Tornadoes are powerful and destructive phenomena. A common question arises regarding the existence of an “EF6 tornado,” suggesting even greater devastation. However, the current scientific classification system for tornadoes tops out at a specific level, reflecting practical limits of observed damage and theoretical understanding of these atmospheric events.
Understanding the Enhanced Fujita Scale
The Enhanced Fujita (EF) Scale is the standard system used to classify tornado intensity based on damage severity. Operational in the United States since 2007 and Canada since 2013, it ranges from EF0 to EF5. This scale replaced the original Fujita (F) Scale, developed in 1971, to provide more accurate wind speed estimates and address its predecessor’s limitations.
The F-Scale often overestimated wind speeds for intense tornadoes. The EF Scale refined this by incorporating engineering studies and a broader range of damage indicators, allowing for a more consistent assessment. Each EF rating, from EF0 (65-85 mph) to EF5 (over 200 mph), corresponds to estimated three-second wind gusts.
Why There Isn’t an EF6 Rating
The Enhanced Fujita Scale culminates at EF5, assigned to tornadoes with estimated wind speeds exceeding 200 mph, capable of causing incredible damage. This upper limit reflects the point where damage to well-built structures is so complete that further wind speed increases cannot be differentiated by destruction alone. An EF5 tornado can sweep foundations clean, destroy steel-reinforced concrete structures, and toss large objects, representing near-total devastation.
There are theoretical and physical limitations to how strong a tornado can become. While some mobile Doppler radar measurements show wind speeds approaching 300 mph, differentiating damage beyond the EF5 threshold is challenging. Atmospheric conditions for significantly higher winds are extremely rare, suggesting a practical upper bound to tornado intensity. The scale effectively covers the full spectrum of observed and possible tornado damage.
How Tornadoes Are Rated
Assigning an EF rating involves a post-storm damage survey conducted by meteorologists and civil engineers. Teams examine wreckage against a comprehensive list of 28 damage indicators (DIs). These indicators cover structures and vegetation, such as residences, retail buildings, and trees.
Each damage indicator has multiple degrees of damage (DoDs) corresponding to different destruction levels. Surveyors match observed damage to the appropriate degree, estimating the range of wind speeds that likely caused it. This assessment, including construction quality, provides the basis for assigning the final EF rating, representing the highest estimated wind speed along the tornado’s path.