Tornado Alley is a loosely defined area of the central United States where tornadoes are most frequent. The term was first used in 1952 as the title of a research project to study severe weather in areas of Texas, Louisiana, Oklahoma, Kansas, South Dakota, Iowa and Nebraska. Tornado climatologists distinguish peaks in activity in certain areas and storm chasers have long recognized the Great Plains tornado belt.
Although the official boundaries of Tornado Alley are not clearly defined, the main alley extends from northern Texas, through Oklahoma, Kansas, Nebraska, Iowa, and South Dakota. States such as Minnesota, Wisconsin, Illinois, Indiana, Missouri, North Dakota and Ohio are sometimes included in Tornado Alley. Research suggests that tornadoes are becoming more frequent in the northern parts of Tornado Alley where it reaches the Canadian prairies.