Landspout or Gust Tornado ?

Discussion in 'Advanced weather & chasing' started by Damien49, Feb 22, 2013.

  1. Damien49

    Damien49 EF0

    Joined:
    Mar 26, 2012
    Messages:
    31
    Likes Received:
    3
    Outflow Boundary Tornado : Hybrid landspout-gustnado ?

    Hello,

    I am a French storm tracker and April 30, 2007, I was confronted with a strange tornado. I know it is a no-mesocyclone tornado (EF0) that developed in front (or long) a shelf cloud. But precisely what kind of tornado ? Is it a landspout, a gust tornado or other ?

    9551adb1b1974cd1a71ff8c348482629.png

    You can find more photos of the tornado here : http://www.meteobell.com/__orage_070430_3.php
    and the shelf cloud : http://www.meteobell.com/__orage_070430_4.php

    Thank you very much. It is very difficult in France to find a clear explanation.


    Sorry if this is the wrong section I do not speak English very well, but I'm looking for detailed technical information.
     
    • Like Like x 2
    #1 Damien49, Feb 22, 2013
    Last edited by a moderator: Apr 13, 2013
  2. Skip Talbot

    Joined:
    May 1, 2004
    Messages:
    3,364
    Likes Received:
    244
    That's really, really neat. Was there a debris cloud at the surface? It looks like there might be a faint column of dust extending from the ground in that picture. I did a contrast enhance on the image, but I'm not seeing much of a pronounced debris cloud and the dusty portions above the ground might be part of the "scud" of the feature. I'd say this is probably a landspout if there was a debris cloud at the surface, and the shape is due to the outflow pushing it forward. I've seen images of spouts including waterspouts in a similar configuration, where the storm's outflow makes it bow out in front of the storm. There's probably some vorticity along that gust front that the updraft is stretching to produce the spout. The disjointed and scuddy appearance of the funnel above is also really interesting. I think this might be the result of the circulation being relatively weak and the outflow having a heavy influence in it's formation. Nice catch! One for the spotter classes.
     
    • Like Like x 1
  3. Damien49

    Damien49 EF0

    Joined:
    Mar 26, 2012
    Messages:
    31
    Likes Received:
    3
    Yes it is. Witnesses nearest reported seeing this tornado touch the ground. In the links I set, you will see more pictures, at other times

    Example 3 minutes after:
    [​IMG]


    Are there several different types of landspout? what category it would rank? wikipedia is very empty : http://en.wikipedia.org/wiki/Landspout
     
    #3 Damien49, Feb 22, 2013
    Last edited by a moderator: Apr 13, 2013
  4. Skip Talbot

    Joined:
    May 1, 2004
    Messages:
    3,364
    Likes Received:
    244
    I looked at the images on the site and am not seeing much of a debris cloud in any of them. That one above shows some scud very close to the ground, but even scud condensing right off the ground is not enough to make it a tornado. You'd need to have a tight, violently rotating circulation on the ground. If other people documented that debris cloud, that would definitely confirm it as a tornado, but if they simply saw the same scud clouds close to the ground, I think this might be just an outflow feature like a scuddy tendril forming along the storm's gust front.

    Spouts, whether they form over land or water, are generally formed under the same processes. There is usually some vorticity at the surface along a boundary that is stretched by an updraft to produce a tornado. They lack the parent storm structure of a supercellular tornado, but supercells do produce spouts as well. As you probably know, another feature that's common along gustfront and shelf clouds is the gustnado, where you get a tight circulation on the ground, but no corresponding funnel or rotation above in the storm's base. They're not tornadoes as result. I was leaning on spout in your image because that tendril does look like a scuddy funnel.
     
  5. Bob Hartig

    Joined:
    Jul 2, 2004
    Messages:
    1,771
    Likes Received:
    84
    While I was writing the following, others beat me to the punch. I haven't yet looked at what they've written, but I'm not going to rewrite my own response. For better or worse, here it is:

    Now that is just plain fascinating. It's certainly not a mesocyclone tornado, but I don't think it fits neatly into the category of either a landspout or a gustnado; it almost seems like a hybrid of the two. Its proximity to the gust front is suggestive of a gustnado; but its connection with the end of the arcus via a condensation tube shows it to clearly be more than just a surface dust whirl.

