Tornado Alley
States such as Missouri, Iowa, Minnesota, Wisconsin, Illinois, Indiana, and western 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.
St. Louis tornado history
These tables describe the tornado history for Greater St. Louis. In Missouri, this includes the counties of St. Louis, St. Charles, Franklin, and Jefferson. In Illinois, this includes the counties of Madison, St. Clair, and Monroe. Data for the independent city of St. Louis is not part of these tables unless part of the path of the tornado striking these counties also struck the city.