Interdimensional portal that is usually invisible but the cleaning lady unplugged the equipment that would induce the cloaking.
has been probed by more than aliens! And, IIRC, didn't old Dave cover... 
that Brokeback Mountain... 
scandal?
David Culver. Jack Tripper. Peas... 
in the same pod!
it has very well defined edges and stays stable longer than I would expect a smoke ring to do, but maybe there were some unusual air currents keeping it together. But the fact that this video is so short leads me to believe there was some creative editing. Probably it dissipates a few seconds later.
Why do UFOs always appear over theme parks?
Nope - not very bright at all.
My brother actually recorded that video when he was at Kings Dominion on Saturday, and put that on YouTube for us family members to see. (He is properly credited on the news sites now as well). He just thinks it was probably the volcano smoke too, and has no trouble with the Kings Dominion explanation. He filmed it because he thought it looked so odd when it retained that shape for 15-20 minutes, and didn’t appear to move away at all. It stayed exactly like that for far longer than this minute-long clip. Lots of people were gathered around to watch it, and no one recalled seeing the obvious gradual ascent the ring would have taken on its way that high.
“DOSWELL, Va.”
That explains it. They were just lost, looking for Roswell.