Tornado Alley
The term was first used in 1952 as the title of a research project to study severe weather in areas of Texas, Oklahoma, Kansas, South Dakota, Iowa, Missouri, Nebraska, Colorado, North Dakota, and Minnesota. It is largely a media-driven term although tornado climatologists distinguish peaks in activity in certain areas and storm chasers have long recognized the Great Plains tornado belt.
Climate of the United States
In the lower Midwest (and southern Plains states, especially), temperatures can rise or drop rapidly; winds can be extreme; and clashing air masses, including hot, dry air of Mexican and/or Southwestern origin, warm, moist air from the Gulf of Mexico and cold, dry air from Canada can spawn severe thunderstorms and tornadoes, particularly from April to June. The "dryline," separating hot, dry air of Mexican/Southwestern U.S. origin from warm, moist air from the Gulf of Mexico, often causes severe, occasionally violent, thunderstorms to fire in central and eastern Texas, Oklahoma and Kansas; these sometimes contribute toward the hailstorms and tornado outbreaks that the Southern Plains are well known for. Reflecting these air-mass conflicts, central Oklahoma, including the Oklahoma City and Moore-Norman areas, has the highest frequency of tornadoes per unit land area on planet Earth, with May the highest-risk month for tornadoes throughout "Tornado Alley," from northern Texas north-northeastward toward western and central Iowa.