Enhanced Fujita Scale

The Enhanced Fujita Scale, or EF Scale, is the scale for rating the strength of tornadoes in the United States estimated via the damage they cause.

Implemented in place of the Fujita scale introduced in 1971 by Ted Fujita, it began operational use on February 1, 2007. The scale has the same basic design as the original Fujita scale, six categories from zero to five representing increasing degrees of damage. It was revised to reflect better examinations of tornado damage surveys, so as to align wind speeds more closely with associated storm damage. Better standardizing and elucidating what was previously subjective and ambiguous, it also adds more types of structures as well as vegetation, expands degrees of damage, and better accounts for variables such as differences in construction quality.

The new scale was publicly unveiled by the National Weather Service at a conference of the American Meteorological Society in Atlanta on February 2, 2006. It was developed from 2000-2004 by the Fujita Scale Enhancement Project of the Wind Science and Engineering Research Center at Texas Tech University, which brought together dozens of expert meteorologists and civil engineers in addition to its own resources.

As with the Fujita scale, the Enhanced Fujita Scale remains a damage scale and only a proxy for actual wind speeds. While the wind speeds associated with the damage listed have not undergone empirical analysis (e.g. detailed physical or any numerical modelling) owing to excessive cost, the wind speeds were attained through a process of expert elicitation based on various engineering studies since the 1970s as well as from field experience of meteorologists and engineers. In addition to damage to structures and vegetation, radar data, photogrammetry, and cycloidal marks (ground swirl patterns) may be utilized when available.

The scale was used for the first time a year after its public announcement when parts of central Florida were struck by multiple tornadoes, the strongest of which were rated at EF3 on the new scale. The first time the EF5 assessment was used was the Greensburg, KS tornado that occurred on May 4, 2007.

Parameters

The six categories for the EF Scale are listed below, in order of increasing intensity. Although the wind speeds and photographic damage examples are updated, the damage descriptions given are those from the Fujita scale, which are more or less still accurate. However, for the actual EF scale in practice, one must look up the damage indicator (the type of structure which has been damaged) and consult the degrees of damage associated for that particular indicator.cite web | title = Enhanced F Scale for Tornado Damage| publisher = Storm Prediction Center| url = http://www.spc.noaa.gov/efscale/ef-scale.html ]

Damage Indicators and Degrees of Damage

The EF Scale currently has 28 Damage Indicators (DI), or types of structures and vegetation, with varying numbers of Degrees of Damage (DOD) for each. cite book | last = McDonald| first = James| authorlink = James R. McDonald| coauthors = Kishor C. Mehta| title = A Recommendation for an Enhanced Fujita Scale (EF-Scale)| publisher = Wind Science and Engineering Research Center| date = 10 October 2006| location = Lubbock, Texas| url = http://www.wind.ttu.edu/EFScale.pdf ]

Differences from the Fujita scale

The new scale takes into account quality of construction and standardizes different kinds of structures. The wind speeds on the original scale were deemed by meteorologists and engineers as being too high and engineering studies indicated that slower winds than initially estimated cause the respective degrees of damage. The new scale lists an EF5 as a tornado with winds at or above 200 mph (324 km/h), found to be sufficient to cause the damage previously ascribed to the F5 range of wind speeds. None of the tornadoes recorded on or before January 31, 2007 will be re-categorized.

Essentially, there is no functional difference in how tornadoes are rated. The old ratings and new ratings are smoothly connected with a linear formula. The only differences are adjusted wind speeds, measurements of which weren't used in previous ratings, and refined damage descriptions; to standardize ratings and to make it easier to rate tornadoes which strike few structures. Twenty-eight Damage Indicators (DI), with descriptions such as "Double-wide mobile home" or "Strip mall", are used along with Degrees of Damage (DOD) to determine wind estimates. Different structures, depending on their building materials and ability to survive high winds, will have their own DIs and DODs. Damage descriptors and wind speeds will also be readily updated as new information is learned.

Since the new system will still use actual tornado damage and similar degrees of damage for each category to estimate the storm's wind speed, the National Weather Service states that the new scale will likely not lead to an increase in a number of tornadoes classified as EF5. Additionally, the upper bound of the wind speed range for EF5 is open — in other words, there is no maximum wind speed designated.cite web | title = The Enhanced Fujita Scale (EF Scale)| publisher = Storm Prediction Center| date = 2007-02-02| url = http://www.spc.noaa.gov/efscale/ ]

See also

* Fujita scale
* TORRO scale
* Beaufort scale
* Saffir-Simpson Hurricane Scale
* Tornado intensity and damage
* List of tornadoes and tornado outbreaks
* List of EF5 tornadoes
* Severe weather terminology

References

External links

* [http://www.noaanews.noaa.gov/stories2006/s2573.htm NOAA National Weather Service Improves Tornado Rating System] (NOAA News)
* [http://www.spc.noaa.gov/efscale/ The Enhanced Fujita Scale (EF Scale)] (SPC)
* [http://www.wind.ttu.edu/F_Scale/ Fujita Scale Enhancement Project] (Wind Science and Engineering Research Center at Texas Tech University)
* [http://ams.confex.com/ams/annual2003/techprogram/program_149.htm Symposium on the F-Scale and Severe-Weather Damage Assessment] (AMS)
* [http://wdtb.noaa.gov/courses/EF-scale/ EF-Scale Training] (NWS [http://wdtb.noaa.gov/ Warning Decision Training Branch] )
* [http://meted.ucar.edu/resource/wcm/ftp/FinalNWSF-scaleAssessmentGuide.pdf A Guide to F-Scale Damage Assessment] (NWS)
* [http://www.srh.noaa.gov/ssd/techmemo/sr146.pdf A Guide for Conducting Convective Windstorm Surveys] (NWS SR146)
* [http://www.srh.noaa.gov/ssd/techmemo/sr147.pdf The Tornado: An Engineering-Oriented Perspective] (NWS SR147)
* [http://tornadoproject.com/fscale/fscale.htm The Fujita Scale of Tornado Intensity] (The Tornado Project)
* [http://www.fema.gov/fima/mat/fema342.shtm Mitigation Assessment Team Report: Midwest Tornadoes of May 3, 1999] (FEMA)