EF scale vs. F scale.

[mike scantlin]

now. i'm going to try to keep this friendly.

lets say there is ONE picture of a house completely collapsed on itself.


on the left side, is the wind speed measurement of 220. an F-scale rating of 4.

on the right side of the picture is the estimated windspeed of 160. and an EF rating of 3.


this is how the scales work. the same damage has 2 wind speed estimates based on the damage. the old scale was flawed in that it doesnt take near as high of a gust to cause certain damage as previously thought. this is why a new scale was needed.

am i going crazy or do i make perfect sense?

 

[Chris Foltz]

Mike,

As has been stated in various other threads (and as I'm sure you are aware), the ratings on the old scale and the new scale are both based on damage, not wind speed. The wind speeds attached to both scales were/are based on estimates of the severity of winds needed to caused a specified amount of damage. The main flaw in the old scale was that it was limited in the types of structures used for damage assessment. Additionally, there were flaws in the estimations of winds speeds as you referenced.

The new scale has a much more detailed list of damage indicators (DI's) as well as varying degrees of damage (DOD's) for each of these structures. A panel of well-renowned engineers and meteorologists met determined the expected wind speed that would cause a specified DOD with an upper bound and a lower bound included to allow some flexibility based on the nature and quality of construction of the structure. It also provides guidance for rating a tornado based upon damage to trees (hardwood or softwood) which was not formally included in Dr. Fujita original damage scale. The other beauty of the new scale is that it's very flexible and additional DI's may be added at a future date.

I've gotten long-winded enough but I hope this helps clarify your question in some fashion.

 

[Bob Schafer]

I just don't give a crap about it any more. I don't care what the ratings are, and I don't care what the estimated wind speeds are. It's obvious nobody knows what they're talking about, so what difference does it even make? If everything was all wrong last year, it's probably all wrong with the stupid EF scale this year, too. I guarantee it'll all be changed again soon, which makes everything a moot discussion.

 

[John Peters]

I just don't give a crap about it any more. I don't care what the ratings are, and I don't care what the estimated wind speeds are. It's obvious nobody knows what they're talking about, so what difference does it even make? If everything was all wrong last year, it's probably all wrong with the stupid EF scale this year, too. I guarantee it'll all be changed again soon, which makes everything a moot discussion.

It sounds to me like there just need to be some clarifications made.

What are you suggesting by "it was all wrong last year?"

From NWS EF Scale Website:

Over the years, the F-Scale has revealed the following weaknesses:

* It is subjective based solely on the damage caused by a tornado
* No recognition in difference in construction
* Difficult to apply with no damage indicators
o if the 3/4-mile wide tornado does not hit any structures, what F-scale should be assigned?
* Subject to bias
* Based on the worst damage (even if it is one building or house)
* Overestimates wind speeds greater than F3

http://www.spc.noaa.gov/efscale/

"F5" or "EF-5" damage was previously thought to be produced by 261-318 mph winds. It is now believed that these wind values were overestimated. The EF-Scale recognizes that it probably only requires 200-234 mph winds to produce "F5" or "EF-5" damage.

The terms F5 and EF-5 should be considered comparable and interchangeable. A tornado rated F-5 in the past would most likely be rated EF-5 if it occurred today.

The exception to this would be if a tornado in the past completely wiped a foundation clean, but the structure was poorly anchored. In the past, this tornado may have been rated F-5 (or EF-5 had the system been implemented earlier). Recently, there has been a lot more emphasis on the structural integrity of buildings damaged by tornadoes. This is unrelated to the introduction of the EF scale. Over the past few years, survey teams under the F scale were incorporating these new considerations into damage assessments. Little to nothing has changed this year (except the addition of the "E" and the adjustment of wind speed estimates).

Also: I think the whole "where have all the violent tornadoes gone" conspiracy theory has been proven moot as well. This year we have had 3 tornadoes rated EF-4 and one rated EF-5, and it is only the middle of may. Thinking back on the past 8 years, i don't think there is a tornado that produced damage to the same degree of totality as that of Greensburg or Moore Oklahoma. Furthermore, based on the damage produced by the recent violent tornadoes, I'm somewhat assured that many of the "high end F-3" tornadoes of 2005 and 2006 that many were so convinced deserved F-4 ratings did not produce damage to the degree of for instance the Enterprise tornado, etc.

So many people were convinced (including myself) that survey teams would never classify a storm as F-5 or EF-5. We know know that is not true; it simply takes an extraordinary event to attain EF-5 status (which we can all agree that Greensburg was a pretty extraordinary event).

Just my .02
- John

PS: We can only hope that the next EF-5 tornado does not pass directly through the center of a town at near peak intensity

 

[Shane Adams]

I just wish they'd call it the "F-scale" like they always have....change the windspeeds/criteria/whatever you want....but not the name. "EF-whatever" compared to just the basic "F-whatever" seems overkill to me. The windspeeds are all changed, people know it's been 'enhanced'. But I'm like Bob....who cares.....we thought it was right for 30 years and it wasn't........I don't see why this one won't be wrong in a few years either, because all the engineers and meteorologists researching all of this still have jobs....which means we don't know everything yet.

Besides, why do we rate tornadoes at all? Weak, strong, and violent is pretty much all we need to know. The important thing is learning how to better warn for them, which science has done a wonderful job of the past few decades.

 

[Chris Foltz]

Besides, why do we rate tornadoes at all? Weak, strong, and violent is pretty much all we need to know. The important thing is learning how to better warn for them, which science has done a wonderful job of the past few decades.

