Tornadoes in the United States
The Midwestern states are very prone to tornado activity, as they are part of "Tornado Alley." States included in the area that are hit by tornadoes the most are Oklahoma, Kansas, Missouri, Nebraska, Iowa, and South Dakota. The Midwestern States are often hit by tornadoes during the late spring and early summer months, especially the months of May and June. This is due to the aforementioned air mass moving northward into the Midwest and combining with another air mass that move southward from Canada. This creates unstable air, creating the potential for storms to strike the most during these months. The frequency begins to decrease in the middle of the summer, as the air mass moves northward into the Great Lakes states.
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.