Tornadoes are more common in the United States than in any other country. The United States receives more than 1,200 tornadoes annually—four times the amount seen in Europe. Violent tornadoes—those rated EF4 or EF5 on the Enhanced Fujita Scale—occur more often in the United States than in any other country.
Most tornadoes in the United States occur in "Tornado Alley", an area including the states of Nebraska, Kansas, Oklahoma, Texas, and Iowa. Central Tornado Alley experiences the most activity, with about five tornadoes per latitude-longitude radius (a circle about 50 miles (80 km) wide) per year.
Although favorable conditions for tornadoes in the United States can occur at any time, they are most common in spring and least common in winter. Because spring is a transitional period for the climate, there are more chances of cooler air meeting with warmer air, resulting in more thunderstorms. Tornadoes can also be spawned by landfalling tropical cyclones, which usually occur in late summer and autumn. In the United States, thunderstorms capable of producing tornadoes usually form when the temperature is at its highest, typically from 4:00 p.m. to 7:00 p.m.
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