Tornado Alley is a colloquial term for the area of the 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 parts of Texas and Oklahoma. Although the boundaries of Tornado Alley are not clearly defined, its core is northern Texas, Oklahoma, Kansas and Nebraska.
In the heart of Tornado alley, building codes are often stricter than those for other parts of the U.S., requiring strengthened roofs and more secure connections between the building and its foundation. Other common precautionary measures include the construction of storm cellars and the installation of tornado sirens. Tornado awareness is also high.