Nebraska Twin Tornado

[Jeff Duda]

That's why my question is: could it be the case that the first 3 tornadoes are associated with 3 different supercells, and that the last EF-4 tornado is associated with a cycle of one of them (because I can't see a different mid-level meso developing before that one forms), or does this all fit the definition of a cyclic supercell?

I think it's quite a stretch to call this a conglomeration of entirely separate supercells. I do see evidence of separate updrafts and separate mesocyclones, but they appear to be close enough to each other to be generally sharing a forward-flank downdraft. What I see from looking at KOAX data is that there are multiple "feeder" cells that join the storm generally from the southwest. The updrafts may help organize some of the mesocyclones that were producing tornadoes, but I can't tell for sure. This just looks to me like a case on the tail end of the distribution of behavior of cyclic supercells. The atmosphere seems to be able to do some weird things with that kind of instability.

 

[Bob Schafer]

Regretfully but not surprisingly I did not save any of the radar images from 6-16, but I did point my vidcam at the screen briefly. Maybe this will be of some value to some, maybe not.

I was on 15 going north the whole time, so I saw/filmed the Stanton tornado from a bit of a distance. A little while after it dissipated all of a sudden I was startled by a rotation/WC much closer to me. My reaction was "Holy ****!" That's not something you're going to forget. I reported that WC on SN as being a new area of rotation. It was the rotation that became the Pilger tornado.

Secondly, here is the radar image I was seeing (OAX). The time was 2120Z/1620 local (timestamp from my vidcam, not radar image time), and the twin EF4's were at their "peak" ATTM. Yes, I use a bizarre color table, but you should get the gist. Smoothing also used. I believe you can see the WC icon from my report on here, a little S of the circle-dot of my position just S of Pilger:

 

[Bram]

I think it's quite a stretch to call this a conglomeration of entirely separate supercells. I do see evidence of separate updrafts and separate mesocyclones, but they appear to be close enough to each other to be generally sharing a forward-flank downdraft. What I see from looking at KOAX data is that there are multiple "feeder" cells that join the storm generally from the southwest. The updrafts may help organize some of the mesocyclones that were producing tornadoes, but I can't tell for sure. This just looks to me like a case on the tail end of the distribution of behavior of cyclic supercells. The atmosphere seems to be able to do some weird things with that kind of instability.

Thanks for your reply. The idea of feeder cells might indeed be a better way to look at it, in stead of seperate supercells, but I don't have the knowledge to judge that.

It seems to be an interesting case for researchers

 

[Paul Knightley]

One should consider how the vast majority of 'thunderstorms' morph over time - they show multicellular traits - I know from experience that many supercells exhibit multicellular activity at times, especially towards the HP end of the spectrum, where outflow aids in 'new' storm development, whereas towards the LP end little surface outflow may exist, and hence just one updraught/downdraught pair (the definition of a 'cell', of course) exist.

 

[Stephen Levine]

I heard, and need confirmation this is true - that the two tornadoes rotated around one another.
If this is indeed true, and they rotated along a common axis, this would give credance to both coming from one large mesocyclone.

 

[rdale]

I heard, and need confirmation this is true - that the two tornadoes rotated around one another.
If this is indeed true, and they rotated along a common axis, this would give credance to both coming from one large mesocyclone.

Damage survey seems to say no. http://www.crh.noaa.gov/news/display_cmsstory.php?wfo=oax&storyid=102897&source=2

 

[Jeff Duda]

I heard, and need confirmation this is true - that the two tornadoes rotated around one another.
If this is indeed true, and they rotated along a common axis, this would give credance to both coming from one large mesocyclone.

This sounds a little demanding (why not do your own research?), but it is an interesting point. The motion of the two tornadoes does resemble interacting cycloids with a nearly 180 degree phase offset (while one is approaching the kink in the cycloid, the other is moving at top speed around the other side of the meso). Additionally, I have argued previously that the velocity data show what appears to be one large mesocyclone in the storm at the time. However, there are some displacement issues between where the meso appears to be and where the tornadoes are, so I'm not sure.

 

[Bram]

I've created an additional video, in which I compare the lower and mid-levels of the storm by showing radar images of 3 radars at the same time. I've done that by putting the data from the KFSD- and KUEX-radar above that from the KOAX-radar. Keep however in mind that there is a small time difference between each radar image, of about 3 minutes at maximum.
This could give a better idea of how the formation of the low-level meso's is related to what happens in the mid-levels of the storm complex.

The video:

Watch video >