Landspout or Gust Tornado ?

[James Hilger]

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.

 

[Stan Rose]

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.

 

[Damien49]

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.

From a local Chief Meteorologist who also chases

Who is it? Maybe I know him.

 

[James Hilger]

Who is it? Maybe I know him.[/QUOTE]

Dan Skoff

 

[Damien49]

Dan Skoff

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.

 

[James Hilger]

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.

That's him and as far as I know he's only chased in the U.S.

 

[Damien49]

ok sorry, so I don't understand what you said

To me, to chase = to track

 

[Tim Shriver]

Gustnado...

Simple..

Tim

 

[Joshua Nall]

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.

 

[Skip Talbot]

Gustnado...

Simple..

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.

 

[Damien49]

Gustnado...

Simple..

Tim

Maybe or maybe not. I know a little about the process gustnado and the least we can say is that it would be atypical. How many Gustnadoes make a long funnel cloud from scud cloud ?

After that, it is largely a matter of definition and to put this in a box and it is indeed the purpose of my coming here. I don't pretend to revolutionize the knowledge of storms.
In France, I undertook to make people vote. We could have had a little this kind of result: 30% Gustnado 40% landspout or tornado, 10% funnel cloud, 20% other or don't know. I don't come here for the same kind of response without further argument. It doesn't progress in what I already know.

 

[Bob Hartig]

Gustnadoes don't have condensation funnels attached to cloud bases. I think the reality is more along the lines of what Paul Knightly has said: it's an unusual phenomenon that doesn't easily fit into any category, and there are some singular processes involved. If it were me, going by definition, I'd feel comfortable calling it a tornado or a hybrid tornado, but beyond that it's weird as all getout. It looks like the end of the arcus cloud is the connecting point. I don't have a box to put something like that into. It just is what it is. It's the atmosphere, after all: it does what it does and doesn't care a rip what we call it or how we explain it. That's one of the things I love about severe weather!

 

[Paul Knightley]

Seeing as I posted in this thread earlier but didn't try to help with the classification, perhaps I will attempt to!

To me, looking at the progression/development of the feature from the photographs, I think the actual cloud material is part of the gust front. It just sees to be a lower-hanging piece of scud, sculpted by the outflow winds. It may then be that some kind of eddy-whirlwind (or gustnado, if you have to!) formed along the leading edge of the outflow. Seeing as any vortex must have lower pressure within its centre, some condensation could have occurred within the whirlwind's circulation, and this joined up with the outflow scud.

To me, this is a vortex not associated with the updraught pulling in/stretching vorticity. I would tentatively suggest that this is not classed as a tornado.

 

[Jeff Duda]

Yes, this is a very interesting feature, one that I have not previously observed through either real life chasing or photographs. That's why I remain hesitant to comment on this.

It looks to me like the storm was some sort of not-well-organized multicell cluster or the tail end of a squall line. The contextual picture shows a cloud formation that resembles that of a shallow shelf cloud. The scud at the ground is an indicator that air has condensed near the ground, likely in response to rain evaporation and the resultant cooling and moistening (i.e., "wet-bulbing"). This implies there was a cold pool advancing generally towards the photographer (perhaps spreading out left and right as well). This leads me to conclude that the vortex was the result of increased vertical vorticity being tilted and stretched by a buoyant plume coming in from the warm, moist region ahead of the cold pool. The leading edge of the cold pool acted as a lifting mechanism for the tilting, and perhaps there was enough instability of near-surface parcels to accelerate vertically enough, or fast enough cold pool relative flow to force parcels up and over the leading edge, to get just enough enhancement of pre-existing environmental horizontal vorticity to get weak tornado-like winds to develop at the surface.

If the above is the case, then this kind of fits into the landspout regime since it was a non-mesocyclonic circulation created by tilting of local vorticity, but not aided by mesocyclonic processes. However, landspouts usually occur in PBLs that are very well mixed (i.e., neutral lapse rate) and somewhat dry (allowing for deep mixing up to the LCL/LFC). I do not know the structure of the PBL in this case, but given the cloudiness, lapse rates may not have been neutral and there was probably more moisture (reaching now).

I've seen a case before when tornadoes formed at regular intervals along the leading edge of a cold pool in a highly unstable and highly sheared environment (and also extremely windy at the surface), and in association with a squall line not containing supercell structure. In this previous case, simple horizontal shear about the leading edge of the cold pool was a significant contributing factor in generating sufficient vertical vorticity to produce tornadoes with condensation funnels from cloud base to ground. These tornadoes were not related to mesocyclonic processes, and they were strong enough to cause damage to buildings.

That's about the most scientific explanation I can come up with for now.

 

[Bob Hartig]

This leads me to conclude that the vortex was the result of increased vertical vorticity being tilted and stretched by a buoyant plume coming in from the warm, moist region ahead of the cold pool. The leading edge of the cold pool acted as a lifting mechanism for the tilting, and perhaps there was enough instability of near-surface parcels to accelerate vertically enough, or fast enough cold pool relative flow to force parcels up and over the leading edge, to get just enough enhancement of pre-existing environmental horizontal vorticity to get weak tornado-like winds to develop at the surface.

If the above is the case, then this kind of fits into the landspout regime since it was a non-mesocyclonic circulation created by tilting of local vorticity, but not aided by mesocyclonic processes.

That explanation makes the most sense to me. The range of opinions here is interesting overall, and it points to how differently people process the same information.