- See also: Chemical precipitation
Precipitation is any condensation of atmospheric water vapor which is left on the ground. Condensations occurs when water molecules slow down as they cool and change into a solid or liquid. Condensation is the opposite of evaporation. When air rises, it cools by an adiabatic process. Air rises when cold air pushes hot air up. Cold air can push hot air up because hot air is less dense. Rain, snow, sleet, dew, frost, hail, and drizzle are all forms of precipitation. If liquid, it can be measured using a rain gauge. The most common form of solid precipitation is snow. Snow is made when temperatures are so cold that water vapor changes directly to solid crystals.