Interesting Comparison: Beaufort, Torro, and Fujita Scales

[Bill Tabor]

This article:
http://www.torro.org.uk/TORRO/ECSS_Slide_S...ide%20show.html

Is a Powerpoint slideshow explaining the origin of the F scale with it's roots in the Beaufort scale along with comparisions to the Torro scale. It tries to make an argument that the International Torro scale is a better scale and we'd be better off with it than the F scale, but I'm not sure it carries it.

It proposes a unified TF scale for 'Tornado Force'.

Not sure I agree that TF or T or Beaufort would be better than the F-Scale. I agree it would be more standardized to international usage and provide more data points covering the 98% F0-F3 tornadoes that we experience in the US. Would this truly be of benefit though? What does standardization buy us?

I think it is interesting that it points out that each F-scale number is a range around the average midpoint value so an F5 really ranges from an F5.0 to an F5.99. This makes that elusive F6 just F.01 away!

 

[Gaetan Cormier]

Speaking of the Fujita scale, wasn't the NWS working on an upgraded version of the Fujiat scale? I think that I've seen this somewhere?

 

[Chris Nuttall]

I'm not going to claim to be real educated on this subject or on the details with any of the scales. I do know that this argument has been around for a long time, and scientists in the international community have been pushing the U.S. to change.

Personally, I'm not sure I buy it. Okay, so the T scale was created to match more closely and correspond with the Beaufort scale.

I find a fault in this argument, which I would be more than happy to have explained to me. Okay, an F0 tornado is rated as such because is produces no damage that can be found. The Harper, TX, storm in the presentation is rated a "T6 or TF6" and a F0 by the NWS. How do you know that this is the proper rating?

I don't understand how a rating can be applied if no damage can be found whether it hits a structure or not. Currently, we have no reliable way to regularly measure the surface winds of a tornado. Thus, the only thing we can estimate a tornado's intensity is on the damage it produces.

The F scale is a damage scale. Nothing more, nothing less. Yes, it could be used to estimate winds inside a tornado. But nothing more than that.

I do not know very much about conducting damage surveys. Maybe our techniques are good enough to make better determination of wind speeds. I think this is why the NWS was looking to revise the Fujita scale.[/b]

 

[Fred Gossage]

I find a fault in this argument, which I would be more than happy to have explained to me. Okay, an F0 tornado is rated as such because is produces no damage that can be found. The Harper, TX, storm in the presentation is rated a "T6 or TF6" and a F0 by the NWS. How do you know that this is the proper rating?

I don't understand how a rating can be applied if no damage can be found whether it hits a structure or not. Currently, we have no reliable way to regularly measure the surface winds of a tornado. Thus, the only thing we can estimate a tornado's intensity is on the damage it produces.

In the slideshow, it mentions that Doppler Radar estimates are one factor in determining the "T scale" rating. If this is true, it goes AGAINST radar meteorology principles. It is WELL KNOWN AND DOCUMENTED that we are not seeing the ground-level circulation on radar....so there is no real way of accurately using Doppler Radar for ground-based wind speeds from within the tornadic ground-level circulation. Also.......how many countless times have there been Armageddon-type mesocyclones on Doppler.....but not even a weak tornado touch down. It just doesn't make sense to use radar to try to assign a rating to a tornado, especially when damage is also a factor for the same scale.....which is probably how they rated that TX tornado.

 

[Bill Tabor]

In the slideshow, it mentions that Doppler Radar estimates are one factor in determining the "T scale" rating. If this is true, it goes AGAINST radar meteorology principles. It is WELL KNOWN AND DOCUMENTED that we are not seeing the ground-level circulation on radar....so there is no real way of accurately using Doppler Radar for ground-based wind speeds from within the tornadic ground-level circulation. Also.......how many countless times have there been Armageddon-type mesocyclones on Doppler.....but not even a weak tornado touch down. It just doesn't make sense to use radar to try to assign a rating to a tornado, especially when damage is also a factor for the same scale.....which is probably how they rated that TX tornado.

Right. That is the interesting part of the slideshow as it mentions the Torro scale is damage and also based on wind measurement. This is something that the F-scale isn't. In fact it is a totally different animal with who knows what implications. Perhaps Torro would use a local DOW vehicle to measure the winds. Then again there aren't any DOW's in Europe.

How many times have we had it hammered into our heads that F scale is a damage scale and not a wind speed? When you start thinking about this it could make your head spin....(like a tornado) - LOL.

 

[Scott Olson]

I would like to see the DOW measurements be taken into account as part of our scale to rate tornadoes. If a tornado forms but doesn't have any substanial structures to destroy and gets rated F1 while the DOW measures near surface windspeeds of F3 force I think they should be able to take that into account. Of course since the F scale is damage based it would have to be changed/compromised in order to do so.

 

[Jeff Snyder]

Speaking of the Fujita scale, wasn't the NWS working on an upgraded version of the Fujiat scale? I think that I've seen this somewhere?

There is a movement called the Enhanced Fujita Scale... There's a load of information on the EF scale (and a good report on it) at http://www.wind.ttu.edu/F_Scale/default.htm ... One of the primary aspects of the project is focused on accurately assessing the damage vs. wind speed relationship for a slew of different structures (trees, large warehouses, schools, antenna towers, etc.). It's a very interesting read, IMO.

 

[Gaetan Cormier]

There is a movement called the Enhanced Fujita Scale... There's a load of information on the EF scale (and a good report on it) at http://www.wind.ttu.edu/F_Scale/default.htm ...

Hey Jeff! Thanks for that link, I had that page before but lost my bookmarks one time.

Cheers!

 

[Chris Nuttall]

I would like to see the DOW measurements be taken into account as part of our scale to rate tornadoes.

