Why does the central United States from Texas to the Ohio Valley experience the greatest frequency of tornadoes on Earth? What time of year do they occur and why?

Question

What will be an ideal response?

Answer 1

(not fully developed in the book, but good students will figure this out from the text)
Tornadoes are prominent in southeastern North America because of the local geography and air masses. Warm maritime tropical air masses from the Gulf of Mexico are drawn into the interior of the continent by large midlatitude cyclone, which are further aided by cold continental polar air masses descending southward from northern North America. The Rocky Mountains deflects these continental air masses southward, where they collide with the maritime air masses in the Great Plains. Simultaneously, the air movement aloft is characterized by a strong jet stream or general East to west or southwest to northeast flow. This upper air flow is nearly 90 degrees from the surface flow around the midlatitude cyclones, which tends to impart a vorticity to the thunderstorms developing along the collision between the air masses (cold front), which tends to form mesocyclones necessary for tornado formation. Most other places in the world lack the western mountain barrier to the air masses that produce the unusual surface flow, and thus, surface flow is not greatly different the flow aloft, minimizing atmospheric vorticity that leads to tornadoes.