Tornadoes are violent rotating columns of air that extend from thunderstorms to the ground. They can reach speeds of 300 mph and destroy buildings and landscapes. Over 1000 tornadoes are reported in the US each year. Tornadoes form when cold dry air collides with warm moist air and begins to spin. They are capable of tearing down houses and destroying almost anything in their paths. Tornadoes most commonly occur in the area known as Tornado Alley, which stretches from Texas through parts of the Midwest up to New York.