Where have all the violent tornadoes gone?

[Shane Adams]

Violent tornadoes haven't gone anywhere. The ratings have.

 

[Josh Morgerman]

Violent tornadoes haven't gone anywhere. The ratings have.
[/b]

If that is the case-- and the ratings standards are, indeed, changing-- I imagine that is going to make comparisons of contemporary and historic events difficult-- unless the historic events are reanalyzed according to the contemporary standards.

 

[Robert Dewey]

Violent tornadoes haven't gone anywhere. The ratings have.
[/b]

Exactly.

It's hard for me to believe some of those tornadoes were only rated F3, when we had an F3 here in MI back in 1997 that did half the damage. The tornado intensity hasn't decreased at all, it's the rediculously strict rating methods that are now being put in place. I am willing to bet that we won't see an F5 in at least the next several years ... if at all. It just seems like there's always something to blame (i.e. it was a slider, there was wind tunneling, it was being pelted by debris, the tornado was moving too slow, etc.).

 

[Jeff Snyder]

It's interesting you say that, because I was just reading Tim Marshall's analysis of the La Plata, MD, tornado (2002), which had been initially over-rated as an F5.

In the report, he makes exactly your point-- that all of the clues matter, not just the house itself. They found examples of homes completely blown off their foundations with 1) roofs still intact, 2) mailboxes still standing, and 3) vegetation on the lawns mostly unscathed. Such observations led them to conclude that the construction was largely responsible for some of these failures, and that some of these homes actually slid off their foundations from winds as low as 100 mph!

The report is very interesting: http://ams.confex.com/ams/pdfpapers/53280.pdf [/b]

Tim Marshall did a presentation on the La Plata tornado at the NSWW'03, which can be viewed online at http://www.nssl.noaa.gov/nsww2003/talks/Tim_Marshall.htm

I've seen another one of his presentations online, which noted that some of the houses in Moore OK on 5-3-99 were "completely destroyed" with winds of only ~140-160mph. If the house is gone, but the mailbox is standing and trees in the front yard are still there, that gives you a clue.

 

[Josh Morgerman]

The tornado intensity hasn't decreased at all, it's the rediculously strict rating methods that are now being put in place. I am willing to bet that we won't see an F5 in at least the next several years ... if at all. It just seems like there's always something to blame (i.e. it was a slider, there was wind tunneling, it was being pelted by debris, the tornado was moving too slow, etc.).
[/b]

See my post above. I feel the exact same thing has been occurring with hurricane landfall intensities-- they seem to be getting more strict with the higher ratings.

Tim Marshall did a presentation on the La Plata tornado at the NSWW'03, which can be viewed online at http://www.nssl.noaa.gov/nsww2003/talks/Tim_Marshall.htm

I've seen another one of his presentations online, which noted that some of the houses in Moore OK on 5-3-99 were "completely destroyed" with winds of only ~140-160mph. If the house is gone, but the mailbox is standing and trees in the front yard are still there, that gives you a clue.
[/b]

Hey Jeff, thanks for sharing that-- it's a cool presentation. Have they concluded that the Moore event was overestimated as well?

 

[Gabe Garfield]

I guess the real question is, how rare are (truly) violent tornadoes?

Personally, I like the practice of being more skeptical about F4/F5 ratings, because it distinguishes the fairly strong tornadoes from the doozies that wipe out everything within a 5 house radius.

Gabe

 

[Joe Nield]

I'm not saying the Gallatin tornado will not end up being rated F4 or F5 (no way I can know that from here), but I'd strongly caution against using pictures of homes to make broad distant judgments on the wind speeds and F-scale damage of a tornado. There are many damage indicators to look at, such as ground marks/scouring, trees and vegetation, utility poles, fences, surrounding structures and so on. For myself, I will let the experts who have done considerable training on wind damage assessment AND have taken the time to take considerable notes from the actual scene assign the ratings...instead of second guessing them with only small pieces of the puzzle from hundreds of miles away.
[/b]

You and Josh are both correct. A good example of this was one of the F3 tornadoes in Indiana on 11/15/05. I rated the tornado that moved through Shelby County that afternoon, and the worst damage along that path was a great example of exactly what you cite. The home had been swept off the foundation. However, the foundation itself was little more than stacked stones, and no evidence of any significant attachment to the foundation could be found on the walls. Indeed, homes on such foundations are rarely attached to the foundation in any appreciable manner, and as such, are capable of being moved off their foundations by winds of less than 100 mph.

In concert with this, we also found several examples of unharmed vegetation, and a large and strong tree near the remaining front porch which had lost only the top third of the tree. The trunk remained standing tall.

I know some seem to have a chip on their shoulder about this subject, but which is better...continuing to overrate tornadoes, which has likely occurred a great deal in the past, or learning more and rating them as accurately as possible based on everything we know? I know which one is more scientifically responsible.

 

[Rick Smith]

The only changes to the rating system have been the addition of the Quick Response Team, which WFO's much use if they suspect that a tornado caused F4 or F5 damage. The criteria has not changed, the F-Scale has not changed (yet) and the tools meteorologists and engineers use to rate damage has not changed.

From what I can tell looking at PNS's from OHX, they are not done with the Gallatin classification. As Kevin mentioned, it is not always possible to make an accurate determination of the tornado damage rating by looking at images and video. And we should also remember that F4 and F5 tornadoes are still very rare.

