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.
Tornado outbreak sequence of April 19–24, 2011
The tornado outbreak sequence of April 19–24, 2011 was an extended period of significant tornado activity that began on April 19th, 2011 and ended on April 24, 2011. It affected the Midwest and Southern United States. The outbreak produced an EF4 tornado that tore through the St. Louis metropolitan area. Other tornadoes caused damage in Illinois, Indiana, and Ohio. Amazingly, no fatalities were reported in this outbreak. However, it was later followed less than 48 hours later by the largest tornado outbreak in the history of the United States.