tornadoes

A tornado is a violently rotating column of air which is in contact with both a cumulonimbus (or, in rare cases, cumulus) cloud base and the surface of the earth. Tornadoes can come in many shapes, but are typically in the form of a visible condensation funnel, with the narrow end touching the earth. Often, a cloud of debris encircles the lower portion of the funnel.

Most have winds of 110 mph (175 km/h) or less, are approximately 250 feet (75 meters) across, and travel a few miles (several kilometers) before dissipating. However, some tornadoes can have winds of more than 300 mph (480 km/h), be more than a mile (1.6 km) across, and stay on the ground for dozens of miles (more than 100 kilometers).^[1][2][3]

They have been observed on every continent except Antarctica; a significant percentage of the world's tornadoes occur in the United States.^[4] This is mostly due to the unique geography of the country, which allows the conditions which breed strong, long-lived storms to occur many times a year. Other areas which commonly experience tornadoes include Australia, south-central Canada, northwestern Europe, south-central and eastern Asia, east-central South America, and Southern Africa.^[5].

Etymology

The word "tornado" is an altered form of the Spanish word tronada, which means "thunderstorm". This in turn was taken from the Latin tronar, meaning "to thunder". It most likely reached its present form through a combination of the Spanish tronada and tornar ("to turn"); however, this may be a folk etymology.^[6][7]

Some common, related slang terms include: twister, whirlwind, cyclone, funnel, wedge, finger of God, Devil's tail, rope, or stovepipe. The word willy-willy is also rarely applied to tornadoes, however, the usual definition of the term is of a dust devil in Australia. ^{citations needed]}

Definitions

A tornado is defined by the National Weather Service (NWS) as "a violently rotating column of air in contact with the ground and extending from a thunderstorm base."^[8] A tornado does not necessarily have to be visible; however, the low pressures caused by the fast wind speeds (see Bernoulli's principle) usually cause water vapor in the air to condense into a visible condensation funnel.^[4]

A funnel cloud is a low-hanging, rotating cloud, with no associated strong winds at the surface. Funnel clouds are not tornadoes, however, many tornadoes initially descend from the parent storm as a funnel cloud. It is often difficult to tell the difference between a funnel cloud and a tornado from a distance. Many tornadoes can produce strong winds at the surface while the visible funnel is still a good distance from the ground.^[3]

Stronger tornadoes are often observed to have multiple vortices, or many columns of violently spinning air rotating around a common center. However, a satellite tornado is a term for a weak tornado which forms very near a large, strong tornado, often lasting no more than a minute. 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 funnel, and is much smaller than the main funnel.^[3]

A waterspout is a tornado over water. In general, most tornadoes over land are associated with a severe thunderstorm; however, the National Weather Service in the United States considers all waterspouts—including "fair weather" waterspouts—to be tornadoes. These less severe relatives of classic tornadoes are almost always weak (F0 or F1 on the Fujita Scale), and spawn from non-rotating thunderstorms, or even regular summer showers. Typically, waterspouts moving onto land cause little or no damage, and dissipate within minutes. However, strong waterspouts from supercells can cause significant damage if they impact land areas. In addition, strong tornadoes can move over lakes or over the ocean, becoming waterspouts, without losing intensity.

A landspout is an unofficial term for a tornado not associated with a mesocyclone. Known officially as a dust-tube tornado, it is usually weak, features a small condensation funnel which often does not appear to reach the ground, and is often marked by a tall tube of dust and/or debris reaching as far up as the parent cloud. Though usually weaker than ordinary tornadoes, they are tornadoes, and can cause serious damage^[3][8].

A gustnado is a small, vertical swirl associated with a gust front or downburst. Because they are technically not associated with the cloud base, there is some debate as to whether or not gustnadoes are actually tornadoes.^{[3] [9]} These usually cause localized areas of heavier damage among areas of straight-line wind damage caused by the gust front.

