Who determines how strong a tornado is and what factors are used to make that ranking?

Cheryl McCloud, Palm Beach Post
·2 min read

The Enhanced Fujita Scale, or EF Scale, is the scale used to estimate the wind speed of a tornado based on the damage it left behind.

The Enhanced Fujita Scale replaced the Fujita scale Feb. 1, 2007. The scale was modified to better reflect what observers discovered during a survey of tornado damage.

It also added more types of structures to analyze damage and takes into consideration the types of construction and their ability to withstand wind damage. An "EF-Unknown" category was later added for tornadoes that cannot be rated due to a lack of damage evidence.

Tornadoes database: A history of twisters in your state since 1950

Who assigns a ranking to a tornado?

The National Weather Service is the only federal agency with the authority to provide an official tornado EF Scale rating. The goal is to assign an EF scale category based on the highest wind speed that occurred along the damage path, according to the Weather Service.

How is a tornado rating assigned?

Trained Weather Service personnel identify damage in the area from one of more than 28 items on a damage indicator list.  The list consists mostly of various types of buildings, but also includes other structures such as sheds and trees.

In the Enhanced F scale, it considers the strengths and weaknesses of different types of construction and assigns standards for each structure, whether it's an anchored wood-frame house, garage, school, skyscraper, barn, factory or utility pole.

The enhanced scale rates the tornado as a whole based on most intense damage along its entire path. The tornado evaluator determines the wind speed based on the structure and the damage. This is done for several structures before a final rating is determined.

Tornadoes are ranked from EF0 to EF5

The scale is divided into six categories:

  • F0: Gale

  • F1: Weak

  • F2: Strong

  • F3: Severe

  • F4: Devastating

  • F5: Incredible

Enhanced Fujita Scale for tornadoes.
Enhanced Fujita Scale for tornadoes.

In a real-life tornado track, these ratings are mapped together to make a damage analysis. Although gaps may exist where there was little or nothing to damage, or damaged material (such as vehicles) isn't on the scale.

As with the original F scale, the enhanced version rates the tornado as a whole based on most intense damage along its entire path.

This article originally appeared on Palm Beach Post: Tornado ranking: who decides how strong a tornado is and how