Lenticular clouds are stationary lens-shaped clouds that form at high altitudes, and are normally aligned perpendicular to the wind direction.
There are three different types of Lenticular clouds which are separated into altocumulus standing lenticular (ACSL), stratocumulus standing lenticular (SCSL), and cirrocumulus standing lenticular (CCSL).
They are usually found where stable moist air flows over a mountain or a range of mountains, since these locations are typical of seeing a series of large-scale standing waves that form on their 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 the 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 because their appearance resembles a smooth saucer-like shape with bright colors sometimes being seen along the edge of lenticular clouds.