Continuing research

Meteorology is a relatively young science and the study of tornadoes even more so. Although studied for about 140 years and intensively for around 60 years, there are still aspects of tornadoes which remain a mystery.[75] Scientists do have a fairly good idea of the development of thunderstorms and mesocyclones, and the meteorological conditions conducive to their formation; however, the step from supercell (or other respective formative processes) to tornadogenesis and predicting tornadic vs. non-tornadic mesocyclones is not yet well understood and is the focus of much research.

Also under study are the low-level mesocyclone and the stretching of low-level vorticity which tightens into a tornado, namely, what are the processes and what is the relationship of the environment and the convective storm. Intense tornadoes have been observed forming simultaneously with a mesocyclone aloft (rather than succeeding mesocyclogenesis) and some intense tornadoes have occurred without a mid-level mesocyclone. In particular, the role of downdrafts, particularly the rear-flank downdraft, and the role of baroclinic boundaries, are intense areas of study.

Reliably predicting tornado intensity and longevity remains a problem, as do details affecting characteristics of a tornado during its life cycle and tornadolysis. Other rich areas of research are tornadoes associated with mesovortices within linear thunderstorm structures and within tropical cyclones.[76]

Scientists still do not know the exact mechanisms by which most tornadoes form, and occasional tornadoes still strike without a tornado warning being issued, especially in under-developed countries. Analysis of observations including both stationary and mobile (surface and aerial) in-situ and remote sensing (passive and active) instruments generates new ideas and refines existing notions. Numerical modeling also provides new insights as observations and new discoveries are integrated into our physical understanding and then tested in computer simulations which validate new notions as well as produce entirely new theoretical findings, many of which are otherwise unattainable. Importantly, development of new observation technologies and installation of finer spatial and temporal resolution observation networks have aided increased understanding and better predictions.

Research programs, including field projects such as VORTEX, deployment of TOTO (the TOtable Tornado Observatory), Doppler On Wheels (DOW), and dozens of other programs, hope to solve many questions that still plague meteorologists.[36] Universities, government agencies such as the National Severe Storms Laboratory, private-sector meteorologists, and the National Center for Atmospheric Research are some of the organizations very active in research; with various sources of funding, both private and public, a chief entity being the National Science Foundation.

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Tonardo Detection

A Doppler radar image indicating the likely presence of a tornado over DeLand, Florida. Green colors indicate areas where the precipitation is moving towards the radar dish, while red areas are moving away. In this case the radar is in the bottom right corner of the image. Strong mesocyclones show up as adjacent areas of bright green and bright red, and usually indicate an imminent or occurring tornado. When these bright colors are one against the other on a radar display when in association with rotation, it is called a Tornado vortex signature.
A Doppler radar image indicating the likely presence of a tornado over DeLand, Florida. Green colors indicate areas where the precipitation is moving towards the radar dish, while red areas are moving away. In this case the radar is in the bottom right corner of the image. Strong mesocyclones show up as adjacent areas of bright green and bright red, and usually indicate an imminent or occurring tornado. When these bright colors are one against the other on a radar display when in association with rotation, it is called a Tornado vortex signature.

Rigorous attempts to warn of tornadoes began in the United States in the mid-20th century. Before the 1950s, the only method of detecting a tornado was by someone seeing it on the ground. Often, news of a tornado would reach a local weather office after the storm.

However, with the advent of weather radar, areas near a local office could get advance warning of severe weather. The first public tornado warnings were issued in 1950 and the first tornado watches and convective outlooks in 1952. In 1953 it was confirmed that hook echoes are associated with tornadoes. By recognizing these radar signatures, meteorologists could detect thunderstorms likely producing tornadoes from dozens of miles away.[59]

Storm spotting

In the mid 1970s, the US National Weather Service (NWS) increased its efforts to train storm spotters to spot key features of storms which indicate severe hail, damaging winds, and tornadoes, as well as damage itself and flash flooding. The program was called Skywarn, and the spotters were local sheriff's deputies, state troopers, firefighters, ambulance drivers, amateur radio operators, civil defense (now emergency management) spotters, storm chasers, and ordinary citizens. When severe weather is anticipated, local weather service offices request that these spotters look out for severe weather, and report any tornadoes immediately, so that the office can issue a timely warning.

Usually spotters are trained by the NWS on behalf of their respective organizations, and report to them. The organizations activate public warning systems such as sirens and the Emergency Alert System, and forward the report to the NWS.[60] There are more than 230,000 trained Skywarn weather spotters across the United States.[61]

In Canada, a similar network of volunteer weather watchers, called Canwarn, helps spot severe weather, with more than 1,000 volunteers.[62] In Europe, several nations are organizing spotter networks under the auspices of Skywarn Europe[63] and the Tornado and Storm Research Organisation (TORRO) has maintained a network of spotters in the United Kingdom since the 1970s.

Storm spotters are needed because radar systems such as NEXRAD do not detect a tornado; only indications of one. Radar may give a warning before there is any visual evidence of a tornado or imminent tornado, but ground truth from an observer can either verify the threat or determine that a tornado is not imminent. The spotter's ability to see what radar cannot is especially important as distance from the radar site increases, because the radar beam becomes progressively higher in altitude further away from the radar, chiefly due to curvature of Earth, and the beam also spreads out. Therefore, when far from a radar, only high in the storm is observed and the important areas are not sampled, and data resolution also suffers. Also, some meteorological situations leading to tornadogenesis are not readily detectable by radar and on occasion tornado development may occur more quickly than radar can complete a scan and send the batch of data.

Visual evidence
A rotating wall cloud with rear flank downdraft clear slot evident to its left rear.
A rotating wall cloud with rear flank downdraft clear slot evident to its left rear.

