I need some help with tornado rating

[Marko Korosec]

Hello all,

It has been a great season in the US also for us during May and now severe weather is also occuring across Europe. Its incredible how much damage has been made across north Italy and Slovenia in the last two weeks from tornadoes, giant hail and downburst.

On July 13th, severe weather was expected in the south Alpine region with issued level 3 (high risk) over Slovenia. You can see detailed outlook from that day made by ESTOFEX here: http://estofex.org/cgi-bin/polygon/...e=2008071406_200807130812_3_stormforecast.xml

A strong supercell developed in north-central Slovenia, a lot of microburst and straight line winds damage was reported, while in a small village at elevation of about 700m and hilly terrain there was a suspicious damage, so we looked at it more into details. It became obvious, that a strong tornado occured there with badly damaged houses. I am now posting some images from several people, including myself being there yesterday, so hopefully a lot of you with much more experiences with tornado damage could give me some opinions regarding the power of this tornado.

Severe damage on this house... roof and upper level floor-garret completely removed!

This image shows "projectiles" of debris stucked into the ground...lot of debris all around.

Very good sign of tornado also deplumed trees...

Another badly damaged building...

The same view over the house on those images above (3, 4, 5) with major damage into the forest behind...

Here you can see more damage images from this tornado and from microbursts in wider are there (its Slovenian language, but images are international):
http://forum.zevs.si/index.php?topic=1337.0
http://forum.zevs.si/index.php?topic=1339.0

As seen from the damage, there could be two tornadoes over that village, as damage was easily recognized in two paths, maybe multi-vortex tornado or something, but I am looking for some more opinion regarding its rating.

Thank you very much!

Marko

 

[Jason Boggs]

Marko, I'm no expert on tornado ratings, but it looks like a solid EF2 from the photos here. That last photo with the snapped trees is just crazy! I'm sure others will chime in that has more experience in rating these than me.

 

[Steve Miller TX]

In the pictures you posted, I would estimate generally EF0 with the more extreme damage being EF1. I had to go back and refresh myself on the EF scale damage thresholds based on the tree and building damage scales. EF1 would correlate to 3-second gust of 86-110mph (138-177km/hr).

Check it out Marko and see what you think.
http://www.wind.ttu.edu/EFScale.pdf

This must have been a very scary experience for those living in those structures. I hope there were no injuries?

Thanks for sharing these images. It's always interesting to see that supercells and tornadoes know no international boundaries.

 

[Angie Norris]

I think I'd put it as a high end EF-1, based on roof damage and how most of the trees are snapped off. It's interesting that even with the total loss of the roof from that one house that all the walls are still up...that shows the strength of masonry construction. It's also cool in the first pic that you can follow the path of the tornado down the ridge into the valley...so much for "tornadoes don't form in hilly or mountainous (I know...not spelled right) regions". Something else interesting...in pic # 8...the low clouds in the damage path. I've seen that before, especially after the Mossy Grove tornado in 2002.
Cool pics, Marko...thanks for sharing!!

 

[Andrea Griffa]

I think I'd put it as a high end EF-1, based on roof damage and how most of the trees are snapped off. It's interesting that even with the total loss of the roof from that one house that all the walls are still up...that shows the strength of masonry construction. It's also cool in the first pic that you can follow the path of the tornado down the ridge into the valley...so much for "tornadoes don't form in hilly or mountainous (I know...not spelled right) regions". Something else interesting...in pic # 8...the low clouds in the damage path. I've seen that before, especially after the Mossy Grove tornado in 2002.
Cool pics, Marko...thanks for sharing!!

Taking apart that trees considerations, I don't agree with EF1 rating just because in some houses you see that a large section of the roof structure is completely gone and this gives you a mean speed of the wind of 122 mph that is sufficiente for EF2 rating, according to the FR12 damage indicator.
As regards the snapped pines this could give you a mean wind of 110mph on the border with EF1 rating.
I should give it a global EF2 rating.

 

[Dennis Sherrod]

Taking apart that trees considerations, I don't agree with EF1 rating just because in some houses you see that a large section of the roof structure is completely gone and this gives you a mean speed of the wind of 122 mph that is sufficiente for EF2 rating, according to the FR12 damage indicator.
As regards the snapped pines this could give you a mean wind of 110mph on the border with EF1 rating.
I should give it a global EF2 rating.

One thing I noticed on the houses and structures that had more substantial roof damage was that the roof construction did not appear to be made with wood roof sheathing. It looks more along the lines that many of the older style Euopean houses have of roof joists with shingle overlay and no substantial wood underlayment. Yet, on some of the surrounding houses the roof appears to more intact and appears to have the underlayment sheathing seen on at least one. Then on some with plank board underlayment versus 4x8 sheathing, the entire roof structure appears to have lifted fairly intact.
Someone with more experience in damage assessment can say how much this does come into consideration as to design and construction differences in regard to the roofs.