Rick

 

[Justin Turcotte]

Are we attempting to rate the estimated wind speed or are we attempting to rate the damage? Fujita's scale used damage (primarily to homes) to estimate wind speeds and the inherent F-rating. Fujita and just about everyone else realized those wind speeds were far too high given changing constuction styles and engineering studies. Despite this, tornadoes have been generally rated according to the "damage" scale rather than the original "wind" scale. Tornadoes in the 1970s were generally overrated based on today's surveys. A plot of F2 tornadoes reveals of decreasing trend after that decade. Most tornadoes prior to 1976 were rated post mortem via newspaper clippings. Now just about all suspected F3+ damage brings in the expert survey crew looking at supports, nails, beams, vegetation, etc. Comparing today's tornado intensities (or should I say survey results) to those in the 1970's should yield inconsitent results. While not quite apples to oranges, perhaps green apples to red apples. The damage is similar but it is now looked upon in a different way. I don't think the violent tornadoes have gone anywhere... they have simply been downgraded based on differing perspectives and new information.

I still think that TN tornado is an F4. It had the classic core of hellish winds that leveled homes with gradually less damage away from the center. I don't care what the wind speed was as the damage is indicative of F4 on the old rating system. It is just not practical to measure every tornado's wind speed directly which is why we have the damage scale in the first place

Some folks here are noting mail boxes and vegetaion with various tornadoes. You can look at a point source of damage thinking you are getting the big picture and still miss the big picture. I have seen F3 and F4 surveyed damage where a mailbox still stands. This may be due to the box or shrub being low to the ground or missed by a subvortex

 

[Tony Lyza]

Are we attempting to rate the estimated wind speed or are we attempting to rate the damage? Fujita's scale used damage (primarily to homes) to estimate wind speeds and the inherent F-rating. Fujita and just about everyone else realized those wind speeds were far too high given changing constuction styles and engineering studies. Despite this, tornadoes have been generally rated according to the "damage" scale rather than the original "wind" scale. Tornadoes in the 1970s were generally overrated based on today's surveys. A plot of F2 tornadoes reveals of decreasing trend after that decade. Most tornadoes prior to 1976 were rated post mortem via newspaper clippings. Now just about all suspected F3+ damage brings in the expert survey crew looking at supports, nails, beams, vegetation, etc. Comparing today's tornado intensities (or should I say survey results) to those in the 1970's should yield inconsitent results. While not quite apples to oranges, perhaps green apples to red apples. The damage is similar but it is now looked upon in a different way. I don't think the violent tornadoes have gone anywhere... they have simply been downgraded based on differing perspectives and new information.

I still think that TN tornado is an F4. It had the classic core of hellish winds that leveled homes with gradually less damage away from the center. I don't care what the wind speed was as the damage is indicative of F4 on the old rating system. It is just not practical to measure every tornado's wind speed directly which is why we have the damage scale in the first place

Some folks here are noting mail boxes and vegetaion with various tornadoes. You can look at a point source of damage thinking you are getting the big picture and still miss the big picture. I have seen F3 and F4 surveyed damage where a mailbox still stands. This may be due to the box or shrub being low to the ground or missed by a subvortex
[/b]

Not to open a can of giant worms, but weren't there at least one or two mailboxes left from the Jarrell tornado?

 

[Tony Lyza]

The original intent of the Fujita Scale was to rate damage. Period. The wind speeds provided should at no point play any factor in the rating of the tornado. Should the speeds be adjusted? Well, if one were to use the Fujita Scale the way it was intended, no, they shouldn't. However, since we live in a number and statistics-oriented age, that makes people want to have accurate numbers. I think that this whole debate is not best solved by recalibrating the winds on the scale but by just getting rid of the wind speeds altogether. If a house is swept away, according to the description provided by Fujita (many of which really seem to be ignored), that house should be at least F4 no matter the construction and F5 if well-built. As best stated in TVC II, the Fujita Scale should not try to rate the strength of a tornado. It is meant to rate the potential threat to human life. If the houses are poorly constructed, the risk to life will be higher, and the rating should mostly reflect that fact.

I have the whole set of TP posters, and I went back and looked at Fujita's examples of each level of tornado damage. What I discovered saddened and frustrated me. Today, the F4 example would probably be rated F3, and the F5 example would probably be rated high-F3/low-F4. That is pathetic. The CREATOR OF THE SCALE would be "wrong" in his ratings today. I think that says something about how poor the rating of tornadoes has really become.

 

[Scott Olson]

I can cofirm from a conversation with St. Louis NWS today that the Monroe County F4 was done by an in-house member of the QRT (or at least a wind damage expert). I would have liked to see a QRT on the Gallatin and Carthursburg tornadoes as some of the damage did appear to at least possibly be F4, but in the end the surveyors on the field have the most avaliable information to make an informed decision. Im looking forward to the introduction of the EF-SCALE and less reliance on people who aren't structural enginers making structural decisions.

 

[Dan Robinson]

I'm wondering by the new standards if true F5 damage, by the new higher-scrutiny surveying, is even possible or has ever really occured in the past. Is it even possible for a tornado to sweep a house clean if it is securely fastened, wasn't being pummeled by debris, was only in the vortex for a short time, was well-built and braced, etc.? Has that ever actually happened? I'd think we would have no F5s in the books if they were all re-evaluated today.

 

[J.B. Dixon]

Question: In my limited glances at the new EF-Scale, the highest rating possible from looking at the most extensive home construction damage will be F3, correct? By that alone, and just as a test case, if one were to look at the damage photos again, the La Plata rating would be argued as being what.....F1, maybe F2?

 

[Rick Smith]

Beginning next February, when the new EF-Scale is implemented, it won't matter if a house is swept from its foundation - if there are no changes to the damage indicators between now and then, the highest rating you can get with homes is F4.