While tornadoes can occur at any time of year, they most often form during early spring and summer. They can happen anywhere, but they are most prevalent throughout the Midwest and Deep South. A map of Tornado Alley USA consists of several states, including Oklahoma, Kansas, Iowa, Missouri, Nebraska and South Dakota.
An average of 1,200 tornadoes occur yearly, with most remaining relatively weak. However, a handful evolve into extremely dangerous and deadly tornadoes, costing hundreds of lives and billions of dollars in damage.
Here are five of the most devastating tornadoes in United States history.
1. The Tri-State Tornado of 1925
One of the deadliest tornado outbreaks occurred on March 18, 1925, across portions of Indiana, Illinois and Missouri. The forecasts were vague because weather reports and records were less detailed than they are now.