 

[Andrea Griffa]

One thing I noticed on the houses and structures that had more substantial roof damage was that the roof construction did not appear to be made with wood roof sheathing. It looks more along the lines that many of the older style Euopean houses have of roof joists with shingle overlay and no substantial wood underlayment. Yet, on some of the surrounding houses the roof appears to more intact and appears to have the underlayment sheathing seen on at least one. Then on some with plank board underlayment versus 4x8 sheathing, the entire roof structure appears to have lifted fairly intact.
Someone with more experience in damage assessment can say how much this does come into consideration as to design and construction differences in regard to the roofs.

Yes Dennis, that could be in one house I saw in one of the Marko's pics, but not in this one: this is a well built roof structure with roof sheating. I considered a FR12 damage indicatore but I'm convinced that this structure is even stronger.

 

[Dennis Sherrod]

Yes Dennis, that could be in one house I saw in one of the Marko's pics, but not in this one: this is a well built roof structure with roof sheating. I considered a FR12 damage indicatore but I'm convinced that this structure is even stronger.

I did wonder about the roof construction of this one house as it did look to be a newer style.

 

[Jim Saueressig]

EF2 "if a tornado" but based on what I see it mostly looks like one directional damage... Are we sure it was a tornado? Even the trees seem to be of a uniform snap off and direction which makes me think a down burst wind of sorts.

Just my opinion.

Edit: The more I look the more I only see a microburst damage pattern. The trees are snapped off in one direction and not shredded or mangled enough for a tornado.... Again I am not there but.....

Its just too clean, there is no real sign of rotational debris damage on the buildings. The sides and such are clean of such damage.

 

[Marko Korosec]

Thanks al for your comments!

Well, as ragarding the buildings and roofs, they're much more powerful than those in US, especially in my part of Slovenia we have massive concrete walls and also roof is concrete (because of "3rd wind zone" as we have 10-20 days per year of strong Bora winds exceeding 80-100mph), while in those area they are made with wood and tiles/shindles atop. You can also see wooden beams on those houses on the photos. This is newer style, indeed.

At first, I was also less optimistic with rating it more than strong EF1, especially as for example that balcony looks like not being touched while roof seems to be blown off so easily. It might show how weak it was. But if you see those images, where even walls were collapsing, its rather weak estimation. Might be because roof smashed into them, its hard to say as they dont have concrete roofs in that region and they could be too easily blown off. But as Andrea Griffa said already, from that table it looks like at least "line 6" (large section of roof structure removed, most wall remain standing)...but again, there was complete roof and also top floor removed on the 4th photo... which makes me doubtful on the other side.

Those trees in the last image are "only" downburst damage, as only small 30-50m paths inside this large area had this tornado damage signs. Areas with downburst damage were several hundreds wide.

 

[Marko Korosec]

EF2 "if a tornado" but based on what I see it mostly looks like one directional damage... Are we sure it was a tornado? Even the trees seem to be of a uniform snap off and direction which makes me think a down burst wind of sorts.

Just my opinion.

Edit: The more I look the more I only see a microburst damage pattern. The trees are snapped off in one direction and not shredded or mangled enough for a tornado.... Again I am not there but.....

Its just too clean, there is no real sign of rotational debris damage on the buildings. The sides and such are clean of such damage.

How can you explain debris all around, deplumed trees in the path (they should have been uprooted or snapped as many others further up), things stacked into the ground? Also, trees were down in backward direction at some places.

 

[beaudodson]

I would lean EF2 "wind speed/wind damage" (whether tornado or not) based on the photographs.

 

[Jim Saueressig]

How can you explain debris all around, deplumed trees in the path (they should have been uprooted or snapped as many others further up), things stacked into the ground? Also, trees were down in backward direction at some places.

Again I am looking at pictures as opposed to actually being there but I see little debris in the opposite direction, I see a lot of tree damage which is more consistent with a down burst and for the most part the debris is all on one side and I am not really seeing the usual debris damage to everything. things here looked pushed over, not all wrapped up.

I am not saying it wasn't a tornado, I am saying I am not seeing enough to convince me it was a tornado in the pictures and that is why I asked if they were sure it was one.

 

[Andy Elliott]

I am going to have to go with a low-end EF2.

 

[Steve Miller TX]

Well, as ragarding the buildings and roofs, they're much more powerful than those in US, especially in my part of Slovenia we have massive concrete walls and also roof is concrete (because of "3rd wind zone" as we have 10-20 days per year of strong Bora winds exceeding 80-100mph

With that kind of information, I'll bump my estimate to EF2 as well. Construction quality is everything.