I think it's something to do with the storm being very high up
So the sound has to go down the long side of a triangle. Or something. I saw a picture in a book, once.
( dr_fonz, Mon 4 Jul 2005, 15:05, archived)

I stand,
very much corrected.

So much for my engineering degree!
( dr_fonz, Mon 4 Jul 2005, 15:09, archived)