That's a good idea in theory, but we all know how hard it is to storm chase. I don't think we could get a DOW on every single tornadic storm, even though I wish we could. Imagine how much more we could learn both in real-time and in later analysis. But I digress.... Even the DOWs succomb to the limitation of Doppler radar. Their measurements, although closer to the ground, are still not necessarily at the surface.

A perfect example is the 5/3/1999 measurement of 318mph in the Bridge Creek/Moore tornado. Contrary to popular belief among the public, that wind speed was not at ground level.

 

[Gaetan Cormier]

Originally posted by Chris Nuttall
A perfect example is the 5/3/1999 measurement of 318mph in the Bridge Creek/Moore tornado. Contrary to popular belief among the public, that wind speed was not at ground level.

Would that mean that the Bridge Creek/Moore tornado reached F6? Because if the winds mesured (318mph) were not at ground level, that means that AT ground level the winds were higher, am I right on this?

 

[Jeff Snyder]

Originally posted by Gaetan Cormier

Would that mean that the Bridge Creek/Moore tornado reached F6? Because if the winds mesured (318mph) were not at ground level, that means that AT ground level the winds were higher, am I right on this?

No. Friction plays a large role on near-surface winds. So, the winds at the surface were likely less than those measured... FWIW, in this case, Dr. Wurman has seemed to have restated the max wind measurement, as he mentioned this past spring in on online chat. I'm don't remember exactly what he said, but it was something like "301mph +/- 17mph" or somehting like that.

Even IF the DOWs had measured 320mph, this DOES NOT mean that the tornado would have been assigned an F6 rating! The F-scale is a damage scale, so a wind measurement should not affect F-scale rating. That said, I'm not sure if a direct wind measurement wouldn't be used in a tornado rating assessment. I mean, I think there's a good chance that, for example, a tornado that produces F0 damage but for which there is an anemometer measurement of 130mph winds IN the tornado would be rated not at F0. Of course, the odds of an anemometer sampling a tornado is pretty small, even when mobile (TOTO project).

 

[Scott Olson]

Originally posted by Chris Nuttall+--><div class='quotetop'>QUOTE(Chris Nuttall)</div>

<!--QuoteBegin-Scott Olson

I would like to see the DOW measurements be taken into account as part of our scale to rate tornadoes.

That's a good idea in theory, but we all know how hard it is to storm chase. I don't think we could get a DOW on every single tornadic storm, even though I wish we could. Imagine how much more we could learn both in real-time and in later analysis. But I digress.... Even the DOWs succomb to the limitation of Doppler radar. Their measurements, although closer to the ground, are still not necessarily at the surface.

A perfect example is the 5/3/1999 measurement of 318mph in the Bridge Creek/Moore tornado. Contrary to popular belief among the public, that wind speed was not at ground level.[/b]

Just to clarify, I didn't mean to actual build a fleet of DOWS and have them chase after tornadoes. I just meant for tornadoes that the DOW scans and when it contradicts with the damage assessment by a good degree. I think it is more accurate than a scale that is built on damage assessment. Verification of ground speeds using Samaras probes will be used and then they can come up with a formula to bring the normal low-level scan mode to represent a best guess ground speed.

 

[Gaetan Cormier]

Thanks Jeff for clarifying this for me! It's much clearer now. I always tought that the winds at surface were higher than higher up, I did not think about friction!

Thanks again

 

[Jeff Snyder]

Originally posted by Scott Olson+--><div class='quotetop'>QUOTE(Scott Olson)</div>

Originally posted by Chris Nuttall@
<!--QuoteBegin-Scott Olson

I would like to see the DOW measurements be taken into account as part of our scale to rate tornadoes.

That's a good idea in theory, but we all know how hard it is to storm chase. I don't think we could get a DOW on every single tornadic storm, even though I wish we could. Imagine how much more we could learn both in real-time and in later analysis. But I digress.... Even the DOWs succomb to the limitation of Doppler radar. Their measurements, although closer to the ground, are still not necessarily at the surface.

A perfect example is the 5/3/1999 measurement of 318mph in the Bridge Creek/Moore tornado. Contrary to popular belief among the public, that wind speed was not at ground level.

Just to clarify, I didn't mean to actual build a fleet of DOWS and have them chase after tornadoes. I just meant for tornadoes that the DOW scans and when it contradicts with the damage assessment by a good degree. I think it is more accurate than a scale that is built on damage assessment. Verification of ground speeds using Samaras probes will be used and then they can come up with a formula to bring the normal low-level scan mode to represent a best guess ground speed.[/b]

I think consistency is desired for any scale... What to do if the damage assessment indicates higher wind speeds than a DOW measurement? What do you do if there is a small-scale eddy not sampled by a radar that has winds >30mph above the "ambient" tornado winds. Do you take radar-sampled winds when the tornado is in a field and does no damage? That means that a tornado may be given an F3 rating when there is no damage to support it. Overall, this may not be too bad, but it leads to inconsistency that can cause disruptions with climo IMO

 

[Chris Nuttall]

Originally posted by Scott Olson
Just to clarify, I didn't mean to actual build a fleet of DOWS and have them chase after tornadoes. I just meant for tornadoes that the DOW scans and when it contradicts with the damage assessment by a good degree. I think it is more accurate than a scale that is built on damage assessment. Verification of ground speeds using Samaras probes will be used and then they can come up with a formula to bring the normal low-level scan mode to represent a best guess ground speed.

Scott, I know that's not what you meant. My bad. I just phrased things wrong. I tried to go back and edit my post, but it wouldn't let me...weird.

I've read in several places that it is believed that the in the strongest F5 tornadoes, particularly multi-vortex tornadoes, that F6 damage has likely been produced. However, with the debris leftover and the fact that an F5 pretty much wipes out everything, F6 damage is not descernible from F5.