Photo by Donald F. Collins
This interesting lenticular cloud appeared over the Swannanoa Valley near Warren Wilson College on April 1, 2004 near sunset. The small dark clouds in the foreground were moving fairly quickly from the left – a strong northwest wind. The big lenticular cloud in the background, still illuminated by the sunlight, is rather stationary, although the winds in the big cloud are perhaps much stronger than at lower elevations.
Notice the layered appearance of this cloud. It is formed by "waves" in the wind on the downwind side of the mountains. The mountains are the Great Craggy Mountains beyond the left edge of the photo and the Black Mountains near Asheville, NC. After the wind reaches the top of the mountain(s), it tends to oscillate as up and down waves – like a flag flapping in the breeze. When the air reaches the top parts of the wave, the cooler temperature causes the water vapor to condense and form the layered cloud. As the air returns back to lower elevations, the warmer temperature evaporates the cloud droplets. Lenticular clouds tend to stay in one place, but the wind rushes through them with considerable speed. See the drawing below.
Here are some links to more Lenticular cloud photographs:
Astronomy Picture of the Day: Dec 1, 2003
See complete list Physics Photo of the Week