The temperature of the moisture content of air varies as it passes over a mountain. Moist air cools in the process of raising upwards on the windward side of a mountain as it merges with cold air at higher elevations (Price, 2013). In that phase, the evaporation rate decreases while condensation takes effect. While at the top of the mountain, the air experiences colder temperatures under negative degrees, which prompts the water vapor to condense to snow. Contrarily, the air could also condense and form tiny droplets of air, which combine to formulate large clouds. Eventually, when the clouds become too heavy, it results in continuous drops, which falls back to land as rain.
Price, F. M. (2013). Mountain geography: Physical and human dimensions. Oakland, CA: University of California Press.