Precipitation

In meteorology, precipitation (also known as hydrometeor) is any product of the condensation of atmospheric water vapor that is deposited on the earth's surface. It occurs when the atmosphere (being a large gaseous solution) becomes saturated with water vapors and the water condenses and falls out of solution (i.e., precipitates) Air becomes saturated via two processes, Cooling and Adding Moisture. Precipitation that reaches the surface of the earth can occur in many different forms, including rain, freezing rain, snow, sleet, and hail. Source: http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29