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Tornadoes are some of the most destructive forces of nature. Learn how tornadoes form, how they are rated, and the country where the most intense tornadoes o...
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- National Geographic
A tornado is a violently rotating column of air, in contact with the ground, either pendant from a cumuliform cloud or underneath a cumuliform cloud, and often (but not always) visible as a funnel cloud. [ 20 ] For a vortex to be classified as a tornado, it must be in contact with both the ground and the cloud base.
- Overview
- What is a tornado?
- What causes tornadoes?
- Characteristics of tornadoes
- Tornado destruction
- How tornadoes are forecasted
- 13 Striking Photographs of Natural Disasters
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Learn how these deadly storms form and wreak havoc, and how you can reduce your risk.
Tornadoes are vertical funnels of rapidly spinning air. Their winds may top 250 miles an hour and can clear a pathway a mile wide and 50 miles long.
Also known as twisters, tornadoes are born in thunderstorms and are often accompanied by hail. Giant, persistent thunderstorms called supercells spawn the most destructive tornadoes.
These violent storms occur around the world, but the United States is a major hotspot with about a thousand tornadoes every year.
A tornado is a violently rotating column of air that extends from a thunderstorm to the ground. It's often portended by a dark, greenish sky. Black storm clouds gather. Baseball-size hail may fall. A funnel suddenly appears, as though descending from a cloud. The funnel hits the ground and roars forward with a sound like that of a freight train approaching. The tornado tears up everything in its path.
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Tornadoes 101
Tornadoes are some of the most destructive forces of nature. Learn how tornadoes form, how they are rated, and the country where the most intense tornadoes occur.
Every U.S. state has experienced twisters, but Texas holds the record: an annual average of 120. Tornadoes have been reported in Great Britain, India, Argentina, and other countries, but they are most often seen in the United States.
Related to tornadoes, waterspouts are weak twisters that form over warm water. They sometimes move inland and become tornadoes.
The most violent tornadoes come from supercells, large thunderstorms that have winds already in rotation. About one in a thousand storms becomes a supercell, and one in five or six supercells spawns off a tornado.
Tornadoes can occur at any time of year, but they are more common during a distinct season that begins in early spring for the states along the Gulf of Mexico. The season follows the jet stream—as it swings farther north, so does tornado activity. May generally has more tornadoes than any other month, but April's twisters are sometimes more violent. Farther north, tornadoes tend to be more common later in summer.
Although they can occur at any time of the day or night, most tornadoes form in the late afternoon. By this time the sun has heated the ground and the atmosphere enough to produce thunderstorms.
Tornadoes form when warm, humid air collides with cold, dry air.
The denser cold air is pushed over the warm air, usually producing thunderstorms. The warm air rises through the colder air, causing an updraft. The updraft will begin to rotate if winds vary sharply in speed or direction.
As the rotating updraft, called a mesocycle, draws in more warm air from the moving thunderstorm, its rotation speed increases. Cool air fed by the jet stream, a strong band of wind in the atmosphere, provides even more energy.
Twisters are usually accompanied or preceded by severe thunderstorms and high wlnds. Hail is also common.
Once a tornado hits the ground, it may live for as little as a few seconds or as long as three hours.
The average twister is about 660 feet wide and moves about 30 miles an hour. Most don't travel more than six miles before dying out.
Massive tornadoes, however—the ones capable of widespread destruction and many deaths—can roar along as fast as 300 miles an hour.
These measurements are scientists' best estimations. Anemometers, which measure wind speed, cannot withstand the enormous force of tornadoes to record them.
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Every year in the United States, tornadoes do about 400 million dollars in damage and kill about 70 people on average.
Extremely high winds tear homes and businesses apart. Winds can also destroy bridges, flip trains, send cars and trucks flying, tear the bark off trees, and suck all the water from a riverbed.
High winds sometimes kill or injure people by rolling them along the ground or dropping them from dangerous heights. But most tornado victims are struck by flying debris—roofing shingles, broken glass, doors, metal rods.
The number of average deaths per year in the United States used to be higher before improved forecasting and warning systems were put into place.
Meteorologists at the U.S. National Weather Service use Doppler radar, satellites, weather balloons, and computer modeling to watch the skies for severe storms and tornadic activity.
Doppler radars record wind speeds and identify areas of rotation within thunderstorms. Since Doppler radar has been in use, the warning time for tornadoes has grown from fewer than five minutes in the 1980s to an average of 13 minutes by the late 2000s.
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A supercell thunderstorm strikes in South Dakota. Among the most severe storms, supercells can bring strong winds, hail, and even tornadoes. ( See more extreme weather pictures .)
Lightning Strikes
A supercell thunderstorm strikes in South Dakota. Among the most severe storms, supercells can bring strong winds, hail, and even tornadoes. (See more extreme weather pictures.)
Photograph by Jim Reed, National Geographic
Learn how tornadoes form, what causes them, and how they affect the environment and human lives. Find out about the characteristics, intensity, forecasting, and prevention of these deadly storms.
3 days ago · tornado, a small-diameter column of violently rotating air developed within a convective cloud and in contact with the ground. Tornadoes occur most often in association with thunderstorms during the spring and summer in the mid-latitudes of both the Northern and Southern Hemispheres.
- A tornado is a relatively small-diameter column of violently rotating air developed within a convective cloud that is in contact with the ground, u...
- The lifetime of a tornado is directly related to its intensity. The strong, intense tornadoes tend to last longer. Most tornadoes are weak, lasting...
- Tornadoes are most common on continents in the midlatitudes (between 20 and 60 degrees north and south), where they are frequently associated with...
- In absolute numbers, the United States has the most tornadoes by far: more than 1,000 per year have been reported there every year since 1990. It a...
- Tornadoes can generate the strongest winds known on Earth: wind speeds in the range of 500 kilometres (300 miles) per hour have been measured in ex...
Learn what a tornado is, where and when it occurs, how it is rated, and how to identify it. Find out the difference between a watch and a warning, and how to prepare for severe weather.
May 21, 2019 · Learn how tornadoes form, where and when they strike, and how they are forecasted. Find out the mysteries and challenges of studying these violent twisters.
Apr 18, 2011 · Learn how tornadoes form... and how to get out of their way. Subscribe: http://bit.ly/NatGeoSubscribe Get More 101 Videos: http://bit.ly/NatGeo101About Nat...
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- National Geographic
