On the Consistency between the Fujita and Enhanced Fujita Scales and Implications for the U.S. Tornado Climatology

Abstract The Fujita (F) and enhanced Fujita (EF) scales have formed the baseline for tornado intensity estimation in the U.S. tornado climatology. Ahead of the EF scale’s debut in 2007, one stated goal was to maintain consistency in the ratings between the two scales (i.e., a rating from the EF scale would have the same climatological “meaning” as a rating from the F scale). However, the highly publicized “drought” of EF5 tornadoes since 2013 brings the broader consistency of present-day tornado rating practices relative to the F-scale era into question. Among a population of significant (EF2–EF5) tornadoes from 2014 to 2023 versus a climatological population of F2–F5 tornadoes from the last 30 years of F-scale use (1977–2006), the fraction of significant tornadoes rated EF2 has increased, while fractions of EF3, EF4, and EF5 have all decreased. Subsequently, the rate of fatalities associated with a given EF3 or EF4 tornado in 2014–23 is substantially greater than for F3 or F4 tornadoes in the 30-yr climatology, with the average EF4 tornado from 2014 to 2023 being over 2.5 times deadlier than the average F4 tornado from 1977 to 2006. Evaluation of an extended violent tornado [(E)F4–(E)F5] climatology back to 1880 reveals that the current frequency of (E)F4–(E)F5 ratings is the lowest it has been across the entire extended 144-yr period, and depending on the analysis method, the recent fatality rate for a typical EF4 tornado is the highest fatality rate associated with (E)F4 tornadoes in the past 55–72 years. Significance Statement When the enhanced Fujita scale replaced the Fujita scale in 2007, one goal was to maintain consistency across the records of ratings applied to tornadoes across the two scales. However, for tornadoes rated (E)F2 or greater, a larger fraction is currently rated EF2 than in the last 30 years of the Fujita-scale era, with smaller fractions of EF3s and EF4s and no EF5s since 2013. The frequency of EF4 and EF5 ratings over the past 10 years is the lowest it has been across 144 years of record. This downshift in higher ratings may also be partially responsible for more fatalities being observed per EF3–EF4 tornado today than in the last 30 years of the Fujita-scale era.