Tornado Alley
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- For the book by William S. Burroughs, see Tornado Alley (book).
Tornado Alley is a colloquial term most often used in reference to the area of the United States in which tornadoes are most frequent. Although an official location of the term is not defined, the areas in between the Rocky Mountains and Appalachian Mountains are the areas usually associated with it.
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[edit] Tornado geography
Although no state is entirely free of tornadoes, they are most frequent in the Plains area between the Rocky and Appalachian Mountains and in the state of Florida. The state where twisters most commonly ocur is Texas (notably due to its size and the area where tornadoes can occur).[1] When land area is taken into account, however, Florida has the highest density of tornado occurrence in the country.[2] However nearly all of Florida's tornadoes are weak, short lived and not produced by supercell thunderstorms; Oklahoma has the highest occurrence of such "classic" supercellular tornadoes. In contrast, the Northeast and West tend to be the least tornado-prone regions in the United States.
[edit] Definition
Although Tornado Alley is generally considered to be in the areas of the Central United States, no official definition of the term has actually been produced by the National Weather Service. According to the National Severe Storms Laboratory FAQ,[3] "Tornado Alley" is a term created by the media to refer to areas that have greater numbers of tornadoes. There are several ideas of what Tornado Alley is, but those ideas are the result of the different criteria used to refer to it.
[edit] Significant Tornado Alley
Perhaps the most common definition of tornado alley is the location of where the strongest tornadoes occur most frequently. In the United States that location is from Texas, northward through Oklahoma, Kansas, Nebraska, Iowa, and into South Dakota. States to the east of this region do experience strong tornadoes,[4] however they do not occur with the frequency as they do in states to the west.
[edit] Other criteria
Another criterion for determining Tornado Alley is to not focus on just the strongest tornadoes, but the location of where tornadoes happen more frequently relative to other places in the country. When using this method tornado alley has a much wider reaching grasp. In addition to Significant Tornado Alley, this area can include the great lowland areas of the Mississippi, Ohio and lower Missouri River valleys, as well as the Southeast into Florida.
[edit] Time of year
Also to be considered is the time of year. The highest frequency of tornadoes, commonly (but incorrectly) called "tornado season", shifts geographically depending on the season. During the winter months the Southeastern United States receives the highest number of tornadoes. During the months of March - May the threat shifts into the central United States. Then during the summer months the highest concentration of tornadoes tends to shift farther north as the weather warms across the U.S. Technically speaking, however, the central plains may be considered part of the tornado alley almost all-year-round, since this is where "temperature swings" between warm and cold air are most common.
[edit] Variations
The nickname "Dixie Alley" is sometimes used for the areas in the southeastern U.S.–notably the lower Mississippi Valley and the upper Tennessee Valley–which are particularly vulnerable to strong tornadoes. More people have been killed by tornadoes in this particular region than those of the Great Plains because of the higher population density in the southeastern United States.[5] The term Dixie Alley is used extensively by The Weather Channel.[6]
[edit] Impact
In the heart of tornado alley, building codes are often stricter than those for other parts of the U.S., requiring strengthened roofs and more secure connections between the building and its foundation. Other common precautionary measures include the construction of storm cellars, and the installation of tornado sirens. Tornado awareness and media weather coverage are also high.
Some studies suggest that there are also smaller tornado alleys located across the United States.[7]
[edit] References
- ^ TORNADO NUMBERS 1950 - 1994. Storm Prediction Center. Retrieved on 2007-04-26.
- ^ Tornado Climatology. National Climatic Data Center (January 29, 2007). Retrieved on 2007-04-26.
- ^ http://www.nssl.noaa.gov/faq/faq_tor.php
- ^ F5 and EF5 Tornadoes of the United States
- ^ Southeast tornadoes are nation's deadliest. USA Today (May 20, 2005). Retrieved on 2007-10-16.
- ^ Gerard, Alan; Gordon, John. Tornado Alley vs. Dixie Alley. National Weather Service. Retrieved on 2007-04-26.
- ^ Broyles, Chris; C. Crosbie (October 2004). "Evidence of Smaller Tornado Alleys Across the United States Based on a Long Track F3-F5 Tornado Climatology Study from 1880-2003". 22nd Conference on Severe Local Storms, Hyannis, MA: American Meteorological Society.