    I'm hardly the most experienced chaser on this forum, but I've seen arcus clouds beyond count and plenty of gustnadoes, and I've never seen anything like that. Your cautious observation of it lends credibility to your conclusion that it was tornadic. I can speculate that it involves vorticity that got tilted upward along the gust front. Beyond that, I'll just say that it's the second unusual vortex that someone has posted about here in the last couple of months, and it's pretty neat!
     
    • Like Like x 1
  6. Damien49

    Damien49 EF0

    Joined:
    Mar 26, 2012
    Messages:
    31
    Likes Received:
    3
    I understand your caution to call it a tornado. In France too, this case is very original. This is why I come to see you. I was about 5km. But several witnesses complementary, well confirmed the rotary outgrowth cloud on site. Several people have even confirmed that a "bush" (I d'ont know if in english, bush is the right name) was visible to the ground "surrounding vegetation was agitated, and this long before the arrival of the gust front, itself."

    In fact, for 6 years I'm looking for answers, now the question is not really whether or not to hit the ground, we affirm Yes (National Observatory of thunderstorms, also assert). The question is if it touches the ground, why and how to nominate this type of tornado.

    In any case thank you for your interest and your analysis.

    EDIT : Yes the storm was not a supercell I think (but we have no doppler here), but probably a severe storm multicell.
     
    #6 Damien49, Feb 22, 2013
    Last edited by a moderator: Apr 13, 2013
  7. Skip Talbot

    Joined:
    May 1, 2004
    Messages:
    3,364
    Likes Received:
    244
    I'd have to side with Bob that this is probably a hybrid tornado then. The circulation at the ground at the ground may be forming in a similar fashion to a gustnado, but it's also being stretched by the updraft in the shelf cloud. If you're searching for a label to stick on it, I would just stay at Non-supercellular tornado or gustnado/landspout hybrid.
     
  8. Damien49

    Damien49 EF0

    Joined:
    Mar 26, 2012
    Messages:
    31
    Likes Received:
    3
    In French, I personally called it "une tornade de front de rafale", which could translate into English in as "tornado boundary outflow" or "tornado gust fronts" but it is a personal name because there is no other similar case listed in France. I like Gustnado-Landspout hybrid.

    Do you have any links listing similar cases in USA or anything that can explain this?

    Anyway Thanks.
     
    #8 Damien49, Feb 22, 2013
    Last edited by a moderator: Apr 13, 2013
  9. Skip Talbot

    Joined:
    May 1, 2004
    Messages:
    3,364
    Likes Received:
    244
  10. Damien49

    Damien49 EF0

    Joined:
    Mar 26, 2012
    Messages:
    31
    Likes Received:
    3
    #10 Damien49, Feb 22, 2013
    Last edited by a moderator: Apr 13, 2013
  11. Paul Knightley

    Joined:
    Feb 6, 2006
    Messages:
    840
    Likes Received:
    105
    I guess the issue here is trying to fit something which has been observed into our narrow definitions!
     
  12. Damien49

    Damien49 EF0

    Joined:
    Mar 26, 2012
    Messages:
    31
    Likes Received:
    3
    Yes, the tornado itself looks like. But the storm not. In Bison tornado there is no shelf cloud and general configuration is not the same. So it is difficult to compare.
     
    #13 Damien49, Feb 27, 2013
    Last edited by a moderator: Apr 13, 2013
  13. Skip Talbot

    Joined:
    May 1, 2004
    Messages:
    3,364
    Likes Received:
    244
    Very different storms right, but they are similar in that they both occurred on the leading edge of a gust front, be it forward flanking as in your case, or from the rear flanking downdraft of a supercell as in Kansas in '08. The wall cloud was bowing out at that time and taking on many of the characteristics of a shelf cloud. Most of the storms in Kansas lined out a short time later too. Some similar mechanics are probably at work. I think Bison was more of a supercellular tornado that was being heavily influenced by outflow, while yours was probably more of a landspout (or gustnado) that was being heavily influenced by outflow if that's where the main difference is. Similar in that they may be gustnado like hybrids due to the influence from the gust front.
     
