Tornadoes: When the Air Begins to Spin

A dark thunderstorm stretches across the sky. Beneath it, a narrow column reaches toward the ground, swirling dust and debris into the air. This is a tornado: a violently rotating column of air that extends from a thunderstorm to the ground. Some tornadoes last only a few minutes, while others remain on the ground much longer. Even a brief tornado can be dangerous.

How tornadoes form

Many tornadoes develop from powerful thunderstorms called supercells. A supercell has a rotating updraft, or a spinning current of rising air. The ingredients for such a storm often include warm, moist air near the ground and cooler, drier air above it. As the warm air rises, it can help build a towering thunderstorm cloud.

Winds at different heights may blow at different speeds or in different directions. This difference, called wind shear, can cause air to begin rotating. A storm’s strong updraft can tilt some of that rotating air upward. Under certain conditions, rotation becomes concentrated near the ground, and a tornado may form.

The details are complicated, however. Not every supercell produces a tornado, and scientists are still investigating why some storms do while similar storms do not. Tornadoes can also form in other kinds of storms, not just supercells.

From funnel to ground