Storm spotters are trained to discern whether a storm seen from a distance is a supercell. They typically look to its rear, the main region of updraft and inflow. Under the updraft is a rain-free base, and the next step of tornadogenesis is the formation of a rotating wall cloud. The vast majority of intense tornadoes occur with a wall cloud on the backside of a supercell.[43]

Evidence of a supercell comes from the storm's shape and structure, and cloud tower features such as a hard and vigorous updraft tower, a persistent, large overshooting top, a hard anvil (especially when backsheared against strong upper level winds), and a corkscrew look or striations. Under the storm and closer to where most tornadoes are found, evidence of a supercell and likelihood of a tornado includes inflow bands (particularly when curved) such as a "beaver tail", and other clues such as strength of inflow, warmth and moistness of inflow air, how outflow- or inflow-dominant a storm appears, and how far is the front flank precipitation core from the wall cloud. Tornadogenesis is most likely at the interface of the updraft and front flank downdraft, and requires a balance between the outflow and inflow.[15]

Only wall clouds that rotate spawn tornadoes, and usually precede the tornado by five to thirty minutes. Rotating wall clouds are the visual manifestation of a mesocyclone. Barring a low-level boundary, tornadogenesis is highly unlikely unless a rear flank downdraft occurs, which is usually visibly evidenced by evaporation of cloud adjacent to a corner of a wall cloud. A tornado often occurs as this happens or shortly after; first, a funnel cloud dips and in nearly all cases by the time it reaches halfway down, a surface swirl has already developed, signifying a tornado is on the ground before condensation connects the surface circulation to the storm. Tornadoes may also occur without wall clouds, under flanking lines, and on the leading edge. Spotters watch all areas of a storm, and the cloud base and surface.[64]

Radar

Today, most developed countries have a network of weather radars, which remains the main method of detecting signatures likely associated with tornadoes. In the United States and a few other countries, Doppler radar stations are used. These devices measure the velocity and radial direction (towards or away from the radar) of the winds in a storm, and so can spot evidence of rotation in storms from more than a hundred miles (160 km) away.

Also, most populated areas on Earth are now visible from the Geostationary Operational Environmental Satellites (GOES), which aid in the nowcasting of tornadic storms.[62]
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Tornado climatology and prediction

The United States has the most tornadoes of any country, about four times more than estimated in all of Europe, not including waterspouts.[45] This is mostly due to the unique geography of the continent. North America is a relatively large continent that extends from the tropical south 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 the world occur, the Rocky Mountains block moisture and atmospheric flow, allowing drier air at mid-levels of the troposphere, and causing cyclogenesis downstream to the east of the mountains. The desert Southwest also feeds drier air and the dry line, while the Gulf of Mexico fuels abundant low-level moisture. This unique topography allows for many collisions of warm and cold air, the conditions that breed strong, long-lived storms many times a year. A large portion of these tornadoes form in an area of the central United States known as Tornado Alley.[4] This area extends into Canada, particularly Ontario and the Prairie Provinces. Strong tornadoes also occasionally occur in northern Mexico.

The United States averages about 1,200 tornadoes per year. The Netherlands has the highest average number of recorded tornadoes per area of any country (more than 20, or 0.0013 per sq mi (0.00048 per km²), annually), followed by the UK (around 33, or 0.00035 per sq mi (0.00013 per km²), per year), but most are small and cause minor damage. In absolute number of events, ignoring area, the UK experiences more tornadoes than any other European country, excluding waterspouts.[45]

Bangladesh and surrounding areas of eastern India suffer from tornadoes of equal severity to those in the US, and occurring more frequently than anywhere else in the world, but such events are under-reported due to the scarcity of media coverage in third-world countries. Tornados kill about 179 people per year in Bangladesh, many more than in the US. This is due to high population density, poor quality of construction, lack of tornado safety knowledge, and other factors.[46] Other areas of the world that have frequent tornadoes include South Africa, parts of Argentina, Paraguay, and southern Brazil, as well as portions of Europe, Australia and New Zealand, and far eastern Asia.[5]

Tornadoes are most common in spring and least common in winter.[8] Since autumn and spring are transitional periods (warm to cool and vice versa) there are more chances of cooler air meeting with warmer air, resulting in thunderstorms. Tornadoes can also be caused by landfalling tropical cyclones, which tend to occur in the late summer and autumn. But favorable conditions can occur at any time of the year.

Tornado occurrence is highly dependent on the time of day, because of solar heating.[47] Worldwide, most tornadoes occur in the late afternoon, between 3 and 7 pm local time, with a peak near 5 pm.[48][49][50][51][52] However, destructive tornadoes can occur at any time of day. The Gainesville Tornado of 1936, one of the deadliest tornadoes in history, occurred at 8:30 am local time.[8]

Associations to climate and climate change

Associations to various climate and environmental trends exist. For example, an increase in the sea surface temperature of source region (e.g. Gulf of Mexico and Mediterranean Sea) increases moisture content, potentially fueling an increase in severe weather and tornado activity, particularly in the cool season.[53]

Although insufficient support exists to make conclusions, evidence does suggest that the Southern Oscillation is weakly correlated with some changes in tornado activity; which vary by season and region as well as whether the ENSO phase is that of El Niño or La Niña.[54]

Climatic shifts affect tornadoes via teleconnections in shifting the jet stream and the larger weather patterns. The climate-tornado link is confounded by the forces affecting larger patterns and by the local, nuanced nature of tornadoes. Although it is reasonable that the climate change phenomenon of global warming may affect tornado activity, any such effect is not yet identifiable due to the complexity, local nature of the storms, and database quality issues. Any effect would vary by region.[55]


Prediction
Probabilistic maps issued by the Storm Prediction Center during the heart of the April 6-8, 2006 Tornado Outbreak. The top map indicates the risk of general severe weather (including large hail, damaging winds, and tornadoes), while the bottom map specifically shows the percent risk of a tornado forming within 25 miles (40 km) of any point within the enclosed area. The hashed area on the bottom map indicates a 10% or greater risk of an F2 or stronger tornado forming within 25 miles (40 km) of a point.
Probabilistic maps issued by the Storm Prediction Center during the heart of the April 6-8, 2006 Tornado Outbreak. The top map indicates the risk of general severe weather (including large hail, damaging winds, and tornadoes), while the bottom map specifically shows the percent risk of a tornado forming within 25 miles (40 km) of any point within the enclosed area. The hashed area on the bottom map indicates a 10% or greater risk of an F2 or stronger tornado forming within 25 miles (40 km) of a point.

Weather forecasting is handled regionally by many national and international agencies. For the most part, they are also in charge of the prediction of conditions conducive to tornado development.

Australia

Severe thunderstorm warnings are provided to Australia by the Bureau of Meteorology. The country is in the middle of an upgrade to Doppler radar systems, with their first benchmark of installing six new radars reached in July 2006.[56]

Europe

The European Union founded a project in 2002 called the European Severe Storms virtual Laboratory, or ESSL, which is meant to fully document tornado occurrence across the continent. The ESTOFEX (European Storm Forecast Experiment) arm of the project also issues one day forecasts for severe weather likelihood.[57] In Germany, Austria, and Switzerland, an organization known as TorDACH collects information regarding tornadoes, waterspouts, and downbursts from Germany, Austria, and Switzerland. A secondary goal is collect all severe weather information. This project is meant to fully document severe weather activity in these three countries.[58]

United Kingdom

In the United Kingdom, the Tornado and Storm Research Organisation (TORRO) makes experimental predictions. The Met Office provides official forecasts for the UK.

