NOAA NATIONAL WEATHER SERVICE’S IMPROVED

TORNADO RATING SYSTEM NOW OPERATIONAL

NOAA’s National Weather Service fully implemented the Enhanced Fujita (EF) on Thursday , February 1, 2007, to rate tornadoes, replacing the original Fujita Scale. The EF scale will continue to rate tornadoes on a scale from zero to five, but ranges in wind speed will be more accurate with the improved rating scale.

"The EF scale provides more detailed guidelines that will allow the National Weather Service to more accurately rate tornadoes that strike the ,” said Brig. Gen. David L. Johnson, U.S. Air Force (Ret.), director of NOAA’s National Weather Service. “The EF scale still estimates wind speeds but more precisely takes into account the materials affected and the construction of the structures damaged by the tornado."

The Fujita scale was developed in 1971 by T. Theodore Fujita, Ph.D., to rate tornadoes and estimate associated wind speed based on the damage they cause. The EF scale refines and improves the original scale. It was developed by the Texas Tech University Wind Science and Engineering Research Center , along with a forum of wind engineers, universities, private companies, government organizations, private sector meteorologists, and NOAA meteorologists from across the country.

Limitations of the original Fujita scale may have led to inconsistent ratings, including possible overestimates of associated wind speeds. The EF scale incorporates more damage indicators and degrees of damage than the original Fujita scale, allowing more detailed analysis and better correlation between damage and wind speed. The original Fujita scale historical data base will not change. An F5 tornado rated years ago is still an F5, but the wind speed associated with the tornado may have been somewhat less than previously estimated. A correlation between the original Fujita scale and the EF scale has been developed. This makes it possible to express ratings in terms of one scale to the other, preserving the historical database.

The Texas Tech University Wind Science and Engineering (WISE) Center, along with a forum of nationally renowned meteorologists and wind engineers from across the country, developed the EF Scale. The forum began their work in March of 2001 and included participants from several government organizations, universities, and private companies.

The EF Scale will still rate tornado categories from zero to five, but the ranges of wind speed in each category are now more accurate.  The EF Scale takes into account more variables than the original F Scale did when assigning a wind speed rating to a tornado.  The EF Scale incorporates 28 damage indicators (DIs) such as building type, structures, and trees.  For each damage indicator, there are 8 degrees of damage (DOD) ranging from the beginning of visible damage to complete destruction of the damage indicator.  The original F Scale did not take these details into account.


Original F Scale

Enhanced F Scale
Rating 3 second gust (mph) Rating 3 second gust speed (mph)
F0 45-78 EF0 65-85
F1 79-117 EF1 86-110
F2 118-161 EF2 111-135
F3 162-209 EF3 136-165
F4 210-261 EF4 166-200
F5 262-317 EF5 >200


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