How the Enhanced Fujita Scale Works

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Being in the direct path of a tornado means doom — and that's not an exaggeration.
The violent winds from a tornado often leave a trail of terror on the land and on the minds of its unfortunate victims.
To measure the strength of such incredible and devastating weather phenomena, meteorologists use the Enhanced Fujita Scale.
In this lesson, you will learn why and how meteorologists use the Enhanced Fujita Scale.

Developed by researcher Dr. Tetsuya Theodore Fujita in 1971, the Fujita Scale is a rating system meteorologists use to determine how strong a tornado is by the amount of damage it causes to buildings, homes and other types of man-made structures.
While the Fujita Scale considers the damage a tornadoes to trees, it focuses greatly on man-made structures.

1. The strength rating of a tornado is based on the damage it causes.
For example, even if a tornado generated winds over 300 miles per hour (480 KPH), it would have a much lower rating if it remained in the open fields and did not impact structures.
2. Only the National Weather Service (NWS) has the authority to determine the official rating of a tornado.

Figure 1: If this tornado were in an open field, it would have a much lower rating.

By being able to classify tornadoes, it is easier for meteorologists and researchers to point out specific tornadoes.
For example, if there is an outbreak of many tornadoes, the Fujita Scale makes it easier for scientists point out the strongest and most damaging tornadoes.
The usefulness of the Fujita Scale became clear after the super tornado outbreak in 1974 where 148 tornadoes touched down. But, because of the Fujita Scale, we know about 30 of them were rated F4 or F5.

Imagine we don't have the Fujita Scale and a major tornado outbreak just happened. Meteorologists would confusingly say something like, "We had many tornadoes. About 30 of them were very strong."
In reality, all tornadoes are "strong" in a sense, because all of them are capable of causing damage. But, the Fujita Scale, makes it easier to perceive or understand the idea of "weak" and "strong" tornadoes.

As indicated by its name, the Fujita scale was eventually 'enhanced' or improved. During the decades after the Fujita Scale, it became apparent improvements needed to be made.
For instance, the orignal Fujita scale was prone to bias and had problems evaluating the damage of different types of structures, especially weak ones.
It also tended to overestimate the winds needed to cause devastating damage. For example, the winds for F-3 and higher were too high.
Therefore, in February 2007, the improved or Enhanced Fujita Scale became operational. It does a more thorough analysis of the damage left by a tornado to ensure consistency and accuracy.

Figure 2: A simplified view of the Enhanced Fujita Scale.

At the moment mobile radar data is not enough. One reason is because the wind profile of a tornado is incredibly complex.
For instance, tornado winds also blow vertically. As such, radar does not give us a complete picture of what's happening inside a tornado [2].
In addition, the wind ratings from the Enhanced Fujita Scale are based on the damage caused by a tornado.
Consider the infamous EL-Reno tornado from May 31, 2013. Mobile radar from estimated wind speeds of around 300 miles per hour in the suction vortices of the tornado.
Despite the wind speeds being well over 200 miles per hour, it was rated as an EF-3 tornado. This was because the tornado was mostly in an open field and did not impact many structures.

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