How Have the Intrinsic Characteristics and Application of the Enhanced Fujita Scale Contributed to a Decreased Frequency of Intense Tornadoes in the United States?

Abstract Recent research has shown that the rating frequency for intense tornadoes (rated ≥EF3 on the Enhanced Fujita or EF scale) dating back to 2014 is at a historical low relative to both the real-time Fujita-Scale rating era (1977–2006) and the early years of the EF-scale rating era (2007–2013, with or without the catastrophic 2011 tornado season). However, with no formal change in National Weather Service directives on rating tornadoes or significant changes to the EF scale applied in the 2013–2014 timeframe, the cause for this sudden decrease in intense-tornado frequency is unclear. This study investigates intense-tornado rating determinations from 2014–2024 to ascertain some potential causes for this sudden downturn in intense-tornado ratings, by comparing how instances of damage are evaluated on the EF scale to their likely evaluation using the legacy Fujita Scale. We find that a series of factors, both intrinsic to the current operational EF scale and related to how it is being applied, has likely contributed to the downshift in intense-tornado ratings. The evaluation of damage associated with indicators that are unique to the EF scale is too infrequent at higher damage intensities to overcome these factors. Given these findings, we suggest that a reanalysis effort for the significant-tornado [(E)F2 or greater] record should be undertaken upon any future operational adoption of a revised EF scale to develop a more consistent intense-tornado record in the United States.