South Dakota Tornado
A category F3 tornado swirls across a South Dakota prairie. The F (Fujita) scale was used to measure wind speeds based on damage left behind after a tornado, and an F3 tornado had wind speeds between 158 and 206 miles an hour (254 to 332 kilometers an hour). The United States now uses the EF (Enhanced Fujita) scale, which takes more variables into account when assigning wind speeds to a tornado. An EF3 tornado now has wind speeds between 136-165 miles per hour (218-266 kilometers per hour), and the tornado pictured could be an EF3, EF4 or EF5.