Lenticular Clouds are stationary lens-shaped clouds that form in the troposphere at high altitude. They are normally aligned at right-angles to the wind direction. They are regularly found near mountainous areas and can appear singular or stacked like pancakes. Lenticular Clouds are different from other clouds because they are stationary. They re-form continuously over the same location by new air rising up and over a mountain, condensing and producing such clouds. Lenticular Clouds have been regularly confused for UFOs due to their smooth, round or oval lens-shaped structure. Power pilots avoid flying near them because of the turbulence of the rotor systems that accompany them.