A dust devil is also a vertical swirling column of air. These phenomena resemble tornadoes, but are rarely as strong as even the weakest tornadoes, and tend to form under clear skies. Dust devils are not considered tornadoes because they form during fair weather, and are not associated with thunderstorms. However, they can, on occasion, result in major damage and fatalities, especially in arid areas.^{[10] [11]}

Life cycle

Most tornadoes follow a recognizable life cycle.^[8] The cycle begins when a strong thunderstorm develops a rotating mesocyclone a few miles up in the atmosphere, becoming a supercell. As rainfall in the storm increases, it 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 rotating mesocyclone towards the ground with it.

As the mesocyclone approaches the ground, a visible condensation funnel appears to descend from the base of the storm, often from a rotating wall cloud. As the funnel descends, the RFD also reaches the ground, creating a gust front that can cause damage a good distance from the tornado. Usually, the funnel cloud begins causing damage on the ground (becoming a tornado) within minutes of the RFD reaching the ground.

Initially, the tornado has a good source of warm, moist inflow to power it, so it grows until it reaches the mature stage. During its mature stage, which can last anywhere from a few minutes to more than an hour, a tornado often causes the most damage, and can in rare instances be more than one mile across. Meanwhile, the RFD, now an area of cool surface winds, begins to wrap around the tornado, cutting off the inflow of warm air which feeds the tornado.

As the RFD completely wraps around and chokes off the tornado's air supply, the tornado begins to weaken, becoming thin and rope-like. This is the dissipating stage, and the tornado often fizzles within minutes. During the dissipating stage, the shape of the tornado becomes highly influenced by the direction of surface winds, and can be blown into fantastic patterns.

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. In particularly intense supercells, tornadoes can develop cyclically. As the first mesocyclone and associated tornado dissipate, the storm's inflow is concentrated into a new area closer to the center of the storm. If a new mesocyclone develops, the cycle may start again, producing a new tornado. Occasionally, the old, or occluded mesocyclone, and the new mesocyclone produce a tornado at the same time.

Though this is 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.^[12]

Characteristics

Shape

Most tornadoes take on the traditional appearance of a narrow funnel, a few hundred yards across, with a small cloud of debris near the ground. However, tornadoes can appear in all manner of shapes and sizes.

Small, relatively weak landspouts might only be visible as a small swirl of dust on the ground. While the condensation funnel may not extend all the way to the ground, if associated surface winds are greater than 40 mph (64 km/h), it is considered a tornado.

Large single-vortex twisters, often violent, can look like a large wedge stuck into the ground, and are known as wedge tornadoes or wedges. Wedges can be so wide that they appear to be a block of dark clouds. Even experienced storm observers may not be able to tell the difference between a low-hanging cloud and a wedge tornado from a distance.

Tornadoes in the dissipating stage can appear like narrow tubes, or ropes, twisting into all manner of curls, twists, and s-shapes. These tornadoes, such as the one pictured at right, are roping out, or becoming a rope tornado. Multiple-vortex tornadoes can appear as a family of swirls circling a common center, or may be completely obscured by condensation, dust, and debris, appearing to be a single funnel.

In addition to these appearances, tornadoes may be obscured completely by rain or dust. These tornadoes are especially dangerous, as even experienced meteorologists might not spot them.^[10]

Size

In the United States, an average tornado is around 500 feet (150 m) across, and stays on the ground for 5 miles (8 km). While this is the average, there is an extremely wide range of tornado sizes, even for typical tornadoes.

Weak tornadoes, or strong but dissipating tornadoes, can be exceedingly narrow, sometimes only a few feet across. In fact, a tornado was once reported to have a damage path only 7 feet (2 m) long.^[10]

On the other end of the spectrum, wedge tornadoes can have a damage path a mile (1.6 km) wide or more. A tornado which affected Hallam, Nebraska on May 22, 2004 was at one point 2.5 miles (4 km) wide^[2].

