A tornado is a violently rotating column of air that extends from a thunderstorm and comes into contact with the ground. In an average year about 1,000 tornadoes are reported nationwide, according to according to the National Oceanic and Atmospheric Administration.
Tornado intensity is measured by the Enhanced Fujita (EF) scale. The scale rates tornadoes on a scale of 0 through 5, based on the amount and type of wind damage. It incorporates 28 different “damage indicators,” based on damage to a wide variety of structures ranging from trees to shopping malls.