I wonder because the storm southwest of Grant NE the other night was awefully darn close to doing that.
Here is an image of Matt Kassawara and Chris Rozoff's chase:
http://gauss.atmos.colostate.edu/~rozoff/chasing/28mar07/t4698.jpg (http://gauss.atmos.colostate.edu/%7Erozoff/chasing/28mar07/t4698.jpg)
I didn't have as good of view around the same time...
http://www.extremeinstability.com/stormpics/2007/07-3-28-1.jpg
Neither of us had good views the entire time, so who knows how this unfolded or what else they looked like. I remember looking south after I found a spot and seeing a crazy looking stout, fat stovepipe doing some wild swinging motions. That was after the above views. It seemed like somehow the two areas merged and that happened. Then it was like they lost the balance after "colliding" and went into the multivortex action for a bit, before gaining it again into the one wedge west of Grant. Did anyone see how it unfolded after that, before the main wedge west of Grant? Seems odd to have a wedge se of another tornado in general, especially when the other isn't just a stovepipe kind of going around, but having a large size to it too.
I ask as if it's possible that the other wedge could be anticyclonic.......
http://www.crh.noaa.gov/iwx/program_areas/wxpics/tornado/Huffman.gif
If I recall correctly, the Harper County storm on May 29th, 2004 had a stovepipe with a satellite wedge for a short time period. That's the closest case I can think of.
I was going to mention this event. I read a fairly detailed case study on the Hesston tornado a while back which included some photos of the twin tornadoes . I'll see if i can dig it up and post the link.
Edit: Here is the link: http://ams.allenpress.com/archive/1520-0477/75/6/pdf/i1520-0477-75-6-1007.pdf
The tornado obliterated most of the Midway Trailer Park approximately two miles south of Dunlap; the photos were taken from a distance of around a quarter mile from the trailer park. A friend of mine lived there and experienced the tornado at ground zero.
http://www.tornadostalker.com/2007/28march2007 (http://www.tornadostalker.com/2007/28march2007.html)
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
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.
http://www.rap.ucar.edu/staff/landolt/2007mar28/
He has a whole sequence of jpg files showing a lot of the evolution of these twin tornadoes (in fact, look for the jpgs entitled twins**.jpg) His documentation of this event is incredible. It does seem to show that they rotate around one another and close in on one another. My preliminary hypothesis - this was a merger event and when the vortices finally emerged (perhaps higher up in the cloud before merging at the surface) and then the new victorious vortex perhaps went on to become the multi-vortex tornado that became a wedge. Perhaps most of the merging was occurring higher up in the low-level mesocyclones rather than at the tornado level? It's hard to say, but this was probably about the coolest thing I could ever imagine seeing in a storm chase. Also, Justin Walker also has some documentation of these tornadoes at
http://www.tornadostalker.com/2007/28march2007.html
Anyway, I imagine this event was analogous to satellite tornado events, but in this case, both tornadoes were visually of similar and appreciable magnitude, which is probably fairly rare. I cannot think of any other events mostly because I am a poor tornado historian. I hope to learn of similar events to compare with how Wednesday's event unfolded.
Yes! http://www.rap.ucar.edu/staff/landolt/2007mar28/twins11.JPG
That is what I saw and was talking about when I first pulled over. It looked crazy. I was like, oh my god that big thing looks wild, not because of size exactly but the motion. My still start right after that.
See second post. :)
When I saw this topic, the first thoughts were, Hesston 1990, the above, and another one which isn't coming into my mind right now. Theoretically two wedge tornadoes next to each other isn't impossible... all we need is low lcl's and a cycling storm could easily produce two very large tornadoes.
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