Wall Cloud vs Outflow/Shelf

[Jason Bolt]

I've got a shot of a wall cloud just west of Sedan from the time in question, but I can't figure out how to make it small enough to post it

 

[Jim Saueressig]

I've got a shot of a wall cloud just west of Sedan from the time in question, but I can't figure out how to make it small enough to post it

You don't have a proggie to shrink it? If not a link to the pic will work.

 

[Skip Talbot]

My take on the genesis of wall clouds is that they form due to the localized area of low pressure under the mesocyclone.

This is also my take on why condensation funnels form...however, my "theory" doesn't explain why some (even strong) tornadoes do not have a condensation funnel all the way to the ground.

Jeff, my understanding is that wall clouds and condensation funnels form due to the entrainment of rain cooled air into the updraft. The cool, saturated air from the storm's downdraft condenses at a lower height as it circulates back into the storm. The amount of precipitation determines how much of a wall cloud or funnel condenses. Low precipitation supercells can produce tornadoes with no condensation funnels at all, while high precipitation supercells can have wall clouds that drag on the ground.

Your ideas definitely sound like they may be contributing factors though.

 

[Jeff Duda]

Skip,
I'll bet you're closer than I am. I've always been very curious as to the dynamics that form wall clouds and condensation funnels. Does anyone else know how/why they form?

 

[Dann Cianca]

Jeff, my understanding is that wall clouds and condensation funnels form due to the entrainment of rain cooled air into the updraft. The cool, saturated air from the storm's downdraft condenses at a lower height as it circulates back into the storm. The amount of precipitation determines how much of a wall cloud or funnel condenses. Low precipitation supercells can produce tornadoes with no condensation funnels at all, while high precipitation supercells can have wall clouds that drag on the ground.

Your ideas definitely sound like they may be contributing factors though.

This LP we were on in August barely had a condensation funnel (or discernible wall) ...

Michael Carlson has the best pic:
http://4.bp.blogspot.com/_xUN6cFdehpM/SKe6x_ubbfI/AAAAAAAAArA/soJpzbPmGss/s1600-h/20080816_9.jpg

 

[Thomas Spence]

Wow, learned a lot about the differences between them. I have had that same problem before since I only started chasing last year and it was hard for me to tell the difference between them sometimes. Great replies and explanations everybody.

 

[Matt Hughes]

"I agree with all this, but I have also witnessed tornadoes (besides gustnadoes) along shelf clouds as well. Matt and I witnessed a brief tornado that formed along a shelf cloud in Barber County, KS on May 6th, 2007 just southwest of Medicine Lodge. The area of interest along the shelf cloud was a little inflow cut into the shelf cloud."

Unfortunately we were behind the shelf cloud at the time and the winds were fierce so posting the video would be vomit-inducing. That storm was clearly outflow dominate but we kept encountering the inflow notches and subsequent tornado warnings throughout that day. Do these notches form simply as a result of strong southeastward near-surface winds toward the eastward moving squall line or something less simple? Thoughts anyone???

 

[Jeff Duda]

Dann, that picture is so deceptive it's creepy. It looks like a beautiful summer day other than the little dusty swirl on the ground. I presume the supercell is behind you in the image (pointing the other way).

Skip, I talked to a professor of mine who knows a lot about severe weather and he corroborates your understanding. I'm glad I finally know what causes wall clouds and condensation funnels to form!

 

[Jim Saueressig]

Just found a pic from the South end of the cell I posted the question for. Since there was a debate to what it really was this might answer it. This was the view looking north on the shelf with the rotational area being the area that does from here look like a wall within the shelf if that is possible with a recycling of the cell...

 

[Dann Cianca]

Dann, that picture is so deceptive it's creepy. It looks like a beautiful summer day other than the little dusty swirl on the ground. I presume the supercell is behind you in the image (pointing the other way).

Jeff, I suppose you could say that ... we were on the main updraft of the storm, which was rooted on an old out-flow boundary (which had become a moisture discontinuity). The main downdraft was miles and miles to the east, behind us. In fact, from the lowered updraft, there was a "cloud bridge" arching back toward the main downdraft. I believe this was due to the limited moisture and the strong westerly winds at 700mb and higher.

Here are a couple more links:
http://stormchaserco.blogspot.com/2008/08/michael-and-danns-elbert-county-tornado.html
http://blog.bigskyconvection.com/2008/08/finally.html


Okay, I'm done jacking the thread.

 

[Jeff Duda]

Dann, was it a supercellular/mesocyclonic tornado or a landspout? I'm guessing supercellular since you were on an LP supercell, but there's no condensation at the ground, and if it's weak it might make it appear to be a landspout.

 

[Dann Cianca]

Dann, was it a supercellular/mesocyclonic tornado or a landspout? I'm guessing supercellular since you were on an LP supercell, but there's no condensation at the ground, and if it's weak it might make it appear to be a landspout.

Most definitely supercellular. There were multiple funnels before the ground circulation appeared (though the previous were higher up on the side of the meso ... shear funnels, I guess you could call them). The updraft (meso/wall ... hard to distinguish at times due to the size) was rapidly rotating and there were many times where horizontal vorticity tubes could be seen. It was only a matter of time before one stretched vertically, and when interacting with the boundary, that is exactly what happened.