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74-445: Whirlwinds are subdivided into two types, the great (or major) whirlwinds, and the lesser (or minor) whirlwinds. The first category includes tornadoes , waterspouts , and landspouts . The range of atmospheric vortices constitute a continuum and are difficult to categorize definitively. Some lesser whirlwinds may sometimes form in a similar manner to greater whirlwinds with related increase in intensity. These intermediate types include

148-472: A thunderstorm is blown through a mass of stationary, warm, moist air near the outflow boundary, resulting in a "rolling" effect (often exemplified through a roll cloud ). If low level wind shear is strong enough, the rotation can be turned vertically or diagonally and make contact with the ground. The result is a gustnado. They usually cause small areas of heavier rotational wind damage among areas of straight-line wind damage. A dust devil (also known as

222-524: A "rope tornado". When they rope out, the length of their funnel increases, which forces the winds within the funnel to weaken due to conservation of angular momentum . Multiple-vortex tornadoes can appear as a family of swirls circling a common center, or they may be completely obscured by condensation, dust, and debris, appearing to be a single funnel. In the United States, tornadoes are around 500 feet (150 m) across on average. However, there

296-496: A T0 for extremely weak tornadoes to T11 for the most powerful known tornadoes. Doppler weather radar data, photogrammetry , and ground swirl patterns ( cycloidal marks) may also be analyzed to determine intensity and award a rating. Tornadoes vary in intensity regardless of shape, size, and location, though strong tornadoes are typically larger than weak tornadoes. The association with track length and duration also varies, although longer track tornadoes tend to be stronger. In

370-441: A block of dark clouds, wider than the distance from the cloud base to the ground. Even experienced storm observers may not be able to tell the difference between a low-hanging cloud and a wedge tornado from a distance. Many, but not all major tornadoes are wedges. Tornadoes in the dissipating stage can resemble narrow tubes or ropes, and often curl or twist into complex shapes. These tornadoes are said to be "roping out", or becoming

444-460: A body of water (as a waterspout), tornadoes can turn white or even blue. Slow-moving funnels, which ingest a considerable amount of debris and dirt, are usually darker, taking on the color of debris. Tornadoes in the Great Plains can turn red because of the reddish tint of the soil, and tornadoes in mountainous areas can travel over snow-covered ground, turning white. Lighting conditions are

518-541: A continuous, deep rumbling, or an irregular sound of "noise". Since many tornadoes are audible only when very near, sound is not to be thought of as a reliable warning signal for a tornado. Tornadoes are also not the only source of such sounds in severe thunderstorms; any strong, damaging wind, a severe hail volley, or continuous thunder in a thunderstorm may produce a roaring sound. Tornadoes also produce identifiable inaudible infrasonic signatures. Unlike audible signatures, tornadic signatures have been isolated; due to

592-462: A few rotations per minute. Steam devils are very rare. They most often form from smoke issuing from a power plant's smokestack. Hot springs and deserts may also be suitable locations for a tighter, faster-rotating steam devil to form. The phenomenon can occur over water, when cold arctic air passes over relatively warm water. The Fujita scale , Enhanced Fujita scale (EF), and International Fujita scale rate tornadoes by damage caused. The EF scale

666-588: A lack of intense property damage, the tornado achieved a rating of EF3 on the Enhanced Fujita scale . Nevertheless, the El Reno tornado is one of the two strongest tornadoes ever recorded in terms of maximum wind speeds, the other being the 1999 Bridge Creek–Moore tornado which doppler radar measured 321 miles per hour (517 km/h) mph. The 1997 Jarrell tornado was another example of a multiple-vortex tornado. The infamous “Dead Man Walking” photo of it

740-435: A major factor in the appearance of a tornado. A tornado which is " back-lit " (viewed with the sun behind it) appears very dark. The same tornado, viewed with the sun at the observer's back, may appear gray or brilliant white. Tornadoes which occur near the time of sunset can be many different colors, appearing in hues of yellow, orange, and pink. Dust kicked up by the winds of the parent thunderstorm, heavy rain and hail, and

