Why does Oklahoma have tornadoes?

Oklahoma gets a large number of tornadoes because there are often colliding air masses of different temperatures and/or dew points. These collisions often produce severe thunderstorms. The region that Oklahoma is in, called Tornado Alley, also gets a lot of wind shear. Wind shear occurs when wind at high altitude blows at a different speed and/or direction. This creates horizontal vortices of air that, when turned vertical, give a storm the spin it needs to produce a tornado.