Where have all the violent tornadoes gone?

[Alex Lamers]

I have noticed that there have been no violent tornadoes (i.e. F4/F5) this year (correct me if I'm wrong) and if there were it must have only been one or two. Despite all these recent "outbreaks" it would seem that none have produced any violent tornadoes.

Thoughts?

 

[Jeff Snyder]

I think we would have seen more (or at least one) yesterday (and other days) had we be able to get 64-67+F dewpoints into the main risk area. Looking at surface observations, Tds yesterday were largely in the 59-62F range, though there were occassional 63-64F obs (there were some 66-68F Td obs, but those were in outflow, where we tend to expect cooler, more moist conditions).

Personally, by afternoon, I don't think I've seen a setup this year that really looked like it would support a supercell with F4-F5 tornadoes (don't get me wrong, I'm not surprised by the plethora of F3 tornadoes we've had, since the low-level shear present on several of the synoptically-evident events was quite intense). 3/12 was close I suppose, as was 4/2... I think being on the low end of true deep, Gulf moisture has been a prohibiting factor thus far. Of course, everything tends to tie into everything else... In the Plains, storms have been fighting the strong shear in rather marginal CAPE and dewpoint environments (sometime yielding relatively high LCLs). Yesterday looked pretty good, but I wonder what the CAPE really was in northern MS, northern AL, and southern TN. We just need to wait until we get widespread >64f dewpoints in the warm sector and widespread >2500 j/kg CAPE, IMO... Yes, there have been violent tornadoes in lesser thermodynamic conditions (i.e. per this paper, the 4-16-98 TN F5 was in an environment of ~1600 j/kg CAPE), but it seems that the "big gun" days (e.g. 5/4/03, 5/3/99, 6/24/03, 7/13/04, etc) have >2000-2500j/kg mlCAPE.

Of course, maybe it's just chance... Perhaps the times when a tornado had winds capable of creating F4 or F5 damage occurred when the tornado was away from any structures (i.e. in a field or forest). Or, perhaps storm-scale processes that we can't really analyze or observe prevented violent tornadoes. Add in the recent 'discoveries' / realizations that >210mph winds are not always required to destroy a house (e.g. Marshall's work on the La Plata tornado showed that ill-anchored houses that were initially marked as F5 damage were actually the result of an F2-F3-level tornado), and you see a decrease in the number of violent tornadoes.

EDIT: Note that damage assesssments from yesterday's tornadoes are just beginning, so there may learn that there was a violent tornado yesterday.

 

[Andy Wehrle]

Alex, there have been two F4 tornadoes in 2005 and 2006 thus far, in Hopkins County, KY on 11/15/05, and Monroe County, Missouri on 3/12/06. I agree survey teams seem to have tightened up on the ratings recently. I don't see what was so much more destructive about those tornadoes compared to, say, Stoughton, Evansville or Caruthersville.

The problem with this IMO is that rating so many tornadoes at F3 implies that they were ALL of equal strength and impact, which is obviously not true but a person reads the record books and that's all they see is the one rating. Hopefully the EF-scale will help clear some of this up but in the meantime we have to make do with the original scale.

 

[Justin Turcotte]

Some images just north of Nashville definately support an F4 rating for that tornado. There were some larger homes that were completely leveled (no walls standing). If that tornado only gets a "strong" F3 than I have lost all faith in the ratings system.

 

[Jeff Snyder]

Some images just north of Nashville definately support an F4 rating for that tornado. There were some larger homes that were completely leveled (no walls standing). If that tornado only gets a "strong" F3 than I have lost all faith in the ratings system. [/b]

Well, the final assessment from the tornado near Gallatin isn't in yet, but the very prelim report noted F3 damage. In addition, there was damage near Goodlettsville that was either the same tornado that hit Gallatin or was an earlier tornado (the PNS makes it sound like it was the same tornado, with the use of "the tornado continued on", although they do say the track was 1.1 miles long, much shorter than the distance to Gallatin)...

THE FINAL TORNADO THAT HIT DAVIDSON COUNTY IN GOODLETTSVILLE WAS RATED AS AN F3 (158-206 MPH). THE TORNADO STRUCK AT 2:10 PM CDT AND HAD A PATH LENGTH OF 1.1 MILES AND A PATH WIDTH OF ABOUT 1/2 MILE. A CHURCH LOST THE ENTIRE FRONT SECTION...EXPOSING BENT STEEL BEAMS. A RESIDENTIAL HOME IN GOODLETTSVILLE ON BELL STREET WAS COMPLETELY BLOWN OFF ITS FOUNDATION AND DEMOLISHED. NUMEROUS HOMES HAD ROOF DAMAGE.[/b]