814-1018: A mesocyclone) waterspouts. Fair weather waterspouts are less severe but far more common, and are similar to dust devils and landspouts . They form at the bases of cumulus congestus clouds over tropical and subtropical waters. They have relatively weak winds, smooth laminar walls, and typically travel very slowly. They occur most commonly in the Florida Keys and in the northern Adriatic Sea . In contrast, tornadic waterspouts are stronger tornadoes over water. They form over water similarly to mesocyclonic tornadoes, or are stronger tornadoes which cross over water. Since they form from severe thunderstorms and can be far more intense, faster, and longer-lived than fair weather waterspouts, they are more dangerous. In official tornado statistics, waterspouts are generally not counted unless they affect land, though some European weather agencies count waterspouts and tornadoes together. A landspout , or dust-tube tornado ,

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888-413: A probe measured a 100- millibar (100  hPa ; 3.0  inHg ) pressure decrease. The pressure dropped gradually as the vortex approached then dropped extremely rapidly to 850  mbar (850  hPa ; 25  inHg ) in the core of the violent tornado before rising rapidly as the vortex moved away, resulting in a V-shape pressure trace. Temperature tends to decrease and moisture content to increase in

962-404: A recognizable life cycle which begins when increasing rainfall drags with it an area of quickly descending air known as the rear flank downdraft (RFD). This downdraft accelerates as it approaches the ground, and drags the supercell's rotating mesocyclone towards the ground with it. As the mesocyclone lowers below the cloud base, it begins to take in cool, moist air from the downdraft region of

1036-436: A small cloud of debris near the ground. Tornadoes may be obscured completely by rain or dust. These tornadoes are especially dangerous, as even experienced meteorologists might not see them. Small, relatively weak landspouts may be visible only as a small swirl of dust on the ground. Although the condensation funnel may not extend all the way to the ground, if associated surface winds are greater than 64 km/h (40 mph),

1110-621: A tornado impacts. A tornado may be much stronger than its damage-based rating indicates if its strongest winds occur away from suitable damage indicators, such as in an open field. Outside Tornado Alley , and North America in general, violent tornadoes are extremely rare. This is apparently mostly due to the lesser number of tornadoes overall, as research shows that tornado intensity distributions are fairly similar worldwide. A few significant tornadoes occur annually in Europe, Asia, southern Africa, and southeastern South America. The United States has

1184-707: A tornado touches the surface and returns to the baseline level when the tornado dissipates. In many cases, intense tornadoes and thunderstorms exhibit an increased and anomalous dominance of positive polarity CG discharges. Luminosity has been reported in the past and is probably due to misidentification of external light sources such as lightning, city lights, and power flashes from broken lines, as internal sources are now uncommonly reported and are not known to ever have been recorded. In addition to winds, tornadoes also exhibit changes in atmospheric variables such as temperature , moisture , and atmospheric pressure . For example, on June 24, 2003, near Manchester, South Dakota ,

1258-593: A tornado. Tornadoes normally rotate cyclonically (when viewed from above, this is counterclockwise in the northern hemisphere and clockwise in the southern ). While large-scale storms always rotate cyclonically due to the Coriolis effect , thunderstorms and tornadoes are so small that the direct influence of the Coriolis effect is negligible, as indicated by their large Rossby numbers . Supercells and tornadoes rotate cyclonically in numerical simulations even when

1332-762: A whirlwind) resembles a tornado in that it is a vertical swirling column of air. However, they form under clear skies and are no stronger than the weakest tornadoes. They form when a strong convective updraft is formed near the ground on a hot day. If there is enough low-level wind shear, the column of hot, rising air can develop a small cyclonic motion that can be seen near the ground. They are not considered tornadoes because they form during fair weather and are not associated with any clouds. However, they can, on occasion, result in major damage. Small-scale, tornado-like circulations can occur near any intense surface heat source. Those that occur near intense wildfires are called fire whirls . They are not considered tornadoes, except in

1406-468: A widely accepted theory for how most tornadoes form, live, and die, it does not explain the formation of smaller tornadoes, such as landspouts, long-lived tornadoes, or tornadoes with multiple vortices. These each have different mechanisms which influence their development—however, most tornadoes follow a pattern similar to this one. A multiple-vortex tornado is a type of tornado in which two or more columns of spinning air rotate about their own axes and at

1480-407: A wind storm. These wind blasts can start to rotate and form minor whirlwinds. Winds from other small storms (such as rain storms and local thunderstorms ) can cause minor whirlwinds to form. Like major whirlwinds, these minor whirlwinds can also be dangerous at times. Eddies and vortices may form in any fluid . In water, a whirlpool is a similar phenomenon. Tornado A tornado