In terms of path length, some meteorologists believe that 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). However, without a modern damage survey, it is impossible to determine whether or not the deadly event was a single tornado or a series of violent tornadoes produced by the same storm. The longest modern-day damage path was caused by a tornado which was on the ground for 160 miles (260 km) in northeastern North Carolina on November 22, 1992.^[13]

Appearance

Tornadoes, depending on the environment in which they form, can have a wide range of colors. Tornadoes which form in a dry environment can be nearly invisible, marked only by swirling debris at the base of the funnel. Condensation funnels which pick up little or no debris can be grey to white. While travelling over a body of water as a waterspout, they can turn very white or even blue. Funnels which move slowly, ingesting a lot 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 brilliantly white in the process.

Lighting conditions are also a major factor in the appearance of a tornado. A tornado which is "back-lit", or viewed with the sun behind it, will appear to be very dark. The same tornado, viewed with the sun at the observer's back, may appear grey or brilliant white. Tornadoes which occur near the time of sunset can be many different colors, appearing in hues of yellow, orange, and pink.^[15]

Dust kicked up by the winds of the parent thunderstorm, heavy rain and hail, and the darkness of night are all factors which can reduce the visibility of tornadoes, making them "invisible", in essence. Tornadoes occurring in these conditions are especially dangerous, since only radar observations, or possibly the sound of an approaching tornado, serve as any warning to those in the storm's path. Fortunately most significant tornadoes form under the storm's rain-free base, or the area under the thunderstorm's updraft, where there is little or no rain. In addition, most tornadoes occur between the hours of 4 and 8 pm, when the bright sun can penetrate even the thickest clouds. Also, night-time tornadoes are often illuminated by frequent lightning.

There is mounting evidence, including doppler radar images^[16] and eyewitness accounts^[17], which suggest that most tornadoes have a clear, calm center with extremely low pressure, akin to the eye found in tropical cyclones. This area would be clear (possibly full of dust), have relatively light winds, and be very dark, with the light blocked out by swirling debris on the outside of the tornado. Lightning is said to be the source of illumination for those who claim to have seen the interior of a tornado.

Rotation

Tornadoes normally rotate in a cyclonic direction (counterclockwise in the northern hemisphere). Large-scale storms always rotate cyclonically because of the Coriolis effect; however, tornadoes are too small in scale to be directly affected by the rotation of the earth. Approximately 1 tornado in 100 rotates in an anticyclonic direction. Typically, only landspouts and gustnados also rotate anticyclonically. However, on very rare occasions, an anticyclonic supercell can develop, producing a tornado that is typical except for its direction of rotation.^[18]

Intensity and damage

Tornadoes vary in intensity regardless of shape, size, and location. While strong tornadoes are typically larger than weak tornadoes, there are several instances of F5 tornadoes with damage paths less than 500 feet (150 m) wide. ^[13]

History of tornado intensity measurements

For many years, before the advent of home movies and doppler radar, scientists had nothing more than educated guesses as to the speed of the winds in a tornado. The only evidence indicating the wind speeds found in the tornado was the damage left behind by tornadoes which struck populated areas. Some thought they might exceed 500 mph, and perhaps even be supersonic.

In the 1950s, however, evidence mounted that the actual wind speeds were much lower than this. On April 2, 1957, a slow moving tornado traversed the south and east parts of Dallas, Texas. Before this day, only a few photographs and motion pictures of tornadoes were known to exist. However, because of many factors, including the tornado's high visibility, slow forward motion, and proximity to an urban center, it became (and still may be) the most filmed and photographed tornado in history. Frame-by-frame analysis of several pieces of footage taken that day showed that the debris flung about by the tornado was travelling at speeds up to 170 mph.^[15] Scientists had thought that faster wind speeds would produce the severe damage seen that day, so this tornado gave them their first real clue as to the range of tornado speeds.

In 1971, Dr. Tetsuya Theodore Fujita introduced the idea for a scale of tornado winds. With the help of colleague Allen Pearson, he created and introduced what came to be called the Fujita scale in 1973. The scale was based on a relationship between the Beaufort scale and the Mach number scale; the low end of F1 on his scale corresponds to the low end of B12 on the Beaufort scale, and the low end of F12 corresponds to the speed of sound at sea level, or Mach 1. In practice, tornadoes are only assigned categories F0 through F5.

