The National Weather Service fully implemented the Enhanced Fujita (EF) scale to rate tornadoes, replacing the original Fujita Scale, on February 1. 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 the 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. 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.
 

For example, with the EF scale, an EF3 tornado will have estimated wind speeds between 136 and 165 mph, whereas with the original F Scale, an F3 tornado has winds estimated between 162-209 mph.  The wind speeds necessary to cause “F3” damage are not as high as once thought and this may have led to an overestimation of some tornado wind speeds.  There is still some uncertainty as to the upper limits of the strongest tornadoes so EF5 ratings do not have a wind speed range.  Wind speed estimations for EF5 tornadoes will be left open ended and assigned wind speeds greater than 200 miles an hour.