United States

In the United States, generalized severe weather predictions are issued by the Storm Prediction Center, based in Norman, Oklahoma. For the next one, two, and three days, respectively, they will issue categorical and probabilistic forecasts of severe weather, including tornadoes. There is also a more general forecast issued for the four to eight day period. Just prior to the expected onset of an organized severe weather threat, SPC issues severe thunderstorm and tornado watches, in collaboration with local National Weather Service offices. Warnings are issued by local National Weather Service offices when a severe thunderstorm or tornado is occurring or imminent.

Other areas

In Japan, predictions and study of tornadoes in Japan are handled by the Japan Meteorological Agency. In Canada, weather forecasts and warnings, including tornadoes, are produced by the Meteorological Service of Canada, a division of Environment Canada.

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Tornado 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. [1]

[edit] 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.
A diagram of the Fujita scale as it relates to the Beaufort scale and the Mach number scale.
A diagram of the Fujita scale as it relates to the Beaufort scale and the Mach number scale.

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. This is what the F stands for in F1, F2, etc. 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, created 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. T0-T1 roughly correspond to F0, T2-T3 to F1, and so on. While T10+ would be approximately an F5, the highest tornado rated to date on the TORRO scale was a T8.[2][3] 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)".[4] In the United States, the Enhanced Fujita scale went into effect on February 2, 2007 for tornado damage assessments and the Fujita scale is no longer used.
An example of F0 damage. The only significant damage to structures in this picture was caused by falling tree branches. Even though well-built structures are typically unscathed by F0 tornadoes, falling trees and tree branches can injure and kill people, even inside a sturdy structure.
An example of F0 damage. The only significant damage to structures in this picture was caused by falling tree branches. Even though well-built structures are typically unscathed by F0 tornadoes, falling trees and tree branches can injure and kill people, even inside a sturdy structure.
An example of F1 damage. F1 tornadoes cause major damage to mobile homes and automobiles, and can cause minor structural damage to well-constructed homes. This particular mobile home appears to be a double-wide, and it was still moved off its foundations, with its roof badly damaged. A mobile home or car is a very poor shelter, even during severe thunderstorms which do not contain a tornado.
An example of F1 damage. F1 tornadoes cause major damage to mobile homes and automobiles, and can cause minor structural damage to well-constructed homes. This particular mobile home appears to be a double-wide, and it was still moved off its foundations, with its roof badly damaged. A mobile home or car is a very poor shelter, even during severe thunderstorms which do not contain a tornado.
An example of F2 damage. At this intensity, tornadoes have a more significant impact on well-built structures, damaging roofs, collapsing walls, and generating large amounts of flying debris. This wood-frame home was unroofed, with many outer walls collapsed or destroyed.
An example of F2 damage. At this intensity, tornadoes have a more significant impact on well-built structures, damaging roofs, collapsing walls, and generating large amounts of flying debris. This wood-frame home was unroofed, with many outer walls collapsed or destroyed.
An example of F3 damage. Here, the roof and some inner walls of this brick building have been demolished. While taking shelter in a basement, cellar, or inner room improves your odds of surviving a tornado drastically, occasionally even this is not enough. F3 and stronger tornadoes only account for about 6% of all tornadoes in the United States, and yet since 1980 they have accounted for more than 75% of tornado-related deaths.
An example of F3 damage. Here, the roof and some inner walls of this brick building have been demolished. While taking shelter in a basement, cellar, or inner room improves your odds of surviving a tornado drastically, occasionally even this is not enough. F3 and stronger tornadoes only account for about 6% of all tornadoes in the United States, and yet since 1980 they have accounted for more than 75% of tornado-related deaths.
An example of F4 damage. Above-ground structures are almost completely vulnerable to F4 tornadoes, which level well-built structures, toss heavy vehicles through the air, and uproot trees, turning them into flying missiles.
An example of F4 damage. Above-ground structures are almost completely vulnerable to F4 tornadoes, which level well-built structures, toss heavy vehicles through the air, and uproot trees, turning them into flying missiles.
An example of F5 damage. These tornadoes cause incredible destruction, obliterating and sweeping away almost anything in their paths. Fortunately, they are extremely rare, and often only a small portion of the tornado's path contains F5 damage. While these tornadoes often destroy everything in their path, it is possible to survive. Some survived a direct hit by the Jarrell Tornado by lying down in a bathtub as the tornado swept the rest of the house away.
An example of F5 damage. These tornadoes cause incredible destruction, obliterating and sweeping away almost anything in their paths. Fortunately, they are extremely rare, and often only a small portion of the tornado's path contains F5 damage.[5] While these tornadoes often destroy everything in their path, it is possible to survive. Some survived a direct hit by the Jarrell Tornado by lying down in a bathtub as the tornado swept the rest of the house away.[6]

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 301±20 mph (484±32 km/h) [7], 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. Also, in practice, the F6 rating is not used.

While scientists have long theorized that extremely low pressures might occur in the center of tornadoes, there were no measurements to confirm it. A few home barometers had survived close passes by tornadoes, recording values as low as 24 in Hg (810 mbar), but these measurements were highly uncertain.[8] However, on June 24, 2003, a group of researchers successfully dropped devices called "turtles" into an F4 tornado near Manchester, South Dakota, one of which measured a pressure drop of more than 100 mbar as the tornado passed directly overhead.[9] Still, tornadoes are widely varied, so meteorologists are still conducting research to determine if these values are typical or not.

[edit] Typical intensity

Further information: Fujita scale

In the United States, F0 and F1 (T0 through T3) tornadoes account for 80% of all tornadoes. The rate of occurrence drops off quickly with increasing strength—violent tornadoes (stronger than F4, T8), account for less than 1% of all tornado reports.[10] Worldwide, strong tornadoes account for an even smaller percentage of total tornadoes. Violent tornadoes are extremely rare outside of the United States, Canada and Bangladesh.

F5 tornadoes are exceptionally rare, occurring on average once every few years. The last confirmed F5 tornado anywhere in the world was the Elie, Manitoba Tornado in Canada, on June 22, 2007. Before that, the last confirmed F5 was the Moore, Oklahoma tornado, which killed 36 people on May 3, 1999.[1] The first, and last, known United States recording of an EF5 tornado occurred in Greensburg, Kansas on May 4, 2007.

[edit] 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, in reality, 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.[11] 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.[1] However, in this time, they can cause both damage and fatalities.