The TORRO scale, developed by the Tornado and Storm Research Organisation (TORRO), was developed in 1974, and published a year later. The TORRO scale has 12 levels, which cover a broader range with tighter graduations. It ranges from a T0 for extremely weak tornadoes to T11 for the most powerful known tornadoes.^[19]

There is some debate as to the usefulness of the TORRO scale over the Fujita scale—while it may be helpful for statistical purposes to have more levels of tornado strength, often the damage caused could be created by a large range of winds, rendering it hard to narrow the tornado down to a single TORRO scale category.

Research conducted in the late 1980s and 1990s suggested that, even with the implication of the Fujita scale, tornado winds were notoriously overestimated, especially in significant and violent tornadoes. Because of this, in 2006, the American Meteorological Society introduced the Enhanced Fujita Scale, to help assign realistic wind speeds to tornado damage. The scientists specifically designed the scale so that a tornado assessed on the Fujita scale and the Enhanced Fujita scale would receive the same ranking. The EF-scale is more specific in detailing the degrees of damage on different types of structures for a given wind speed. While the F-scale goes from F0 to F12 in theory, the EF-scale is capped at EF5, which is defined as "winds ≥ 200 mph (≥ 320 km/h)".^[3] In the United States, the Enhanced Fujita scale will be used for tornado damage assessments beginning February 2, 2007.

The first observation which confirmed that F5 winds could occur happened on April 26, 1991. A tornado near Red Rock, Oklahoma was monitored by scientists using a portable Doppler radar, an experimental radar device that measures wind speed. Near the tornado's peak intensity, they recorded a wind speed of 115-120 m/s (257-268 mph or 414-432 km/h). Though the portable radar had uncertainty of ± 5-10 m/s (± 11-22 mph or ± 18-36 km/h), this reading was probably within the F5 range, confirming that tornadoes were capable of violent winds found nowhere else on earth.

Eight years later, during the Oklahoma Tornado Outbreak of May 3, 1999, another scientific team was monitoring an exceptionally violent tornado (one which would eventually kill 36 people in the area near Moore, Oklahoma). At about 7 pm, they recorded one measurement of 318 mph ^[1], 50 mph faster than the previous record. Though this reading is just short of the theoretical F6 rating, the measurement was taken more than 100 feet in the air, where winds are typically stronger than at the surface. In rating tornadoes, only surface wind speeds, or the wind speeds indicated by the damage resulting from the tornado, are taken into account.

Typical intensity

In the United States, F0 and F1 (T0 through T3) tornadoes account for 80% of all tornadoes. On the other hand, violent tornadoes (stronger than F4, T8), account for less than 1%.^[22] Worldwide, strong tornadoes account for an even smaller percentage of total tornadoes. Violent tornadoes are extremely rare outside of the United States and Bangladesh.

Typical damage

Further information: Fujita scale

As stated in the lede section, a typical tornado has winds of 110 mph (175 km/h) or less, is approximately 250 feet (75 meters) across, and travels a mile (1.6 km) or so before dissipating. However, there is no such thing as a typical tornado.

Two tornadoes that look almost exactly the same can produce drastically different effects. Also, two tornadoes which look very different can produce similar damage. This is due to the fact that tornadoes form by several different mechanisms, and also that they follow a life cycle which causes the same tornado to change in appearance over time. People in the path of a tornado should never attempt to determine its strength as it approaches. Between 1997 and 2005 in the United States, 38 people were killed by F1 tornadoes, and 3 were killed by F0 tornadoes.^[23] Even the weakest tornado can kill.

• Weak tornadoes

As stated in the previous section, an overwhelming majority of tornadoes are designated F1 or F0, also known as "weak" tornadoes. However, weak is a relative term for tornadoes, as even these can cause significant damage. F0 and F1 tornadoes are typically short-lived—since 1980 almost 75% of tornadoes rated weak stayed on the ground for one mile or less.^[13] However, in this time, they can cause both damage and fatalities.