1554-407: Is a tornado not associated with a mesocyclone. The name stems from their characterization as a "fair weather waterspout on land". Waterspouts and landspouts share many defining characteristics, including relative weakness, short lifespan, and a small, smooth condensation funnel that often does not reach the surface. Landspouts also create a distinctively laminar cloud of dust when they make contact with

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1628-460: Is a violently rotating column of air that is in contact with both the surface of the Earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud . It is often referred to as a twister , whirlwind or cyclone , although the word cyclone is used in meteorology to name a weather system with a low-pressure area in the center around which, from an observer looking down toward

1702-411: Is a wide range of tornado sizes. Weak tornadoes, or strong yet dissipating tornadoes, can be exceedingly narrow, sometimes only a few feet or couple meters across. One tornado was reported to have a damage path only 7 feet (2.1 m) long. On the other end of the spectrum, wedge tornadoes can have a damage path a mile (1.6 km) wide or more. A tornado that affected Hallam, Nebraska on May 22, 2004,

1776-418: Is also commonly referred to as a "twister" or the old-fashioned colloquial term cyclone . 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. For a vortex to be classified as a tornado, it must be in contact with both the ground and the cloud base. The term

1850-437: Is no break in activity, this is considered a tornado outbreak (although the term "tornado outbreak" has various definitions). A period of several successive days with tornado outbreaks in the same general area (spawned by multiple weather systems) is a tornado outbreak sequence, occasionally called an extended tornado outbreak. Most tornadoes take on the appearance of a narrow funnel , a few hundred meters (yards) across, with

1924-447: Is not precisely defined; for example, there is disagreement as to whether separate touchdowns of the same funnel constitute separate tornadoes. Tornado refers to the vortex of wind, not the condensation cloud. A tornado is not necessarily visible; however, the intense low pressure caused by the high wind speeds (as described by Bernoulli's principle ) and rapid rotation (due to cyclostrophic balance ) usually cause water vapor in

1998-456: Is the satellite tornado . Unlike the multiple-vortex tornado, where smaller vortices form inside the main tornado, a satellite tornado develops outside the main tornado's circulation. It forms through a different mechanism, typically as a result of interactions with the parent storm's environment. Despite appearing close to the primary tornado, satellite tornadoes are independent and can have their own rotation. The largest tornado ever documented

2072-602: The La Plata Basin area, portions of Europe, Australia and New Zealand, and far eastern Asia. Multiple-vortex tornado A multiple-vortex tornado is a tornado that contains several vortices (called subvortices or suction vortices) revolving around, inside of, and as part of the main vortex . The only times multiple vortices may be visible are when the tornado is first forming or when condensation and debris are balanced such that subvortices are apparent without being obscured. They can add over 100 mph to

2146-682: The Latin tonāre 'to thunder'). The metathesis of the r and o in the English spelling was influenced by the Spanish tornado (past participle of tornar 'to twist, turn,', from Latin tornō 'to turn'). The English word has been reborrowed into Spanish, referring to the same weather phenomenon. Tornadoes' opposite phenomena are the widespread, straight-line derechos ( / d ə ˈ r eɪ tʃ oʊ / , from Spanish : derecho Spanish pronunciation: [deˈɾetʃo] , 'straight'). A tornado

2220-466: The equator and are less common at high latitudes . Other tornado-like phenomena that exist in nature include the gustnado , dust devil , fire whirl , and steam devil . Tornadoes occur most frequently in North America (particularly in central and southeastern regions of the United States colloquially known as Tornado Alley ; the United States has by far the most tornadoes of any country in

2294-428: The gustnado and the fire whirl . Other lesser whirlwinds include dust devils , as well as steam devils , snow devils , debris devils, leaf devils or hay devils, water devils, and shear eddies such as the mountainado and eddy whirlwinds. Major whirlwind A major whirlwind (such as a tornado ) is formed from supercell thunderstorms (the most powerful type of thunderstorm) or other powerful storms . When

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2368-406: The "funnel cloud" term is strictly defined as a rotating cloud which is not associated with strong winds at the surface, and condensation funnel is a broad term for any rotating cloud below a cumuliform cloud. Tornadoes often begin as funnel clouds with no associated strong winds at the surface, and not all funnel clouds evolve into tornadoes. Most tornadoes produce strong winds at the surface while

