Rate the damage

[Justin Turcotte]

From discussion on a different thread... The Fujita Scale is subjective in nature. Some attempt to utilize it as a wind scale while others attempt to utilize it as a damage scale. I suspect we are in an F5 drought because the damage surveys are becoming increasingly picky. Add to this, temporal and spatial difference in home construction and you have very inconsistent application (less TM hits every survey). A tornado is given an F-rating based upon the single most intense spot of damage along the path, yet in general most of the path will not contain max damage. The pic below was taken after the 5/22 Hallam, NE tornado which was rated F4 by OAX. There are no walls standing. There is some wood left on the foundation. This was not a slider as the home was more or less disintegrated. Note how the pole is left standing along with a tree with leaves still attached... keep in mind sub vorticies can cause highly localized damage. I'll call this F4. I heard an F3 from Gene.

Edit: While we have Tim and others doing detailed damage surveys these days, most tornadoes prior to F-scale inception were rated post-mortem by some student interns mostly based on newpaper photos and accounts. A photo like this, yet worse in black and white with lower resolution migh be all those folks had to go by to determine an F-rating. We are likely not in an F-rating drought, but rather, the older storms were simply overrated as significant damgage from tornadoes today get detailed surveys.

[Broken External Image]:http://snrs.unl.edu/amet898/turcotte/photos/damage22052004/damage16.JPG

Very hi res images:
http://snrs.unl.edu/amet898/turcotte/photo...tos/damage1.JPG

http://snrs.unl.edu/amet898/turcotte/photo...tos/damage2.JPG

 

[George Tincher]

If it was a well built home that was bolted down to a slab foundation, I'd likely give it an F4. While the damage is complete, the foundation isn't totally swept clean. Therefore it would not meet the definition of what an F5 is in my mind. Also, the fact that tree and telephone pole look relatively unscathed would weigh heavily on my mind.

If it was a well built home on a pier and beam foundation, I couldn't go higher than F3.

Of course I'd have to see more angles and be able to physically inspect the site to check every detail before I'd personally feel comfortable giving it any sort of rating.

At any rate, an interesting topic.

-George

 

[Thomas Loades]

It is possible that, in this case, something large — say, a farm vehicle — was lofted through the air and hit the house, damaging the structure and leaving it open to the wind, which may not have been in the F3–4 range, as evidenced by the still-green tree, but capable of demolishing the rest.

 

[Robert Dewey]

I would have to say F4 damage... Perhaps the tornado didn't move directly over the house either though (thus missing the tree)... I can see some indication of that by the way the debris is laying (the board stabbed into the ground), which would indicate the tornado was on the oposite side of the house as the tree...

Heres a site to help you out: http://www.spc.noaa.gov/faq/tornado/f-scale.html

With the current tornado picture in question, I definately wouldn't go lower than F4...

 

[Shane Adams]

We surveyed this entire damage track and rated it F4. We found evidence of F5, going by the Fujita scale damage level descriptions themselves. I was told the tornado was rated F3 because the tree wasn't debarked. I guess the completely-leveled home (including two walls removed from the basement) and vehicle thrown 275 yards weren't enough.

The car was obviously rolled and slammed with debris at some point, because it was unrecognizable as the classic 1969 Mustang it was when we found it. The ground between its final resting spot and its starting point was, for the first 50-75 yards, made up of hard ground (the property and the road that runs in front of it.) The rest of the path was a muddy wheat field. I walked the path four times through the field and couldn't find a single gouge or "bounce" mark anywhere, which suggests the car was bounced and pummeled with debris sometime during the initial impact of the tornado (hard ground and structures surrounding it). This also suggests the car was airborne for at least the length of the wheat field portion of its path (175 yards or more), making it by Fujita scale definitions an F5.

Another note of interest, a second vehicle had been tossed 70-80 yards from its starting point, but only had damage at the point of impact upon being dropped; the car was found nosed into the ground, with the rear end sticking up in the air. The only damage on the car was from this "drop" impact, which suggests the car had been airborne and was dropped nose-first into the ground (dropped is a subtle term, perhaps "slammed" better fits).