F0 damage is characterized by superficial damage to structures and vegetation. Well-built structures are typically unscathed, sometimes sustaining broken windows, with minor damage to roofs and chimneys. Billboards and large signs can be knocked down. Trees have large branches broken off, and can be uprooted if they have shallow roots.

F1 damage has caused significantly more fatalities than that caused by F0 tornadoes. At this level, damage to mobile homes and other temporary structures becomes significant, and cars and other vehicles can be pushed off the road. Permanent structures can suffer major damage to their roofs.

• Significant tornadoes

F2 tornadoes are the lower end of "significant", and yet are stronger than most tropical cyclones (though tropical cyclones affect a much larger area). Well-built structures can suffer serious damage, including roof loss and collapse of outer walls. Mobile homes, however, are almost totally destroyed. Vehicles can be lifted off the ground, and lighter objects can become small missiles, causing damage outside of the tornado's main path. Wooded areas will have a large percentage of their trees snapped or uprooted.

F3 damage is a serious risk to life and limb. Few parts of affected buildings are left standing; well-built structures lose outer and inner walls. Cars are lifted off the ground, and can be tossed through the air for some distance. Wooded areas will suffer almost total loss of vegetation.

• Violent tornadoes

F4 damage typically results in a total loss of the affected structure. Well-built homes are reduced to a short pile of debris. Even heavy vehicles can become airborne, with very large projectiles being flung some distance.

F5 damage is almost always total. F5 tornadoes demolish well-built houses and sweep the foundation clean. The official description of this damage states that "incredible phenomena will occur". In history, F5 tornadoes have twisted skyscrapers, levelled entire communities, and stripped asphalt from the ground.

Prediction and detection

United States

In the United States, severe weather predictions are issued by the Storm Prediction Center, based in Norman, Oklahoma. Issued for the next three days, as well as for the four through eight day period, they will determine the probability of severe weather, including tornadoes. The SPC uses computer models, such as the NAM, GFS, WRF, and RUC to predict severe weather. They issue their outlooks based on data from these models, using such indicies as Lifted Index, CAPE, as well as temperature and dewpoint.

Warnings are issued by the regional National Weather Service offices, while watches are issued directly from the SPC.

The National Weather Service trains Skywarn spotters, consisting of local sheriff's deputies, state troopers, and ordinary citizens, to spot key features of storms which indicate severe hail, strong winds, and tornadoes. When severe weather is anticipated, local weather service offices request that these spotters be on the lookout for severe weather, and report any possible tornadoes immediately, so the office can issue a timely warning.

United Kingdom

In the United Kingdom, the Tornado and Storm Research Organisation (TORRO) makes experimental predictions.

Other countries

In the Japan, predictions and study of tornadoes in Japan are handled by the Japan Meteorological Agency.

Climatology

Geography

The UK has the highest average number of recorded tornadoes per area of any country (about 30 per year), but most are small and result in minor damage.^[24] . Bangladesh also suffers from tornadoes of equal severity to those in the USA but these tend to be less well reported because of the scarcity of media coverage. The annual human death toll at about 179 deaths per year from tornadoes in Bangladesh is however much greater than in the USA^[25].

Frequency of occurrence

Time of occurrence

As stated in previously, worldwide statistics for tornado occurrences are intermittant at best, so data presented here may not be valid worldwide.

Tornado occurrence in the United States is highly dependant on the time of day. ^[26]

Extremes

Main article: Tornado records

Tornadoes are the most violent weather events in the world. As such, they have been recorded to produce some incredible phenomena.

In terms of the most extreme tornado in history, the honor undoubtedly goes to the Tri-State Tornado which roared through parts of Missouri, Illinois, and Indiana on March 18, 1925. This tornado set (and still holds) records for the deadliest single United States tornado (695 dead), longest path length (219 miles, 352 km), longest duration (more than three hours), and fastest forward speed for a significant tornado (73 mph, 117 km/h).