2442-422: The Coriolis effect is neglected. Low-level mesocyclones and tornadoes owe their rotation to complex processes within the supercell and ambient environment. Approximately 1 percent of tornadoes rotate in an anticyclonic direction in the northern hemisphere. Typically, systems as weak as landspouts and gustnadoes can rotate anticyclonically, and usually only those which form on the anticyclonic shear side of

2516-563: The RFD also reaches the ground, fanning outward and creating a gust front that can cause severe damage a considerable distance from the tornado. Usually, the funnel cloud begins causing damage on the ground (becoming a tornado) within a few minutes of the RFD reaching the ground. Many other aspects of tornado formation (such as why some storms form tornadoes while others do not, or what precise role downdrafts, temperature, and moisture play in tornado formation) are still poorly understood. Initially,

2590-405: The RFD, now an area of cool surface winds, begins to wrap around the tornado, cutting off the inflow of warm air which previously fed the tornado. The flow inside the funnel of the tornado is downward, supplying water vapor from the cloud above. This is contrary to the upward flow inside hurricanes, supplying water vapor from the warm ocean below. Therefore, the energy of the tornado is supplied from

2664-538: The UK (around 33, 0.00013/km , 0.00034/sq mi per year), although those are of lower intensity, briefer and cause minor damage. Tornadoes kill an average of 179 people per year in Bangladesh, the most in the world. Reasons for this include the region's high population density, poor construction quality, and lack of tornado safety knowledge. Other areas of the world that have frequent tornadoes include South Africa,

2738-506: The air to condense into cloud droplets due to adiabatic cooling . This results in the formation of a visible funnel cloud or condensation funnel. There is some disagreement over the definition of a funnel cloud and a condensation funnel. According to the Glossary of Meteorology , a funnel cloud is any rotating cloud pendant from a cumulus or cumulonimbus, and thus most tornadoes are included under this definition. Among many meteorologists,

2812-457: The audible sound depends on atmospheric conditions and topography. The winds of the tornado vortex and of constituent turbulent eddies , as well as airflow interaction with the surface and debris, contribute to the sounds. Funnel clouds also produce sounds. Funnel clouds and small tornadoes are reported as whistling, whining, humming, or the buzzing of innumerable bees or electricity, or more or less harmonic, whereas many tornadoes are reported as

2886-554: The case of the Tri-State Tornado. In fact, modern reanalysis of the path suggests that the tornado may have begun 15 miles (24 km) further west than previously thought. Tornadoes can have a wide range of colors, depending on the environment in which they form. Those that form in dry environments can be nearly invisible, marked only by swirling debris at the base of the funnel. Condensation funnels that pick up little or no debris can be gray to white. While traveling over

2960-544: The case of violent tornadoes, only a small portion of the path is of violent intensity, most of the higher intensity from subvortices . In the United States, 80% of tornadoes are EF0 and EF1 (T0 through T3) tornadoes. The rate of occurrence drops off quickly with increasing strength—less than 1% are violent tornadoes (EF4, T8 or stronger). Current records may significantly underestimate the frequency of strong (EF2-EF3) and violent (EF4-EF5) tornadoes, as damage-based intensity estimates are limited to structures and vegetation that

3034-493: The circulation is considered a tornado. A tornado with a nearly cylindrical profile and relatively low height is sometimes referred to as a "stovepipe" tornado. Large tornadoes which appear at least as wide as their cloud-to-ground height can look like large wedges stuck into the ground, and so are known as "wedge tornadoes" or "wedges". The "stovepipe" classification is also used for this type of tornado if it otherwise fits that profile. A wedge can be so wide that it appears to be

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3108-418: The cloud above. As the RFD completely wraps around and chokes off the tornado's air supply, the vortex begins to weaken, becoming thin and rope-like. This is the "dissipating stage", often lasting no more than a few minutes, after which the tornado ends. During this stage, the shape of the tornado becomes highly influenced by the winds of the parent storm, and can be blown into fantastic patterns. Even though

