A very cool picture on EPOD today, taken in Olympic National Park, Washington. That is a lenticular cloud forming as a breeze of very-nearly saturated air rises over a sea stack, cools a tiny amount, leading to condensation and cloud formation. As the air descends again, it warms, and the cloud droplets evaporate. So this would look like a standing wave in a stream; the cloud would appear to be constantly moving, but not going anywhere. Click the pic for bigger, and over to the site for more info.
Actually I just went back to the site and re-read the blurb... it's quite dissimilar to breath condensation. In that case, very warm, moist air is being introduced to a cooler, drier environment. The "fog" dissipates when it mixes enough with the drier air to bring the overall moisture content below the dewpoint. The formation and evaporation of the mist has nothing to do with adiabatic processes.
Followup: I took a smaller version and ran it through autolevels in Paint.Net: the result is nice...
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