In 1971, the first widely recognized tornado damage classification scale was implemented by Dr. Theodore Fujita and his assistants at the University of Chicago.  Based on his pioneering research studies, this Fujita Scale system of rating tornadoes became widely accepted and was officially used by the National Weather Service for the next 35 years.

However, in February 2007, a redesigned and much more accurate tornado-rating scale was officially introduced.  This new scale for rating tornadoes is known as the Enhanced Fujita Scale, or simply the EF Scale.  The EF Scale was first developed at Texas Tech University in Lubbock, Texas, by a collaboration of researchers, engineers, meteorologists, and other professionals from across the country.   These individuals developed this new scale and presented it for implementation to the National Weather Service on October 2006.  The National Weather Service then adopted the EF scale and put it into official use on February 1, 2007.

Next, the EF Scale determines the Degree of

Damage, or DOD, that occurred to a building.  The amount of damage done to a structure is given a range of wind speed estimates for a particular observed DOD.  Whether the structure is built to normal construction standards, or above or below such standards, is then taken into consideration.  Finally, an official estimated wind speed is determined, and an EF Scale rating is applied.

A comparison of the old and new Fujita scales shows changes in both the lower and higher level categories.  Researchers and engineers have determined that wind speeds do not need to be nearly as strong as previously thought to cause severe damage to buildings.  Thus, the wind speeds for EF3, EF4, and EF5 tornadoes are much lower than in the original Fujita Scale.  In addition, at the lower wind speeds, it was determined that a slightly stronger wind velocity is necessary to cause visible damage to structures.

In the future, additional revisions to the EF scale are possible, as more research and engineering studies further determine the correlations between specific types of tornado damage and wind speeds.  For now, the new EF scale will be a significant improvement in the way tornadoes are rated by the National Weather Service.