Is a "wedge" tornado fundamentally different to other tornadoes?

[Paul Knightley]

Hi all - I posed this question in the thread about forecasting tornadoes, but I would like to give it it's own thread, and try to garner opinion.

We know that tornadoes form in a number of different environments. For example, one may form under a rapidly growing cumulonimbus along a convergence zone whilst another develops under a mesocyclone. Many of these tornadoes "look" *fairly* similar - i.e. funnel shaped, rope shaped, or whatever, and most are *fairly* narrow. Now, I can kind of picture these as being the result of vertical vorticity being stretched from above - many tornadoes within mesocyclones are much smaller than the parent meso, and rotate about them. Perhaps these are all formed in a similar manner albeit under different conditions. Now (and this is where we approach the question I want to ask!) - occasionally a tornado assumes (by most other tornadoes) a fairly huge size (e.g. the Greensburg tornado), and my question is this:

Are these monster tornadoes actually the same kind of phenomenon as a "normal" tornado (including those which develop under mesocyclones and those which don't), or are they actually more akin to the whole mesocyclone itself being "on the ground" (for want of a better term!)?

I say "normal" because most tornadoes spawned beneath mesocyclones are nowhere near the size of the meso, but these monster storms could, perhaps, be closer to the size of the meso (although I understand that generally most mesos are larger).

It was seeing some of the footage from the May 3 OKC tornado, in which the tornado *seems* to be beneath a column of cloud, and as wide as this column of cloud which may me wonder whether these are formed in a totally different way to most other tornadoes.

 

[Nigel Bolton]

I think you have answered your own question there Paul.

Tornadoes and other vortices are all different sizes, ranging from my 'Teanado', a vortex that formed atop my hot cup of coffee two years ago, some 15cm tall and 1cm across to a massive extra tropical low over the Pacific or Atlantic Oceans, these sometimes thousands of miles across. All of these are spinning columns of air.

Your explaination of a 'wedge' tornado sounds very plausible; consider Birmingham UK July 2005. The whole Cb was within an area of high helicity at a triple point, the intersection between trough in warm air and a slowly northwards moving warm front. It is likely, that the motion of the storm was translate downwards towards the ground, as stretching of vorticity by updrafts caused the vorticity within the storm to stretch.

This also to me negates the need of the 'tilting term' to turn horizontal vorticity into vertical, such as explained within the other thread.

Meso winds within an American supercell last year sometime were recorded at, I believe over 200 mph. If this was translated downwards, it is more than likely you would have had a very wide 'wedge' that may have attained EF5.

Nigel B.

 

[Jeff Miller]

Here's a concept about wedge tornadoes I would like to throw out:

I have seen video, I forget where, where there is an intense "inner tube" inside some wedges. In other words, first you have the dusty wedge part. But as that breaks, you often see the "tornado cone" that is often seen in non-wedge situations. Therefore, in at least *SOME* wedge tornado situations, there seems to be a tornado within the tornado. The inner tornado resembles what is often seen with cone and/or elephant trunk tornadoes in some situations, only visible as the dust clears or condensation in the wedge evaporates. It is these situations where it is plausible that the meso is indeed visible as a large wedge, due to either A) insane moisture availability and high dewpoint or B) large dust content on the surface sucked into the meso.

That being the case, there have also been instances where there have been violent tornadic winds surrounding skinny stovepipe/trunk tornadoes without the wedge visibility, only marked by intense debris motions, as the actual tornadic circulation is NOT visible with a condensation funnel or dust due to again, lack of moisture availability or dust - an unfavorable environment. Indeed, it's still a tornado circulation surrounding the intense tornado, by all rights a "Wedge" - but it's just not visible - the intense tornado part certainly is. This is why it is often dangerous to venture close to tornadoes because the tornado circulation may be much larger than the visible tornado itself.

Obviously this isn't the case in all tornadic situations, but enough to merit mention here. I am of the belief, in answer to your question, that the entire meso can and often does become pulled down to the surface by a strong rfd in some situations, and that would indeed become a tornado. Remember the old question - "If a wall cloud is violently rotating and climbs a mountain - because it is in contact with the ground, is it a tornado"? The answer in my mind is yes, and it is yes the same if that meso circulation is pulled earthward and in contact with the ground.

 

[Shane Adams]

I don't think wedges are formed much (if any) differently than an average-sized tornado (in mesocyclones). Most wedges don't start out as wedges, they grow to be wedges. I think one component that may or may not contribute to a "wedge" shape is the LCL heights within the near-storm environment. With a strong to violent mesocyclone and extremely low LCLs in a given area, this would seem to lend itself to "dropping" the meso down to the ground (the tornado cyclone actually), but even when you have a monster wedge on the ground, there is going to be rotation around the periphery, regardless of the tornado's size. So I don't believe wedge tornadoes are the manifestation of the entire meso on the ground (that would be miles wide). The entire tornado cyclone...maybe.

I really can't say if a mesocyclone's size reflects the size of the tornado (every time, as a rule), but I think it's intensity does. When you get a violent mesocyclone/tornado cyclone (like on 5-29-04 near Conway Springs, KS) you can just tell it's going to produce a strong to violent tornado, and in some cases (like that day) the tornadoes will also be large. I don't know the scientific angle to this, but from a chaser perspective, you just know when you see that type of merry-go-round, violent carouseling motion on a large scale, that it's going to transition itself down to the ground in the form of a fairly large tornado.

