The Enhanced Fujita (EF) Scale is the standardized system for classifying tornado intensity. It provides a uniform method for meteorologists and damage assessment teams to measure tornado strength, primarily based on the destruction left behind. By examining damage to structures and vegetation, experts assign a rating reflecting the tornado’s estimated wind speeds.
Categorizing Tornadoes
The EF Scale categorizes tornadoes into six levels, from EF0 to EF5. Each level corresponds to a specific range of estimated wind speeds and distinct damage characteristics. An EF0 tornado, the weakest, has estimated wind speeds between 65 and 85 miles per hour, causing light damage like peeled roof surfaces or broken tree branches. An EF1 tornado, with winds from 86 to 110 miles per hour, can cause moderate damage, including severely peeled roofs and overturned mobile homes.
An EF2 tornado, with estimated winds of 111 to 135 miles per hour, results in considerable damage, often tearing roofs off well-constructed homes and demolishing mobile homes. An EF3 tornado is characterized by severe damage, with wind speeds ranging from 136 to 165 miles per hour, capable of destroying entire stories of well-built houses and overturning trains. An EF4 tornado causes devastating damage from estimated wind speeds of 166 to 200 miles per hour, leveling well-constructed frame houses and throwing cars.
The highest classification, an EF5 tornado, represents incredible damage caused by estimated wind speeds exceeding 200 miles per hour. These tornadoes can sweep strong frame houses clean from their foundations and hurl automobiles great distances.
Assessing Tornado Strength
Assigning an EF rating to a tornado occurs after the event, through meticulous post-storm surveys conducted by meteorologists and structural engineers. This assessment relies on the observed damage, rather than direct wind speed measurements during the tornado’s passage. Teams examine various structures and objects within the damage path, looking for specific indicators of destruction.
The process utilizes a framework of “Damage Indicators” (DIs) and “Degrees of Damage” (DoD). Damage Indicators are specific types of structures or objects, such as residential homes, mobile homes, schools, or different types of trees. For each DI, there are multiple Degrees of Damage, which describe the extent of destruction observed for that particular indicator. For instance, a residential home might have different DoDs ranging from minor roof damage to complete destruction. By matching the observed damage to the appropriate DI and DoD, experts can estimate the range of wind speeds that likely caused that specific level of destruction, thereby determining the tornado’s EF rating.
From Fujita to Enhanced Fujita
The current Enhanced Fujita (EF) Scale superseded the original Fujita (F) Scale, which was developed by Dr. Tetsuya Fujita in 1971. The transition to the EF Scale, implemented in 2007, became necessary due to limitations of the older system. The original F-scale’s damage descriptions were often subjective and lacked specific engineering standards, sometimes overestimating actual wind speeds required to cause observed damage.
The development of the EF Scale involved a collaborative effort among meteorologists, engineers, and wind science experts. This revised scale incorporated more precise damage indicators and better correlated observed damage with actual wind speeds, based on extensive engineering and meteorological research. The EF Scale provides a more accurate assessment of tornado intensity, based on a deeper understanding of how structures respond to wind forces. This allows for more consistent and reliable tornado ratings.