Final answer:
Tornadoes are more common in specific regions of the U.S. during certain seasons. They form from severe thunderstorms and are caused by a difference in wind speeds.
Step-by-step explanation:
Tornadoes are more common in the southeast U.S. (e.g., Alabama & Mississippi) in early spring, central U.S. in late spring to early summer, and in the Northern Plains (e.g., Dakotas) in mid-summer.
The most active part of the world for tornadoes, called tornado alley, is in the central United States, between the Rocky Mountains and Appalachian Mountains.
Tornadoes come out of severe thunderstorms called supercells, which have a column of air rotating around a horizontal axis. The difference in wind speeds between the strong cold winds higher up in the atmosphere and weaker winds traveling north from the Gulf of Mexico causes the column of rotating air to shift, creating a tornado.