Tornadoes are nature’s most violent storms, capable of producing localized wind speeds that exceed the strength of a major hurricane. They are classified by intensity using a system that assigns a rating based on the severity of the damage they inflict. The most extreme rating a tornado can receive is EF5, representing the pinnacle of destructive power and the rarest category of this atmospheric phenomenon. Understanding the criteria for this highest rating illustrates the truly exceptional nature of these events.
Defining the Highest Rating on the Enhanced Fujita Scale
The intensity of a tornado is officially measured using the Enhanced Fujita (EF) Scale, which assesses the destruction left behind to estimate wind speeds. The scale ranges from EF0, which causes light damage with estimated wind gusts between 65 and 85 miles per hour, to the maximum rating of EF5. An EF5 tornado is characterized by estimated wind speeds exceeding 200 miles per hour, resulting in what is termed “Incredible damage.”
Assigning this rating requires evidence of catastrophic destruction across various structures and materials. The most telling sign of an EF5 is the complete leveling of well-built, strong frame houses, where the debris is swept clean from the foundation slab. While EF4 tornadoes can level frame homes, an EF5 must show an extreme degree of structural obliteration that goes beyond simple flattening.
Meteorologists and engineers analyze 28 different Damage Indicators (DIs), such as residential homes, commercial buildings, and trees, each with multiple Degrees of Damage (DoD). For a tornado to be classified as an EF5, the damage must match the highest possible degrees on these indicators. Examples include pulverizing steel-reinforced structures or gouging scars half a meter deep into the ground. The final rating is assigned based on the highest wind speed estimated from the damage along the entire path.
Historical Frequency and Statistical Rarity
The extreme criteria for the EF5 rating ensure that these events are exceptionally uncommon compared to all other tornadoes. Annually, the United States experiences over 1,200 tornadoes, but EF5 or the historical F5 events represent a tiny fraction of that total. Only about 0.06% of all recorded tornadoes reach this top classification, meaning roughly one out of every 1,666 tornadoes is this strong.
The statistical rarity of EF5s is evident when examining the historical record since reliable data collection began in 1950. In the United States, only 60 tornadoes have been officially rated at the highest category—50 F5s and 10 EF5s—throughout more than seven decades. This low number demonstrates that the average frequency of an F5 or EF5 event occurring is only about once every 16 months, or less than one per year.
Periods without any confirmed EF5 tornadoes can be extensive, highlighting their profound infrequency. The United States has experienced long “droughts” where multiple years passed between confirmed EF5 events. The record for the longest period without one was broken after the last confirmed EF5 in May 2013. This scarcity confirms that while the potential for extreme tornadoes always exists, the probability of encountering one is remarkably low.
Transitioning from the F-Scale to the EF-Scale
The original Fujita (F) scale was the standard for rating tornadoes from the 1970s until it was officially replaced by the Enhanced Fujita (EF) scale on February 1, 2007. This transition was prompted by engineering studies that suggested the wind speed estimates for the higher categories on the F-scale were often significantly overestimated. The F5 category, for instance, had estimated wind speeds ranging from 261 to 318 miles per hour, which was found to be unnecessarily high to cause the observed damage.
The new EF-scale was developed to provide a more accurate correlation between wind speed and observed damage. It features standardized Damage Indicators and Degrees of Damage, allowing surveyors to account for the quality of construction and other variables when assigning a rating. Consequently, the wind speed estimate for an EF5 was revised to simply “over 200 miles per hour,” a lower threshold that engineers determined was sufficient to cause the most extreme destruction.
The implementation of the EF-scale did not retroactively change the rating of historical tornadoes, meaning a tornado previously rated F5 remains an F5 in the historical database. However, the historical F5 rating is now understood to correlate more closely with the damage criteria of the modern EF5. This system preserves the historical record while ensuring that new tornado ratings are based on more scientifically accurate wind estimates.