Tornadoes tend to occur during late spring to early summer in the United States. During this time of year, conditions are ripe for producing tornadoes across an area called Tornado Alley.
By far, the United States produces the most tornadoes each year; about 1,200 tornadoes occur in the U.S. alone. When cold, dry air from the Arctic meets warm, moist air from the Gulf, conditions become favorable for the formation of tornadoes. The most dangerous tornadoes form from thunderstorms called supercells. Tornado Alley, which sees the most tornadoes in the world, stretches from central Texas northward to Iowa. Historically, Oklahoma City has been the city hit with the most tornadoes. Many tornadoes that occur in the United States do not cause damage because they are weak, ranging from a rating of EF-0 to EF-1.