Lenticular clouds also called Altocumulus lenticularis are stationary lens-shaped clouds that form in the troposphere, usually in perpendicular alignment to the wind direction. Lenticular clouds can be separated into ACSL, (Altocumulus Standing Lenticularis) or SCSL (Stratocumulus Standing Lenticular), and CCSL, (Cirrocumulus Standing Lenticular). Due to their shape, they’ve been offered as an explanation for some UFO (Unidentified Flying Object), sightings. As air flows along the surface of the Earth, it comes across obstacles. However, our atmosphere, the envelope of air surrounding of planet, is always in motion. We have a tendency to to think of the motion of our atmosphere as horizontal across the ground, namely wind. Though, air can move vertically as well.
Therefore, these are man-made objects, such as bridges, and buildings, & natural features, like hills, Mountains and valleys. Hence all of them disturb the flow of air into eddies. Moreover, the strength of eddies depends on the size of the object and the speed of the wind. It results in turbulence classified as “mechanical” because it is shaped through the “mechanical disruption of the ambient wind flow”. Where constant 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 the dew point, moisture in the air may abridge to form lenticular clouds. Thus, as the moist air moves back down into the trough of the wave, the cloud may evaporate back into vapor.
Moreover, under definite conditions, long strings of lenticular clouds can form nearby the crest of each sequential wave, forming a formation recognized as a "Wave Cloud." The wave systems reason big vertical air movement; adequate that water vapor may condense to create precipitation. The clouds have been mistaken for UFOs or "Visual Cover" for UFOs, mainly the round "flying saucer"-type, since these clouds have a characteristic lens appearance and level saucer-like shape; also, as lenticular clouds usually do not form over low-lying or flat terrain, numerous people have never seen one and are not aware clouds with that shape can exist. Bright colors called irisation are sometimes seen along the edge of lenticular clouds.
Thus, these clouds have also been recognized to form in cases where a mountain does not exist, but somewhat as the result of shear winds created by a front. Moreover, pilots of powered aircraft tend to stay away during flying near lenticular clouds because of the turbulence of the rotor systems that accompany them, but glider pilots actively seek them out. The exact location of the rising air mass is justly easy to envisage from the orientation of the clouds. "Wave lift" of this kind is often very smooth and robust, and enables gliders to soar to extraordinary altitudes and great distances. The present gliding world records for both distances is over 3,000 km; and altitude 50,721 feet was set using such lift. Well, standing lenticular clouds are associated with a phenomenon famous as mountain wave turbulence. Following are few breathtaking shots of one of those mountain weather spectacles, standing lenticular clouds.Source: Wikipedia