Development of the EF-Scale for Tornado Intensity

Tornado intensity in terms of wind speed is rated indirectly from building and structure damage because random nature and the short life of tornadic storms make measurements difficult. Dr. Theodore Fujita, Professor of Meteorology at the University of Chicago developed Fujita F-scale, F0 to F5, to rate intensity of tornado in 1971. With new damage documentation of tornado damages the F-scale needed to be upgraded. The Enhanced Fujita EF-scale was developed with a consensus among meteorologists, engineers and insurance personnel. The EF-scale uses 28 different damage indicators (DI) and several degrees of damage (DOD) for each DI. The elicitation process is used to assign wind speeds, expected, upper, and lower bound, for each DOD in every DI. The presentation contains documentation of the development process of the EF-scale and the motivation for the same with the background of the F-scale. Wind speeds in the F-scale and the EF-scale are correlated to preserve the previous database. The EF-scale overcomes the shortcomings of the F-scale of too few damage indicators, postulation of damage irrespective of building characteristics, and the high wind speeds assigned to F4 and F5 ratings. The U.S. National Weather Service implemented use of the EF-scale beginning February 2007.