to the northeast at about 30 mph. Tornadoes have been known to move in any direction at speeds up to 70 mph. Some have sat nearly stationary for several minutes. But, it is unusual for tornadoes to change speed and direction during their lifetime.