View Full Version : Rotation in wall clouds
06-01-2005, 05:08 PM
I was looking at the Target Area forum for yesterday's information and pictures and I saw a picture that looked a lot like a tornado. The author, however, said that there wasn't any rotation. How can you tell, just by looking at the cloud, if there's any rotation? It sure as heck looked like a tornado to me.
06-01-2005, 05:38 PM
I am no expert but the things that I would check is to look at the edges of the cloud and the movement should be in a somewhat horizontal direction if it is a tornado. Also I would suspect that the movement would be fairly noticeable. The edges would normaly appear to be smoother but this may not always be the case.
The cloud in question I suspect was a scud cloud which is caused by rising air condensing as it is pushed or lifted up. This is a slow process and it may be difficult to tell which direction that it is moving without looking at it for a while.
Hope im not too far off base here.
06-01-2005, 07:46 PM
Photos can be deceiving that way. You can't spot rotation from looking at a still picture. You may know what a tornado looks like, but less obvious circulations require time spent watching them move to really determine if there's rotation happening.
06-01-2005, 09:52 PM
Some tips to determine rotation in hard to determine situations
1. If you are not close enough to the circulation/meso, distance may cause you to not be able to ascertain rotation. This would be a "suspicious lowering" type of situation. If it is safe to do so, getting a little closer to confirm rotation would be helpful.
2. The suspect cloud's edges will change -- will not be static. A non-rotating cloud formation will have very little changes with the edges -- or perhaps a slow UPWARD motion. Upward however does not mean definitely indicate rotation - but does indicate the presence of an updraft.
3. Look AROUND the suspect cloud for rotating clouds or cloud formations. It should be fairly easy to ascertain rotation as the clouds to the front of the formation will move from left to right and the clouds behind the formation will move right to left in a typical cyclonic tornado situation, and vice-versa for anticyclonic situations.
4. Most importantly, do not make a rash decision -- take a minute or two to study the feature if you are not certain. If you are in doubt, say so.
5. Identify between sustained rotation and short spin-up type rotation. "Eddies" on forward flanks may briefly exhibit rotation but are usually not tornadic threats. In meso situations on the business end of the storm -- If its rotating fast enough to tornado, you won't have much doubt about it.
As was mentioned, you can never tell from a still picture what is and is not a rotating feature, no matter how convincing it would look -- you'd have to study video or "have been there". :) There's actually a great page out there on the web on tornado lookalikes including smokenadoes, scud features, inflow lookalikes and others. WIsh I had that link available while I am here at work.
Hope this is helpful.
06-17-2005, 05:21 PM
Discerning rotation is not always easy for me, either, especially at a distance. I can recall instances where I was close enough that a wall cloud appeared as a donut visibly rotating. In such cases, there is no doubt. However, it usually isn't that easy.
One interesting case for me this year occurred near Okmulgee, OK on 3/21/05. The storm had previously tornadoed, and I spotted several "suspicious lowerings" under the storm's rain-free base about 3 miles north of me. I could not positively identify any of these as rotating (probably due to my distance from them) but took some video anyway. Later, upon reviewing my video, I was able to positively identify rotation on one of them.
I can also remember a time in June 1998 where an isolated tornadic supercell passed along U.S. highway 64 near Morrison, OK. The wall cloud shape was "textbook" -- easily identifiable from Stillwater -- but from that distance, I couldn't actually see the rotating motion, even though I knew it was there.
As storm chasers, we want to see rotation, but let's face it -- most thunderstorm features are non-tornadic and do not exhibit quite what we're most looking for. I strongly agree with the previous poster that we should report suspicious lowerings as such and not be overly hasty to report rotation when perhaps none exists.
06-17-2005, 09:22 PM
I was pretty much a newbie in 2001 when I shot this:
Apparently, this scud didn't even show up on the DDC radar....about a mile away.
06-22-2005, 05:39 PM
Rotation from far away from a cloud that is lying high up, is sort of tough to see, even if perhaps the clouds lies low, if you are far away, rotation may not be visable. In order for me to see rotation I have to get close to the area in which I suspect to be rotating.
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