The enhanced F-scale takes effect February 2006.

I came across this while searching the F-Scale on the internet.
How is tornado damage rated? The most widely used method worldwide, for over three decades, was the F-scale developed by Dr. T. Theodore Fujita. In the U.S., and probably elsewhere within a few years, the new Enhanced F-scale is becoming the standard for assessing tornado damage. In Britain, there is a scale similar to the original F-scale but with more divisions; for more info, go to the TORRO scale website. In both original F- and TORRO-scales, the wind speeds are based on calculations of the Beaufort wind scale and have never been scientifically verified in real tornadoes. Enhanced F-scale winds are derived from engineering guidelines but still are only judgmental estimates. Because:

1. Nobody knows the "true" wind speeds at ground level in most tornadoes, and
2. The amount of wind needed to do similar-looking damage can vary greatly, even from block to block or building to building,

...damage rating is (at best) an exercise in educated guessing. Even experienced damage-survey meteorologists and wind engineers can and often do disagree among themselves on a tornado's strength.
Souce: http://www.spc.noaa.gov/faq/tornado/index.html#Damage

Fujita Tornado Damage Scale
Developed in 1971 by T. Theodore Fujita of the University of Chicago
No longer used operationally -- see the Enhanced F Scale.
http://www.spc.noaa.gov/faq/tornado/f-scale.html

Enhanced F Scale for Tornado Damage
An update to the the original F-scale by a team of meteorologists
and wind engineers and implemented in the U.S. in February 2006.

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

Mike
 
It is intriguing but I have a hard time believing they would change it. That would be a lot of work to go back and rerank everything in the archives and teach everyone the new process.

Since nobody really knows the true windspeed with the surface...the existent Fujita Scale would seem fine to me...especially with the DOW recording the 318mph wind on the Moore, OK tornado. While it is a statistical anomaly...that would be an easy 118 mph over the EF-5 threshold which seems like too much room for variance.

...Alex Lamers...
 
Alex Lamers wrote:
It is intriguing but I have a hard time believing they would change it. That would be a lot of work to go back and rerank everything in the archives and teach everyone the new process.
There are no plans to systematically re-evaluate historical tornadoes using the Enhanced F-scale.
Souce:http://www.spc.noaa.gov/faq/tornado/index.html#f-scale1

What is the original F-scale? Dr. T. Theodore Fujita developed a damage scale (Fujita 1971, Fujita and Pearson 1973) for winds, including tornadoes, which was supposed to relate the degree of damage to the intensity of the wind. This scale was the result. The original F-scale should not be used anymore, because it has been replaced by an enhanced version. Tornado wind speeds are still largely unknown; and the wind speeds on the original F-scale have never been scientifically tested and proven. Different winds may be needed to cause the same damage depending on how well-built a structure is, wind direction, wind duration, battering by flying debris, and a bunch of other factors. Also, the process of rating the damage itself is largely a judgment call -- quite inconsistent and arbitrary (Doswell and Burgess, 1988). Even meteorologists and engineers highly experienced in damage survey techniques often came up with different F-scale ratings for the same damage. Even with all its flaws, the original F-scale was the only widely used tornado rating method for over three decades. The enhanced F-scale takes effect February 2006.

What is the Enhanced F-scale? The Enhanced F-scale (simple table or detailed 95 page PDF) is a much more precise and robust way to assess tornado damage than the original. It classifies F0-F5 damage as calibrated by engineers and meteorologists across 28 different types of damage indicators (mainly various kinds of buildings, but also a few other structures as well as trees). The idea is that a "one size fits all" approach just doesn't work in rating tornado damage, and that a tornado scale needs to take into account the typical strengths and weaknesses of different types of construction. This is because the same wind does different things to different kinds of structures. In the Enhanced F-scale, there will be different, customized standards for assigning any given F rating to a well built, well anchored wood-frame house compared to a garage, school, skyscraper, unanchored house, barn, factory, utility pole or other type of structure. In a real-life tornado track, these ratings can be mapped together more smoothly to make a damage analysis. Of course, there still will be gaps and weaknesses on a track where there was little or nothing to damage, but such problems will be less common than under the original F-scale. As with the original F-scale, the enhanced version will rate the tornado as a whole based on most intense damage within the path. There are no plans to systematically re-evaluate historical tornadoes using the Enhanced F-scale. A full PDF document on the Enhanced F-scale is online.
http://www.wind.ttu.edu/F_scale/images/efsr.pdf

The enhanced F-scale takes effect February 2006.

