A Recommendation for an Enhanced Fujita Scale (EF-Scale)

Authors

Date of this Version

6-2004

Citation

Submitted to the National Weather Service and other interested users. Wind Science and Engineering Center, Texas Tech University, Lubbock, Texas, June 2004.

Comments

Public domain material.

Abstract

Background

National Weather Service (NWS) personnel who are responsible for rating tornadoes have expressed frustrations in applying the Fujita Scale in a consistent and accurate manner. Weak links in a structural system or a slow-moving storm sometimes lead to an overrating of a tornado event. Several technical articles suggest that wind speeds associated with some descriptions of damage are too high. For example, a 260 mph wind speed is not required to completely destroy a well constructed house and blow away the debris. The damage occurs at significantly lower wind speeds. Minor et al. (1977) and Phan and Simiu (2003) confirm that F4 and F5 ratings of housing damage overestimate the wind speeds required to produce the damage. In the Fujita Scale, there is a lack of clearly defined and easily identifiable damage indicators. A larger catalog of damage 2 indicators is needed along with estimates of the wind speed required to cause a certain type of damage.

Recognizing the need to address these limitations, Texas Tech University (TTU) Wind Science and Engineering (WISE) Center personnel proposed a project to examine the limitations, revise or enhance the Fujita Scale, and attempt to gain a consensus from the meteorological and engineering communities. A steering committee was first organized to initiate the project. Members of the Steering Committee are listed in Table 1. The next step was to organize a forum of users to identify the issues and develop strategies to improve or replace the Fujita Scale. The steering committee established the following objectives for the forum:

• Bring together a representative group of Fujita Scale users

• Identify key issues

• Make recommendations for a new or modified Fujita Scale

• Develop strategies for reaching a consensus from a broad cross section of users

Of the 26 users of the Fujita Scale invited, twenty attended the Fujita-Scale Forum, which was held in Grapevine, Texas, March 7-8, 2001. Forum participants are listed in Table 2. The group met for a day and a half and developed the following strategies for an Enhanced Fujita Scale:

• Identify additional damage indicators

• Correlate appearance of damage and wind speed

• Preserve the historical database

• Seek input from users