  14. Damien49

    Damien49 EF0

    Joined:
    Mar 26, 2012
    Messages:
    31
    Likes Received:
    3
    Thank you, it is very interesting to read you. I should have come on stormtrack earlier. :)
     
    #15 Damien49, Feb 28, 2013
    Last edited by a moderator: Apr 13, 2013
  15. James Hilger

    Joined:
    Mar 14, 2010
    Messages:
    275
    Likes Received:
    22
    From a local Chief Meteorologist who also chases-Doesn't look like a tornado to me... I would say back edge of a roll cloud. More like a previous horizontal vortex that has lost its rotation. It just isn't smooth enough on the edges to be a funnel.
     
  16. Stan Rose

    Stan Rose EF4

    Joined:
    Mar 8, 2006
    Messages:
    476
    Likes Received:
    69
    Looks like a smooth funnel to me. The scud around it is separate. And since there was apparently confirmation of ground circulation, id call it a tornado.
     
  17. Damien49

    Damien49 EF0

    Joined:
    Mar 26, 2012
    Messages:
    31
    Likes Received:
    3
    This is not because my own photos don't show debris flying to the ground, he didn't hit the ground. From my position I was absolutely impossible to photograph. I was about 5km and topography rises, then descends. (hill). And there is a city, with urban architecture between my position and the supposed place of the tornado. There was little or few damage, knowing that it is fields with a few groves difficult to access (as classified EF0 by the French Observatory Tornado and Violent Storms and not with my photos). At the time, I hadn't gone there to check. But I repeat that several different witnesses have reported seeing many plant debris flying just above rotating cloud growths and that before the arrival of the gust front itself and a "bush" was visible to the apparent ground. I invent nothing.

    Who is it? Maybe I know him.
     
    #18 Damien49, Mar 2, 2013
    Last edited by a moderator: Apr 13, 2013
  18. James Hilger

    Joined:
    Mar 14, 2010
    Messages:
    275
    Likes Received:
    22
    Who is it? Maybe I know him.[/QUOTE]

    Dan Skoff
     
  19. Damien49

    Damien49 EF0

    Joined:
    Mar 26, 2012
    Messages:
    31
    Likes Received:
    3
    This Dan Skoff http://nwahomepage.com/fulltext?nxd_id=9 ? He has chases this storm in 2007 near Angers in France ? Absolutely incredible. Sorry I don't know him. Or I've misunderstood.

    Sorry, but you must write clearly with me because I'm French, I do my best to read and write English, but I don't understand everything.
     
    #20 Damien49, Mar 2, 2013
    Last edited by a moderator: Apr 13, 2013
  20. James Hilger

    Joined:
    Mar 14, 2010
    Messages:
    275
    Likes Received:
    22
    That's him and as far as I know he's only chased in the U.S.
     
  21. Damien49

    Damien49 EF0

    Joined:
    Mar 26, 2012
    Messages:
    31
    Likes Received:
    3
    ok sorry, so I don't understand what you said

    To me, to chase = to track :confused:
     
    #22 Damien49, Mar 3, 2013
    Last edited by a moderator: Apr 13, 2013
  22. Tim Shriver

    Joined:
    Apr 10, 2008
    Messages:
    387
    Likes Received:
    1
    Gustnado...

    Simple..

    Tim
     
  23. Joshua Nall

    Joined:
    Feb 27, 2009
    Messages:
    426
    Likes Received:
    9
    Is everyone reading the whole thread???

    The only thing that I thought of that hasn't been mentioned is that it might be a type of bookend vortex which is common on the ends of a squall line. Only this would be on much smaller scale, a gust front from a storm. but that is just a thought.

    It's not simply a gustnado (which isn't a tornado) in that there is more than just a surface circulation. There is a funnel in association with a gustfront and cumulonimbus above it. Damien49 has affirmed it was a tornado that caused EF0 damage. His question was about how to classify it.
     
  24. Skip Talbot

    Joined:
    May 1, 2004
    Messages:
    3,364
    Likes Received:
    244
    Not sure what the reasoning is here, since none was given. I think you do have to make an attempt at explaining some of the processes involved here since the atmosphere is rarely a simple, textbook case of something, this one in particular. If the photos show anything, it's that there is some sort of cloud based feature (be it a scuddy, disjointed funnel, or simply scud) that's interacting with the storm's base, which is an interaction that gustnadoes do not have. There's more to it than that.
     

Share This Page