I am getting this information from reading the SPC pages online.
Maybe Roger Edwards and Rich Thompson of SPC, can elaborate
more on this.

Mike
 
Original F-scale
Fujita Tornado Damage Scale
Developed in 1971 by T. Theodore Fujita of the University of Chicago
No longer used operationally -- see the Enhanced F Scale.

SCALE WIND ESTIMATE *** (MPH)
F0 < 73
F1 73-112
F2 113-157
F3 158-206
F4 207-260
F5 261-318
Source: http://www.spc.noaa.gov/faq/tornado/f-scale.html

Enhanced F Scale for Tornado Damage
An update to the the original F-scale by a team of meteorologists and wind engineers and implemented in the U.S. in February 2006.

SCALE WIND ESTIMATE *** (MPH)
F0 65-85
F1 86-110
F2 110-135
F3 136-165
F4 166-200
F5 Over 200
Source: http://www.spc.noaa.gov/faq/tornado/ef-scale.html

Mike
 
Originally posted by Alex Lamers
That would be a lot of work to go back and rerank everything in the archives

I was wondering about the same thing, Alex. How much is this going to mess with a data base that is far from the best, but all one has to look at??

I suppose we will now just assume the tornadoes ranked as F4s (or whatever) in the data base caused the damage with weaker winds with no need for reclassification. I don't think the new scale is implying that a tornado previously ranked deserves a higher ranking than before, only that it has been decided that weaker winds can cause the same type of damage...

Pat
 
Actually, I don't think it will mess with the database that much...

The "F" scale will still be in place, it's just the wind speeds that are being changed.
 
Originally posted by rdewey
Actually, I don't think it will mess with the database that much...

The "F" scale will still be in place, it's just the wind speeds that are being changed.

I agree, although it's still really weird that, until the new scale is gotten used to, come February there's gonna be about 500 more F5s in the books then there were in January, LOL. I just sat here thinking about it and drew the opposite conclusion back and forth about five times. So every past F3 isn't an F5 now, it just had "lower windspeeds" than the data presents. Still kinda confusing.
 
It seems to be a much improved, more specific damage scale. 8 levels of damage and 28 damage indicators -- much better than 6 levels of damage (F0-F5) on 1 damage indicator (well-constructed house) on the current F-scale. As has been noted, previous tornadoes will not be re-rated, and I don't think the damage expected from an EF-3 is much different than a current F3. As Shane and others have noted, the difference looks to lie primarily in the wind speeds attached to each category (and the gross over-estimation of the wind speeds previously attached to the F-scale).
 
Interestingly, this change can actually make it harder to get an EF5 rating than the old F5 even though windspeeds have been reduced.

In the old Fujita scale, a frame-house tossed off its foundation would normally elicit an F5 rating if it was properly secured with the foundation. However, under the new scale, total destruction of a home yields an expected wind speed of 170 mph. Even under a totally wiped clean foundation the upper bounds to be assigned would be 198 mph. So, it would have to be destructive damage to a more substanial structure (thus making it slightly less likely to find EF5 damage). This new system puts more emphasis on a standard than personal interpretation and this is a big improvement in my opinion.

From a climatological standpoint, I don't see too much of a problem, other than the added DOD's but IMO, the same ratings would imply just with infrared lower wind speeds than was typically expected.

-Scott Olson.
 
How do you account for the REALLY strong EF5's then like the Moore tornado would have been? 318 mph?

IDK. What is the basis for the change anyways. Why can't they just make damage indicators for the old fujita scale?

Someone tell me the advantage of the switch, not just information about it.

...Alex Lamers...
 
