During a ski ascent of Mt. San Jacinto (10,834'), we had paused for a moment on a steep slope part way up the mountain, when I glanced up and saw these sheets and filaments of translucent cloud sweeping past in the west-northwest flow.
Six months ago, I'd seen a similar series of clouds on Boney Mountain, in the Santa Monica Mountains.
These vaporous, turbulence-induced clouds bear a striking resemblence to interstellar molecular clouds. Both appear to occur in a high-Reynolds-number regime, and each seems to consist of a cohesive, thin sheet of condensate that can be stretched, sheared, undulated and torn. As in the case of its interstellar counterpart, when viewed edgewise, the clouds look like they are comprised of thin filaments.See:
(The vertical band is an artifact caused by the sun.)