The deadliest tornado in world history occurred on April 26, 1989 in Bangladesh, killing 1300 people. ^[25]

Tornado safety

Precautions

Though it is uncommon to get more than a few minutes warning before a tornado strikes, there are precautions and preventative measures that you can take in order to increase the chances of surviving a tornado. ^[27]

In tornado-prone areas, most homes have a storm cellar on the property. These underground refuges have saved thousands of lives.^{citation needed]}

If a tornado approaches...

If a tornado approaches and you are outside, seek shelter immediately in a well structured building. If a building is out of your reach, drop in a ditch.

If on the road, try to look for shelter. If there isn't any near try to look for a ditch and stay there until the danger passes. Never try to outrun a twister, for it may cost you your life as it may take an unexpected turn.

If in a house or building, seek shelter in the basement. If the structure does not have a basement, or if the tornado's so close that it won't allow you to reach a basement(for houses that have a storm cellar), go to the most innermost part of the house, preferably and usually a bathroom, and lay in the bathtub or hang on to the plumbing.^[27]

Myths and misconceptions

Main article: Tornado myths

An old american folk lore has it that when the sky is green in coloration it means the atmospheric conditions are favorable for a tornado to occur; hence the saying "when the clouds are green, they're gonna be mean." ^{citation needed]}

Continuing research

Though scientists have learned much from years of research, there are still many things about tornadoes which remain a mystery. ^[28] In fact, scientists still don't know exactly how a rotation in the middle of the thunderstorm descends to become a tornado. Research programs, including VORTEX, deployment of TOTO (the TOtable Tornado Observatory), and dozens of other programs, hope to solve many questions that still plague meteorologists.^[29] Using highway overpasses as shelter Myth: Highway overpasses are adequate shelter if a tornado approaches while you are on a road.

Sensational footage taken by a television crew hiding from a tornado under an overpass during the 1991 Andover, Kansas Tornado Outbreak helped to convince some that bridges are good shelters when a tornado is nearby. The members of the television crew (and several other travelers) survived by huddling high underneath the bridge and bracing themselves against support columns while a weak tornado appeared to pass directly over the bridge.

In reality, when directly hit by tornadoes, the confined spaces beneath overpasses increase the speed of the winds due to the Venturi effect, and thus make them potentially less safe. In the case of the Andover tornado footage, it was discovered that the tornado did not pass directly over the bridge, but instead over the ground slightly south of the bridge and camera crew, exposing them to much weaker winds.

[edit] Opening windows or doors Myth: Most tornado damage is due to the low pressure in the tornado causing the house to explode. Opening your windows or doors while a tornado approaches will equalize atmospheric pressure and help prevent property damage.

Since windows are typically the most fragile external feature of a house, they are in more danger from flying debris. Opening them during an active tornado wastes time and effort that could be spent on other, more useful protective measures. Homes do not "explode" when hit by a tornado, though it often appears so. Commonly, a tornado will break the windows first, allowing strong winds to enter the home. These winds may then push on the underside of the roof upwards, blowing it off. Without the roof, the walls lose structural support and will often fall outwards. Observing the wreckage after the collapse may give the impression the house was pushed apart from the inside.

Flying debris from a tornado will break any windows, so opening them only wastes valuable time and is even counterproductive to the soundness of the structure. It is the debris that breaks windows, not the difference in pressure.

As a note, this also applies to homes or structures that are hit by a hurricane. Studies from the National Hurricane center suggest that closed containers do not explode during high wind scenarios. But rather, an opening, such as a broken window, will allow the hurricane force winds to enter a room and subsequently destroy an entire building.

[edit] Mobile home and trailer parks Myth: Twisters are attracted to mobile homes and/or trailer parks.

Trailer parks consist of low-cost mobile homes with less structural integrity than traditional houses. A weak storm that leaves little damage to well-built structures might devastate a trailer park. Mobile homes do not attract tornadoes; they are just more susceptible to damage from them.

