When an air mass encounters a large terrestrial mass (i.e. a mountain) the air is forced to a higher altitude and cooled. As the air cools humidity increases and clouds form. If there is sufficient moisture in the air, this process may result in precipitation on the side of the mountain facing the wind (leading to the orographic effect). The video below is a time-lapse of Mt. Fuji. As the day goes on, air temperature increases, gradually dissipating the clouds. Note that the clouds progressively dissipate toward the point where the orographic lift is occurring.