Volcanic Lightning - Stefnisson
Gravity Tides or Gravity Waves
The undulating pattern of a Gravity Wave is caused by air displaced in the vertical plain, usually as a result of updrafts coming off the mountains or during thunderstorms. Nature then tries to restore the fluid changes caused by updrafts within the atmosphere, which present in a visible oscillating pattern within the cloud.
This framegrab taken from video provided by StormChasingVideo.com shows two tornadoes approaching Pilger, Neb., Monday June 16, 2014. The National Weather Service said at least two twisters touched down within roughly a mile of each other Monday in northeast Nebraska.
HH: Evil Twins
Not that I think nature is evil, but I am guessing people on the ground thought so.
These rare shapes are formed—under perfect temperature conditions only—when a mass of snow either falls or is blown by the wind. If it manages to catch on to some other snow, and gravity or the wind is in its favor, then the new snowball will roll itself in the exact same way we all used to. In this case, though, the middles tend to collapse to create a donut shape, which can end up as tall as 26 inches (66 cm).