3182-428: The darkness of night are all factors that can reduce the visibility of tornadoes. Tornadoes occurring in these conditions are especially dangerous, since only weather radar observations, or possibly the sound of an approaching tornado, serve as any warning to those in the storm's path. Most significant tornadoes form under the storm's updraft base , which is rain-free, making them visible. Also, most tornadoes occur in

3256-414: The descending rear flank downdraft (RFD) in a cyclonic supercell. On rare occasions, anticyclonic tornadoes form in association with the mesoanticyclone of an anticyclonic supercell, in the same manner as the typical cyclonic tornado, or as a companion tornado either as a satellite tornado or associated with anticyclonic eddies within a supercell. Tornadoes emit widely on the acoustics spectrum and

3330-524: The efforts of storm spotters . There are several scales for rating the strength of tornadoes. The Fujita scale rates tornadoes by damage caused and has been replaced in some countries by the updated Enhanced Fujita Scale . An F0 or EF0 tornado, the weakest category, damages trees, but not substantial structures. An F5 or EF5 tornado, the strongest category, rips buildings off their foundations and can deform large skyscrapers . The similar TORRO scale ranges from T0 for extremely weak tornadoes to T11 for

3404-401: The first mesocyclone and associated tornado dissipate, the storm's inflow may be concentrated into a new area closer to the center of the storm and possibly feed a new mesocyclone. If a new mesocyclone develops, the cycle may start again, producing one or more new tornadoes. Occasionally, the old (occluded) mesocyclone and the new mesocyclone produce a tornado at the same time. Although this is

3478-528: The ground for more than 100 km (62 mi). Various types of tornadoes include the multiple-vortex tornado , landspout , and waterspout . Waterspouts are characterized by a spiraling funnel-shaped wind current, connecting to a large cumulus or cumulonimbus cloud. They are generally classified as non- supercellular tornadoes that develop over bodies of water, but there is disagreement over whether to classify them as true tornadoes. These spiraling columns of air frequently develop in tropical areas close to

3552-479: The ground, due to their differing mechanics from true mesoform tornadoes. Though usually weaker than classic tornadoes, they can produce strong winds which could cause serious damage. A gustnado , or gust front tornado , is a small, vertical swirl associated with a gust front or downburst . Because they are not connected with a cloud base, there is some debate as to whether or not gustnadoes are tornadoes. They are formed when fast-moving cold, dry outflow air from

3626-689: The ground, thus becoming visible. Major whirlwinds last longer because they are formed from very powerful winds, and it is hard, though not impossible, to interrupt them. Minor whirlwinds are not as long-lived; the winds that form them do not last long, and when a minor whirlwind encounters an obstruction (a building , a house , a tree , etc.), its rotation is interrupted, as is the windflow into it, causing it to dissipate. Supercell thunderstorms, other powerful storms, and strong winds are seen with major whirlwinds. Wind storms are commonly seen with minor whirlwinds. Also, small, semi-powerful “wind blasts” may be seen before some minor whirlwinds, which can come from

3700-400: The ground-relative wind in a tornado circulation and are responsible for most cases where narrow arcs of extreme destruction lie right next to weak damage within tornado paths. Suction vortices, also known as suction spots, are substructures found in many tornadoes, though they are not always easily visible. These vortices typically occur at the base of the tornado, where it makes contact with

3774-717: The ground. Sub-vortices tend to form after vortex breakdown reaches the surface, resulting from the interaction of cyclonically incoming and rising air. Although multi-vortex structures are common in tornadoes, they are not unique to them and can occur in other circulations, such as dust devils. This is a natural result of vortex dynamics in physics.Multi-vortex tornadoes should not be confused with cyclically tornadic supercells . Supercells are large, rotating thunderstorms that can produce multiple, distinct tornadoes, often referred to as tornado families . These tornadoes may form at different times or exist simultaneously but are separate from one another. A phenomenon similar to multiple vortices

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3848-592: The immediate vicinity of a tornado. Tornadoes often develop from a class of thunderstorms known as supercells. Supercells contain mesocyclones , an area of organized rotation a few kilometers/miles up in the atmosphere, usually 1.6–9.7 km (1–6 miles) across. Most intense tornadoes (EF3 to EF5 on the Enhanced Fujita Scale ) develop from supercells. In addition to tornadoes, very heavy rain, frequent lightning, strong wind gusts, and hail are common in such storms. Most tornadoes from supercells follow