Originally posted by Alex Lamers
How do you account for the REALLY strong EF5's then like the Moore tornado would have been? 318 mph?

IDK. What is the basis for the change anyways. Why can't they just make damage indicators for the old fujita scale?

Someone tell me the advantage of the switch, not just information about it.

...Alex Lamers...

How do we account for REALLY strong Cat 5s? There is no upper bound, so a 300mph MEASURED wind speed is still in the EF5 range, just as a 215mph sustained speed in a hurricane is still a Cat 5.

The old F-scale HAD wind speeds attached to it that were unrealistically high. It's been tested that 220mph winds aren't required to obliterate a house, like the original F-scale implied (F4 or greater). It doesn't make sense to me to enhance the scale without making necessary changes to the wind speeds associated with each category.

As stated above, even if a tornado is MEASURED (by a miracle anemometer) to have 500mph winds, it'll still be given an EF-5 rating if I understand things correctly. In addition, the obliteration of a wellbuilt structure will still earn a 'violent' rating. This just gives us an advantage of having more indicators to deal with those situations in which there aren't well-built homes damaged (which happens a lot). Heck, even having tree damage as an indicator is nice, and I'd expect that it'll help standardize rating assessments when those 'well-built' homes aren't affected or aren't affected directly.

I'm not sure we'll see a large rise in level-4 or level-5 rated tornadoes (compared to historical F4 and F5 tornadoes) when the EF scale comes out since it's still based on damage! I DO think we may see a couple more EF-4s than F4s we've had recently since there are more damage indicators to help with an assessment. Even at that, violent tornadoes from at least the past few years were rated by a panel of damage experts that were no doubt well-qualified to make such assessments. So, a tornado that rips the roof off a house won't be rated EF5, just as it wouldn't be rated an F5 now. Just my 2 cents. This just goes to show how many previous tornadoes had winds that were likely considerably weaker than previously thought. I don't think it says much about whether previous tornadoes were over-rated, since the F-scale is a damage scale, so F5 damage is F5 damage. Now, however, we just see that 300mph probably aren't necessary to obliterate structures.

I also like how the wind bounds don't imply a precision that we don't have. By saying that the an F3 tornado has winds of 158-207mph implies a precision that is unfounded. The EF-scale rounds the upper-bounds to x0 or x5 (e.g. EF3 foes from 136-165mph).

Damage indicators:
1 Small barns, farm outbuildings SBO
2 One- or two-family residences FR12
3 Single-wide mobile home (MHSW) MHSW
4 Double-wide mobile home MHDW
5 Apt, condo, townhouse (3 stories or less) ACT
6 Motel M
7 Masonry apt. or motel MAM
8 Small retail bldg. (fast food) SRB
9 Small professional (doctor office, branch bank) SPB
10 Strip mall SM
11 Large shopping mall LSM
12 Large, isolated ("big box") retail bldg. LIRB
13 Automobile showroom ASR
14 Automotive service building ASB
15 School - 1-story elementary (interior or exterior halls) ES
16 School - jr. or sr. high school JHSH
17 Low-rise (1-4 story) bldg. LRB
18 Mid-rise (5-20 story) bldg. MRB
19 High-rise (over 20 stories) HRB
20 Institutional bldg. (hospital, govt. or university) IB
21 Metal building system MBS
22 Service station canopy SSC
23 Warehouse (tilt-up walls or heavy timber) WHB
24 Transmission line tower TLT
25 Free-standing tower FST
26 Free standing pole (light, flag, luminary) FSP
27 Tree - hardwood TH
28 Tree - softwood

Since it wasn't directly linked to previously, you can read the full report at http://www.spc.noaa.gov/faq/tornado/ef-ttu.pdf , which explains how the EF scale was derived, how the EF scale correlates to the F scale, etc.

Originally posted by EF-Scale Report+ page 15 of the pdf--><div class='quotetop'>QUOTE(EF-Scale Report]
Members of the Forum were very specific in their opinion that a single building, structure, or other DI should not be used to rate a tornado event. Several DIs should be considered in assigning an EF-Scale rating to a tornado event.[/b]

That would imply that a single damage indicator that would imply an EF4, for example, does not necessary guarantee that an EF4 rating would be accurate.

