Enhanced Fujita scale confusion

[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.