Why Does Tornado Alley Have So Many Tornadoes?

Cold Dry Air

• The first ingredient for tornado formation is cold, dry air. This ingredient is provided by continental polar and maritime polar air masses that sweep down over the Rocky Mountains from Canada or the North Pacific. As these cold air masses traverse the mountains, their moisture is squeezed out. The result is cold, dry air flowing down off of the Rockies and into the Central Plains, aka tornado alley.

Warm Moist Air

• The second ingredient for tornado formation is warm, moist air. This ingredient is provided by maritime tropical air masses that develop over the Gulf of Mexico. These air masses move northward, providing a steady inflow of warm, moist air to the Central Plains.

Atmospheric Instability

• The third ingredient for tornado formation is atmospheric instability. This ingredient is provided by the clash of air masses along a cold front. Along the front, the dense cold air plows under the lighter warm air. This wedge of cold air rapidly lifts the warm air, creating instability. This instability produces the vertical development that is required for the formation of thunderstorms and, ultimately, tornadoes.

Wind Shear

• The final ingredient for tornado formation is wind shear. As wind direction and speed change with height, a horizontally spinning column of air is formed. When this column is tilted upward by the powerful updraft in a thunderstorm, it produces a vertical area of circulation within the storm cell. If this area of circulation, called a mesocyclone, continues to intensify within the thunderstorm, it can extend to the ground as a tornado.

Tornado Alley

• Tornado alley sits in the cross hairs of where these air masses typically meet and wind shear is prone to occur. A cold front forms at the leading edge of the cold air mass, extending southward from a center of low pressure. This front moves eastward into the warm, moist air that is flowing northward, producing instability and severe thunderstorms. The low-pressure system circulates counterclockwise, producing easterly flowing winds aloft. These winds flow perpendicular to the inflow of surface winds from the warm air mass, triggering wind shear. Together, these ingredients combine to produce a heightened potential for tornado formation over tornado alley.