<!--QuoteBegin-EF-scale Report
@ pg. 17-18 of the pdf
The estimated wind speed then determines the EF-Scale category appropriate for the observed damage. The categories range from EF0 to EF5. The wind speed ranges in each category are related to Fujita Scale ranges by a correlation function (Equation 1). This correlation between Fujita-Scale and EF-Scale wind speeds provides a link between the two scales and thus makes it possible to express a Fujita-Scale rating in terms of an EF-Scale rating. The only difference is the wind speed ranges in each scale. Thus, the historical tornado database is preserved and can be easily converted to the criteria of the EF Scale.

The problem of no DIs in open country remains. Research is currently underway to identify additional damage indicators and to obtain estimates of the wind speeds to cause defined damage. Of particular interest are damage to various crops, farm equipment, silos, grain storage facilities, and irrigation equipment. These indicators can be incorporated as DIs in the EF Scale as reliable data become available. The technology of portable Doppler radar should also be a part of the EF Scale process, either as a direct measurement, when available, or as a means of validating the wind speeds estimated by the experts.
[/quote]
{Emphasis added by me}

The last sentence is interesting, in that it implies (to me at least) the mobile Doppler radar measurements CAN now be ground for assigning a rating to a tornado. Of course, there are plenty of unknowns still, such as the problem of estimating near-surface (10m) winds from velocity data obtained well above that level. I would take this to mean that if a tornado sits in a field and does very little damage, a DOW ob (surface-extrapolated, however that will happen) of 180mph may be sufficient in assigning an EF4 rating. On the other hand, this now makes wind speeds a more integral part of the EF-scale (e.g it's no longer a PURELY damage-based scale!).

Of course, my understanding of this may be incorrect, so it'd be nice to hear from someone more involved in the EF-scale.
 
Thanks Jeff. The only question I have is...are they going to redo the archives or are they gonna let those be and just transition.

Ah nevermind I found it. They say it will be easily convertible but we shall see. :)

...Alex Lamers...
 
Old now defunct F-Scale

F0 < 73
F1 73-112 39mph
F2 113-157 44mph
F3 158-206 48mph
F4 207-260 53mph
F5 261-318 57mph
Note that the old F-Scale increments are not equal


New EF Scale (effective from Feb 2006)
F0 65-85 20mph
F1 86-110 24mph
F2 110-135 25mph
F3 136-165 29mph
F4 166-200 34mph
F5 Over 200 118mph **

** Note winds in the Moore 1999 tornado were measured by Doppler at 318mph

As can be seen that the new EF-Scale increments are also not equal and therefore scientifically flawed from the word go!
 
"So every past F3 isn't an F5 now, it just had "lower windspeeds" than the data presents."

Remember that the wind speeds listed before were nothing but an educated guess from Fujita. Everyone KNEW that the wind speeds were too high.

"Note winds in the Moore 1999 tornado were measured by Doppler at 318mph "

Not at the ground they weren't. Friction causes a large reduction in wind speeds from aloft to the surface. And that still doesn't matter, because the F-Scale is there to measure damage only. Re-read any of the countless threads before (or read the nice report on the new one) to get a better handle on it.

"As can be seen that the new EF-Scale increments are also not equal and therefore scientifically flawed from the word go!"

I'm not sure I understand, unless there's a missing smiley in there somewhere.
 
Originally posted by Stuart Robinson
As can be seen that the new EF-Scale increments are also not equal and therefore scientifically flawed from the word go!
Why must the scale be linear to not be flawed?
 
Originally posted by Stuart Robinson

** Note winds in the Moore 1999 tornado were measured by Doppler at 318mph
Just as an update... Dr. Wurman mentioned in his stormchase chat last year that it's more like 301mph +/- 17mph. There are statistical assumptions and approximations inherent to radar signal processing, so one should never be 100% confident that velocity (and reflectivity for that matter) from any particular range bin are exactly true, thus the likely reason it was changed from 318mph to a range.
 
