Glaciation in clouds is the rapid growth of ice crystals, most often in cirrus clouds, usually leading to precipitation of the crystals. Those cirrus clouds featured above floated over Warren Wilson College near Asheville, North Carolina. Photographer: Donald Collins; Don’s Physics Photo of the Week site
The upper parts of the cirrus clouds (the top “roots” of the clouds) are receding from the observer, moving from the west.
Lower altitude wind is from the south, from the right in the photograph.
The movement and formation of the comma-like tails can be seen in the time-lapse animation (click here).
Photo taken December 3, 2011.