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.
1998 Eastern tornado outbreak
The 1998 Eastern Tornado Outbreak stands out, because it spawned an unusually high number of supercell thunderstorms, occurrences of damaging winds and hail, and tornadoes, in the central Appalachian Mountain area, where most residents were unaccustomed to experiencing such violent thunderstorms that are commonly believed to only occur in Tornado Alley in the central part of the United States.