A tornado is a violent windstorm characterized by a twisting, funnel-shaped cloud. It is spawned by a thunderstorm (or sometimes as a result of a hurricane) and produced when cool air overrides a layer of warm air, forcing the warm air to rise rapidly.

Tornadoes can occur at any time, but are most likely to occur between 3 pm and 9 pm. Peak tornado season in the southern states is March to May; in the northern states it is late spring through early summer.