Author Topic: Enhanced Fujita Scale  (Read 7616 times)

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Offline Jimmy Deguara

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Enhanced Fujita Scale
« on: 23 July 2007, 04:18:28 PM »
Although mentioned within other threads, no official topics cover the Enhanced Fujita Scale specifically. The following is a link for those who would like to dwell and comment further:

http://www.spc.noaa.gov/faq/tornado/ef-scale.html

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Jimmy Deguara
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Offline Jimmy Deguara

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Re: Enhanced Fujita Scale
« Reply #1 on: 23 July 2007, 04:20:48 PM »
Hi,

Whilst on the topic of the Enhanced Fujita Scale, I came across this particular link and guess what they used as a sample given what we knew all along:


http://www.newschannel10.com/Global/story.asp?S=6042581

The May 29 2001 White Deer Tornado which could have been classed at least E-F4 - well that's interesting!

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Jimmy Deguara
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Offline David C

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Re: Enhanced Fujita Scale
« Reply #2 on: 25 July 2007, 11:03:47 AM »
The problem with White Deer is that it did not hit very much at all, Jimmy, and certainly not as it appeared to max out as it crossed the HWY in front of us.  eg from article "If you have a tornado that stays mainly over open country where structures aren't affected than the tornado was probably rated much lower on the scale than the force it actually contained," says "Dopplar" Dave Oliver."
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Offline Mike

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Re: Enhanced Fujita Scale
« Reply #3 on: 26 July 2007, 05:38:08 AM »
So if you have a mile wide wedge that roars across the plains and hits nothing what is it rated then if there's no damage except to shrubbery?  Doesn't that detract from the whole theory by Fujita of wind speed in determining damage to structures?  Why can't they just have one system and be done with it and not change it all the time?!  It confuses assessors, insurance companies and clients alike.  Not to mention chasers and spotters who may see a monster tornado but clasify it as a lower scaled because it does not flatten anything!

I understand they're trying to streamline things and it is the wind that creates all this havoc - projectile damage comes along as a subsidiary factor no?

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Offline David C

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Re: Enhanced Fujita Scale
« Reply #4 on: 26 July 2007, 10:06:24 AM »
So if you have a mile wide wedge that roars across the plains and hits nothing what is it rated then if there's no damage except to shrubbery?

Remember Mike that the F-scale, EF-scale are damage assessment tools only - designed to measure and record the impact of tornadoes on us. To that end, a seemingly violent wedge that roars across the high plains knocking only a fence down, well, it's F1 I guess. I'm not sure to what extent the Ef scale addresses this (ie considers vegetation type etc), but what else can you do? Although an experienced observer would recognise a probable high-end tornado simply by the cloud motion visible, for the most part tornado appearance does not correlate with strength of the wind inside the funnel. If the Greensburg tornado did not hit town, or any other substantial buildings, it would have been rated accordingly and by now would be long forgotten (esp given it was at night).
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Offline Jimmy Deguara

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Re: Enhanced Fujita Scale
« Reply #5 on: 26 July 2007, 10:12:52 AM »
Mike,

First of all, we have to be careful of relating tornado width with strength but I know what you mean.

With the lack of resolution of radar specifically at a distance, it would be difficult to confirm the wind strength within a reasonable estimate. If the tornado does not hit structures, then unfortunately, unless there are other visual clues to go by then it is difficult to always determine the wind strength. The Enhanced Fujita Scale at least goes further but including vegtation and field scouring as well as other clues in trying to estimate wind strength and provide a better estimate of the rating than the old system did. I guess that was the whole point of the article I provided above. David and I chased this tornado and we knew it was very violent based on the extreme rotation and tornado behaviour. It hit a house and the minimum damage attributed to cause this damage was assessed as F3. If it was a stronger house it may have sustained a higher rating. Was it a direct hit by the fiercest winds? It snapped power poles as well but the rating was still only given an F3.

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Jimmy Deguara
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Offline David C

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Re: Enhanced Fujita Scale
« Reply #6 on: 26 July 2007, 10:19:14 AM »
Well, it is all academic, but one chaser (indeed one of the most respected in the US) said it was probably F5 strength when we asked (based on experience and observation). The cloud motions were astonishing, satellite tornado, the whole bit. It would have absolutely torn White Deer apart. It appeared to be in a very steady state I can tell you, as will Jimmy. Luckily the meso occluded, no idea what happened really as it became rain-wrapped.
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Offline Mike

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Re: Enhanced Fujita Scale
« Reply #7 on: 26 July 2007, 10:25:49 AM »
I see, yes becoming clearer.  (I should have known re the size debate as i argued that very point in another thread!) - but yes, agree with both your assessments.

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Offline Jimmy Deguara

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Re: Enhanced Fujita Scale
« Reply #8 on: 26 July 2007, 04:51:58 PM »
John,

Just need to clarify:

Quote
Look at the actual DOW windspeed measurements from Moore: Windspeeds indicated 318mph +-5%

The wind speed was taken with the doppler aimed above ground level so wind speed would have been lower at ground level - so we must be careful in comparing the two. I am not sure what the calculated wind speeds were from Greensburg.

You have commented in the past about the scouring of asphalt but I am not sure I/we saw any and you continuously suugest you detected this from aerial photographs. Can you please lead me to any sources that back up your claims here?

Now back to the Enhanced Fujita Scale....

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Jimmy Deguara
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Offline Mike

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Re: Enhanced Fujita Scale
« Reply #9 on: 27 July 2007, 07:38:37 AM »
It's safe to say also that engineers and damage assessors and meteorologists have and will continue to argue the point of what is important and what is not. 

Whether structures are classed on age, size or material and the like, this will always be in debate - things can be coded like we have for our purposes and if they get blown over then does that reflect on insurance companies arguing the point of paying out or not because the structure was coded for 'this' rating and not 'that' rating.   Wind doesn't have standards!   

I don't even know how the US insurance companies work with tornado coverage and it would be interesting to find out the margins and scales upon reflection of the Greensburg event where there was chatter re damage scale and insurance payouts.

I know that a lot of professional people argue on what determines tornado damage when assessing it and I think it's correct to have a happy medium for all to follow.  They've adjusted the wind scale to cover just about everything - it's the damage left behind that is what's causing everyone to argue what EF scale to put to it. 

It's a broad topic that covers a lot of areas.  As Jimmy mentioned, it's not size that matters, it's what happens afterwards.

 Perhaps one day they'll find an single, abandoned car wrapped around a single tree on the plains of Oklahoma in the middle of nowhere and try and work out what EF scale the tornado must have been.  That will get them thinking.

Mike
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