2011-07-11 MISC: NE

[Skip Talbot]

Quite an eventful day for me! Started off the day heading toward Scottsbluff and arrived in town shortly after 1pm local time. Storms were starting to fire off of the higher terrain in Wyoming and were making their way toward the Nebraska panhandle. We slowly made our way toward the storms and set up just southwest of Scottsbluff. One of the suddenly intensified on radar and developed a nice hook on radar with decent rotation on the velocity scans. We noticed some lowerings in the distance with the storm and saw some dirt being picked up into the updraft. Unfortunately, with the bluffs and hills in the way, it was hard to determine if a tornado occurred for sure in that area; however, there was a visible debris cloud beneath what I think was the main circulation (and there were even small funnels), so I believe a tornado may have touched down briefly. I submitted my report online with some pictures as well, but have yet to hear anything back about it yet.

The storm didn't last too long, however, died within a half hour to an hour after it dropped the possible tornado. New storms were firing off in the northern pandhandle and eastern Wyoming, so we made our way north to check out those storms. One storm in Wyoming a tornado warning on it, and according to GRLevel3, had over a 100 knots of gate to gate shear and 3.75 inch hail on it. We made our way to that storm, but by the time we had gotten to it, it had weakened significantly. Still, the storm had impressive structure with it, and we watched the meso of the storm come toward us while slowly becoming outflow dominant.

A friend had some software that did panamora's and helped me stitch together the above image. I thought it came out very well considering I did not have a tripod handy!

I also got a video timelapse of the feature as it moved toward us. I think I may have captured some Kelvin-Helmholtz wave action going on between the 28 and 45 second mark in the meso (it's a little easier to see in HD on the video).

Watch video >

Great shots, Dan. Loved the stacked meso. The funnel and debris cloud shot looks a lot more like scud and curling outflow rather than a tornado, however. Do you have video of these features showing any strong rotation? When the forward flanking downdraft associated with the precipitation (right side of the image) hits the ground, it fans out and curls back at the ends. There's a hill in the foreground blocking where you'd see the outflow fanning out, but you can make out the top of the curl where the outflow hits the warmer air/inflow ahead of the storm. This warmer air gets forced up over the top of the outflow and you wind up with a bunch of scud marking the edge of this outflow boundary. I've contrast enhanced and labeled the image to make it a little more clear:

Check out some of Doswell's shots for reference:
http://www.flame.org/~cdoswell/microbursts/Additions.html

That's my one picture analysis, so its definitely suffering from some tunnel vision and may not be completely accurate, but it looked like a pretty classic outflow/curling rain foot example to me.

 

[dmckemy]

Skip, thanks for the input! Concerning that image, I did see the scud rotating, although I did not have my video camera out at the time. I probably should have included this image (below) as well:

It's a little easier to see where the dirt is being picked up in this image, almost in a 'tube' like fashion near what I think may be a ragged wall cloud. This image was taken before the image in the first post. And I did note rotation in the scud.

Given my distance from the storm, though, I can't confirm that a tornado touched down. And you may be quite right Skip about it being outflow in that one image. But the storm did show rotation visibly and on radar (in fact, it even had a TVS signature). I'll see if I can post some of the radar/velocity images of the storm during the time I was out observing it. Again, I appreciate you bringing this up for discussion, and would also be curious to know what others thought about it as well!

 

[dmckemy]

Here is a radar/velocity image around the time that the pictures were taken.

 

[Stan Rose]

Storm sure is rotating. Looks like 50kts or so gate to gate--but the strongest vleocities appear to be some distance away--so i wouldnt characterize it as a TVS. Question i have is the inconsistency in your two photos--the 'ragged wall cloud' in pic 2 looks very similar to the 'funnel' in #1--what was the time interval between the photos? Is it the same general feature (aside from slight changes in appearance)? If so, it looks like the 'debris' cloud in #1 (which from the photo does look more like a rain foot) is on the opposite side of the 'funnel' from the inflow/dirt in #2. You can't tell from the photo whether anything is rotating; to call something "tube like" is completely subjective (doesn't look tube-like to me). You were in the best position to know wheter it was a rotating funnel or not. There's not much you can tell from the 2D photos. Neat case though.

 

[dmckemy]

I believe the TVS signature occurred later in the storm's lifetime --- I was just trying to pull up some of the radar data during the time I observed what could have been a possible tornado to show that the storm did have rotation in it. The time interval between the two photos is probably no more than 5 to 10 minutes.

Is it the same general feature (aside from slight changes in appearance)? If so, it looks like the 'debris' cloud in #1 (which from the photo does look more like a rain foot) is on the opposite side of the 'funnel' from the inflow/dirt in #2.

Good catch, I did not even notice that until you pointed that out. I believe that the funnel in question did form in the area where the ragged wall cloud was at, and if that were the case, I think that the dirt we see in the 'funnel' picture is actually a rain foot produced by the outflow. There was rotation in the clouds above that outflow, but from my distance away from the storm it's impossible to tell if that rotation reached the ground. Still, though, that leads to the question of what caused the dirt to rise in a tube like (or circular? It's confined to a small area) in that one particular area in the photo on the second post.