Lenticular clouds are unique compared to other common clouds as they look like UFO, seem stable in the sky, and are found to have a smooth texture. Lenticular clouds are formed when air mass is lifted up to a high elevation, like a mountain or city area. When the air mass is lifted, the air temperature will decrease and the relative humidity will rise. This is similar to forming any cloud, only, the high elevation will assist in creating the right conditions. Once the air mass descends down the high elevation, the air temperature of the air mass with increase and the relative humidity will decrease. Usually the cloud will evaporate and the cloud will not follow down the elevated area. Think of the pattern of oscillating waves, like waves that you can see in the lake/ocean. The wave will move up then down. These is comparable to what the air mass will look like within the atmosphere above the high elevation.
The air mass will be moving almost perpendicular to the way the upper level wind are blowing, which will give the lens-like smooth appearance that they give. As these conditions continue, the Lenticular cloud will stay over the mountain top. This is why it seems stable and not moving within the atmosphere. It will continue to develop over a mountain and evaporate down hill of a mountain.