Gabe Joseph took this photo of clouds over Vancouver, B.C. last Sunday -- sort of like a zebra sky with strips of clouds.
I'm thinking these were caused by gravity waves where you can get turbulence over mountain ranges, such as the Cascades in this instance. The turbulence can be such that when the air rises just enough to cool and condense into a cloud, the sinks a a bit, drying it out and then rises, cools, condenses, etc., as it propagates forward.
Here is a visible satellite image from roughly the same time.
Note how up in southern B.C. you can see the wavy clouds. Actually, if you watch the visible satellite from time to time you can catch these clouds.
Speaking of clouds, take a look at this time lapse video of a storm as it passed over McDonald Observatory in Texas. This is a fish-eye camera more used for astronomical observations but watch the sky as it bubbles during a storm as it passes overhead.
My first thought was, wow, look at those swirling clouds. And my second thought was, wow, they sure do have a lot of bugs in Texas! :)
Have a great weekend!