It WAS a Tornado...

[David Drummond]

I already know what I think about this comment, but I would like to see what other members think as well.

I noted on one of the news reports on the Mississippi tornadoes the other day, a guy made the following comment:

"It was a tornado because the tops are twisted out of the trees," he said. "No question it's a tornado."

This is not the first time I have heard this comment from non-weather people. Have you ever heard it before? How do you normally respond to it?

 

[John Wetter]

I've heard that said many times. I normally respond with, "If it was a tornado, the whole tree would probably be down or damaged. Normal winds can do the same amount of damage as a tornado to trees."

-John

 

[Greg Stumpf]

Even with exact straight line winds, tree canopies are not symmetrical. Therefore, it is very easy to "twist" limbs no matter what "curvature" the wind has. One should never draw this conclusion.

The preferred method of distinguishing straight line winds from tornado winds is to look at the damage pattern upscale (e.g., many trees). Tornadoes typically lay out debris in a convergent pattern. Straight line winds, or microbursts, are typically straight or divergent debris patterns. Mapping the direction of debris helps in this regard.

That being said, after many years (20+) of doing wind damage surveys, I do tend to see a difference with still-standing trees between the tree limb "twisting" in straight-line winds and tornado winds that is hard to describe (or, "I know it when I see it"). The difference may be because of the rapid three-dimensional angular (some upward) accelerations of the wind in the corner regions of the vortex.

 

[Doug Raflik]

I try to explain that no tree is symmetricly exact across its width, so wind may be putting more pressure on one side of the tree due to more surface being pushed on. This causes that side of the tree to get blown over first, causing the twisting effect. Hell, even things that are symmetrical can have a twisted look in straightline winds. We had a 100+ mph wind event here about 10 years ago, and hwy signs were bent over with one side farther down than the other.

Here is a picture of what I am meaning...

http://www.atl.ec.gc.ca/weather/hurricane/juan/photos2/100.jpg

Doug Raflik

Looks like Greg and I were posting at the same time, saying about the same thing.

 

[Doug Lee]

You could ask them, "If I were to push on one of your shoulders, would you twist or fall straight back?" Or you could just start pushing.

 

[Bart_Comstock]

Have you ever heard it before? How do you normally respond to it?

Haha, yes I heard this today when talk to people about the damage in my fathers back yard where he lost about 8 large oak trees. The damage came from straight line winds off of the squall line that blew over the area as the cold front raced across Benton County. Looking at the pattern of the trees it is easy to see that straight line winds brought them down, but a few people out there clearing them asked me if a tornado did them in, noting that a tree's top was "twisted off." I simply told him that if a tornado had hit the trees they would have fallen in an erratic fashion instead of falling in line like a line of dominoes and that the top looks twisted just because it either it hit something on its way down or just landed funny.