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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 Enhanced Fujita scaleFujita scale
or F-Scale,
scale for rating the severity of tornadoes as a measure of the damage they cause, devised in 1951 by the Japanese-American meteorologist Tetsuya (Ted) Fujita (1920–98).
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 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 cyclonecyclone,
atmospheric pressure distribution in which there is a low central pressure relative to the surrounding pressure. The resulting pressure gradient, combined with the Coriolis effect, causes air to circulate about the core of lowest pressure in a counterclockwise direction
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 or hurricanehurricane,
tropical cyclone in which winds attain speeds greater than 74 mi (119 km) per hr. Wind speeds gust over 200 mi (320 km) per hr in some hurricanes. The term is often restricted to those storms occurring over the N Atlantic Ocean; the identical phenomenon occurring over
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, a tornado covers a much smaller area but can be very violent and destructive. Under the right conditions, however, a large storm system can produce multiple (more than a hundred in rare cases) and longer-lasting tornadoes over a wide area, leading to widespread damage. The atmospheric conditions typically 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. Wind shear at the back of large thunderstorm can create horizontally spinning vortices that are pulled into the stormcloud by updrafts to form a mesocyclone, a rotating, upward-flowing columnar air mass; a tornado may form from the base of an intense mesocyclone.

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 historically located in Oklahoma. Tornadoes are also common in the South from Louisana and Arkansas east to Georgia, an area sometimes called Dixie Alley, where they may be more destructive and deadly due to greater population density. 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 waterspoutswaterspout,
tornado occurring at sea or over inland waters. The characteristic funnel-shaped cloud is formed at the base of a cumulus-type cloud and extends downward to the water surface, where it picks up spray.
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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).



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.

What does it mean when you dream about a tornado?

Dreams about tornadoes may indicate issues or conditions that make one feel overwhelmed and out of control. There may well be repressed rage. Tornadoes can also reflect some sort of tremendous upset in the immediate environment.


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.


A violently rotating column of air hanging down as a funnel-shaped cloud below a cumulonimbus cloud. Tornados are localized, extremely violent whirlwinds common in certain parts of the United Sates.


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


The software development environment previously distributed with VxWorks.


A tornado is a violent storm in nature, and it may represent violent emotional storms in your dreams. If you have reoccurring tornado dreams, consider the emotional changes in your life and also the amount of anger and rage that you may be currently experiencing. Tornadoes could also represent disruptions and upsets in you immediate environment and specific or current issues that may be overwhelming.
References in periodicals archive ?
If a tornado is made of air, how come you can see it?
From the few measurements we have, as few instruments survive a tornado, the pressure created in a strong tornado can measure about 27 inches on your home barometer.
A tornado usually first appears as a rotation in a huge thundercloud, often behind heavy rain or hail.
If a tornado looks as if it's not moving, it may either be moving straight away or straight towards you.
The tornado obliterated several trailer homes, a two story brick home and other structures, with debris scattered for several hundred yards.
The few decades of reports now available simply don't include enough twisters to permit a reliable analysis of the nation's tornado risk.
First, the model calculated the probability of a tornado occurring on a particular day.
This force is applied to try to force the door open by simulating the vacuum created by a tornado with wind speeds of 250 miles per hour.
The Wind Engineering Research Center is the world's preeminent tornado and analysis center, and recently collaborated with FEMA on a safety shelter book.
PHOTO (1 -- color) Firefighters examine the wreckage of a camper that was tossed by a tornado onto an overturned car.
The 73-year-old said she lost everything in the tornado.
The tornado touched down north of Chickasha, 26 miles northeast of the capital, and stayed on the ground until it reached Tinker Air Force Base, just east of the capital.