3922-523: The interior of British Columbia , and western New Brunswick are also tornado-prone. Tornadoes also occur across northeastern Mexico. The United States averages about 1,200 tornadoes per year, followed by Canada, averaging 62 reported per year. NOAA's has a higher average 100 per year in Canada. The Netherlands has the highest average number of recorded tornadoes per area of any country (more than 20, or 0.00048/km , 0.0012/sq mi annually), followed by

3996-402: The late afternoon, when the bright sun can penetrate even the thickest clouds. There is mounting evidence, including Doppler on Wheels mobile radar images and eyewitness accounts, that most tornadoes have a clear, calm center with extremely low pressure, akin to the eye of tropical cyclones . Lightning is said to be the source of illumination for those who claim to have seen the interior of

4070-718: The long-distance propagation of low-frequency sound, efforts are ongoing to develop tornado prediction and detection devices with additional value in understanding tornado morphology, dynamics, and creation. Tornadoes also produce a detectable seismic signature, and research continues on isolating it and understanding the process. Tornadoes emit on the electromagnetic spectrum , with sferics and E-field effects detected. There are observed correlations between tornadoes and patterns of lightning. Tornadic storms do not contain more lightning than other storms and some tornadic cells never produce lightning at all. More often than not, overall cloud-to-ground (CG) lightning activity decreases as

4144-543: The most powerful known tornadoes. The International Fujita scale is also used to rate the intensity of tornadoes and other wind events based on the severity of the damage they cause. Doppler radar data, photogrammetry , and ground swirl patterns ( trochoidal marks) may also be analyzed to determine intensity and assign a rating. The word tornado comes from the Spanish tronada (meaning 'thunderstorm', past participle of tronar 'to thunder', itself in turn from

4218-405: The most tornadoes of any country, nearly four times more than estimated in all of Europe, excluding waterspouts. This is mostly due to the unique geography of the continent. North America is a large continent that extends from the tropics north into arctic areas, and has no major east–west mountain range to block air flow between these two areas. In the middle latitudes , where most tornadoes of

4292-406: The rare case where they connect to a pyrocumulus or other cumuliform cloud above. Fire whirls usually are not as strong as tornadoes associated with thunderstorms. They can, however, produce significant damage. A steam devil is a rotating updraft between 50-and-200-metre wide (160 and 660 ft) that involves steam or smoke. These formations do not involve high wind speeds, only completing

4366-502: The record-holding tornado for path length—the Tri-State Tornado , which affected parts of Missouri , Illinois , and Indiana on March 18, 1925—was on the ground continuously for 219 miles (352 km). Many tornadoes which appear to have path lengths of 100 miles (160 km) or longer are composed of a family of tornadoes which have formed in quick succession; however, there is no substantial evidence that this occurred in

4440-530: The same mesocyclone. The satellite tornado may appear to " orbit " the larger tornado (hence the name), giving the appearance of one, large multi-vortex tornado. However, a satellite tornado is a distinct circulation, and is much smaller than the main funnel. A waterspout is defined by the National Weather Service as a tornado over water. However, researchers typically distinguish "fair weather" waterspouts from tornadic (i.e. associated with

4514-400: The same time revolve around a common center. A multi-vortex structure can occur in almost any circulation, but is very often observed in intense tornadoes. These vortices often create small areas of heavier damage along the main tornado path. This is a phenomenon that is distinct from a satellite tornado , which is a smaller tornado that forms very near a large, strong tornado contained within

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4588-417: The sounds are caused by multiple mechanisms. Various sounds of tornadoes have been reported, mostly related to familiar sounds for the witness and generally some variation of a whooshing roar. Popularly reported sounds include a freight train, rushing rapids or waterfall, a nearby jet engine, or combinations of these. Many tornadoes are not audible from much distance; the nature of and the propagation distance of

4662-468: The southerly flow to its east. This unique topography allows for frequent collisions of warm and cold air, the conditions that breed strong, long-lived storms throughout the year. A large portion of these tornadoes form in an area of the central United States known as Tornado Alley . This area extends into Canada, particularly Ontario and the Prairie Provinces , although southeast Quebec ,

4736-409: The storm. The convergence of warm air in the updraft and cool air causes a rotating wall cloud to form. The RFD also focuses the mesocyclone's base, causing it to draw air from a smaller and smaller area on the ground. As the updraft intensifies, it creates an area of low pressure at the surface. This pulls the focused mesocyclone down, in the form of a visible condensation funnel. As the funnel descends,

