What Classifies the Strength of a Tornado?

Fujita Tornado Damage Scale

• Ted Theodore Fujita of the University of Chicago recognized the need to be able to rate the intensity, or strength, of tornadoes, based upon the damage they cause. In 1971, he released his Fujita Tornado Damage Scale. This scale rated tornadoes by six categories, called F0 through F5. This scale provided investigators with the ability to estimate the winds of a tornado, thus generating a comparable strength rating for each twister.

Enhanced F Scale for Tornado Damage

• Beginning in the early 1990s, scientists began to recognize a number of limitations inherent in the original Fujita Scale, including a lack of damage indicators, a failure to account for construction quality, and the lack of a definitive correlation between damage and wind speed. These limitations were leading to inconsistent damage estimates and overestimating of wind speeds. As a result, scientists and engineers worked together to create the Enhanced F Scale for Tornado Damage, which became the official scale used by storm-damage surveyors in 2007.

Factors Used to Classify Tornado Strenght

• The Enhanced F Scale uses eight levels of damage, called degrees of damage. The DODs begin with level 1, representing the threshold of visible damage, and progresses up to level 8, representing total destruction. These eight DODs are used to grade the damage sustained by 28 types of structures, called indicators. Examples of indicators include single-wide mobile homes, strip malls, and single or double-family residences. Each DOD for each separate indicator is assigned a corresponding F level. The Enhanced Fujita Scale then provides an estimate of the three-second wind gust speed to cause that type of damage. Again, the scale only provides an estimate of the strength, expressed in wind speed, for a given tornado.

Classifications of Tornado Strenght

• According to the Enhanced F Scale, an F0 tornado produces three-second wind gusts of between 65 and 85 mph, causing light damage. An F1 tornado produces three-second wind gusts of between 86 and 110 mph, causing moderate damage. An F2 tornado produces three-second wind gusts of between 111 and 135 mph, causing considerable damage. An F3 tornado produces three-second wind gusts of between 136 and 165 mph, causing severe damage. An F4 tornado produces three-second wind gusts of between 166 and 200 mph, causing devastating damage. An F5 tornado produces three-second wind gusts of more than 200 mph, causing complete destruction.