Changes in Tornado Climatology Accompanying the Enhanced Fujita Scale

Abstract

United States tornado records form the basis for a variety of meteorological, climatological and disaster-risk analyses, but how reliable are they in light of changing standards for rating, as with the 2007 transition of Fujita (F) to Enhanced Fujita (EF) damage scales? To what extent are recorded tornado metrics subject to such influences that may be nonmeteorological in nature? While addressing these questions with utmost thoroughness is too large of a task for any one study, and may not be possible given the many variables and uncertainties involved, some variables that are recorded in large samples are ripe for new examination. We assess basic tornado-path characteristics—damage rating, length, width, and occurrence time, as well as some combined and derived measures—for a 24-yr period of constant path-width recording standard that also coincides with National Weather Service modernization and the WSR-88D deployment era. The middle of that period (in both time and approximate tornado counts) crosses the official switch from F to EF. At least minor shifts in all assessed path variables are associated directly with that change, contrary to the intent of EF implementation. Major and essentially stepwise expansion of tornadic path widths occurred immediately upon EF usage, and widths have expanded still further within the EF era. We also document lesser increases in path lengths, and in tornadoes rated at least EF1 compared to EF0. These apparently secular changes in the tornado data can impact research dependent on bulk tornado-path characteristics and damage-assessment results.

ERA5‐Based Significant Tornado Environments in Canada Between 1980 and 2020

“…Canada began using the EF‐scale in April 2013 (Sills et al., 2014) and was implemented in the database after this date. Although difficult to quantify, errors associated with the F/EF scale transition are not expected to be significant for F/EF2 + events; <2% increases (shifts) in F2 + from F to EF scales (Edwards et al., 2021).…”

“…Section 4 concludes by summarizing the key findings and future research. errors associated with the F/EF scale transition are not expected to be significant for F/EF2 + events; <2% increases (shifts) in F2 + from F to EF scales (Edwards et al, 2021).…”

Climatology of 500‐hPa geopotential height anomalies associated with May tornado outbreaks in the United States

“…Recently, Edwards et al . (2021) highlighted that the change in tornado rating standards has led to increases in tornadoes that are being rated as EF1+ after the year 2007, which could potentially affect the identification of the TOs in this work. However, as shown by Edwards et al .…”

“…However, as shown by Edwards et al . (2021, fig. 1), that increase is not substantial (only ~2% for all EF2+ tornadoes).…”

“…Here, it is important to acknowledge the limitations of that database, such as, for instance, the influence of the 2007 transition of Fujita (F) to enhanced Fujita (EF) damage scale. Recently, Edwards et al (2021) highlighted that the change in tornado rating standards has led to increases in tornadoes that are being rated as EF1+ after the year 2007, which could potentially affect the identification of the TOs in this work. However, as shown by Edwards et al (2021, fig.…”