F0 (T0-T1) 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 may have large branches broken off, and can be uprooted if they have shallow roots.

F1 (T2-T3) 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 (T4-T5) 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 (T6-T7) 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 (T8-T9) 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, including airplanes, trains, and large trucks, can become airborne, with other large projectiles being flung some distance.

F5 (T10+) 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". The damage they cause is an extreme hazard to life and limb—since 1950 in the United States, only 50 tornadoes (0.1% of all reports) have been designated F5, and yet these have been responsible for more than 1000 deaths and 11,000 injuries (21.5% and 13.6%, respectively).[1] In recorded history, F5 tornadoes have performed awesome displays of power, including twisting skyscrapers, levelling entire communities, and stripping asphalt from the ground.

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Definitions

A tornado near Seymour, Texas.

Tornado
A tornado is defined by the Glossary of Meteorology as "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..."[6] In practice, for a vortex to be classified as a tornado, it must be in contact with both the ground and the cloud base. Scientists have not yet created a complete definition of the word; for example, there is disagreement as to whether separate touchdowns of the same funnel constitute separate tornadoes.[3]

Condensation funnel
A tornado is not necessarily visible; however, the intense low pressure caused by the high wind speeds (see Bernoulli's principle) and rapid rotation (due to cyclostrophic balance) usually causes water vapor in the air to condense into a visible condensation funnel.[4] The tornado is the vortex of wind, not the condensation cloud.
A funnel cloud is a visible condensation funnel with no associated strong winds at the surface. Not all funnel clouds evolve into a tornado. However, many tornadoes are preceded by a funnel cloud. Most tornadoes produce strong winds at the surface while 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.[3]

Tornado family
Occasionally, a single storm will produce more than one tornado, either simultaneously or in succession. Multiple tornadoes produced by the same storm are referred to as a tornado family. [7]

Tornado outbreak
Occasionally, several tornadoes are spawned from the same large-scale storm system. If there is no break in activity, this is considered a tornado outbreak, although there are 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.[6][8][9]

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Types of Tornadoes

A multiple-vortex tornado outside of Dallas, Texas on April 2, 1957.

True tornadoes

Multiple vortex tornado
A multiple vortex tornado is a type of tornado in which two or more columns of spinning air rotate around a common center. Multivortex structure can occur in almost any circulation, but is very often observed in intense tornadoes.

Satellite tornado
A satellite tornado is a term for a weaker tornado which forms very near a large, strong tornado contained within 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 funnel, and is much smaller than the main funnel.[3]

A waterspout near the Florida Keys.
A waterspout near the Florida Keys.

Waterspout
A waterspout is officially defined by the US National Weather Service simply as a tornado over water. However, researchers typically distinguish "fair weather" waterspouts from tornadic waterspouts.

* Fair weather waterspouts are less severe but far more common, and are similar in dynamics to dust devils and landspouts.[13] They form at the bases of cumulus congestus cloud towers in tropical and semitropical waters.[13] They have relatively weak winds, smooth laminar walls, and typically travel very slowly, if at all.[13] They occur most commonly in the Florida Keys.[14]
* Tornadic waterspouts are more literally "tornadoes over water". They can form over water like mesocyclonic tornadoes, or be a land tornado which crosses onto water. Since they form from severe thunderstorms and can be far more intense, faster, and longer-lived than fair weather waterspouts, they are considered far more dangerous.

A landspout near North Platte, Nebraska on May 22, 2004.
A landspout near North Platte, Nebraska on May 22, 2004.

Landspout
Landspout is an unofficial term for a tornado not associated with a mesocyclone. The name stems from their characterization as essentially a "fair weather waterspout on land". Waterspouts and landspouts share many defining characteristics, including relative weakness, short lifespan, and a small, smooth condensation funnel which often does not reach the ground. Landspouts also create a distinctively laminar cloud of dust when they make contact with the ground, due to their differing mechanics from true mesoform tornadoes. Though usually weaker than classic tornadoes, they still produce strong winds and may cause serious damage.[3][15]

Tornado-like circulations

Gustnado
A gustnado (gust front tornado) 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. They are formed when fast moving cold, dry outflow air from 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 horizontally (or diagonally) and make contact with the ground. The result is a gustnado.[3][16] They usually cause small areas of heavier rotational wind damage among areas of straight-line wind damage. It is also worth noting that since they are absent of any Coriolis influence from a mesocyclone, they seem to be alternately cyclonic and anticyclonic without preference.

Dust devil in Johnsonville, South Carolina.
Dust devil in Johnsonville, South Carolina.

Dust devil
A dust devil resembles a tornado in that it is a vertical swirling column of air. However, they form under clear skies and are rarely as strong as even 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 actual cloud. However, they can, on occasion, result in major damage, especially in arid areas.[17][18]

Winter Waterspout
A winter waterspout, also known as a snow devil, an icespout, an ice devil or a snowspout, is an extremely rare meteorological phenomenon in which a vortex resembling that of a waterspout forms under the base of a snow squall.

Fire whirl
Tornado-like circulations occasionally occur near large, intense wildfires and are called fire whirls. They are not considered tornadoes except in 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. However, they can produce significant damage.[8]

Cold air vortex
A cold air vortex or shear funnel is a tiny, harmless funnel cloud which occasionally forms underneath or on the sides of normal cumuliform clouds, rarely causing any winds at ground-level.[19] Their genesis and mechanics are poorly understood, as they are quite rare, short lived, and hard to spot (due to their non-rotational nature and small size).
Extracted from Wikipedia

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Characteristics of Tornadoes

A wedge tornado, nearly a mile wide.
A rope tornado in its dissipating stage.

Shape

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

Small, relatively weak landspouts may 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), the circulation is considered a tornado.[15] Large single-vortex tornadoes can look like large wedges stuck into the ground, and so are known as wedge tornadoes or wedges. A wedge can be so wide that it appears to be 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.[20]

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 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.[21]

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.[17]

Size

In the United States, on average tornadoes are around 500 feet (150 m) across, and stay on the ground for 5 miles (8 km).[17] Yet, 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. A tornado was once reported to have a damage path only 7 feet (2 m) long.[17] 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 was at one point 2.5 miles (4 km) wide at the ground.[2]

In terms of path length, the Tri-State Tornado, which affected parts of Missouri, Illinois, and Indiana on March 18, 1925, was officially 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 actually a family of tornadoes which have formed in quick succession; however, there is no substantial evidence that this occurred in the case of the Tri-State Tornado.[8] In fact, modern reanalysis of the path suggests that the tornado began 15 miles (24 km) further west than previously thought.[22]

Appearance

Tornadoes can have a wide range of colors, depending on the environment in which they form. Those 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 gray 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.[17]
Photographs of the Waurika, Oklahoma tornado of May 30, 1976, taken at nearly the same time by two photographers. In the top picture, the tornado is front-lit, with the sun behind the east-facing camera, so the funnel appears nearly white. In the lower image, where the camera is facing the opposite direction, the tornado is back-lit, with the sun behind the clouds.
Photographs of the Waurika, Oklahoma tornado of May 30, 1976, taken at nearly the same time by two photographers. In the top picture, the tornado is front-lit, with the sun behind the east-facing camera, so the funnel appears nearly white. In the lower image, where the camera is facing the opposite direction, the tornado is back-lit, with the sun behind the clouds.[23]

Lighting conditions are 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.[24][12]

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. 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. 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 in the late afternoon, when the bright sun can penetrate even the thickest clouds.[8] Also, night-time tornadoes are often illuminated by frequent lightning.

