1. Elevation It gets colder the higher in elevation you go. As air rises, it expands because of lower air pressure. As the air expands, it cools. When air is cooled, it eventually reaches a temperature at which it is saturated with water vapor (it is holding the maximum amount of water at that temperature and air pressure). This is called the dewpoint.

2. Further cooling leads to condensation (changing water vapor into a liquid). Liquid becomes clouds, and if the droplets grow large, they will fall as precipitation. The type of precipitation is dependant on the weather conditions at that time. The following diagram illustrates how to calculate the temperature of an air mass as it rises up a mountain.