"Why must the scale be linear to not be flawed?"

The hurricane scale wind breakdowns are not linear either...
 
If this is the case they should remove Fujitas name from the scale.

:eek:
 
Ok, just read the entire 95 page PDF and then skimmed it back and forth a few times so I have a pretty good handle on it.

Torns won't be re-rated. EF-scale correlates to F scale but with different wind ranges. Biggest problem I see is even though their method was systematic and scientific they used an expert classification system as wind speed determination similar to the old Fujita scale. This can mean garbage in = garbage out at least in estimating accurate wind speed ranges to predict a damage level simply because (as they mention in the paper) that research hasn't been done either deterministically or experimentally using modeling. They do reference that some studies of the past have suggested that F-scale ratings can be higher than needed to cause the actual damage. If the goal is to accurately represent wind speed that caused this damge then EF is somewhat inadaquate. As a way to further quantify and define F-scale so it can be better applied and compared to various damage cases then EF should work well.

I also see there may be a problem integrating actual windspeed / damage scenarios (such as those measured by DOW) to EF if those initial expert wind speed estimates were very far off.

It may be harder to get a higher rating in EF than F because the specificity based on building materials and construction is implied whereas in F scale it was arbitrary and hard to determine. Note also that top ranges of F-scale were not used only the median values to equate to EF ranges.

All that said, it may still be a very useful improvement for future database research efforts and insurance appraisal purposes as well. On the other hand it doesn't sound as macho because now when we see a tornado later ranked EF5 it's speed may only be suggested as > 200mph as opposed to maybe 318 mph winds to cause that damage.

So :lol: from the chaser perspective this is going the wrong way. Instead EF should have upper range at the Mach level. That way we could really boast of something during after chase parties while sitting around drinking beer :wink: .
 
I've believed for years that any tornado possessing wind speeds of 200 mph or greater should be categorized as "violent"; as we know from past tornadoes and hurricane Andrew's peak gusts, few structures will withstand 200 mph winds.....and tornadoes of this intensity are capable of taking many lives, especially if they strike a mobile home community or RV park (i.e.- Evansville, IN 11/05; Camilla, GA 2/14/00; Kissimmee and near Orlando, FL 2/23/98 ).

Over the years, I've spoken or corresponded with several meteorologists who were involved with the 1974 "superoutbreak"; either as forecasters on duty or as part of post tornado surveys (incl a couple who were with Dr Fujita when assessing Alabama tornado damage), and none of them believe wind speeds at GROUND level reached 300 mph. I'm not foolish enough to state a maxi tornado's peak winds couldn't reach 300 mph, but in my years of experience and research, even if they were......we'd have difficulty determining it (because once you reach 225-250 mph, virtually everything is obliterated; even most well built homes completely leveled and swept away from their foundations).

At age 44, I'm old enough to remember school encyclopedia and even weather books which estimated tornado wind speeds at 500-600...or even 800 mph. In those same encyclopedias and weather books, there was speculation it took such unbelievable winds to "defeather" chickens and blow automobiles hundreds of yards. We now know that was incorrect; that such incredible phenomena can occur at much lower wind speeds. As someone else mentioned, the National Hurricane Center catergorizes a hurricane as cat-5 once sustained wind speeds reach 156 mph, no matter how high they go (IMO the infamous 1935 Labor Day hurricane may have possessed 190-200 mph sustained winds with peak gusts possibly exceeding 230 mph;, based on the gruesome aftermath and exceedingly small diameter of eyewall and max winds/ pressure gradient; about the same size as 2004's Charley at landfall on SW Florida....except the central pressure of the Labor Day hurricane was about 50 millibars lower :shock:

This new enhanced rating scale does the same.....once a tornado is judged to have reached 200 mph wind speeds, it will be recorded as a F5...no matter whether it peaks at 200 or reaches the upper limit possible (IMO 250-275 mph in rare cases [i.e.- Xenia, OH & Guin, AL on 4/03/74).
 
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