Development of the EF-Scale for Tornado Intensity
Kishor C. Mehta
*National Wind Institute (NWI), Texas Tech University, 2500 Broadway, Lubbock, TX 79409, USA
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. The Enhanced Fujita EF-scale was developed with a consensus among meteorologists, engineers and insurance personnel to rate tornadoes. 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 paper contains documentation of the development process of the EF-scale and the motivation for the same with background of the Fscale. Wind speeds in the F-scale and the EF-scale are correlated to preserve the previous database. The EFscale overcomes the shortcomings of the F-scale, developed by Dr. Ted Fujita in 1971, of too few damage indicators, postulation of damage irrespective of building characteristics, and the high wind speeds assigned to F4 and F5 ratings. The US National Weather Service implemented use of the EF-scale beginning February 2007.
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