Wednesday, April 1, 2009

Lenticular Clouds

We had some strong cold winds today and passing Mount Shasta you could see the lenticular clouds forming again. The bottom picture is almost a "three layer" effect.
As always, click the images for larger pictures.

Lenticular clouds are stationary lens-shaped clouds that form at high altitudes, normally aligned at right-angles to the wind direction. Lenticular clouds can be separated into altocumulus standing lenticularis (ACSL), stratocumulus standing lenticular (SCSL), and cirrocumulus standing lenticular (CCSL).
Where stable moist air flows over a mountain or a range of mountains, a series of large-scale standing waves may form on the downwind side. If the temperature at the crest of the wave drops to or below the dewpoint, moisture in the air may condense to form lenticular clouds. As the moist air moves back down into the trough of the wave, the cloud may evaporate back into vapor. Under certain conditions, long strings of lenticular clouds can form near the crest of each successive wave, creating a formation known as a 'wave cloud'. The wave systems cause large vertical air movements and so enough water vapor may condense to produce precipitation. The clouds have been mistaken for UFOs (or "visual cover" for UFOs) because these clouds have a characteristic lens appearance and smooth saucer-like shape. Bright colors (called Irisation) are sometimes seen along the edge of lenticular clouds