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. This area would be clear (possibly full of dust), have relatively light winds, and be very dark, since the light would be blocked 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.[25][26][27]

Rotation

Tornadoes normally rotate cyclonically in direction (counterclockwise in the northern hemisphere, 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 Coriolis effect is inconsequential, as indicated by their large Rossby numbers. Supercells and tornadoes rotate cyclonically in numerical simulations even when the Coriolis effect is neglected.[28][29] Low-level mesocyclones and tornadoes owe their rotation to complex processes within the supercell and ambient environment.[30]

Approximately 1% of tornadoes rotate in an anticyclonic direction. Typically, only landspouts and gustnados rotate anticyclonically, and usually only those which form on the anticyclonic shear side of the descending rear flank downdraft in a cyclonic supercell.[31] However, 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.[32]

Sound and seismology

Tornadoes emit widely on the acoustics spectrum and the sounds are cased by multiple mechanisms. Various sounds of tornadoes have been reported throughout time, 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 jet engine from close proximity, or combinations of these. Many tornadoes are not audible from much distance; the nature and propagation distance of 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 a continuous, deep rumbling, or an irregular sound of “noise”.[33]

Since many tornadoes are audible only in very close proximity, sound is not reliable warning of a tornado. And, any strong, damaging wind, even a severe hail volley or continuous thunder in a thunderstorm may produce a roaring sound.[34]
An illustration of generation of infrasound in tornadoes by the Earth System Research Laboratory's Infrasound Program.
An illustration of generation of infrasound in tornadoes by the Earth System Research Laboratory's Infrasound Program.

Tornadoes also produce identifiable inaudible infrasonic signatures.[35] Unlike audible signatures, tornadic signatures have been isolated; due to 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.[36] Tornadoes also produce a detectable seismic signature, and research continues on isolating it and understanding the process.[37]

Electromagnetic, lightning, and other effects

Tornadoes emit on the electromagnetic spectrum, for example, with sferics and E-field effects detected.[36][38] The effects vary, mostly with little observed consistency.

Correlations with patterns of lightning activity have also been observed, but little in way of consistent correlations have been advanced. Tornadic storms do not contain more lightning than other storms, and some tornadic cells never contain lightning. More often that not, overall cloud-to-ground (CG) lightning activity decreases as a tornado reaches the surface and returns to the baseline level when the tornado lifts. In many cases, very intense tornadoes and thunderstorms exhibit an increased and anomalous dominance in positive polarity CG discharges.[39] Electromagnetics and lightning have little to nothing to do directly with what drives tornadoes (tornadoes are basically a thermodynamic phenomenon), though there are likely connections with the storm and environment affecting both phenomena.

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 been recorded.

In addition to winds, tornadoes also exhibit changes in atmospheric variables such as temperature, moisture, and pressure. For example, on June 24, 2003 near Manchester, South Dakota, a probe measured a 100 mbar (hPa) (2.95 inHg) pressure deficit. The pressure dropped gradually as the vortex approached then dropped extremely rapidly to 850 mbar (hPa) (25.10 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 the immediate vicinity of a tornado.[40]
Extracted from Wikipedia.

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Life cycle

A sequence of images showing the birth of a tornado. First, the rotating cloud base lowers. This lowering becomes a funnel, which continues descending while winds build near the surface, kicking up dust and other debris. Finally, the visible funnel extends to the ground, and the tornado begins causing major damage. This tornado, near Dimmitt, Texas, was one of the best-observed violent tornadoes in history.
A sequence of images showing the birth of a tornado. First, the rotating cloud base lowers. This lowering becomes a funnel, which continues descending while winds build near the surface, kicking up dust and other debris. Finally, the visible funnel extends to the ground, and the tornado begins causing major damage. This tornado, near Dimmitt, Texas, was one of the best-observed violent tornadoes in history.

Further information: Tornadogenesis

Supercell relationship

See also: Supercell

Tornadoes often develop from a class of thunderstorms known as supercells. Supercells contain mesocyclones, an area of organized rotation a few miles up in the atmosphere, usually 1–6 miles (2–10 km) 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 a recognizable life cycle.[15] That 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.

Formation

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 becomes a tornado within minutes of the RFD reaching the ground.

Maturity

Initially, the tornado has a good source of warm, moist inflow to power it, so it grows until it reaches the mature stage. This can last anywhere 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 one mile (1.6 km) 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.

Demise

As the RFD completely wraps around and chokes off the tornado's air supply, the vortex begins to weaken, and become thin and rope-like. This is the dissipating stage; often lasting no more than a few minutes, after which the tornado fizzles. 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.[23][24][8]

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 may be concentrated into a new area closer to the center of the storm. 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.

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.[41]

Extracted from Wikipedia.

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Remembering The Tornado Outbreak of May 3rd, 1999

In the fair State of Oklahoma, there are two dates on the calendar that will stir raw emotion in the hearts and minds of the people you meet here. One of those dates is April 19th and the other is May 3rd.

As you may recall, April 19th, 1995 was the date that Oklahoma City was struck by terrorists with the bombing of the Alfred P. Murrah Federal Building in downtown Oklahoma City at 9:02 a.m. Then on May 3rd, 1999, Oklahoma was struck again, this time by the raw fury and awesome power of Mother Nature.

On this single day, over 70 tornadoes touched down in North Texas, Central Oklahoma and Southern Kansas. 59 of those tornadoes alone wrecked their havoc in the State of Oklahoma, making the May 3rd outbreak the largest outbreak in Oklahoma history. The largest tornado of the day, "The Big One" rumbled through Central Oklahoma leaving a trail of devastation nearly 40 miles long.

