Enhanced Fujita Scale?

[Simon Timm]

Well, I have a couple questions regarding the scale.

1. Why is it that the scale does not take into account, that there have been several windspeed measurements that support the old scale?(Spencer SD tornado)

2. The damage indicators on the scale say "upper bounds" and "lower bounds", what does this mean?

 

[rdale]

1) Don't know what you mean

2) Likely highest and lowest wind speeds in that range

 

[IAN GIAMMANCO]

Remember the EF scale is still a damage scale first. However i thought the EF-5 was left with no upper bound but i maybe wrong. The scale was revised to account for more current research showing that certain types of damage actually occured at lower wind speeds and also to provide more indicators to rate a given event. The upper and lower bounds are simply the high and low ends of the category for either wind speed or the degree of damage as rob mentioned, unless i am misunderstanding the question

 

[Chris Nuttall]

1. Why is it that the scale does not take into account, that there have been several windspeed measurements that support the old scale?(Spencer SD tornado)

I assume you are referring to measurements taken by the Doppler on Wheels. As has already been stated, the EF scale is a damage scale, which is then used to infer probable wind speeds. Second, readings taken from mobile radars present their own issues.

Currently, these measurements are not recorded anywhere near often enough for us to have any idea if they are reliable. Secondly, the radar is measuring the wind well above the surface. Surface wind measurements are taken at 10m-AGL. Thus, we have no measurements of surface wind speeds in a tornado...not yet anyway. This paper details some of the limitations of radar-based measurements:
http://ams.confex.com/ams/annual2003/techprogram/paper_58862.htm

 

[Matt Gingery]

Also keep in mind this scale is only used when a tornado hits structures. Wind speeds based on scale of damage. What we need is a scale to measure tornado strength in an open field of an unpopulated area. The only real measurement tool is the E.F. scale. Can't have a DOW at every tornado. I agree, I think the question needs further description.

 

[rdale]

Also keep in mind this scale is only used when a tornado hits structures.

The EF-scale does have indicators for trees...

However they are useless, since they don't differentiate tree types

 

[Bobby Prentice]

The EF-scale does have indicators for trees...

However they are useless, since they don't differentiate tree types

The EF-Scale does differentiate between hardwood trees and softwood trees. It's certainly not complete or perfect, but the EF-Scale provides a somewhat better W.A.G. ("Wild-Ass Guess") of tornado wind speeds than the old F-Scale.

 

[Mike Smith]

EF-Scale[/URL] provides a somewhat better W.A.G. ("Wild-Ass Guess") of tornado wind speeds than the old F-Scale.

Bobby, on what do you base that? I believe the opposite is likely to be true (the F-scale was better) but I am very open-minded to being educated.

Happy New Year!!

Mike

 

[Greg Stumpf]

Bobby, on what do you base that? I believe the opposite is likely to be true (the F-scale was better) but I am very open-minded to being educated.

Hardwood and softwood trees were not included as damage indicators in the old F-Scale, thus, the WAG when encountering tornado damage to them.

 

[rdale]

The EF-Scale does differentiate between hardwood trees and softwood trees.

In the Fujita conference up here back in 2007(?) we had a tree expert who said that you can't make that sort of a cutoff in determining wind speeds... It's more on the tree orientation / individual strength / root structure / area of tree coverage / etc. Not the "soft" or "hard" wood that makes up the tree family.

 

[STurner]

Well, I have a couple questions regarding the scale.

1. Why is it that the scale does not take into account, that there have been several windspeed measurements that support the old scale?(Spencer SD tornado)

2. The damage indicators on the scale say "upper bounds" and "lower bounds", what does this mean?

I am no expert but think different windspeeds are variable on the types of damage they cause. The DOW clocked windspeeds of approximately 258mph in the Spencer tornado and it was rated an F4 on the old scale. If you look at the old scale an F4 has windspeeds ranging from 207-260mph. On the other hand the DOW clocked winds around 213mph near Moore, Oklahoma and that corresponds to an F4 on the old scale. Even though the DOW at one point clocked winds in excess of 300mph in this tornado it did F5 damage in Moore with winds just slightly above 200mph. It also could be how the tornado hits the structure or projectiles hitting the structures causing that type of damage. In a way I believe it still remains a mystery as to why tornadoes do different types of damage with different wind speeds. The EF-scale just states that you may not necessrily need higher windspeeds to cause that type of damage.

 

[rdale]

shane - read Chris' reply above about DOW windspeeds again.

 

[Greg Higgins]

One also must factor in that the Fujita scale is a "damage assessment" tool based not only on wind speed but also on how a structure was designed and built. There are MANY substandard structures out there that do not conform to any type of building code and can be blown over / damaged in a light breeze. Another example of why structural engineers are included in damage assessment teams.

Greg Higgins

 

[STurner]

shane - read Chris' reply above about DOW windspeeds again.

I read it again but could be missing the point entirely. Is there something that you wanted to tell me that I could be missing. It seems like he is discussing windspeeds that correspond to the old fujita scale. So I used a couple of examples to show how they correspond to the old fujita scale and how they did not.

 

[rdale]

You said that the Moore damage was from wind speeds just more than 200mph - we have no idea what the windspeeds were. You also compared DOW measured speeds to the old scale - you cannot compare measured wind speeds to the Fujita scale.