Couldn't agree more with your thoughts Shane. Unless it's an EF5, I don't understand people getting so wrapped up in whether the damage was high-end EF-2 or low-end EF-3. It's not like someone's gonna get more money from their insurance company or the government if it's and EF-3 vs. and EF-2.

 

[John Peters]

I just wish they'd call it the "F-scale" like they always have....change the windspeeds/criteria/whatever you want....but not the name. "EF-whatever" compared to just the basic "F-whatever" seems overkill to me. The windspeeds are all changed, people know it's been 'enhanced'. But I'm like Bob....who cares.....we thought it was right for 30 years and it wasn't........I don't see why this one won't be wrong in a few years either, because all the engineers and meteorologists researching all of this still have jobs....which means we don't know everything yet.

Besides, why do we rate tornadoes at all? Weak, strong, and violent is pretty much all we need to know. The important thing is learning how to better warn for them, which science has done a wonderful job of the past few decades.

I think it is great that we have a system of rating tornadoes. It provides a basis of comparison in terms of what conditions will produce stronger tornadoes and what conditions will produce weaker tornadoes. It is also human nature to rate and compare natural phenomena, especially destructive ones. Should we abolish the hurricane rating scale? Granted it is a little more accurate and is a before-the-fact deal rather than after-the-fact damage surveys, but it simply provides a basis of comparison.

Perhaps we will change the system again in the future, but that doesn't mean we shouldn't amend it now. To resist improvements now simply because further improvements will be needed in the future is absurd and unscientific in my opinion.

 

[John Peters]

Couldn't agree more with your thoughts Shane. Unless it's an EF5, I don't understand people getting so wrapped up in whether the damage was high-end EF-2 or low-end EF-3. It's not like someone's gonna get more money from their insurance company or the government if it's and EF-3 vs. and EF-2.

If nothing else, human curiosity, and the desire to compare similar natural phenomena. I don't think there is anything wrong with this.

Imagine if mountains were only classified as "very tall, tall, medium, etc." rather than by their exact elevation in feet/meters. There would be many "very tall" mountains and no basis of comparison between them. Adding the exact elevation simply makes the comparison more accurate.

The same goes with the 6 number classifications of the F and EF scales, they allow for a slightly higher degree of accuracy

 

[Mike Peregrine]

The "EF scale" is the "New Coke" of weather.

I just love how chasers have been arguing the merits of the F-scale for years ... and just when that stuff was quieting down, now we have brand new standards to debate.

 

[mike scantlin]

chris, i wasnt saying its rated on wind speed. i was saying that the estimated wind speeds in realtion to damage is very different between scales. read what i said again and maybe you will get what i'm trying to say.

 

[Chris Foltz]

Hey Mike, I was pretty sure you understood. That's why I put "(and as I'm sure you are aware)" in my response.

I would strongly encourage everyone to read the SPC link that John provided above as it will hopefully address any questions you might have regarding the changes made. As with anything that changes, it will take some time to adjust to the new "wind speeds" associated with each tornado rating. As has been said elsewhere, a "3" is still a "3", a "4" is still a "4", etc... It can be a little confusing but hopefully the information out there will resolve any concerns.

 

[Shane Adams]

I'm not opposed to better understanding, but it's a moot point for me personally. I spent a lot of time and effort reading up on the old F-scale damage parameters, and while I was of course no expert, I was pretty good at guessing ratings before the official ratings came out. When it was all changed, all that knowledge I'd gained was wasted....so I'm just frustrated with having to relearn a HUGE glossary of specific damage parameters all over again to relearn this damage scale.....and after years of being criticized for putting too much emphasis on what the tornadoes I saw were rated (i.e., 'who cares if it was an F5 Shane?'), I've finally gone to the other side of the fence: who needs ratings?

And now everyone else wants to rate tornadoes by a 150-point process, LOL.

I'm ok with adjusting the scale...whatever works. But I'm still calling it simply the "F-scale".

 

[Greg Stumpf]

...all that knowledge I'd gained was wasted....

You didn't waste the knowledge. With the EF-scale, you add to your knowledge.

It's so simple I still can't understand why folks don't get the changes:

1. For single/double family residential structures (DI-2):

F0=EF0
F1=EF1
F2=EF2
F3=EF3
F4=EF4
F5=EF5

The only difference being the wind speed estimates have been changed.

2. More Damage Indicators (DI) are available for rating.

3. The scale is expandable to include more DIs (e.g., automobiles, if and when ever added), and the scale is flexible to allow research to refine the wind speed esitmates associated with said degrees of damage (DoD).

That's it folks!

 

[Mike Peregrine]

That's a helpful breakdown. But I do have to ask ... what about just going back to calling it the F-scale then since the primary things that changed were associated windspeeds? Previously everyone seemed so adamant about keeping these associated windspeeds as subjective numbers that should be only loosely coordinated with the scale ... but since that is where the clarification is emphasized, why not stick with the original nomenclature? It's not a big deal I guess, but anytime I hear the words "enhanced Fujita" all I can picture in my head is Dr. Ted on steroids or something. It's going to be forever (or never) for the media to get this right ...

 

[Shane Adams]

So basically, if I know the old scale, I know the new one? If a "1" is still a "1" and so on, I can dig it......just the windspeeds assigned to each rating are different. I'm gonna try to do some estimations the next time the situation arises and see if I'm still in the ballpark with the new system.