--> Damage Assessment

So, the house must have been a 'slider'. There's another report that sounds F4, but was given F3:
<div class='quotetop'>QUOTE("OHX NWSFO")</div>

THE TORNADO IN DICKSON COUNTY TOUCHED DOWN ON MAPLE VALLEY ROAD IN
NORTHERN DICKSON COUNTY AS AN F2 TORNADO (113-157 MPH) AT 1:30 PM
CDT. THREE MOBILE HOMES WERE LEVELED AND DEMOLISHED. NUMEROUS TREES
WERE UPROOTED AND SNAPPED. THE TORNADO PRESUMABLY CARRIED A TRUCK
UPON A UTILITY POLE, WHERE IT LEFT A WINDOW GASKET ON TOP OF THE
POLE. THE TORNADO CONTINUED ALONG HIGHWAY 49 AND REACHED BELLSBURG
AT AS AN F3 (158-206 MPH). A ONE STORY BRICK HOME WAS DEMOLISHED.
THERE WERE NO WALLS OR ROOF LEFT STANDING...LEAVING ONLY A HALF
BASEMENT AND GARAGE. A TRUCK WAS THROWN INTO THE BASEMENT BY THE
TORNADO. THE DRYWALL...FURNITURE...AND APPLIANCES WERE HURLED INTO
THE WOODS AT LEAST 100 YARDS. THE TORNADO ENDED AT THIS LOCATION.[/b]

--> Damage Assessment

 

[Perry Williams]

Some images just north of Nashville definately support an F4 rating for that tornado. There were some larger homes that were completely leveled (no walls standing). If that tornado only gets a "strong" F3 than I have lost all faith in the ratings system.
[/b]

I feel exactly the same as you....clearly the damage to well built brick homes in Gallatin meet F4 criteria. I've seen the same type of destruction to large, well constructed brick homes before; near Kennesaw GA (11/22/92), Brandon MS (11/21/92), Rydal, GA (3/27/94), and NW of Madison, MS (11/24/01).....all of which were rated as F4.

 

[George Tincher]

Justin, I find myself feeling similarly. It just seems that something has changed recently and that the same standards used to rate tornadoes 5 years ago is different than today. I realize the EF Scale revisions on wind speeds will change beginning next year. But even with reduced wind speeds, the amount of damage needed to reach a certain F-level will still be similar. Only the estimated wind speed needed to do that damage has changed. Besides, this is still 2006. The new guidelines are yet to take effect, so we should be rating them the same way we did in say, 1997 or 1998.

I dunno what to make of it. But it seems somewhere, something is up.

Can anyone here tell me what sort of process the local offices must go through to rate F4/F5's these days? I understand that if they suspect anything higher than F3 damage, they have to bring in the team of experts to do further investigation. Does doing this somehow create a big hassle for the local offices? Just curious. If it does, perhaps this may have something to do with it. I could see some of those guys saying "you know, I think this is a minimal F4....but since calling in the special team is going to create a headache for us, let's just call it an upper end F3 and be done with it." I mean these folks are only human and if the new process that came along in 2002 did create a bunch of new hassles for the local offices, I could understand how they might at times "hold back" just a bit. Again, I have no proof whatsoever that such a scenario has actually been playing out. But it is just one theory that crossed my mind. And I have noticed some of the surveys have keyed in on certain aspects of the damage. One of yesterday's tornado surveys in TN I read stressed at one point a particularly interesting piece of damage....where a well constructed home had been leveled and perhaps cleaned of the foundation. Then there was another hint dropped that the preliminary rating was currently strong F3...but that further evaluation was taking place. Basically, the same was said of the April 2 tornado in Marmaduke, AR.

This just all makes we wonder. I don't mean to suggest that there is some sort of vast conspiracy within the NWS to limit the number of tornadoes recorded as violent. That would make no sense whatsoever. But I do wonder if something else is either directly or indirectly having an effect on how some of these tornadoes are rated. I don't think it's just coincidence that we haven't seen an F5 since 1999 and that over the past 5 years, there appears to be a downturn in the number of tornadoes rated F4 as well. IMHO, I don't feel that this is all a result of the weather. As many huge outbreaks of very damaging tornadoes that we have seen in 2002, 2003, 2005 and so far in 2006, it's hard to convince me that not a single F5 was among them, especially considering we seemed to average about 1 per year in the previous decade. Something here just doesn't seem right, but what I don't know. But I will say something has changed. If there has been a change, then that calls into question all the previous ratings assigned over the previous 30 years. It also causes me to have some doubts about the credibility of the F-Scale ratings as a whole. I just want to see some consistency. And if a tornado today does the same damage that an F4/F5 tornado did in the 90's, then it should be given the same rating. Otherwise, they are all meaningless.

