Two wedge tornadoes at the same time?

[Justin Walker]

Finally got a little bit done on my website on the "dual wedges" near Grant, NE. I have a sequence of photos taken from the south, shooting north. You can clearly see that there is the main wedge tornado with a satellite rotating around it. It starts on the east side of the main tornado, then by the time it rotates around the west side, it had become very large also. I will try to get a little more done this weekend.

http://www.tornadostalker.com/2007/28march2007

 

[Dan Dawson]

These "twin tornado" scenarios are very interesting in that they can presumably come about from different physical "starting points". My own feeling is that many of the cases where two tornadoes are rotating around each other and both are large and spaced significantly further apart than their own diameters (i.e. on the order of 4-5 diameters) may actually be cases of multiple vortices within the mesocyclone itself, with each sub-mesocyclone-scale circulation producing a tornado. In these cases, the tornadoes can indeed righly be considered individual tornadoes in their own right, and not just large subsidiary vorticies of an even bigger multiple vortex tornado. However, each tornado may itself be multiple-vortex. So, these are cases where one can potentially witness two simultaneous scales of multiple-vortices, one on the scale of the mesocyclone, and the other on the scale of an individual tornado.

Another way I think one might get this phenomenon of two large tornadoes rotating around each other is through the classic cycling mechanism, whereby the tornado remains in its mature stage (i.e. never fully occludes and ropes out), but the storm begins to create a brand new mesocyclone and new tornado in the "usual" manner. If the two tornadoes are sufficiently intense and close enough together, you can get a Fujiwhara-type interaction, whereby both the tornadoes and their associated low-level mesocyclones begin to rotate around each other, and eventually may come close enough together to merge. Different physical starting points are involved in this case (the first requires some preexisting multiple-vortex structure in the original mesocyclone, while this case is two mesocyclones that formed as part of the cycling process), but the end result may be very similar.

The question to ask is, which mechanism occurs most often in nature? My guess is the latter, but I feel that some cases, supported by cycloidal damage tracks of certain tornado families, support the idea that some supercell storms have multiple circulations rotating around each other on the mesocyclone scale. My undergraduate research advisor back at Purdue first told me of this possibility, and I haven't been able to get it out of my head since. As such, this is actually an area I've been interested in looking into in my research in the future, to see if this can really be explained as the result of bonafide "multiple-vortex mesocyclones" or if it is a variation on the classic "cyclic mesocyclogenesis". My hunch is that both mechanisms can and do occur, possibly at the same time in the same storm in cases.

 

[Willie Dines]

Hey guys

First I gotta say that the picture of the Palm Sunday "Gruesome Twoesome", is one of my all time favourite tornado images , although I can't remember where, but I remember once reading a book in the local library that had a similar picture of 2 wedge tornadoes, that were both about a 1/3 - 1/2 a mile wide and were about 1 mile apart from each other, and I'm not too sure on what the date/location was, but I think that they were pictured during the super outbreak in '74, but don't quote me on that, as it was about 9 years ago that I had saw the picture and haven't been able to find it since

Now then, back to buisness... from what you have mentioned Dan in your post and from a reasonable understanding of tornado structures, I feel that both scenarios given, may be the reason for the occurance of tornadic families, especially in the beast dep't

I feel that both the 2 examples that you have given, Dan, have pretty much covered 2 of the 3 main reasons for "Twins" or "Families" to occur

The 3rd option which I feel is most common, is a supercell have 2 (Or possibly more depending on intensity and structure) mesocyclones, spawning their own tornaodes and in some cases they can either be atoppositte sides of the parent storm, or they can be neighbours (Right beside each other) and I feel that either of these 3 scenario's would be the most logical and plausible as to the reason why we have this pheonominon, but I'm still open to other suggestions as to the reasons for this occurance

Willie