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User:RingtailedFox/Tornado myths

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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

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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 1999 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.

Tornado behavior

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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 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.

Opening windows or doors

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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.

Mobile home and trailer parks

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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.

Safest location in a house

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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.

Escaping a Tornado

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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.

Tornadoes in rough terrain and crossing rivers

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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.

Tornadoes in urban areas

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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.

Tornadoes in far-northern latitudes or in winter

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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.

Canada and other northern areas can't get F5s

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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.

References

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  • "Tornado Myths, Facts, and Safety". National Oceanic and Atmospheric Administration. 17 August 2006. Retrieved November 12, 2007. {{cite web}}: Check date values in: |year= (help)CS1 maint: year (link)

See also

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