Before finally dying out, this dangerous storm drove its' attack down the western edge of Tinker Air Force Base, finally dying just north of Tinker AFB and 6 miles due east of the former location of the Alfred P. Murrah Federal Building.

Though the storm has consistently been referred to as an "F5 tornado", it spent less than 10% of its' life span in the F5 range of the Fujita Scale. A F5 tornado is a tornado that produces wind speeds estimated between 261 and 318 mph. This particular storm actually touched every point from F1 to F5 on the Fujita Scale, but it spent just over 50% of its' life span as a "F4" tornado, which by definition is a tornado that produces estimated wind speeds of between 207 and 260 mph.

There was some discussion as to whether the tornado entered into the realm of the so far unrealized territory of a "F6" tornado, but the F6 status has since been written off. For the analysis of the "F5 or F6 Controversy", go to: http://www.srh.noaa.gov/oun/storms/19990503/may3faqs.html

Nearly 80% of all storm related damage in Oklahoma on May 3rd was a direct result of "The Big One", during its track through Cleveland and Oklahoma counties in Central Oklahoma. The damage from the May 3rd outbreak is staggering, $1.2 billion dollars worth of staggering to be exact.

In Cleveland and Oklahoma counties alone, "The Big One" went down in the history books as the most costly tornado in history in terms of the overall dollars and cents of recorded damage. The following figures on damages resulting from the May 3rd outbreak are taken from The Daily Oklahoman on May 14, 1999. http://www.oklahoman.com/

Cleveland and Oklahoma Counties:

Homes destroyed: 1,780. Homes damaged: 6,550.
Apartments destroyed: 473. Apartments damaged: 568.
Businesses destroyed: 85. Businesses damaged: 42.
Churches destroyed: 3. Schools destroyed: 2.

The following figures represent the damage recorded in other counties around the State of Oklahoma on May 3rd, 1999:

Homes destroyed: 534. Homes damaged: 878.
* Businesses destroyed: 79.
(Includes 53 stores at the Tanger Outlet Center in Stroud.)
Businesses damaged: 54. Churches destroyed: 2.
Public buildings destroyed: 4. Public buildings damaged: 7.

With this level of property damage occurring in Oklahoma on May 3rd, 1999, one has to tip their hats to the Storm Prediction Center and the Oklahoma Media Outlets, for preparing Oklahomans for the worst and working to keep the death toll down. Amidst this astonishing level of destruction, only 44 people lost their lives. The names, ages and locations of the 44 people who died on May 3rd can be seen also at The Daily Oklahoman website at: http://www.oklahoman.com/cgi-bin/shart?ID=313997&TP=getarticle

Compared to the bombing of the Alfred P. Murrah Federal Building, the death toll from the May 3rd tornado outbreak was really light. 168 people died in the bombing. For the names and stories of those who died in the Alfred P. Murrah bombing, point your browsers to: http://www.oklahoman.com/bombing/bvic/ and to learn more about the bombing, turn to: http://www.oklahoman.com/bombing/index.html

For pictures of the storms and pictures of the aftermath, as well as more information regarding the May 3rd outbreak and information on tornadoes in general, please visit: http://www.srh.noaa.gov/oun/storms/19990503/

I could spend hours learning more about tornadoes by visiting this one site alone, in fact, I already know how I am going to spend my next free weekend.

On May 3rd, please take a moment to pay your respects to those souls who lost their lives in Oklahoma on that dreadful day. And please, for your own sake, visit the website listed above, or visit the main site for the National Weather Service Forcast Office in Norman, Oklahoma at: http://www.srh.noaa.gov/oun/ to learn about what to do and what not to do in the event of a tornado in your area. Through proper education, the life that you save may be your own.

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How to Prepare Your Home for a Tornado

The Federal Emergency Management Agency reports that 1,000 tornadoes strike the United States each year, with winds reaching up to 300 miles per hour.
Instructions
Difficulty: Easy
Things You’ll Need:

* Candle Pantry
* Waterproof Matches
* Battery Radios
* Waterproof Boxes For Valuables
* Canned Foods
* First Aid Kits
* Can Openers
* Cellular Phone Batteries
* Cellular Phone Covers/carrying Cases
* Cellular Phone Minutes
* Cellular Phone Services
* Cellular Phones

Step 1:
Understand the danger involved and take it seriously. The worst tornado ever to hit the nation killed 606 people in Illinois in 1925.

Step 2:
The safest place to be when a tornado hits is inside.

Step 3:
Identify a safe spot in your house where you can take cover if you need to. Basements are a good choice because they are below ground. Other options include closets, bathrooms or hallways on the first floor, as long as they are away from windows.

Step 4:
Make you sure you have insurance for your home.

Step 5:
During a tornado watch, store your car in a garage or underneath a carport to protect it from hail or flying debris.

Step 6:
Bring outdoor furniture and yard equipment into the garage or house so it does not get blown around in the heavy winds and injure someone.

Step 7:
Find out what kind of tornado warning signals are used in your community and what they mean.

Step 8:
Practice a tornado drill with your family so you can see how you will respond if a tornado warning is issued.

Step 9:
Educate an existing neighborhood group about safety procedures and set up a plan to alert senior citizens in case of a warning. Or start a new group with your neighbors.

Step 10:
Prepare supplies in a waterproof container for an emergency, including candles, matches and a battery-operated radio.

Step 11:
Order a free copy of a booklet called "Taking Shelter from the Storm" from the Federal Emergency Management Agency, or view it online at www.fema.gov/mit/tsfs01.htm.

Step 12:
Many injuries or deaths resulting from tornadoes occur when buildings collapse. If you are building a new house or remodeling, include a "safe room" - a room built below ground out of reinforced concrete or wood and steel walls that are anchored by a concrete slab foundation or floor.


Tips & Warnings

* After a tornado occurs, do an inventory of the damage for your insurance company.
* Repair any serious problems right away to prevent further ruin from rain, wind or vandalism.
* Double-check your utility lines and appliances to be sure they were not harmed.
* If you smell gas, do not light any matches and take care of the problem right away.
* Be sure to teach your children what to do if they're home alone when a storm comes. If there is a storm coming and you must leave them alone, remind them to keep a cell phone or a cordless phone, a flashlight, and a TV or portable radio handy. Be sure they know to go go directly to the basement or safe room if there's an emergency broadcast or if the civil defense sirens go off.

By eHow Health Editor

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Understanding a Twister

Perhaps on of the most feared weather anomalies is the tornado. The Unpredictability of a tornado produces terror in many families. Some people are so afraid it is a phobia called Lilapsophobia. Part of the anxiety is due to the development of a tornado from a seemingly normal thunderstorm producing their characteristic haphazard and crazy paths.

