What geographical factors make tornadoes common in the US?

Two main geographic factors make tornadoes common in the U.S. The Gulf of Mexico. which provides the warm, moist air that powers thunderstorms, and the Rocky Mountains, which provide dry air. When a low pressure system forces the dry air into the moist air it creates a dry line, along which very powerful thunderstorms can form. The system will also likely pull in cool air from the north, which,, when forced into the warmer air creates a cold front. Strong thunderstorms may also form hear, but they tend to be more stronger along the dry line. If the cold front and dry line intersect the result is a triple point. Here the storms can become exceptionally powerful.

Given strong wind shear these powerful thunderstorms can produce tornadoes. Most tornadoes in the U.S. form between the Appalachian and Rocky Mountains.