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.
-  AMS 2013, “Meteorology Glossary,” American Meteorological Society,
retrieved from http://glossary.ametsoc.org [accessed October 2013]
-  Y. K.Wen and S. L. Chu, “Tornado risks and design wind speed,” J. of the Struc. Div., ASCE, Vol.99, No.12, pp. 2409-2421, 1973.
-  T. T. Fujita, “Proposed characterization of tornadoes and hurricanes by area and intensity,” Satellite and Mesometeorology Research Project Report Vol.91, the University of Chicago (available from National Wind Institute, Texas Tech University, Lubbock, Texas), 42p., 1971.
-  J. Wurman, K. A. Koshiba, and P. Robinson. “In-situ, Doppler Radar, and Video Observations of the Interior Structure of a Tornado Wind-damage Relationship,” Bull. Amer. Met. Soc., Vol.94, pp. 835-846. 2013.
-  J. Wurman, K. Koshiba, P. Markowski, Y. Richardson, D. Doswell, and P. Robinson, “Fine Scale Single and Dual Doppler Analysis of Tornado Intensification, Maintenance, and Dissipation in the Orleans, Nebraska Tornado Supercell,” Mon. Weather Rev., Vol.138, No.12, pp. 4439-4455, 2010.
-  J. Wurman, C. Alexander, P. Robinson, and Y. Richardson, “Low level winds in Tornadoes and Potential Catastrophic Tornado Impacts in Urban Areas,” Bull. Amer. Met. Soc., Vol.88, pp. 31-46, 2007.
-  W. Zhang and P. P. Sarkar, “Near-ground Tornado-like Vortex Structure Resolved by Particle Image Velocimetry (PIV),” Exp. In Fluids, Vol.52, No.2, pp. 479-493, 2012.
-  F. H. Haan, V. K. Balaramudu, and P. P. Sarkar, “Tornado-Induced Wind Loads on a Low-Rise Building,” J. of Struc. Eng., ASCE, Vol.136, No.1, pp. 106-116, 2010.
-  D. O. Prevatt, J. van de Lindt, R. Gupta, and B. Coulbourne, “Tuscaloosa Tornado,” Struc. Mag., Reedsburg, WI, NCSEA, Vol.18, No.7, pp. 24-27, 2011.
-  J. E. Minor, J. R. McDonald, and K. C. Mehta, “The tornado: An engineering oriented perspective,” NOAA Technical Memorandum, ERL NSSL-82, National Severe Storms Laboratory, Norman, OK, 103pp., 1977,
available online at http://www.depts.ttu.edu/nwi/Pubs/Reports/The%20Tornado.pdf [accessed November 1, 2013]
-  L. T. Phan and E. Simiu, “The Fujita tornado intensity scale: a critique based on observations of the Jarrell tornado of May 27, 1997,” NIST Tech. Note 1426, U.S. Department of Commerce, Gaithersburg, MD, 20pp., 1998.
-  J. R. McDonald and K. C. Mehta, “Summary report of the Fujita Scale forum,” Wind Science and Engineering, Texas Tech University, Lubbock, TX, 36pp., 2001.
-  SSHAC, “Recommendations for probabilistic seismic hazard analysis: guidelines on uncertainty and use of experts,” NUREG/CR6372, UCRL-ID-122160, Vol.I, Lawrence Livermore National Laboratory, Livermore, CA, 131pp., 1997.
-  WISE, “A recommendation for an enhanced Fujita scale (EFscale),” Texas Tech University, National Wind Institute, 95pp., 2006,
available online at http://www.depts.ttu.edu/nwi/Pubs/FScale/EFScale.pdf [accessed November 1, 2013]
-  “Minimum Design Loads for Buildings and Other Structures,” Ame. Soc. of Civ. Eng., ASCE, Vol.7, No.10, pp. 241-358, 2010.
-  C. S. Durst, “Wind speeds over short periods of time,” Meteorological Magazine, Vol.89, London, England, 6pp., 1960.
-  K. C. Mehta, J. E. Minor, and J. R. McDonald, “Wind Speed Analysis of April 3-4, 1974 Tornadoes,” J. Struc. Div., ASCE, Vol.102, No.ST9, pp. 1709-1724, 1976.
-  K. C. Mehta, “Wind Speed Estimates: Engineering Analyses,” R. E. Peterson (Ed.), Proc., Symposium on Tornadoes: Assessment of Knowledge and Implications for Man, published by Institute of Disaster Research, Texas Tech University, Lubbock, Texas, USA, pp. 89-103, 1976.
This article is published under a Creative Commons Attribution-NoDerivatives 4.0 Internationa License.