Where is Tornado Alley why do so many occur there?

Tornado Alley is located on the central plains of the United States and stretches from Texas north to Iowa. Tornado Alley is not just famous for the number of tornadoes it gets but for the frequency of strong tornadoes. This high frequency of strong tornadoes is due to an ideal climate setup. In the spring, warm, moist air from the Gulf of Mexico creates hot, humid conditions on the Plains. Storm systems bring in fronts that push cool and from Canada and dry air from the Rockies into this tropical air, triggering strong thunderstorms that are fueled by the heat and humidity. The thunderstorms are further aided by a layer of stable air called a cap that forms about a mile above the ground. This cap initially prevents storms from forming, allowing the air beneath it to become even more unstable. When thunderstorms do form they do so explosively and are stronger than they would otherwise be. As the storms form they encounter yet another conditions called wind shear, which occurs when the wind at different heights blows at different speeds and in different directions. The wind shear has two effects. First, it separates the updraft and downdraft portions of the storm. The separation prevents the rain-cooled air of the downdraft from choking off the updraft, which is how ordinary thunderstorms usually die. The storms are able to become even stronger and last longer than normal. Finally the wind shear can cause the storms to start rotating, becoming supercells, the most powerful thunderstorms on Earth. It is the strong rotation in such storms that produces most tornadoes.