Tornadoes are one of natures most devastating storms, but they do not last long. The average length of a tornado is only five to thirty minutes, but the places they travel are often devastated.

Tornadoes Cause Damage in Three Ways.
Strong Winds

The strong winds of a tornado can rip just about anything off of the ground including trees, vehicles, and even houses. The winds inside of tornadoes travel at over 310 miles per hour. Even weak tornadoes can pull shingles and siding off houses.

Debris

The second damaging effect of tornados is actually from the debris that the storm picks up. People have been buried alive by houses or mud picked up and then dropped by a tornado. Smaller objects become damaging projectiles when thrown by tornadoes. One tornado took a child’s bicycle and wrapped it around a tree!

Hail and Lightning

It is not only the wind that causes damage in a tornado, but also the hail and lightning that the storm produces. Large hailstones can damage cars and injure people, and lighting can cause fires and electrical problems.

The Environment Suffers From Tornadoes As Well

Tornadoes produce devastating effects on the environment. They can uproot trees, cause mass migrations of animals, and destroy the habitats of local wildlife.

Family Safety During a Tornado

If there is a tornado approaching, what safety measures should you take? First, it is important to realize that there is no specific way to know if a storm is going to produce a tornado. Meteorologists have developed warning systems that tell them if a storm is capable of producing a tornado.

During severe weather, have a weather radio on. If you do not currently have a weather radio, you can compare prices of weather radios here. They are relatively in expensive and could save your life. If you hear the announcer say there is a tornado watch, that means the conditions are correct for forming a tornado. A tornado warning means a tornado has been spotted. If you hear a tornado warning, you may be in danger!

If You Hear a Tornado Warning...
First, find shelter in the lowest possible place, such as a basement. If your home does not have a basement, go to the innermost room. Stay clear of windows or anything heavy like furniture or appliances. A bathroom is a good location.

Take your battery-powered weather radio to your shelter and turn it on. Kneel on the floor and cover your head with your hands. This is the best position to be in to avoid damage during a tornado.

Should you be caught out in the open with a tornado approaching, do not try to outrun the storm. Find a low lying spot such as a ravine and crouch down with your arms over your head. Because tornadoes are so unpredictable, you are in much more danger if you try to outrun them.

While tornadoes cause much damage in the areas where they hit, one good thing about tornadoes is that the area they damage is relatively small. If you take a few safety precautions, you have the best chance of making it through a dangerous tornado.
Written by Associate Writer Nicole Harms

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Tornado Myths

As a powerful force of nature, tornadoes have become a source of some persistent urban legends and common misconceptions. These urban legends are typically in the form of folk wisdom on how to find safe shelter from a tornado, or how to minimize property damage.

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 (somewhat like being in a windtunnel). 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. The overpass was also of a specific design which included a hollow crawlspace at the top of the embankment under the bridge surface. As shown in the video, it was large enough to allow the people to crawl inside and use the exposed girders for grip, reducing the chances they would be blown away and largely shielding them from airborne debris. This is a relatively uncommon design in bridge overpasses, and many are completely exposed underneath, with nothing to hold on to and no shelter from the wind.

The danger was highlighted during the Oklahoma Tornado Outbreak, when 3 deaths and several severe injuries were caused when an F4 tornado crossed two overpasses being used as shelters. One individual actually left her well-built home and drove several miles to shelter under an overpass, in the mistaken belief that it was safer than her house. All of the individuals received massive injuries from windborne debris and several were swept out to their deaths.

[edit] Tornado behavior

Myth: Tornadoes sometimes "skip houses".

It is true that a house that is in between two destroyed homes can be "untouched", but this is not the result of a tornado "skipping" as was previously thought. After the Super Outbreak, Dr. Fujita[citation needed] studied many films of tornadoes from that day. Included in his review was damage and tornado film footage of F4 and F5 tornadoes. Fujita concluded that the multiple vortices of an F-4 or F-5, which are highly volatile but small vortices that dance around the main funnel, are responsible for making tornadoes appear to "skip houses".

The way it works is that the main funnel, moving along in a general straight path, will miss several houses that are just to the left or just to the right of it. However, the "multiple vortices", which are dancing in circles around the main funnel, do hit these houses, since they swing out and around, in a circle around the funnel. But because they are constantly spinning in circles around the main funnel as it moves forward, then a multi-vortex may hit one house as the main funnel passes by, but that same multi-vortex may already have moved to other side of the main funnel by the time the main funnel passes the next house, making it appear that the main funnel "skipped over" a house.

Myth: I don't have to worry about skinny tornadoes, only the fat ones are strong

A lethal myth. Firstly: all tornadoes are dangerous, and should never be dismissed as "not powerful". Secondly, although large tornadoes are generally more powerful, this is not always the case. There have been many instances where "classic" funnels (normal size) or even skinny funnels were deadly F-4 or F-5 tornadoes, where-as a large 1/2 mile wide "wedge" tornado (which make up a lot of F-4 or F-5's) might be an F-3. So the width of a tornado is not a good indicator of how powerful it is, and all tornadoes should be taken very seriously.

[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. A common tornado witticism states "Don't bother opening your windows; the tornado will do that for you." 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.

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. While the popular assumption is that trailer parks are "tornado magnets", they are no more likely to be hit than a selected field, farm house, or town than anything else in a tornado-prone area.

Myth: In a trailer or mobile home, the best place to be is in a closet or bathroom

There is no safe place inside a mobile home or trailer when a tornado strikes. Unlike a house, a mobile home is easily ripped apart by even the weakest tornadoes. The majority of all tornado fatalities are attributed to mobile-home dwellers who were in their homes when struck. The NWS advises all mobile home residents to have access to either a sturdy house or underground shelter to shelter in whenever a tornado warning is issued. Most standard tornado warning messages include a directive that mobile home dwellers should immediately evacuate to one of these pre-planned shelters.

[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 U.S. National Weather Service has now adopted the advice that the central-most-room on the lowest level of a structure is the safest, with centrally-located rooms in an underground level being far safer than any above-ground location. 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. Bathrooms are considered particularly safe as the plumbing fixtures strengthen the walls and anchor them to the ground, while a bathtub can provide some degree of protection from flying debris. The void space underneath a stairwell is also a recommended shelter, as the stairway itself braces and strengthens the walls.

Bank vaults are probably the safest above-ground shelters from tornadoes; in a number of cases, small towns have been entirely swept away by violent tornadoes, but the vault at the local bank was left undamaged. Other potential shelters in commercial buildings include restaurant walk-in freezers and interior stairwells.

