Elkhart, 1965

[Steve Dedman]

After seeing the big double tornado in Nebraska today, and a lifetime of seeing pictures of the big 1965 Elkhart double, I got to wondering...what are the mechanics at play in a situation like that? It seems reasonable that one tube would be cyclonic and the other would be anti cyclonic. Is that the case in reality? What atmospheric craziness is happening that would produce two updrafts capable of becoming significant tornadoes that close together? Normally, one would undercut the other. Why did that not happen today or on Palm Sunday 1965?

 

[Shawn Schuman]

The two situations are quite different. The Palm Sunday "twins" was actually a single multivortex tornado. Fujita theorized that a very rapid expansion in size (the tornado grew significantly in ~15 seconds) essentially caused a breakdown in the near-surface airflow, causing it to "split" into two large vortices before merging again. You can see the whole process play out if you look at all six photos in Paul Huffman's sequence.



(Not to plug myself, but I have higher resolution photos of several of them on my blog post on the Palm Sunday Outbreak)

Today, there were two distinct large, strong/violent tornadoes, each of which appeared to be associated with its own discrete mesocyclone. Judging by the radar signatures, it appeared they were 2-3 miles apart at times. It was a very interesting evolution, but it's hard to piece together exactly what happened without having full access to the radar sequence; I can't wait until the archived data become available via HDSS to really dig into it.

 

[rdale]

Disregard - I didn't realize it was still in that paper

http://docs.lib.noaa.gov/rescue/mwr/098/mwr-098-01-0029.pdf

 

[Dan Robinson]

Cyclic supercells producing simultaneous tornadoes as new mesocyclones develop are indeed very common. What made Pilger truly rare was the close proximity of the two tornadoes, the strength/size/violence/long lifespan of both of them occurring nearly simultaneously, and the fact that both were highly visible/photogenic for extended periods. I can think of many cyclic supercell double tornado events - I've seen a few myself (4/14/12, 5/4/07, 5/5/07, etc), but cannot think of one that comes close to the visual quality of Pilger.