Tornado

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Tornado, violently rotating column of air extending from within a thundercloud down to ground level. The strongest tornadoes may sweep houses from their foundations, destroy brick buildings, toss cars and school buses through the air, and even lift railroad cars from their tracks. Tornadoes vary in diameter from tens of meters to nearly 2 km (1 mi), with an average diameter of about 50 m (160 ft). Most tornadoes in the northern hemisphere create winds that blow counterclockwise around a center of extremely low atmospheric pressure. In the southern hemisphere the winds generally blow clockwise. Peak wind speeds can range from near 120 km/h (75 mph) to almost 500 km/h (300 mph). The forward motion of a tornado can range from a near standstill to almost 110 km/h (70 mph).

A tornado becomes visible when a condensation funnel made of water vapor (a funnel cloud) forms in extreme low pressures, or when the tornado lofts dust, dirt, and debris upward from the ground. A mature tornado may be columnar or tilted, narrow or broad—sometimes so broad that it appears as if the parent thundercloud itself had descended to ground level. Some tornadoes resemble a swaying elephant's trunk. Others, especially very violent ones, may break into several intense suction vortices—intense swirling masses of air—each of which rotates near the parent tornado. A suction vortex may be only a few meters in diameter, and thus can destroy one house while leaving a neighboring house relatively unscathed.

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