State of the Science Fact Sheet: Tornadoes, Climate Variability, and Climate Change

Tornadoes are intense rotating vertical columns of air that pose a great threat to lives and property. They typically form in an environment where winds are rapidly changing direction and speed with height (referred to as wind shear) and the atmosphere is unstable. Tornado damage has historically been classified according to the Fujita (F) scale, with F0 causing the least amount of damage and F5 the most. In 2007, the F-scale was replaced by the Enhanced Fujita (EF) scale, with tornado rating assigned similar EF0–5 designations as the F-scale. While tornadoes can occur during any season in the U.S., they are most frequent during the spring months of April, May, and June. Given the right set of atmospheric conditions, tornadoes can occur almost anywhere. In fact, tornadoes have been documented on every continent except Antarctica. The United States, by far, has the most frequent and strongest tornadoes in the world. This is related to its unique geography (Rocky Mountains and proximity to the Gulf of Mexico), which contribute to the development of large-scale weather systems capable of supporting severe thunderstorms and tornadoes. The areas of the U.S. most susceptible include the Great Plains, Midwest, and South.