Was I even tempted to type in an intro, when there are images like that? Follow the link below to a weather blog in Alabama, and you will see many pictures of these incredible things near Birmingham -- a long line of what are called "Kelvin-Helmholtz Wave Clouds". The one here is a compromise between seeing one with a long line of them across the screen, and ones with a close up of one or two of them. They look like the vanguard of some fluffy War of the Worlds.
If the atmosphere near the ground moves at one speed/velocity, and the atmosphere above it moves along the same direction but at a different speed, the instability can easily produce this. But we don't see it like this often.
Now ... STEP TWO. On the following Monday in that blog, someone posted an analysis. I haven't read it yet, but there are more pictures. Take a glance. For one thing, this is a 3-D sort of thing as the clouds had formed long lines sideways as well, starting way back in Texas.
But move on to ... STEP THREE. At the bottom of the original blog entry, there is a link to the Wikipedia article on the subject. There you will read lots about these things, because you see them all the time on Jupiter and Saturn. After all, different speeds in the same direction is the forte of those two planets.
Then ... STEP FOUR. One of my favorites. At the bottom of the Wikipedia article is a reference to a NY Times article on how similar waves (with frequencies of 50 seconds) are found at the bottom of the Atlantic Ocean, and how they relate to stirring up the bottom and distributing nutrients down there.
Absolutely mind blowing. If you were standing on a mountain at the bottom of the Atlantic, you might have an experience similar to the one of being in Birmingham, staring up at a HUGE WAVE THING passing right over you.
(Sorry for all the "gosh wow" sentiment. But ... c'mon!)