Tornado

tornado, dark, funnel-shaped cloud containing violently rotating air that develops below a heavy cumulonimbus cloud mass and extends toward the earth. The funnel twists about, rises and falls, and where it reaches the earth causes great destruction. The diameter of a tornado varies from a few feet to a mile; the rotating winds may attain velocities of 200 to 300 mi (320–480 km) per hr, and the updraft at the center may reach 200 mi per hr. The Fujita scale is the standard scale for rating the severity of a tornado as measured by the damage it causes. A tornado is usually accompanied by thunder, lightning, heavy rain, and a loud "freight train" noise.

In comparison with a cyclone or hurricane, a tornado covers a much smaller area but can be violent and destructive. The atmospheric conditions required for the formation of a tornado include great thermal instability, high humidity, and the convergence of warm, moist air at low levels with cooler, drier air aloft. Although tornadoes have occurred on every continent except Antarctica, they are most common in the continental United States, where tornadoes typically form over the central and southern plains, the Ohio valley, and the Gulf states. The area where the most violent storms commonly occur in the United States is known as Tornado Alley, which is usually understood to encompass the plains from N central Texas north to the Dakotas, with the peak frequency located in Oklahoma. A tornado typically travels in a northeasterly direction with a speed of 20 to 40 mi (32–64 km) per hr, but tornadoes have be reported to move in a variety of directions and as fast as 73 mi (117 km) per hr—or to hover in one place. The length of a tornado's path along the ground varies from less than one mile to several hundred. Tornadoes occurring over water are called waterspouts.

Bibliography

See J. Verkaik and A. Verkaik, Under the Whirlwind: Everything You Need to Know about Tornadoes but Didn't Know Who to Ask (1998); H. B. Bluestein, Tornado Alley: Monster Storms of the Great Plains (1999).

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tornado

Violent, low-pressure storm, relatively small in diameter but with very rapidly rotating winds and an intense updraft near the centre. The relatively low pressure at the centre of a tornado's funnel-like vortex causes cooling and condensation, making the storm visible as a revolving column of cloud, called the funnel. Tornadoes normally travel at 30–40 mph (50–65 kph). The winds around the vortex average nearly 300 mph (500 kph) and have been known to reach 500 mph (800 kph). Tornadoes often occur in groups.

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tornado

1. a violent storm with winds whirling around a small area of extremely low pressure, usually characterized by a dark funnel-shaped cloud causing damage along its path

2. a small but violent squall or whirlwind, such as those occurring on the West African coast

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tornado [tȯr′nād·ō]

(meteorology)

An intense rotary storm of small diameter, the most violent of weather phenomena; tornadoes always extend downward from the base of a convective-type cloud, generally in the vicinity of a severe thunderstorm.

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(programming)

Tornado - The software development environment previously distributed with VxWorks.

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Tornado 

an atmospheric vortex that originates in a cumulonimbus cloud and then reaches toward the surface of land or sea, assuming the shape of a dark hose or snout. Its upper part exhibits a funnel-shaped widening that blends with the clouds. When a tornado descends to the land surface, its lower part also expands and resembles an inverted funnel. The height of a tornado may attain 800–1,500 m. Air within a tornado usually rotates in a counterclockwise direction, simultaneously rising upward in a spiral and sucking in dust and water; the velocity of rotation is several tens of meters per second. In connection with the lowering of air pressure inside the funnel, there is condensation of water vapor. The water vapor, as well as the funnel cloud, dust, and water, makes the tornado visible. The diameter of a tornado above sea is measured in tens of m, and above dry land in hundreds of m.

A tornado usually originates in the warm sector of a cyclone, most frequently in advance of a cold front. It travels in the same direction as the cyclone, which moves at a rate of 10–20 m/sec. While in existence, a tornado travels a path of 40–60 km. The formation of tornadoes is associated with extremely unstable atmospheric stratification.

Tornadoes are accompanied by thunderstorms, rain, and hail. They almost always cause large-scale destruction when sweeping the ground because they draw in water and objects in their path; they are lifted to considerable heights and moved over great distances. Tornadoes formed at sea, which are called waterspouts, pose a grave danger to ships. Tornadoes over dry land are sometimes called twisters.