As the parent thunderstorm travels along, tornadoes can come down from the cloud, run along the ground and lift back up to be followed by other tornadoes. Generally, tornadoes move along the ground at around 20 to 50 mph, but some race along faster than 70 mph. The most destructive tornadoes also often have smaller suction vortices rotating around the main vortex. These show up in some photos and leave distinctive, looped patterns in fields of corn or other crops knocked over by the winds. Tornado debris can be huge.
Debris blown by tornado winds can pound buildings to pieces.
The strongest tornadoes come from the kind of long-lasting, especially fierce thunderstorms known as supercells. As the name implies, these are intense thunderstorms which can produce large hail and downbursts in addition to tornadoes. Some bring heavy rain while others are relatively dry. Supercells are most common on the Plains in the Southeast and across the Midwest, but do occur elsewhere. Storms form when there is unstable air, a source of lifting, and humidity.