[edit] Safest location in a house Myth: During a tornado, the southwest corner of a building is the safest.

An unfortunately fatal belief, and for a long time it was considered sound advice but without any proof of safety compared to any other parts of a building. After the increase in tornado research during the turn of the millennium, the US National Weather Service has now adopted the advice that the central-most-room (or underground—absolute best) is the safest. In reality, a tornado can hit any part of a building thereby making any part of the exterior subject to damage from rapidly changing winds.

Some of the worst places during a tornado are in a room with many windows, any room with an exterior wall, or a large theater-like room such as a church or indoor basketball court. The best places are small rooms like closets or bathrooms.

[edit] Tornadoes in rough terrain and crossing rivers Myth: Tornadoes cannot form near rivers or cross them.

Myth: Tornadoes cannot follow terrain into steep valleys.

Myth: Tornadoes cannot travel over steep hills or mountains.

During the Super Outbreak, a tornado formed near Sayler Park section of Cincinnati, Ohio (near the Ohio River). It was among the six F5s of the outbreak. The city of Cairo, Illinois, which lies at the confluence of the Ohio and Mississippi Rivers, was also hit by a tornado that day.

The Tri-state tornado of 1925 crossed the Mississippi and possibly several other small bodies of water.

The F5 tornado of May 3, 1999 crossed the Yukon River in Oklahoma before it hit Moore, Oklahoma.

During the Super Outbreak, after destroying three schools, the Monticello tornado crossed over a 60-foot bluff and the Tippecanoe River and damaged several homes.

During the Super Outbreak, the Guin tornado crossed Monte Sano mountain (1,650 feet) and gained in intensity as it descended the mountain. An F4 tornado caused damage in Murphy, NC after crossing a 3,000-foot ridge, and F2 tornadoes were confirmed in Roanoke, VA and Great Smoky Mountains National Park, NC. Tornadoes formed elsewhere in West Virginia, western Virginia, southwestern North Carolina, and north Georgia - regions of four states that are in the ranges of the Appalachian mountains.

Also, it's not too high for a tornado. In Salt Lake City, Utah, a tornado formed and damaged a streak of the city near downtown. Salt Lake City is well above 4000 feet. However, it should be noted that it is a rare occurrence for tornadoes to form west of the Rocky mountains.

[edit] Tornadoes in urban areas Myth: You're safe from a tornado in a big city.

Closely related to the "terrain" story (See Salt Lake City tornado just above), it is commonly believed that a tornado will dissipate in an urban area because of the tall skyscrapers. The May 3, 1999 tornado outbreak which struck urban Oklahoma City, the tornado that ripped through the heart of downtown Fort Worth, Texas in May of 2000, and the F-0 South San Francisco, California tornado of March 2004 are just three of many examples that negate this belief. While urban areas seem to be less susceptible to tornado strikes than rural areas, it is simply a matter of percentage of land area covered by these types of regions. Urban areas take up a relatively tiny surface area compared with the sprawling suburbs and the thousands of rural communities. Downtown Dallas is no less likely to have a tornado cross through it than an empty field in southern Oklahoma. While it is true that the typical urban building is a much more rugged structure than many comparable rural structures, it is not to be assumed that there is an increased measure of safety.

Social implications of tornadoes

Tornado damage to man-made structures is a result of the high wind velocity and windblown debris. Tornadic winds have been measured in excess of 300 mph (480 km/h). Tornado season in North America is generally March through November, although tornadoes can occur at any time of year. They tend to occur in the afternoons and evenings; over 80% of all tornadoes strike between noon and midnight.

Some individuals and hobbyists, known as storm chasers, enjoy pursuing thunderstorms and tornadoes to explore their many visual and scientific aspects. Attempts have been made by some storm chasers from educational and scientific institutions to drop probes in the path of oncoming tornadoes in an effort to analyze the interior of the storms, but only about five drops have been successful since around 1990.