4810-434: The storms start to spin, they react with other high altitude winds, causing a funnel to spin. A cloud forms over the funnel, making it visible. Minor whirlwind A minor whirlwind is created when local winds start to spin on the ground. This causes a funnel to form. The funnel moves over the ground, pushed by the winds that first formed it. The funnel picks up materials such as dust or snow as it moves over

4884-890: The surface of the Earth, winds blow counterclockwise in the Northern Hemisphere and clockwise in the Southern. Tornadoes come in many shapes and sizes, and they are often (but not always) visible in the form of a condensation funnel originating from the base of a cumulonimbus cloud, with a cloud of rotating debris and dust beneath it. Most tornadoes have wind speeds less than 180 kilometers per hour (110 miles per hour), are about 80 meters (250 feet) across, and travel several kilometers (a few miles) before dissipating. The most extreme tornadoes can attain wind speeds of more than 480 kilometers per hour (300 mph), can be more than 3 kilometers (2 mi) in diameter, and can stay on

4958-421: The tornado has a good source of warm, moist air flowing inward to power it, and it grows until it reaches the "mature stage". This can last from a few minutes to more than an hour, and during that time a tornado often causes the most damage, and in rare cases can be more than 1.6 km (1 mile) across. The low pressured atmosphere at the base of the tornado is essential to the endurance of the system. Meanwhile,

5032-427: The tornado is dissipating, it is still capable of causing damage. The storm is contracting into a rope-like tube and, due to conservation of angular momentum , winds can increase at this point. As the tornado enters the dissipating stage, its associated mesocyclone often weakens as well, as the rear flank downdraft cuts off the inflow powering it. Sometimes, in intense supercells, tornadoes can develop cyclically . As

5106-434: The visible funnel is still above the ground, so it is difficult to discern the difference between a funnel cloud and a tornado from a distance. Occasionally, a single storm will produce more than one tornado, either simultaneously or in succession. Multiple tornadoes produced by the same storm cell are referred to as a "tornado family". Several tornadoes are sometimes spawned from the same large-scale storm system. If there

5180-597: The world occur, the Rocky Mountains block moisture and buckle the atmospheric flow , forcing drier air at mid-levels of the troposphere due to downsloped winds, and causing the formation of a low pressure area downwind to the east of the mountains. Increased westerly flow off the Rockies force the formation of a dry line when the flow aloft is strong, while the Gulf of Mexico fuels abundant low-level moisture in

5254-640: The world). Tornadoes also occur in South Africa , much of Europe (except most of the Alps), western and eastern Australia, New Zealand, Bangladesh and adjacent eastern India, Japan, the Philippines, and southeastern South America (Uruguay and Argentina). Tornadoes can be detected before or as they occur through the use of pulse-Doppler radar by recognizing patterns in velocity and reflectivity data, such as hook echoes or debris balls , as well as through

5328-442: Was a multiple-vortex tornado. It struck El Reno, Oklahoma, on May 31, 2013 , as a rain-wrapped tornado, taking the lives of tornado researcher Tim Samaras , his son Paul, and their TWISTEX colleague, Carl Young. This storm also took the life of local amateur chaser, Richard Henderson. It had a maximum width of 2.6 miles (4.2 km) and a maximum recorded windspeed of at least 313 miles per hour (504 km/h). However, because of

5402-584: Was an update to the older Fujita scale, by expert elicitation , using engineered wind estimates and better damage descriptions. The EF scale was designed so that a tornado rated on the Fujita scale would receive the same numerical rating, and was implemented starting in the United States in 2007. An EF0 tornado will probably damage trees but not substantial structures, whereas an EF5 tornado can rip buildings off their foundations leaving them bare and even deform large skyscrapers . The similar TORRO scale ranges from

5476-438: Was up to 2.5 miles (4.0 km) wide at the ground, and a tornado in El Reno, Oklahoma on May 31, 2013, was approximately 2.6 miles (4.2 km) wide, the widest on record. In the United States, the average tornado travels on the ground for 5 miles (8.0 km). However, tornadoes are capable of both much shorter and much longer damage paths: one tornado was reported to have a damage path only 7 feet (2.1 m) long, while

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