Furthermore, this tornado was very narrow, which makes it easy to imagine how it could affect both vehicles in the garage and completely miss the tree and powerpole; have we not seen numerous instances of one house being obliterated while its neighbor is untouched? This type of "hit or miss" damage is done by suction vortices within a main tornado circulation. The Mulvane tornado itself was a very narrow vorticy, so this damage isn't at all surprising.

Finally, I've learned that since the La Platte, MD tornado a few years back, they send a special survey team out to give the violent class tornado F-scale ratings. This team has to of course make a special trip to do the survey. There are some folks (myself included) who believe that since the Mulvane tornado affected only rural areas, and wasn't much of a "newsworthy" event as it would've been in a metro area/city, the NWS just slapped an F3 on it and called it a day, to avoid further headaches with an additional survey for a not-so-newsworthy tornado event.

Bluntly - there's no doubt in my mind the Mulvane tornado would've been F4 had it hit a major city. Bluntly again - I don't think we'll see the F5 rating anymore, as the growing number of engineers/mets who believe the F-scale is skewed will no longer acknowledge top-end windspeeds (per F-scale) exist, and will rate tornadoes with the F-scale using their own beliefs about windspeeds. I've read that some experts believe top-end tornadic windspeeds rarely top 200mph.

I see two new trends coming from all of this:
(1) F4 is the new F5
(2) Violent top-end tornadoes are far more common than we thought

 

[James McCormick]

The problem with the Hallam tornado is that the most impressive, significant damage happened at Norris High School. What that tornado did to that building was nothing short of amazing. However, you don't just completely level a new, brick high school.

I disagree that the F4 is the new F5, but I think in lieu of the May 3 1999 tornado, we do need to be very, very careful in issuing the F5 rating, because that type of tornado needs to be on its own pedestal in elite company. LaPlatta was quickly tagged an F5 by the media but a glance at the damage and what actually happened revealed that the tornado was not nearly of the Moore or Jarrell category. I've heard similar comments about the Mulvane tornado, but I can't really think of a tornado that had F5 qualities that has been shortchanged. Hallam was close, particularly by the high school, but looking at the OAX pictures from the survey, keeping in mind that they have one of the world's foremost experts on tornado damage as their WCM, it is understandable as to why the tornado got the F4 label. That said, OAX had another tornado in their CWA in 2003 that came very close to the F5 label but it occurred in a very rural area, so how do you know what actually happened in the tornado? I think it is smart to not put a tornado that you are uncertain about in the same breath as Moore or Jarrell. We will see the F5 rating again. We just need to see the right tornado in the wrong area. F4 ratings are fairly common, which to me means that a lot of surveyors are still getting out, looking at the damage, and not afraid to put a large rating on a tornado.

I think the question from Hallam is how do we rate tornadoes as buildings are built in a better, stronger fashion.

 

[Justin Turcotte]

(2) Violent top-end tornadoes are far more common than we thought

The subject of my thesis research. Some results found here...
http://snrs.unl.edu/amet898/turcotte/primary/climo.htm

Note how as population density increases in the Norman CWA, the number of reports increases (F0+) as well as the number of "significant" tornadoes on a logarithmic plot. This makes sense as population goes to infinity, every tornado will hit a structure and earn its due respect. The rate of change at infinity is zero which makes sense from a mathematical standpoint. Could be some reporting issues but it's hard to miss significant damage.

[Broken External Image]:http://snrs.unl.edu/amet898/turcotte/misc/cwaplots/Norman.jpg

 

[Kyle Masters]

The car was obviously rolled and slammed with debris at some point, because it was unrecognizable as the classic 1969 Mustang it was when we found it.

A 69 Mustang!?!?!? DESTROYED?!?!?!

I think i'm going to be sick... :x :cry:

 

[Howard Robinson]

I would rate the damage as a strong f3-f4.

