Tornadoes in the United States

Every state in the union has experienced them, and the destruction caused by tornadoes each year can climb into the billions of dollars. Scientists have learned a great deal about tornadoes over the past several decades, though, and warning systems are now able to prevent many of the casualties that tornadoes used to cause. To determine what has been learned and what steps have been taken for warning systems, this paper provides a review of the relevant peer-reviewed and scholarly literature concerning tornadoes, followed by a summary of the research and important findings in the conclusion.

Tornadoes are violently rotating columns of air that reach from a cloud to the earth’s surface (What is a tornado?, 2014). The spring months of April, May, and June are the period in which the majority of tornadoes in the Northern Hemisphere are formed (Cavendish, 2000). During these months, the sun gradually but unequally warms the ocean and land surfaces following the cold of winter (Cavendish, 2005). Although they can occur, tornadoes do not typically occur in the Tropics because there is not as much seasonal variation in temperatures (Cavendish, 2005). Likewise, although they can occur in the cold polar regions and winter months anywhere, the more stable atmospheric conditions do not generally result in the formation of tornadoes (Cavendish, 2005). According to Cavendish, “Although tornadoes can appear anywhere and at any time of year, the United States experiences the largest number of anywhere in the world. A normal year will be marked with 600 to 1,000 tornadoes, with an average of 850 tornadoes per year; in 1973, a record 1,107 tornadoes hit the country” (2005, p. 1597). Although typically caused by thunderstorms, East Coast and Gulf Coast hurricanes and tropical storms are also responsible for generating numerous tornadoes (Moore & Dixon, 2011). For instance, during the period 1950 to 2005, 60 land-falling hurricanes along the Gulf coast alone produced 734 tornadoes (Moore & Dixon, 2011).

The United States has three distinct geographical regions that facilitate tornado formations. The first region, frequently called “Tornado Alley,” runs from Texas through central Oklahoma, Kansas, Nebraska, and North and South Dakota (Cavendish, 2005). According to Cavendish, “During tornado season — from April to June — warm, moist air from the Gull of Mexico encounter cold, dry air from the Pole. This area tends to experience most of the strongest as well as the greatest number of tornadoes” (2005, p. 1597). Comparable geographic features over the southern Atlantic states and over the southern plains also produce tornado belts (Cavendish, 2005).

The National Weather Service (NWS) implemented the F-Scale in the early 1970s as the official tornado-intensity classification system and tornado reports prior to this year do not include tornado-intensity estimates (Moore & Dixon, 2011). In 1976, the National Severe Storms Forecast Center and the Nuclear Regulatory Commission reviewed and assigned F-Scale ratings to tornado reports back to 1950 (Moore & Dixon, 2011). The F-Scale begins with F0 for the weakest tornadoes that are capable of breaking tree branches and felling trees that have shallow roots with 40- to 72-mph. winds (Rosenfeld, 1999). By contrast, an Fl tornado has 73- to 112-m.p.h. winds and is capable of blowing an automobile off the road or mobile homes off their foundations (Rosenfeld, 1999). An F2 tornado has 113- to 157-mph winds and is capable of uprooting large trees or tearing the roofs off wood-frame houses (Rosenfeld, 1999). In February 2007, the NWS implemented the Enhanced Fujita Scale (EF Scale) as the official tornado-intensity classification used in the United States (Moore & Dixon, 2011).

There has been some controversy concerning the data about tornadoes, though, involving potential biases and limitations regarding the documentation and reporting of relevant spatial and temporal information as well as the F-Scale ratings that have been assigned (Moore & Dixon, 2011). In this regard, Moore and Dixon advise that, “Tornado data provided by untrained witnesses and the dependency of assigned F. Scale ratings on the qualifications of the person reporting the damage are possible sources of much of the reporting errors” (2011, p. 372). In addition, the increase in reported tornadoes since the 1950s has been a source of controversy (Moore & Dixon, 2011). According to Moore and Dixon, “This increase can be partially attributed to population growth and sprawl, which increases reporting and documentation, to increased public awareness, and to advances in detection technology” (2011, p. 372).

Scientists categorize two different types of tornadoes, ordinary and supercell (Cavendish, 2005). Ordinary tornadoes are relatively brief in duration (typically around 5 minutes), move at grounds speeds lower than 30 miles per hour and leave a damage field of around 150 feet across (Cavendish, 2005). The winds from ordinary tornadoes rarely cause more damage than an F-2 on the Fujita-Pearson wind damage scale (Cavendish, 2005). By contrast, supercell storm tornadoes can persist for several hours, travel at grounds speeds in excess of 60 miles per hours and leave a damage field more than a mile across (Cavendish, 2005).

Conclusion

The research showed that tornadoes are violently rotating columns of air that extend from a cloud to the earth’s surface. Although they can occur anywhere, tornadoes generally form in the so-called “Tornado Alley” of the United States as well as the southern Atlantic states and the southern plains. The destruction caused by tornadoes can be severe, but supercell tornadoes were shown to be much more destructive than ordinary tornadoes. Finally, the United States will experience between 850 and 1,000 tornadoes each year, making them an ongoing threat to Amreicans.

References

Cavendish, M. (2005). Encyclopedia of earth and physical sciences. New York: Marshall

Cavendish.

Moore, T.W. & Dixon, R.W. (2011, July). Climatology of tornadoes associated with Gulf

Coast-landfalling hurricanes. The Geographical Review, 101(3), 371-377.

Rosenfeld, J.O. (1999). Eye of the storm: Inside the world’s deadliest hurricanes, tornadoes, and blizzards. New York: Plenum Press.

What is a tornado? (2014). The Weather Channel. Retrieved from http://www.weather.com / outlook/weather-news/severe-weather/articles/tornado-what-is-a-tornado_2010-03-30.