May has the highest tornado activity in the United States on average.
May is typically the busiest month for U.S. tornadoes because spring places several key ingredients together: increasing warmth, abundant moisture from the Gulf of Mexico and strong contrasts between warm and cool air masses. These conditions help create the instability and wind shear that severe thunderstorms need to produce tornadoes.
The peak is not identical everywhere. Tornado activity begins earlier in the Southeast, where winter and early-spring systems can be dangerous, while the southern Plains often reach their peak in May and early June. Farther north, the seasonal maximum can arrive in June or even July. Thus, May describes the national average, not every state’s local tornado season.
April and June are commonly the next busiest months nationally. Another common misconception is that tornadoes are confined to “Tornado Alley”; all 50 states have reported tornadoes, and seasonal risk shifts across the country. Individual years can also break the normal pattern, with major outbreaks occurring in other months.