Enhanced Fujita scale confusion

[J Allen]

Not suggesting its a political stunt, rather a systemic under-rating during the period caused by an institutional policy which i'm sure Greg Stumpf would be happy to tell you more about.

I wouldn't say that the database in its current form is particularly useful or based on total accuracy, only database that can be given that honour is the ESWD database which actually concerns itself with quality control, but thats a whole other story.

Jared I am well and truly familiar with the EF-scale and its application. Spent a significant time investigating it out of personal interest and reached the point where its still a poor mans substitute for a real understanding and isn't solidly based on observations but alot of speculation at least to some degree, whether its our best option and better than Fujita's adjusted scale I am not totally sure, the assumptions regarding building codes and the effect of a tornadic circulation are certainly questionable.

Apologies folks, seems you can't believe everything you read these days, nor can everyone above read what was written either . Thankfully Rdale has corrected a few of the mythconceptions and misconceptions I had so Im satisfied and I will leave it there. Suffice to say that I wouldn't say the EF-scale is completely impartial and to believe it so is nieve.

 

[Greg Stumpf]

Not suggesting its a political stunt, rather a systemic under-rating during the period caused by an institutional policy which i'm sure Greg Stumpf would be happy to tell you more about.

You certainly did suggest it was a political stunt! What are you really talking about? The only institutional "policy" that raised the concerns of survey experts like me was the change in the use of the "Quick Response Team" (QRT) from a team of nationally recognized experts (of which I used to be a member) to in-house NWS meteorologists with survey experience. But that has nothing to do with lowering ratings based on saving government disaster payouts, which is as I said, complete hogwash.

Suffice to say that I wouldn't say the EF-scale is completely impartial and to believe it so is nieve.

Of course the rating system, both the F- and EF-scales, have a large degree of subjectivity. They aren't based on instrument measurements, but by evidence in damage. Not every surveyor comes to the exact same conclusion on events, and the "accuracy" of those conclusions are based on experience level. But even Tim Marshall, probably the world's foremost wind damage assessor (and it's his studied profession) will provide you a range of suspected wind speeds based on observed damage, and sometimes that range will span across two scale categories.

 

[Jake Orosi]

I don't know about funding thresholds, but some tornado-devastated communities seem to use F-ratings of storms as some sort of source of community pride. I may be wrong, but maybe you guys can help me out - I seem to remember one particular Plains town being devastated a few years back; the NOAA preliminarily rated it an F5, but subsequent scientific investigation caused them to "downgrade" the final rating to F4 - still incredibly destructive of course. But for some reason that's quite beyond me, the community was shocked and incensed by the NOAA's scientific findings...made t-shirts that said things like "'Not an F5', my a**!" and such. It seems as if they felt that designating the tornado an F4 was somehow either an attack on the town or a downplaying of the damage the tornado caused.

 

[Tim Shriver]

The Jackson image shows, from what I can see, there are no straps or bolts that would secure the house to the foundation.

The foundation itself appears to be brick, non-reinforced. Not sure what the house was made of itself. I see timber off to the left. Did it just move the house off the foundation?
The trees that can be seen are not debarked. No uprooted trees either. Smaller tree damage.

Without seeing to the left of the image I would suspect that is where the remaining part of the house is, if not the full house (with damage)

I suspect the rating of EF-3 to be correct. The Damage Indicators and Degree of Damage are consistent with an EF3.

Brick can handle a great deal of downward force, but by itself does not do well with side forcing.
Thus a car can drive through a non-reinforced brink wall from the side, but try it downward into the wall, the car will loose every time.
Again, the photo is limiting.

The second photo you cannot see the foundation and how the house was secured to it. Stoughton was a powerful tornado (multi-vortex at times)
and from what we saw many houses that were bolted to concrete foundations were destroyed. It was high end F3 and in many spots the DOD indicated low F4.

Again the images are limited as a wider view of things would be needed for fully rate it.

Tim

 

[Tim Shriver]

That *used* to be the case. However, it is my understanding, from different sources, that the National QRT no longer exists. It used to consist of selected damage experts, with the goal of supporting damage assessments for high-end tornadoes. However, there may still be separate QRTs organized by each NWS region, and they may or may not be called for any particular event. Why this resource (the national QRT) went away, I do not know. Now, it may be a budget issue, but how much does it really cost to bring in a couple of experts (e.g. Tim Marshall, NSSL/WDTB damage scientists, etc.) for a few events every year? It's neither here nor there now, regardless.

Each WFO does the damage assessments in its CWA. For large events other teams can be brought in.
Our group, is trained and has an active Damage Assessment Team (DAT), trained by the NWS over the years.

We go out and assign what the DI (Damage Indicators) are and the Degree of Damage (DOD). Structure by structure.

We assemble this information along with maps of the path, images and video of the damage, interviews from affected people and witnesses.

We submit this to the WCM and he assigns the EF rating. It is not hard to tell
what the EF rating is with the collected information and we know what it is
before submitting the information to the WCM. But he makes the final "public" call.

If they question our finding, they will take us out and reexamine the data, but so far
we have been spot on.

Tim

 

[Tim Shriver]

I guess I'm confused about a few things... Having worked in Federal funding after tornadoes, I can guarantee you that the EF number has -no- bearing on that process. It's entirely based on the amount of uninsured damages..

rDale is correct, but storm damage history is considered in your home insurance. Insurance companies use
LSRs to help determine an areas risk/liability.

There are a few other factors that do come into play, uninsured damage dollar amount/percentage etc.
The EF rating is a side note, but does not factor into the formula used to determine if an area
gets Federal help or not.


