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For the book by William S. Burroughs, see Tornado Alley .
A diagram of tornado alley's rough location (red), and its contributing weather systems
Tornado Alley is a colloquial term most often used in reference to the area of the United Statesmarker in which tornadoes are most frequent. Although an official location is not defined, the areas in between the Rocky Mountains and Appalachian Mountainsmarker are the areas usually associated with it.

Tornado geography

Tornado activity in the United States.
Although no U.S. state is entirely free of tornadoes, they are most frequent in the plains between the Rocky and Appalachian Mountains. According to the storm events database of the National Climatic Data Center , Texas reports more tornadoes than any other state, though this state's very large land area should be taken into account. Kansas and Oklahoma are second and third respectively for sheer number of tornadoes reported but report more per land area than Texas. However, the density of tornado occurrences in northern Texas is comparable to Oklahoma and Kansas. Florida also reports a high number and density of tornado occurrences though only rarely do tornadoes here approach the strength of those which sometimes strike the southern plains..

Definition

Although Tornado Alley is 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, "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. 90% of tornadoes hit this region of the U.S because cold, dry air from Canadamarker and the Rocky Mountains meets warm, moist air from the Gulf of Mexicomarker and hot, dry air from the Sonoran Desertmarker, which causes atmospheric instability, heavy precipitation, and many intense thunderstorms.

The most common definition of Tornado Alley is the location where the strongest tornadoes occur most frequently. The core of Tornado Alley can be considered as consisting northern Texas (including the Panhandle), Oklahoma and Kansas. However, Tornado Alley can be also be defined as an area stretching from central Texas to the Canadian prairies and from eastern Colorado to western Pennsylvania. It can also be argued that there are numerous Tornado Alley's. In addition to the Texas/Oklahoma/Kansas core, such area's include the Ohio Valley, the Tennessee Valley and the lower Mississippi valley.

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. This region is particularly vulnerable to violent, long tracked tornadoes. Much of the housing in this region is less robust than in other parts of the USA and many people live in mobile homes. As a result, tornado related casualties in the southern USA are particularly high.

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.

Number of U.S. tornadoes per state

These figures,reported by the National Climatic Data Center for the period between January 1 1950 and July 31 2009, show the ten most affected states. As reports are taken from individual counties within States, sometimes the same tornado can be reported more than once as it crosses county lines.

  1. Texas: 8049
  2. Kansas: 3809
  3. Oklahoma:3442
  4. Florida: 3031
  5. Nebraska: 2595
  6. Iowa: 2368
  7. Illinois: 2207
  8. Missouri: 2119
  9. Mississippi: 1972
  10. Alabama: 1844


References

  1. Tornado FAQ
  2. http://www.nssl.noaa.gov/faq/faq_tor.php


See also



External links




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