Why Tornado Alley Happens

Geography

• The National Climatic Data Center defines Tornado Alley as an area in the central plains ranging from central Texas to northern. Also included is the territory from central Kansas and Nebraska east to western Ohio. The National Severe Storms Laboratory map shows Tornado Alley as including eastern South Dakota, southern Minnesota, a small part of southeast Wyoming, almost all of Nebraska, western Iowa, eastern Colorado and western Kansas, western Oklahoma and northern Texas. All of these areas possess common characteristics that make them prone to severe tornadoes.

Flat Land

• The topography of Tornado Alley tends to be flat prairie land. This lack of mountains or high elevations allows strong winds and thunderstorms to move across the land. Oklahoma, the state in Tornado Alley with the highest threat of tornadoes, is an example of Tornado Alley's landscape.

Collision of Air Masses

• Tornado Alley is the region where warm moist air masses from the south collide with cold air masses from the north, primarily Canada. The point of intersection is known as the "dryline." The dryline is the dividing line between substantial differences in dew points. Dew point temperatures measure the point at which air can no longer hold its water vapor. Dew point temperatures vary as much as 40 degrees on either side of the dryline, indicating the difference in the amount of moisture in the air. This collision of air masses normally generates the supercell thunderstorms that produce tornadoes in the late afternoon or early evening when cold air pushes the warm air upward.

Timing

• The most deadly time of year in Tornado Alley is late spring to early summer, mostly the months of May and early June. While tornadoes can occur at any time of the year, residents of Tornado Alley know that in the beginning of April through June are the prime times for warm and cold air to produce tornadoes.