I have no idea if this answered your question at all, but that's my thoughts.

 

[Bob Schafer]

I don't think wedges are formed much (if any) differently than an average-sized tornado (in mesocyclones). Most wedges don't start out as wedges, they grow to be wedges. I think one component that may or may not contribute to a "wedge" shape is the LCL heights within the near-storm environment. With a strong to violent mesocyclone and extremely low LCLs in a given area, this would seem to lend itself to "dropping" the meso down to the ground (the tornado cyclone actually), but even when you have a monster wedge on the ground, there is going to be rotation around the periphery, regardless of the tornado's size. So I don't believe wedge tornadoes are the manifestation of the entire meso on the ground (that would be miles wide). The entire tornado cyclone...maybe.

That's an interesting analysis and perspective that makes me ask these questions: What defines the mesocyclone? (Where are its outermost elements? Where does the mesocyclone end and transition to "simply" rotating storm out beyond the meso's periphery?) Does any such definition exist?

 

[Maggie Kahman]

I don't think wedges are formed much (if any) differently than an average-sized tornado (in mesocyclones). Most wedges don't start out as wedges, they grow to be wedges. I think one component that may or may not contribute to a "wedge" shape is the LCL heights within the near-storm environment. With a strong to violent mesocyclone and extremely low LCLs in a given area, this would seem to lend itself to "dropping" the meso down to the ground (the tornado cyclone actually), but even when you have a monster wedge on the ground, there is going to be rotation around the periphery, regardless of the tornado's size. So I don't believe wedge tornadoes are the manifestation of the entire meso on the ground (that would be miles wide). The entire tornado cyclone...maybe.

What about the Hallam, Nebraska tornado?? That monster was the largest ever recorded--2.5 miles across!

 

[fplowman]

Here is a pic I found of the hallam wedge. It has always fascinated me.

 

[Paul Knightley]

Thanks for your insights so far!

Yes, the dust thing has crossed my mind many times - tornadoes can look very large when crossing a dusty patch of ground. And yes, sometimes very high humidity can make the condensation part very wide.

Perhaps I should qualify my question a little more and speak about tornadoes with wide damage paths rather than a wide appearance.

 

[Maggie Kahman]

Is that what Jeff was talking about, a "tornado within a tornado"? I cant see the meso in this picture. Not unless that IS the meso. Nice picture, BTW.

 

[Mike Hollingshead]

Here is a pic I found of the hallam wedge. It has always fascinated me.

That's actually near Daykin there. I'm not sure it was all the same tornado by the time it got to Hallam or not. Also, at the time of that photo there was a much smaller cone tornado in there, with that wall of dirt around it(many "wedges" are probably this way).

http://members.cox.net/jondavies2/052204sne/052204sne.htm
Jon Davies has an excellent page before the storm got to Hallam. It even produced a wedge before that tornado above. God it's great I left that area like everyone else that day, an hour before that formed.

 

[scott r currens]

That's an interesting analysis and perspective that makes me ask these questions: What defines the mesocyclone? (Where are its outermost elements? Where does the mesocyclone end and transition to "simply" rotating storm out beyond the meso's periphery?) Does any such definition exist?

You can ask the exact same questions about a tornado and the answers are just as unclear. One the problems is that we cannot see the tornado because the tornado is the wind. We only see tracers in the form of condensation, dirt and debris. A tornado can occur without any visible tracers. Another complicating factor is that tracers can extend outside the tornadic circulation. Like the dust at the end of the May 12, 2004 Attica tornado or debris in the RFD of a damaging tornado. How about the Mulvane tornado? Visually it was an intense compact tornado. But the reality is that it had a 1/4 to 1/3 mile wide damage swath. I've seen wedges that had narrower damage swaths.

 

[Dan Robinson]

The condensation funnel size is a factor of the pressure drop within the vortex and the moisture content in the boundary layer. A lower pressure drop or higher dewpoints will result in a wider condensation funnel for the same size tornado that might be a thin rope or have no funnel at all in a drier environment. Tornadoes in a high DP environment can have a condensation funnel boundary outside a debris cloud.

 

[Dick McGowan]

That's actually near Daykin there. I'm not sure it was all the same tornado by the time it got to Hallam or not. Also, at the time of that photo there was a much smaller cone tornado in there, with that wall of dirt around it(many "wedges" are probably this way).

http://members.cox.net/jondavies2/052204sne/052204sne.htm
Jon Davies has an excellent page before the storm got to Hallam. It even produced a wedge before that tornado above. God it's great I left that area like everyone else that day, an hour before that formed.

Andy Fischer has some pretty cool images from that day

This one is my favorite...... http://tornadohead.com/1232310e.jpg !!!

 

[Mike Hollingshead]

Andy Fischer has some pretty cool images from that day

This one is my favorite...... http://tornadohead.com/1232310e.jpg !!!

A lot of the images from that day make me think of June 9, 2003 O'Neill Nebraska. Another likely cone tonrado forming a dirty wedge thanks to the dusty conditions, as well as walls of RFD dirt to base level.

 

[Martin North]

Wow...great example of an RFD really coming down. That second image is a great one for the admirer of supercell structure....