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 EF Scale

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PostSubject: EF Scale   Sun Jan 13, 2008 1:17 am

Dr. T. Theodore Fujita first introduced The Fujita Scale in the SMRP Research Paper, Number 91, published in February 1971 and titled, "Proposed Characterization of Tornadoes and Hurricanes by Area and Intensity". Fujita revealed in the abstract his dreams and intentions of the F-Scale. He wanted something that categorized each tornado by intensity and area. The scale was divided into six categories:

F0 (Gale)
F1 (Weak)
F2 (Strong)
F3 (Severe)
F4 (Devastating)
F5 (Incredible)

Dr. Fujita's goals in his research in developing the F-Scale were categorize each tornado by its intensity and its area estimate a wind speed associated with the damage caused by the tornado Dr. Fujita and his staff showed the value of the scale's application by surveying every tornado from the Super Outbreak of April 3-4, 1974. The F-Scale then became the mainstay to define every tornado that has occurred in the United States. The F-Scale also became the heart of the tornado database that contains a record of every tornado in the United States since 1950.

The Fujita Scale is a well known scale that uses damage caused by a tornado and relates the damage to the fastest 1/4-mile wind at the height of a damaged structure. Fujita's scale was designed to connect smoothly the Beaufort Scale (B) with the speed of sound atmospheric scale, or Mach speed (M). Fujita explains explicitly that "F-scale winds are estimated from structural and/or tree damage, the estimated wind speed applies to the height of the apparent damage above the ground."

Over the years, the F-Scale has revealed the following weaknesses:


It is subjective based solely on the damage caused by a tornado
No recognition in difference in construction
Difficult to apply with no damage indicators
if the 3/4-mile wide tornado does not hit any structures, what F-scale should be assigned?
Subject to bias
Based on the worst damage (even if it is one building or house)
Overestimates wind speeds greater than F3
And the F-Scale has had its misuses over the years:

Too much reliance on the estimated wind speeds
Oversimplification of the damage description
Judge the F-scale by the appearance of the tornado cloud
Unrecognizing weak structures
mobile homes
modified homes


The Enhanced Fujita Scale
When the committee met to develop the Enhanced Fujita Scale (see original document) one point was made very clear: it must continue to support and maintain the original tornado database.; In other word, there must be some conformity to that of the F-Scale that is listed in the database. Other ideas were agreed to including:

Consistent Assessment of Damage
enhance description of damage with examples and photos
include not only structures, but also vegetation
base damage assignment on more than one structure, if available
develop a PC-based expert system
develop training materials
Data Collection
maintain current tornado database
surveys should include additional data
mean and maximum damage path width
basis for damage assignment
latitude/longitude of where the path began and ended
number of hours spent on the damage survey
names of survey team member(s)
When using the EF-Scale to determine the tornado's EF-rating, begin with the 28 Damage Indicators. Each one of these indicators have a description of the typical construction for that category of indicator. Then, the next step is to find the Degree of Damage (DOD). Each DOD in each category is given and expected estimate of wind speed, a lower bound of wind speed and an upper bound of wind speed.

Let's take the earlier example, a tornado moves through a neighborhood and walls are knocked down of an area of homes. Here the Damage indicator would be #2, One or Two Family Residences (FR12). The typical construction for this fits being a brick veneer siding home. The DOD would be a 9, most walls collapsed in bottom floor. Thus, the estimated winds would be 127 - 178 mph with the expected wind speed of 152 mph. Now, taking this number to the EF-Scale, the damage would be rated EF-3 with winds between 136 - 165 mph.

The EF Scale can be view here....http://www.spc.noaa.gov/efscale/ef-scale.html

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PostSubject: Re: EF Scale   Sun Jan 13, 2008 10:31 am

Thanks admin for the link and the breif on the enhanced "EF" scale . I think that is step in the right direction to better improve the study of the science of tornados. I think since vegatation can now be taken it can tell much more as well. All tree and even other plants grow in a unique enviroment with regards to soil density and bark etc..etc.. that will give more numbers to crunch for the experts.
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