How Tornadoes are Categorized

Due to the tremendous natural forces involved in the development of a tornado, it turns out almost impossible to place measuring weather instruments inside a tornado to calculate its force.  The best method which meteorologists have devised for estimating the intensity of a tornado has been a system known as the enhanced Fujita Tornado Intensity Scale. The Fujita Scale works by assessing the damage and then estimating the wind speeds that produced that damage. The intensity of a tornado is categorized from F 0-5 with F0 as the weakest and F5 the strongest. The following explains how tornadoes are categorized.

The Fujita Scale was created by a scientist with the name of Theodore Fujita from the University of Chicago in 1971. This scale assessed tornadoes based on the severity of the damage produced. By the use of a scale going from F0 to F5, with the less intense tornadoes rated F0 and the more intense rated F5, Fujita approximated wind speeds to the damage they created in each category rating. Dr. Fujita and his staff demonstrated the usefulness of the Fujita scale by surveying every tornado occurring in the U.S. since 1974.

It was after the Oklahoma tornado that occurred on May 3, 1999 that damage estimates revealed that there was a probability that the wind calculations were too high in the Fujita Scale; since the damage caused didn´t correspond with the wind speeds. Tornadoes sometimes did not reached the wind speeds specified by the Fujita Scale; it wasn´t possible to estimate damages to locations without structures, since the Fujita estimates were based on damage to structures, and the damage estimates did not take into account the fragility of structures.

In 2006, the National Weather Service developed the Enhanced Fujita Scale. The enhanced Fujita Scale conserves the basic design of its predecessor, with six distinct categories from 0 to 6 representing the increasing degrees in damage; however, it includes 28 different damage indicators which give a description for the type of construction in a given damage indicator, as well as an estimate for the degree of damage and the expected calculation of the wind speeds involved.

The enhanced Fujita Scale includes 28 damage indicators. These are clearly defined objects that risk the possibility of being damaged by a tornado, including warehouses, residences, automobiles, transmission line towers, schools, etc. Each damage indicator is assigned a different number of degree of damage (DOD), for instance, 1 DOD corresponds to threshold of visible damage, and 10 DOD for complete destruction. Three wind speeds estimations are assigned for each DOD.

The Enhanced Fujita Scale is widely utilized by meteorologists to classify the damage caused by tornadoes on the same scale as the original Fujita Scale; however, the Enhanced Fujita Scale includes more damage indicators, allowing more accurate analysis of the damaged caused and a more accurate correlation between the damaged produced and the wind speeds attained.