Just my opinion.

 

[Dan Robinson]

I just returned from the Nashville area after chasing southern Tennessee and northern Alabama Friday. I've got a lot of video and photos to go through but I'll post a quick comment. Lisa Wadlow and I saw the Gallatin-Goodlettsville damage path first hand and witnessed damage that easily qualifies for an F4 rating. Well-built houses in nice neighborhoods leveled in Gallatin, some of brick construction. In Goodlettsville, we found a large metal dumpster deposited at least 1/4 mile away from the damage path in the driveway of a nearby house. In Gallatin we saw a car thrown into a driveway of house just outside the damage path. There were gouge marks in the pavement on the street and in the yard where the car impacted as it was tossed/rolled at least 200 feet (we couldn't find evidence of where the car was initially). I'll post a few pictures soon.

 

[George Tincher]

Dan, if that is the case, then perhaps that particular tornado will end up being rated F4 afterall. They are still working on that one and have yet to make a final determination. All of the other intense tornado paths have already been rated. The fact that this is the only remaining intense tornado track (in the Gallatin area) to not be rated, makes me think they might be debating F3 vs F4.

But, if you say it's F4 (with as many storm paths as you've seen), then it's an F4. That damage you describe certainly sounds like lower end F4 to me.

 

[Josh Morgerman]

This is a very interesting thread to read. I am a hurricane chaser-- my interest in severe local weather is more casual-- but tropical weather watchers are having these exact same discussions Re: recent trends in the intensity ratings of landfalling hurricanes.

The National Hurricane Center over the last few years seems to have gotten more stringent with its rating requirements. For example, Katrina's final rating for its LA landfall was lowered to Cat 3 (despite its extremely low 920-mb landfall pressure) because the wind data just didn't support Cat 4. Similarly, Rita was barely rated a Cat 3 for its TX/LA landfall despite a very low central pressure of 937 mb and the complete destruction of several SW LA communities. It seems the NHC is making an extra effort to really qualify each rating. As can be expected, these downward adjustments in the ratings of these big "headline storms" have proven very controversial with online bloggers.

The question that arises: if the NHC is using newer, stricter methodology for rating the intensities of modern landfalling hurricanes, how do we compare these modern hurricanes to big historic ones that may have been overestimated? The NHC is currently doing a reanalysis of all USA hurricane landfalls dating back to 1851. It is widely expected that the estimated intensities of some big, historic storms may be adjusted downward based on the new knowledge and methodologies. The benefit to this will be a consistent standard-- and cleaner comparisons between modern and historic events.

Getting back to twisters… If they have, indeed, changed their criteria for rating contemporary tornadoes, I am wondering if they need to do a similar reanalysis of historic tornadoes. Otherwise, there will be no way to meaningfully compare modern and historic events-- no common yardstick, no gold standards.

 

[Tony Lyza]

If you notice the survey of the Gallatin tornado, it says that the rating is very preliminary and subject to change. I think Greg Stumpf might know if the expert survey team (forgive me, I can't recall the actual name of it) was deployed to that area.

Two things I will say about the Gallatin tornado:
1. Huge $300,000+ homes being pancaked in most often at least F4 damage (and looks to be in this case), and
2. From the video I've seen of the tornado, it was one of those classic violent tornado structures, with a pretty narrow funnel comprised of tiny but powerful multiple vorticies, such as the West Lafayette F4 tornado of 3/20/76, the Saylor Park tornado (F5) of 4/3/74, and the Granite Falls, MN, tornado (F4) in July 2000.

 

[Justin Turcotte]

Simple: Compare the Tennessee damage to the rated F4 damage in La Plata, MD. No question that the Tennessee twister did more damage. Those were $500,000 homes that were piles of debris. Not talking about a ranch house that slid into a small ravine.

 

[Kevin Scharfenberg]

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.

 

[Josh Morgerman]

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]

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

 

[Kevin Scharfenberg]

Yep, that's what I was thinking of, Josh. Local building codes and practices have a lot more to do with the structural soundness of a home than the price tag. I know there are some $500K+homes built today with all sorts of safety corners cut that might make them disintegrate in an F3 tornado, while a 1960 home worth $75K today with hurricane straps and strong roof<->walls<->foundation anchoring might withstand the same tornado. I'm sure all that will be factored into the final F scale rating, along with the other nearby damage indicators. To address the broader point, a lot of these things were learned and documented in the Moore and La Plata damage surveys, so I think we're seeing a lot more (healthy) skepticism about the initial tendency to automatically rate high on tornadoes that blow away homes.