Below are some link to the DOD an DI items on our website as supplied to us by the NWS

http://www.midwestsstrc.org/downloads/DamageIndicators.doc

http://www.midwestsstrc.org/downloads/dod.doc

The Stoughton event, FEMA denied aid as most of the structures damaged were privately insured. WEM (Wisconsin Emergency Management
knew the request did not meet the criteria even before they submitted the request to FEMA.

Tim

 

[Wes Carter]

We need to take the Enahnced Fujita scale for what it is: A method for distinguishing between weak and strong tornadoes for the historical record. There were some serious shortcomings with the Fujita Scale that were recognized, and the Enhanced Fujita Scale was brought about to use what has been learned since the early 1970's to address some of those shortcomings. It's not perfect, and the people that worked on the new EF scale as well as Dr. Fujita (if he were still alive) would probably be some of the first to admit that. I've never read anything that claims the EF scale is infallible or even accurate. But it's the best system we have, so it's the one we use. It is logistically impractical to do any kind of accurate scientific study to determine the wind speeds required to do specific amounts of damage to the multitude of designs and methods of construction of 'well built homes', schools, churches, etc... Neither can we accurately compare tree damage even in trees of the same species. It's a best guess, and it's the best we can do until the day we can have DOW trucks on every tornado that occurs.

In the old Fujita Scale a tornado that did F5 damage was estimated to have wind speeds from 261-318 miles per hour. But somewhere along the way it was discovered that winds much less than 261 miles per hour could cause what was considered F5 damage. Thus the Enahnced Fujita scale has the EF5 tornado with winds 'greater than 200mph'. However, in 1999 Dr. Josh Wurman directly measured the winds in the Moore, OK F5 tornado several hundred feet above the ground in excess of 300mph. It's not clear whether or not those intense of winds were experienced at ground level, however it does demonstrate that there can be a wide range of wind speeds that can cause EF5 damage, and it is hard to differentiate between 200mph and 300mph winds because both can cause complete devastation. Although this might present a bit of a dilemma to engineers and scientists studying tornado damage, it should have no bearing on John Q. Public because complete devastation is complete devastation.

Insurance companies, FEMA, the Red Cross, and all the powers that be don't care what the damage rating is on a tornado. They send assessors and adjusters out to evaluate the properties they insure, or how many people they have to provide food, clothing, and shelter for. I've done damage assessments for the Red Cross, and all they do is look at each home and do a curbside assessment of the damage to get an idea of how much assistance they will have to provide and to whom they will have to provide it to. The EF rating never comes into play that I'm aware of.

I don't think that the EF rating is a badge of honor or a source of pride as some have said, but rather these people perceive that if they get a lesser rating it somehow downplays their losses. But an EF1 can be a devastating tornado if it hits the wrong place, has a long enough track, and hits at the right time of day. In Tennessee we had an F5 that hit in 1998 that killed two people, but 10 years later we had the EF3 that hit Castillian Springs and tracked into Lafayette and killed 22 people. The 1998 F5 is commonly referred to as the 'forgotten F5' because there is little reference to it because it did not have the human impact many other tornadoes have had.

I think the rating carries more weight with the general public than it does insurance companies, the federal and state agencies, and the academics that are constantly working on refining it. It's a classification tool that is still a work in progress, nothing more.

 

[Tim Supinie]

Probably should just stay out of this, but ...

What was once an F-0 is now an EF-1, what was an F-1, is now an EF-2, what was once an F-2, is now an EF-3, what was once an F-3, is now an EF-4, and what was once an F-4 is now an EF-5.

Well, it was determined that the type of damage assigned to the "F1" category usually occurs at wind speeds lower than the stated lower bound of the "F1" category, and likewise for all the other categories. So rather than change the damage thresholds, they changed the wind speed thresholds. The idea behind changing the wind speed thresholds was to minimize the break in tornado statistics between the period of F-scale usage and EF-scale usage.

Keep in mind that the Fujita scale was originally conceived as a bridge between the Beaufort scale and the Mach scale. The original F-scale has 13 categories, and the upper wind speed bound of the F12 category is Mach 1. I think later, Dr. Fujita went back and used the lowest 6 categories (F0 to F5) from that scale to rate damage from tornadoes. I'm not sure what methods he used to assign damage descriptions to F-scale categories, but in practical usage (rating damage from a tornado), I don't think the specific wind speed bounds on the scale mattered a whole lot.

 

[John Wetter]

What was once an F-0 is now an EF-1, what was an F-1, is now an EF-2, what was once an F-2, is now an EF-3, what was once an F-3, is now an EF-4, and what was once an F-4 is now an EF-5.

How does this figure? A zero is still a zero, a 1 is still a 1, etc... I think you're confusing the fact that this is a damage scale, NOT a wind scale... There should be no difference in what an EF-1 vs. an F-1 looks like.

 

[STurner]

To me damage is the most important thing when determining the F or EF rating for a tornado. Winds are winds. On the original F-scale sometimes higher winds such as 250mph were clocked inside a tornado which only did F4 damage but on the other hand I heard of like 220mph winds clocked inside another tornado but it did F5 damage. It must be the way the tornado moves, how it hits the structure, and how slow/fast it moves. sometimes I wonder if there may be very weak winds(almost nonexistent) in part of a tornado where a small object stays but 10 or 20 feet away there is 200mph winds and the a strong whole framed home is completely removed from the foundation. Another thing do you think debris inside a tornado may shield one object from destruction but destroys another structure nearby.