Another tornado or downburst damage case

[Marko Korosec]

Hi all,

probably you remember the other topic I opened several days ago about wind damage: http://www.stormtrack.org/forum/index.php?showtopic=11789

Few days after that we got news that there was another extreme event on that day, but much bigger than the one mentioned. It happened on June 29th, 2006 at around 14:30 UTC (16:30 local time).

A friend of mine was there few days ago and took these incredible pics of devastation (images are copyrighted to Jaka Ortar, Slovenia):

http://www3.shrani.si/files/tnimg644712880.jpg

http://www3.shrani.si/files/tnimg648712897.jpg

http://www3.shrani.si/files/tnimg619712848.jpg

http://www3.shrani.si/files/tnimg649712901.jpg

http://www3.shrani.si/files/tnimg650712905.jpg

http://www3.shrani.si/files/tnimg651712909.jpg

Radar image at the time of event:
http://www3.shrani.si/o.php?newimgpr714175.gif

June 29th 12z sounding diagram for Udine, Italy about 50km west-southwest of event location:
http://img72.imageshack.us/my.php?image=udine29jun12z8hs.png

Here is a link to European Storm Forecast Experiment (ESTOFEX) forecast for that day: http://estofex.org/cgi-bin/polygon/showfor...ormforecast.xml

What do you think, guys and girls? Thanks for help!

Regards,
Marko

 

[David Wolfson]

Wow! That was quite a microburst!

 

[Mike Smith]

Clearly a downburst per the orientation of the fallen trees.

 

[joel ewing]

First off, thanks so much Marko for taking the time and effort to show us StormTrackers this incredible event. It's fascinating, to say the least!
Like seemingly everybody else who had offered their opinions on this...I'll say that I'm no expert either. That being said.....I'm inclined to agree with those that believe that this was the result of straight-line winds. BUT....in the 3rd. photo from the top...I definitely see trees laying in opposite directions. In the front of the picture, the trees are laying one way. But toward the rear of the photo, you can see trees laying just the opposite. What kind of straight line winds do that??
I also believe I noticed evidence of rotating wind damage in some of the other photos you posted...perhaps the ones from the first event you showed us. In particular, I remember a photo or two illustrating damaged corn. This looks like many of the post-tornadic corn damage that I've seen during my chasing years.
If I had to make a very un-educated guess on this...I'd say the majority of damage was from extreme downburst winds...with the possibility of brief peripheral tornadic activity too.

 

[Chris Vagasky]

Like seemingly everybody else who had offered their opinions on this...I'll say that I'm no expert either. That being said.....I'm inclined to agree with those that believe that this was the result of straight-line winds. BUT....in the 3rd. photo from the top...I definitely see trees laying in opposite directions. In the front of the picture, the trees are laying one way. But toward the rear of the photo, you can see trees laying just the opposite. What kind of straight line winds do that??
[/b]

When a downburst hits the ground, it spreads out in all directions. It doesn't travel solely in one direction.

Think of turning the hose on and pointing it towards the ground. The water hits the ground and splashes in all directions.

 

[Joe Guerra]

Right, here's a diagram I found from www.weatherquestions.com.

Like Chris said, when the winds reach the ground it pans out in all directions, so trees would not all be knocked down the same way.

 

[Laura Duchesne]

If a tornado was fast moving, lets say, would it cause the debris to go kinda in the same direction instead of the classic swirl look associated with large slow moving tornadoes?

That does look like a straight line wind or microburst event though. That is quite a lot of trees. They seemed to be "plowed over" instead of twisted and snapped off.

 

[Jeff Snyder]

If a tornado was fast moving, lets say, would it cause the debris to go kinda in the same direction instead of the classic swirl look associated with large slow moving tornadoes?

That does look like a straight line wind or microburst event though. That is quite a lot of trees. They seemed to be "plowed over" instead of twisted and snapped off.
[/b]

Tornadoes are attached to storms, and there tends to be storm-relative symmetry to the wind field. When we look at damage at the ground, however, we're often concerned with ground-relative winds. For example, suppose a tornado has a perfectly circularly-symmetric wind field, with peak winds of 100mph. If the storm (and tornado) is moving eastward at 50mph, there will be asymmetry to the ground-relative wind field. In this case, assuming it's a cyclonic tornado, the areas north of the center of the tornado will see peak ground-relative winds of 50mph (100mph tornado winds - 50mph tornado translation/movement); conversely, areas south of the tornado center will see peak winds of 150mph (100mph + 50mph). The winds on the east and west side of the tornado will be altered from a ground-relative sense as well (squareroot[100^2+50^2]). With that said, there could be a weak tornado (e.g. F0) that has a forward/translational motion faster than the max tornadic winds. For example, a cyclonic tornado with tornado-relative winds of 50mph that moves east at 60mph will result in all ground-relative winds having a westerly component (in other words, there should be no organized damage that indicates easterly winds were present). There are slight complications to this, however, including asymmetries and that fact that winds near the surface converge towards the center of the tornado most of the time (neglecting winds near/at the center during vortex breakdown, etc).

Ideally, if a tornado is stationary, you should see nearly perfect swirl marks. Adding in storm motion artificially intensifies the tornado from a ground-relative standpoint (which is how tornadoes are classified). That makes a supercell moving 70mph that much more dangerous.