Classification Schemes: A Look at Tornadoes Elizabeth Hoffman-Lohmeyer October 26, 2010 Syracuse University Professor Barbara Kwasnik: IST 616

Tornadoes  A tornado is a spinning column of air that stretches from a cloud to the ground. Inside the funnel the winds spin extremely fast thereby sweeping up whatever is in its path.  Tornadoes are some of the most violent storms on Earth. The most powerful twisters can produce winds of up to 300 miles per hour.

 The United States is hit with more tornadoes than any other country. Approximately 1,200 tornadoes hit the U.S. each year.  A classification system was needed that could help categorize tornadoes according to a unified set of terms. The Enhanced Fujita Tornado Scale is used today across the U.S. by the National Weather Service, scientists who study climatology, and by engineers who study structural damage.

Domain & Scope In 1971, University of Chicago meteorologist Dr. T. Theodore Fujita developed the Fujita Tornado Damage Scale. In 2007, this scale was updated by a team of meteorologists and wind engineers. The new scale is referred to as the Enhanced Fujita Tornado Damage Scale. The domain for classifying tornadoes is very specific. The entities being classified are tornadoes. The Enhanced Fujita Scale (EF Scale) measures two things: 1. The estimated wind speed of a tornado, and 2. The level of damage the tornado causes. The scope of the EF Scale is limited to tornadoes only. It does not apply to storms such as hurricanes. Dr. Ted Fujita Source: University of Chicago Source:

Explanation of Structure for the Enhanced Fujita Scale  The EF Scale is hierarchical in nature since tornadoes on the scale are listed from the most mild (EF 0) to the most severe (EF 5).  However, the EF Scale also follows the structure of a paradigm since the level of the tornado is determined by the intersection of two factors: 1. Estimated wind speed, and 2. Degree of Damage (DOD).

 Inside each category the estimated wind speeds are noted and increase within each category. For example, an EF 3 tornado would have approximate wind speeds of miles per hour. An EF 4 tornado would have approximate wind speeds of miles per hour.

 An EF rating is not reported until after the tornado occurs.  Meteorologists use the reported damages to the 28 structure scale to help estimate wind damage and then assign an EF rating accordingly.

The Enhanced Fujita Scale FUJITA SCALEDERIVED EF SCALEOPERATIONAL EF SCALE F Number Fastest 1/4- mile (mph) 3 Second Gust (mph) EF Number 3 Second Gust (mph) EF Number 3 Second Gust (mph) Over 200 This chart shows the comparison between the original Fujita Scale and the Enhanced Fujita Scale which went into effect in Source:

Source: The EF Scale incorporates damage indicators which allows for more detailed analysis and improved correlation between damage and wind speed than the original Fujita Scale. The chart on the left is an example of one of the 28 different types of construction that are used as indicators for tornado damage.

Summary The Fujita Scale is a great example of a classification system that has changed over time due to its weaknesses. The original scale did not take into account the differences in damage to various types of structures and did not contain specific damage indicators. There was no correlation between damage and wind speed. In response to this, the Enhanced Fujita Scale was developed. This new classification system is much more consistent and contains detailed descriptions of damage (including damage to vegetation) which was not available in the earlier scale. As a result of these changes, the EF Scale is a powerful tool that provides accurate and specific documentation of tornadoes.

Sources Consulted Doeden, M. (2008). Tornadoes. Minneapolis: Lerner Publications Company. The Enhanced Fujita Tornado Scale. (2008). Retrieved October 8, 2010, from NOAA Satellite andScale Information Service website: fujita.html The Fujita Scale. (1999). Retrieved October 5, 2010, from The Tornade Project website: Fujita Tornado Damage Scale. (2010). Retrieved October 10, 2010, from The National Weather Service website: Orme, D., & Orme, H. (2005). Tornadoes. Danbury, CT: Children's Press. Prokos, A. (2009). Tornadoes. Pleasantville, NY: Gareth Stevens Publishing.