In Harm’s Way

Tornadoes have touched down in every state. But big ones happen most regularly each spring in Tornado Alley, from Texas to the northern Great Plains. Here warm, moist air from the Gulf of Mexico collides with fast-moving cold, dry air from the Rockies, generating strong wind shear and atmospheric instability—key elements of tornadic thunderstorms.

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How a Tornado Forms

Wind Shear

Fast-moving winds roll air below into a horizontal vortex—a spinning tube—above opposing surface winds.

El Reno Time line, May 31, 2013

Forecasters note extreme atmospheric instability in Oklahoma.

Warm, moist air rises until it hits warm, dry air—the cap.

GRAPHIC: LAWSON PARKER, NGM STAFF
ART: NICK KALOTERAKIS
SOURCE: GABE GARFIELD, NATIONAL WEATHER SERVICE AND COOPERATIVE INSTITUTE FOR MESOSCALE METEOROLOGICAL STUDIES