 

[Scott Currens]

Based on the photo alone I would go with F2. The lack of base plates remaining attached to the foundation suggests to me that the home was not well anchored. If this is in fact the case, winds of 110-140 mph winds could cause the home to slide or rotate off its foundation as a unit then disintegrate into the adjacent field.

There are two other factors that lead me to believe that the home was not impacted by winds stronger than 150 mph. First, is the relative lack of damage to vegetation. Some of this can be explained by the small size of the Mulvane tornado. A point along the damage track would be in tornadic winds for only a few seconds as opposed to several minutes in a slow moving wedge tornado. This being said, the grass looks perfect and the tree is only minimally damaged.

Second, there is an A/C unit on the side of the house that looks like it just fell over in the winds. I would suspect that winds over 160 mph would have caused more damage to the unit if not removing it completely.

The car sized missiles I would rate F4. Without any other damage to vegetation, or structures that suggests F4 I don't thing I would rate the tornado an F5 based on the Mustang that was thrown 175 yards or more.

All of this brought to you by someone that didn’t survey the damage. LOL!

 

[David Drummond]

Scott, actually, many of the baseplates were still attached to the foundation. I took video of these, looking at how the nails were sticking up (not of the metal stress plates were used, only nails). There were also 3 walls from INSIDE the basement that were completely "sucked out" for lack of a better description.

SE of the house (and east of that tree) was a fairly large barn which had been constructed from cemented in posts and sheet metal that was COMPLETELY removed (which I believe is where much of the shiny sheet metal we all saw came from).

Seems the two cars are the most baffeling of all in this particular tornado. A note on the telephone pole, and I am not sure what difference this makes, is that is was a large diameter pole than you typically see for this type use, perhaps 25% larger? At the ground, you can see about a foot wide hole around the base of it where if one could imagine someone taking the top of the pole and just violently shaking it side to side.

In the wheat field across the road from the house where the cars were, the path was VERY visually evident and you could even see the wind patterns in the wheat field. I would have given anything to get an aerial picture of that! If I remember right, I stepped out the width of that at about 100 yards across that near where the mustang landed.

It's a very interesting case to study for a lot of reasons, and it seems with a little more observational data and eyes that have looked at it.

 

[Shane Adams]

Originally posted by David Drummond

If I remember right, I stepped out the width of that at about 100 yards across that near where the mustang landed.

Actually it was 86 yards, to be exact :wink:

 

[David Drummond]

Originally posted by Shane Adams+--><div class='quotetop'>QUOTE(Shane Adams)</div>

<!--QuoteBegin-David Drummond

If I remember right, I stepped out the width of that at about 100 yards across that near where the mustang landed.

Actually it was 86 yards, to be exact :wink:[/b]

Thanks Shane, it's been a while and much has happened since then. One of these days I want to go back to that survey I posted online and add more to it when I get time. We were able to compare some notes with Scott Blaire Saturday night after his presentation on it that afternoon and some interesting points came out between stuff they noted and things we noted.

 

[Jeff Snyder]

I think the examination of structural integrity of the structures damaged is very important for determining the damage rating... Heck, take a look at one of Tim Marshall's presentation about the La Plata tornado given at the NSWW03 at http://www.nssl.noaa.gov/nsww2003/talks/Ti...im_Marshall.htm ... It's very interesting, since he shows that some of the areas thought to be F5 damage (houses completely off their foundations, wiped clean) were actually more in the F2-F3, thanks to very poor fastening of the houses to their foundations ("sliders"). It's an interesting damage assessment.

 

[Glen Romine]

Justin, I think your premise that if this were a historical picture of an event that the tendency would have been to rate this as F4. However, with the benefit of the color and higher resolution images and the more prevelent knowledge of sub-standard housing construction - it looks more likely that this is only F3. It would be helpful to see the debris trail away from the house - but given the PVC pipe, ductwork, A/C unit, and chimney top so close to the home, large lumber pieces adjacent to the house, as well as still green leaves and grass, seems rather unlikely that the winds were in the F4 range here. Why the entire house failed is unknown - but I'd be supicious of the house construction.

Glen