Due to the relative rarity and large scale of destructive power that tornadoes possess, their occurrence or the possibility that they may occur can often create what could be considered sensationalism in their reporting. This results in so-called weather wars, in which competing local media outlets, particularly TV news stations, engage in continually escalating technological one-upsmanship and drama in order to increase their market share. This is especially evident in tornado-prone markets, such as those in the Great Plains.

According to Environment Canada, the chances of being killed by a tornado are 12 million to 1 (12,000,000:1). One may revise this yearly and/or regionally, but the probability may be factually stated to be low. Tornadoes do cause millions of dollars in damage, both economic and physical, displacement, and many injuries every year.^{citations needed]}

Cultural significance

Tornadoes as a metaphor

The tornado has been used by cartoonists for over 100 years as a metaphor for political upheaval. For example, according to political interpretations of The Wizard of Oz, the tornado takes Dorothy to a utopia, the Land of Oz, and kills the Wicked Witch of the East, who had oppressed a little people, the Munchkins. The storm cellar has also been used as a metaphor for seeking safety, as shown in the cartoon from 1894 at right.

A 1960s advertising campaign for the household cleaner, Ajax, claimed the product "Cleans like a white tornado".

Tornadoes in dreams are sometimes said to be associated with fear, chaos, and upheaval. It is alleged that the location where one is during a tornado dream, e.g. at home, can help to determine the meaning.^{citations needed]}

Motion pictures with a tornado theme

• The Wizard of Oz, 1939.
• Mr. and Mrs. Bridge, 1990.
• Night of the Twisters (TV), 1996.
• Tornado! (TV), 1996.
• Twister, 1996.
• Atomic Twister (TV), 2001.
• The Day After Tomorrow, 2004.
• Perfect Disaster: Super Tornado (Discovery Channel), premiered on March 19, 2006.
• Category 7: The End of the World, 2005.

See also

• Cyclone
• Derecho
• Downburst
• Dust Devil
• Emergency Alert System
• Fire whirl
• Funnel cloud
• Gustnado
• History of tropical cyclone-spawned tornadoes
• Landspout
• List of F5 tornadoes
• List of tornadoes and tornado outbreaks
• List of tornado-related deaths at schools
• Mesocyclone
• Multiple vortex tornado
• NLM Cityhopper Flight 431
• Severe weather
• Supercell
• Tornado Alley
• Tornado records
• Tornadoes of 2006
• Waterspout

References

Further reading

• Thomas P. Grazulis (1993). Significant Tornadoes 1680-1991, A Chronology and Analysis of Events. The Tornado Project of Environmental Films. ISBN 1-879362-00-7

External links

General

• Storm archives (including tornadoes since 1950)
• Real Time storm reports overlaid on Google Maps.
• United States Year to date tornado reports.
• The Tornado Project
• NWS Jet Stream Online Weather School
• Birth of a Tornado ~ Animation from MSNBC Interactive
• Tornado Newspaper Articles Archive Free archive of more than 50,000 newspaper articles detailing tornadoes through out history.

Regional prediction

• Storm Prediction Center (United States)
• The Tornado and Storm Research Organisation (United Kingdom)
• European Severe Storms Laboratory

Research

• Tornado research and education (National Severe Storms Laboratory)
• U.S. Severe Weather and Meteorology and Climatology
• TorDACH: Centre of Competence for Severe Local Storms in D, A, CH (Central Europe)
• Electronic Journal of Severe Storms Meteorology

Images

• Tornado images (Public Domain)
• National Severe Storms Laboratory Photo Album
• National Weather Service Historical Image Collection
• The Central Oklahoma Tornado Outbreak of May 03, 1999

Safety and Preparedness

• NOAA Tornado Preparedness Guide
• Tornado Safety (The Tornado Project)
• Tornado Preparedness Tips for School Administrators (NOAA / SPC)
• Highway Overpasses as Tornado Shelters: Fallout from the May 3, 1999 Tornado Outbreak (National Weather Service, Norman, Oklahoma)
• FEMA for Kids: Tornado

Miscellaneous

• Chasing Tornadoes (National Geographic Magazine)
• StormWiki