Archive for the 'Tornadoes' Category

As we are in the midst of the peak season for tornadoes in the southern half of the United States (the peak season for the southern states is March-May and the late spring-early summer in the northern states), I thought a good article would be a discussion of tornado myths.

Myth: Rivers, lakes, and mountains are safe from tornadoes.
Truth: No place is safe from tornadoes, Yellowstone National Park was hit by a tornado that did extensive damage to a 10,000 foot mountain

Myth: Highway overpasses are good shelters from tornadoes
Truth: Absolutely not. Overpasses can be extremely dangerous because there is little protection from flying debris. Plus, in the event of the direct hit, you would most likely be blown out of the overpass shelter and would in the midst of the deadly wind of debris moving 100-200 miles per hour.

Myth: You should also take cover in the southwest portion of your basement.
Truth: You are far better off hiding in a place where there is sturdy table or stairwell, no matter what part of the basement of the house. In general, hiding in a basement will protect you from injury in any situation. This myth came into being because tornadoes often approach from the southwest and it was assumed that storm would force debris towards the northeast and away from you. Actually, the southwest corner is often the least safe because most tornadoes only shift houses off their foundations in a northeast direction. The unsupported part of the house then might collapse in the southwest part of the basement where you thought it was safest! The few deaths that have occurred in basements were caused by collapse portions of the house that were ripped from the foundations, not debris from the wind which the myth was based on. As mentioned above, location doesn’t matter all that much if you can hide under the stairwell or a sturdy table.

Myth: This is by far the most common myth: opening your windows will lessen damage. If you can equalize the pressure between the interior and vortex of the tornado, your home won’t “explode”.
Truth: Even the most powerful storms have a pressure drop that a typical building can vent in mere seconds. However, your home is already destroyed by the time the maximum pressure drop reaches you. There is also zero evidence that opening windows strategically to allow wind to vent through the house will do any good. Bottom line: get to the basement and forget the windows. If you have a powerful tornado bearing down on your house, nothing will prevent catastrophic damage but being in the basement will save your life.

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Because it never hurts to refresh your memory, here are tornado safety guidelines from the National Weather Service:

- In a home or building, move to a pre-designated shelter, such as a basement. If an underground shelter is not available, move to a small interior room or hallway on the lowest floor and get under a sturdy piece of furniture. Put as many walls as possible between you and the outside.

- Stay away from windows.

- Get out of automobiles. Do not try to outrun a tornado in your car; instead, leave it immediately for safe shelter. If caught outside or in a vehicle, lie flat in a nearby ditch or depression and cover your head with your hands.

- Be aware of flying debris. Flying debris from tornadoes causes most fatalities and injuries.

- Mobile homes, even if tied down, offer little protection from tornadoes. You should leave a mobile home and go to the lowest floor of a sturdy nearby building or a storm shelter.

- Finally, if you live in a rural area that doesn’t have tornado sirens – you should definitely get a NOAA weather radio with alarm tone and battery backup. They are sold in many stores and some even have crank devices that allow you to charge cell phone batteries during long-term power outages (this is especially useful if you live in a hurricane prone area).

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Posted by Tim Roth, author of the political blog Think Anew and Act Anew

Sources:
1. “Thunderstorms, Tornadoes, Lightning” – Weather Safety Guide from The National Weather Service – PDF file
2. “Overpasses are tornado death traps”, by Chris Cappella, USATODAY.com
3. Myths and Misconceptions about Tornadoes, The Tornado Project – not a rock-solid source like a newspaper or the National Weather Service but from what I can tell, the author(s) have done their homework as they mention interviews with structural engineers so I think it’s a credible source.

The past two articles talked about the recent storm system that caused a blizzard in Wisconsin and heavy freezing rain in Illinois. The third and final article about this storm is about the southern end of the recent storm and a powerful tornado that devastated the town of Dumas, Arkansas.

What caused these tornadoes?
The cold front associated with low pressure system that causes a blizzard in Wisconsin and freezing rain in Illinois generated the formation of thunderstorms. The cold front brought in cold winter air from the northern US. This cold air combined with moist warm air to create updraft of air that formed the thunderstorm clouds. Once again, the currently strong jet stream over Arkansas played a big role. These upper levels winds enhanced spinning columns of air that are found in all thunderstorms. The updraft winds rotated these columns of air to a vertical position and this results in a rotating wall cloud.

As the storm becomes more powerful, heavy rainfall causes an area of air called the rear flank downdraft (RFD). The RFD’s rapid descent drags the rotating wall cloud close to the surface. At this point, a funnel cloud drops out of the funnel cloud and causes death and destruction on the ground.

Why does the funnel cloud form?
At this point, it remains unclear but many scientists are working on figuring this out. Stay tuned for more on this.

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Posted by Tim Roth, author of the political blog Think Anew and Act Anew

Sources:
1. “Neccessary Ingredients for Thunderstorms”, NOAA’s JetStream – Online School for Weather
2. “Thunderstorm Hazards – Tornadoes”, NOAA’s JetStream – Online School for Weather
3. “Cyclogenesis”, Wikipedia entry