April 9th, 2007 by 
imagery
In February 1971, Dr. T. Theodore Fujita published a research paper entitled “Proposed Characterization of Tornadoes and Hurricanes by Area and Intensity”. In the paper, he discussed how tornadoes should be rated on a scale to better understand the damage associated with intensity and wind speed. Over the next few years and the super outbreak of 1974, Dr. Fujita’s scale for measuring tornadoes became invaluable and the F-Scale became widely adopted.
The thing to note about the F-Scale is that the wind speeds are estimates based on localized damage. That is to say, the way to gauge the intensity of a tornado and rate it on the F-Scale is to look at the damage after it has passed. There is no reliable way of measuring a tornado’s real-time wind speed for a couple of reasons. One, an anemometer is rarely in place to measure the wind speeds of a tornado, and if it was, would most likely not survive due to debris. Two, the winds within a tornado constantly vary in intensity. That is to say, a tornado may have wind speeds that fluctuate enough to make it cover three categories and not just one.
The F-Scale is broken up into 6 categories based upon estimated wind speeds. The pictures below offer visual estimates as to the type of damage one might expect given a tornado’s intensity.
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F-0 | 40 mph - 72 mph | Light Damage
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Minimal structural damage. Most damage will be observed in trees, billboard signs, and high profile vehicles. Damage to homes is usually superficial caused by downed trees.
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F-1 | 73 mph - 112 mph | Moderate
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| Minimal structural damage. Some shingles ripped off roofs, chimney’s blown over, mobile homes blown off foundations. Older and weaker homes may see more damage. Vehicles start getting blown off the road. |
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F-2 | 113 mph - 157 mph | Considerable
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| Substantial structural damage to well constructed homes. Roofs torn off, windows broken, some external wall failures. Train cars de-railed or overturned. |
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F-3 | 158 mph - 206 mph | Severe
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| Severe structural damage to well constructed homes. Roofs demolished and internal wall failures. Mobile homes completely gone. Large vehicles become airborne. Most trees are uprooted. Basement or tornado shelters are required for survival. |
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F-4 | 207 mph - 250 mph | Incredible
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| Most well constructed home completely destroyed and little remains. In some cases, the concrete foundation is the only thing that remains. Large vehicles are thrown hundreds of feet. Surrounding area becomes very difficult to recognize. |
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F-5 | 261 mph - 318 mph | Devastating
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| Complete and total destruction of most buildings. Concrete foundations are all that remain. Asphalt scoured from road surfaces. Cars thrown great distances. Large car-sized objects become airborne missiles and are thrown hundreds of feet. |
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It’s not possible to visually look at a tornado and derive its intensity on the F-Scale. Just because a tornado looks big doesn’t mean it’s an F5. Debris and condensation can easily make a tornado look a lot more powerful than it really is and conversely, a small tornado can have extremely fast winds yet look far less menacing. So once again, the path of destruction left behind is usually the best means of figuring out how powerful a tornado was, which can be difficult to infer due to the large variations in structures, their integrity, and building codes.
The new Enhanced Fujita scale tries to create a more accurate means of estimating a tornado’s wind speeds by refining the destruction patterns into finer granularity. This in no way changes the F-Scale rating for wind speeds that has been in place for decades, but instead only helps to get a more accurate tornado wind speed estimate.
Tornado Myths
Posted in Weather Myths & Facts | 