Tornado myths
From Wikipedia, the free encyclopedia
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.
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[edit] Using highway overpasses as shelter
Myth: Highway overpasses are adequate shelter if a tornado approaches while you are on a road.
Sensational footage taken by a television crew hiding from a tornado under an overpass during the 1991 Andover, Kansas Tornado Outbreak helped to convince some that bridges are good shelters when a tornado is nearby. The members of the television crew (and several other travelers) survived by huddling high underneath the bridge and bracing themselves against support columns while a weak tornado appeared to pass directly over the bridge.
In reality, when directly hit by tornadoes, the confined spaces beneath overpasses increase the speed of the winds due to the Venturi effect, and thus make them potentially less safe. In the case of the Andover tornado footage, it was discovered that the tornado did not pass directly over the bridge, but instead over the ground slightly south of the bridge and camera crew, exposing them to much weaker winds.
[edit] Opening windows or doors
Myth: Most tornado damage is due to the low pressure in the tornado causing the house to explode. Opening your windows or doors while a tornado approaches will equalize atmospheric pressure and help prevent property damage.
Since windows are typically the most fragile external feature of a house, they are in more danger from flying debris. Opening them during an active tornado wastes time and effort that could be spent on other, more useful protective measures. Homes do not "explode" when hit by a tornado, though it often appears so. Commonly, a tornado will break the windows first, allowing strong winds to enter the home. These winds may then push on the underside of the roof upwards, blowing it off. Without the roof, the walls lose structural support and will often fall outwards. Observing the wreckage after the collapse may give the impression the house was pushed apart from the inside.
Flying debris from a tornado will break any windows, so opening them only wastes valuable time and is even counterproductive to the soundness of the structure. It is the debris that breaks windows, not the difference in pressure.
As a note, this also applies to homes or structures that are hit by a hurricane. Studies from the National Hurricane Center suggest that closed containers do not explode during high wind scenarios. But rather, an opening, such as a broken window, will allow the hurricane force winds to enter a room and subsequently destroy an entire building.
[edit] Mobile home and trailer parks
Myth: Twisters are attracted to mobile homes and/or trailer parks.
Trailer parks consist of low-cost mobile homes with less structural integrity than traditional houses. A weak storm that leaves little damage to well-built structures might devastate a trailer park. Mobile homes do not attract tornadoes; they are just more susceptible to damage from them.
[edit] Safest location in a house
Myth: During a tornado, the southwest corner of a building is the safest.
An unfortunately fatal belief, and for a long time it was considered sound advice but without any proof of safety compared to any other parts of a building. After the increase in tornado research during the turn of the millennium, the US National Weather Service has now adopted the advice that the central-most-room (or underground—absolute best) is the safest. In reality, a tornado can hit any part of a building thereby making any part of the exterior subject to damage from rapidly changing winds.
Some of the worst places during a tornado are in a room with many windows, any room with an exterior wall, or a large theater-like room such as a church or indoor basketball court. The best places are small rooms like closets or bathrooms.
[edit] Tornadoes in rough terrain and crossing rivers
Myth: Tornadoes cannot form near rivers or cross them.
Myth: Tornadoes cannot follow terrain into steep valleys.
Myth: Tornadoes cannot travel over steep hills or mountains.
During the Super Outbreak, a tornado formed near Sayler Park section of Cincinnati, Ohio (near the Ohio River). It was among the six F5s of the outbreak. The city of Cairo, Illinois, which lies at the confluence of the Ohio and Mississippi Rivers, was also hit by a tornado that day.
The Tri-state tornado of 1925 crossed the Mississippi and possibly several other small bodies of water.
The F5 tornado of May 3, 1999 crossed the Yukon River in Oklahoma before it hit Moore, Oklahoma.
During the Super Outbreak, after destroying three schools, the Monticello tornado crossed over a 60-foot bluff and the Tippecanoe River and damaged several homes.
During the Super Outbreak, the Guin tornado crossed Monte Sano mountain (1,650 feet) and gained in intensity as it descended the mountain. An F4 tornado caused damage in Murphy, NC after crossing a 3,000-foot ridge, and F2 tornadoes were confirmed in Roanoke, VA and Great Smoky Mountains National Park, NC. Tornadoes formed elsewhere in West Virginia, western Virginia, southwestern North Carolina, and north Georgia - regions of four states that are in the ranges of the Appalachian mountains.
Also, it's not too high for a tornado. In Salt Lake City, Utah, a tornado formed and damaged a streak of the city near downtown. Salt Lake City is well above 4000 feet. However, it should be noted that it is a rare occurrence for tornadoes to form west of the Rocky Mountains.
[edit] Tornadoes in urban areas
Myth: You're safe from a tornado in a big city.
Closely related to the "terrain" story (See Salt Lake City tornado just above), it is commonly believed that a tornado will dissipate in an urban area because of the tall skyscrapers. The May 3, 1999 tornado outbreak which struck urban Oklahoma City, and the tornado that ripped through the heart of downtown Fort Worth, Texas in May 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.
Some research has indicated that tornadoes are less likely to *form* over urban areas, as the skyscrapers tend to dissipate the vortex before it can reach the ground; however, the effect of the buildings is not enough to disrupt a fully-formed tornado that enters the urban area from a more rural area.[citation needed]
[edit] References
- Tornado Myths, Facts, and Safety. National Oceanic and Atmospheric Administration (17 August 2006). Retrieved on August 23, 2006.
- Tornado Myths. Indiana Department of Homeland Security (14 July 2005). Retrieved on August 23, 2006.
