Most tornadoes are found in the Great Plains of the central United States – an ideal environment for the formation of severe thunderstorms. In this area, known as Tornado Alley, storms are caused when dry cold air moving south from Canada meets warm moist air traveling north from the Gulf of Mexico. Tornadoes can form at any time of year, but most occur in the spring and summer months along with thunderstorms. May and June are usually the peak months for tornadoes.

Which two states have the highest number of tornadoes per year per 10,000 sq miles?
Choose one of the answers below:

Texas and Florida
Oklahoma and Indiana
Oklahoma and Texas
Florida and Indiana

Notice that the location with the highest number of thunderstorms does not match the location with the highest number of tornadoes. Click here to compare the two maps.

Why do so many tornadoes form in this part of south central North America?
Choose one of the answers below:

Many important crops are grown here.
The land is very flat.
The area experiences very unstable atmospheric conditions that can lead to the development of supercell thunderstorms.
This region of the U.S. is known for dry, cool surface air temperatures.

The Great Plains are conducive to the type of thunderstorms (supercells) that spawn tornadoes. It is in this region that cool, dry air in the upper levels of the atmosphere caps warm, humid surface air. This situation leads to a very unstable atmosphere and the development of severe thunderstorms.

Look at the map above. The blue lines show the paths of tornadoes produced by storms on April 3rd & 4th, 1974. Why are the lines all parallel and pointing in a southwest to north direction?

The storms were moving from the southwest to the northeast.
They follow major highways.