[edit] Escaping a Tornado

Myth: When a tornado approaches your home, the best thing to do is to get in a car and drive away

The official directive from the NWS, past and present, has been for house-dwellers in the path of a tornado to shelter in place rather than risk an escape by vehicle. This is a result of several factors and statistics. An interior room inside of a well-built frame house (especially one with a basement) provides a reasonable degree of protection from tornadoes rated F0-F2, approximately 85% of all tornadoes. This means that in an average scenario, even a direct hit (while highly damaging to the walls and roof) is unlikely to destroy the house enough to severely injure or kill a well-sheltered occupant.

By comparison, a vehicle encountering all but the weakest tornadoes would immediately have the windows shattered (subjecting the occupant to lethal flying debris), and be quickly flipped by the ground-level winds. With stronger tornadoes, the vehicle could also taken airborne and thrown a considerable distance. Since most individuals are untrained at visually identifying subtle severe weather phenomena, they stand an excellent chance of accidentally driving into additional severe weather (including tornadoes) while blindly trying to escape. Flash flooding, torrential rain, severe thunderstorms, hail, and debris on the roadway could easily cause nearly impassable driving conditions, which, aggravated by driver panic, might well result in a dangerous and preventable accident. The disorganized peril of such a situation would be magnified greatly if all the residents of a warned area felt the need to flee by car.

If a person spots a nearby tornado while driving, the official NWS directive has always been to abandon the car and shelter in a ditch or culvert. No data has been produced on the efficacy of this method, but unscientific analysis of storm chaser video shows that no driver has ever actually been filmed abandoning their car for a ditch. The colloquial opinion at the NSSL currently states that a tornado encountered while driving can be successfully fled from at right angles (90-degree) from its direction of apparent movement. If an encounter is too sudden to flee from, the advice is still to shelter in the ditch rather than the car.

Note that the NWS has consistently advised mobile home residents to immediately evacuate their residences for the nearest sturdy house or storm shelter whenever a tornado warning is issued for their area.

[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 river and the Wabash river, and possibly several other small bodies of water.

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

The Windsor - Tecumseh, Ontario Tornado of 1946 crossed the Detroit River from River Rouge, Michigan into downtown Windsor, Ontario, where the river is roughly 3/4 of a mile wide. The F3 tornado that struck on July 2, 1997 also crossed the river into Windsor.

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 Huntsville tornado crossed Monte Sano mountain (1,650 feet) and gained in intensity as it descended the mountain.

During the same outbreak, 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.

Appalachia has been struck by other destructive tornado outbreaks: during the "Enigma" outbreak (Feb. 19, 1884), at least one major tornado family struck the mountains of SW North Carolina. On May 1, 1929, a destructive tornado outbreak swept from SW to NE up the Appalachians from Alabama to Maryland, spawning destructive tornadoes at Rye Cove, VA, Morgantown, WV, and in a series moving from Rappahannock County, VA to Frederick, MD. In 1944, a devastating tornado outbreak swept from NW to SE through parts of Ohio, West Virginia, Pennsylvania, Maryland and Virginia, with the worst damage seen in mountainous areas between Pittsburgh and Washington, DC. And in May 1985, several large tornadoes associated with a wide outbreak crossed the Alleghenies in central Pennsylvania.

High altitudes are not necessarily an impediment to tornado formation - the 1999 Salt Lake City Tornado in Utah formed at elevations of over 4000 feet and produced F2 damage in the downtown area. Farther north, a 1989 tornado shredded timber and left a mile-wide path of F4 damage over extremely rugged terrain in the Teton Wilderness in Wyoming, crossing the continental divide at an elevation of over 11,000 feet. In 2004, a tornado was photographed near Rockwell Pass in the Sierra Nevada of California at nearly 12,000 feet. However, it should be noted (for other climatological reasons) 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, and the tornado that ripped through the heart of downtown Fort Worth, Texas in March of 2000 are just two 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. See also: List of tornadoes striking downtown areas.

[edit] Tornadoes in far-northern latitudes or in winter

Tornadoes can, and do, form in extreme northern or southern latitudes. Tornadoes that form in winter are rare, but have also been documented, when warm air meets a strong storm front, causing a tornado that becomes a brilliant white (instead of a dirt-brown) from picking up snow on the ground.

* The Edmonton Tornado of 1987, a powerful F4, struck the Metropolitan Edmonton, Alberta area, which is located 53.57 degrees north. See article for more in-depth information.
* A funnel cloud was sighted on Upper Garry Lake, Northwest Territories, the most northerly funnel cloud on record in Canada. August 10, 1973.
* Yellowknife Tornado of 1978. A tornado touches down near Yellowknife, Northwest Territories toppling a tower and destroying a transmission tower at Rae-Edzo. It is the third tornado in 16 years there.
* White Point Beach, Nova Scotia Tornado of January 30, 1954. A great deal of hail and lightning along the coast, touched down near Liverpool, Nova Scotia during mid-winter at a latitude of almost 44 degrees north.
* November 1989 Tornado Outbreak. A late-season tornado touches down on November 16, in Mont-Saint-Hilaire. It was rated F2.
* Sudbury, Ontario Tornado (August 20, 1970). A strong F3 tornado strikes the Northern Ontario mining city of Sudbury, Ontario and its suburbs, with Lively, Ontario being the hardest hit in the early morning hours. This is the first recorded major tornado in Northern Ontario. The terrain is not too hilly (actually fairly flat for Northern Ontario standards), but its strength is unusual for its location. Tornadoes are thought to be more common in Northern Ontario than prevalence maps indicate, this is mostly because many go unreported as they travel through very remote forest, far away from any roads or human settlements. Damage is usually assessed from the air, after the fact and the number of reported tornadoes each year in the north are increasing in recent years, as a result of better technology to confirm them. However, larger, severe tornadoes are more common in the Great Plains and Canadian Prairies.

[edit] Canada and other northern areas can't get F5s

This is another myth, that is incorrect, and is related to the above myth. Recently, Environment Canada (Canada's national weather service) had re-classified a "strong F4" as the first confirmed F5 tornado in Canada's history (Elie, Manitoba Tornado). The country has also seen other very strong tornadoes that have approached or even became F5's in strength, such as the Edmonton Tornado of 1987 (which is disputed, but may have briefly achieved F5 strength), the 1920 Frobisher - Alameda, Saskatchewan Tornado, and the 1935 Benson, Saskatchewan Tornado, which were both strong F4's, but may have also achieved brief F5 strength.

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