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Surprise! Tornadoes form from the ground up

Call Dorothy—the formation of tornadoes has been knocked on its head. New measurements from tornadoes in Oklahoma and Kansas suggest these storms’ swirling winds first develop near the ground. That’s contrary to the long-accepted theory that tornado winds are born several kilometers up in clouds and only later touch down on Earth’s surface.

Researchers analyzed four tornadoes, including a monster known as El Reno (shown above), which holds the record as the widest tornado ever measured, at 4.2 kilometers. They noticed something odd when they compared radar measurements that tracked wind speed with hundreds of photographs and videos of El Reno taken by storm chasers: The storm’s funnel was already on the ground several minutes before the radar data—taken roughly 250 meters off the ground—recorded any rotation.

Out of curiosity, the scientists reanalyzed radar measurements taken near the ground. (A hilltop vantage point during the storm serendipitously allowed the team to scan close to the ground without the interfering effects of trees and telephone poles.) They found rapid rotation near the ground before it appeared higher up, a pattern that was confirmed in three other tornadoes, as they will report tomorrow at the semiannual meeting of the American Geophysical Union in Washington, D.C.

These findings have important implications for how weather forecasters issue tornado warnings, the researchers suggest. That’s because forecasters often rely on measurements of wind speeds high up in clouds. Because wind might already be swirling at dangerous speeds near the ground, weather warnings might be tardy in sounding the alarm for tornado-strength winds.