Storm Structure Question

[J Trueblood]

Let's see..this was about two weeks ago. A line of severe thunderstorms was pushing straight south through northwest Iowa. They started to really organize once they got over the south dakota border. Since it was a line moving straight south, southeast, we stayed on the front western edge of them.
Now i know that squall lines have the updraft in the front rather the back of the storm with very straight winds, and because of that tornadoes are very rare in squall lines. But as we were racing to stay ahead of the storm, this really intense lowering (?) became evident.
Obviously as you can see it was at the front of the line. Literally, you could watch as the thing was rotating UPWARDS into the storm base. Where there was sky one moment, would be newly condensed clouds being sucked upwards the next. Something I have never seen before. Slowly the whole lowering(?) started to rotate horizontally over the road, and then back out into the field again to our west, keeping it's upward convective motion the whole time.
Nothing really happened after that, the following are some pictures of what I am describing.
The storm put down some baseball size hail and 70 mph wind gusts behind us before nightfall, but no tornadoes. Was this lowering just a shelf cloud, or was it a tail end- charlie type occurrence?...any thoughts are appreciated!

Also, on the last photo, is that a tail cloud or just scud?

 

[Skip Talbot]

Rotating lowerings and tornadoes are certainly possible on the leading edge of a line. These occur most commonly when there are breaks in the line or mesovortices on the leading edge. With the breaks you have enough spacing to get more classic supercell structure embedded in the line. A mesovortex will often look like a hook on the leading edge, underwhich you can see rotating lowerings and tornadoes. I'd like to see some video or radar of this storm to better understand what we're seeing here, but it definitely sounds like you had a leading edge, rotating wall cloud, and that does look like a tail cloud in the last image.

 

[Scott Weberpal]

Was this south of Fairmont, MN near Armstrong, IA?

When I was chasing on July 14, the line began to separate and what I would call a legitimate, albeit short lived forward flank mesocyclone developed. I was about a mile in front of it, and it had persistent rotation for 4 or 5 minutes and scud rising into it. The area of interest appeared to "curl" out ahead of the rest of the line before precip again caught up with it.

Ron Riemersma has a distant picture of the feature I am referring to. Is it what you were looking at?

http://www.stormtrack.org/forum/showpost.php?p=235695&postcount=7

 

[J Trueblood]

Was this south of Fairmont, MN near Armstrong, IA?

When I was chasing on July 14, the line began to separate and what I would call a legitimate, albeit short lived forward flank mesocyclone developed. I was about a mile in front of it, and it had persistent rotation for 4 or 5 minutes and scud rising into it. The area of interest appeared to "curl" out ahead of the rest of the line before precip again caught up with it.

Ron Riemersma has a distant picture of the feature I am referring to. Is it what you were looking at?

http://www.stormtrack.org/forum/showpost.php?p=235695&postcount=7

WOW...that's extremely impressive. Unfortunately I was out of town on July 14. Otherwise I might have seen it! My photos are from July 7, around 8:30 pm, just south of Maurice/north of Le Mars...But they certainly do have some similarities don't they?

Skip, is there some archive I can go to and find old radar shots of this storm, since I know when it happened? I would love to be able to show them to you. I have a few more pictures of this structure, and they show the upward motion really well, but no video of this happening. This was the first time I'd actually seen anything like this so I didn't feel comfortable stopping to take video. There was also the hail not far behind us.. haha

 

[J Trueblood]

Okay I found an SPC report archive of this storm. It has a radar reflectivity animation of the whole day. I don't think it can zoom in, but at least you can get some sort of an idea of what I was looking at. http://w1.spc.woc.noaa.gov/exper/archive/events/090707/index.html

Here are three snags from right around the time we saw it.