Precipitation is the condensation of water vapor under natural weather conditions. Depending on temperature and weather dynamics precipitation may occur as rain, snow, hail, or sleet. The condensation of water vapor releases the heat used in its evaporation increasing the ambient temperature and adding to the vigor of weather dynamics.
Global weather patterns result in wide disparity in the amount and type of precipitation which falls in various regions. Central to this variation is whether air is rising or falling. Rising air will release precipitation; falling air makes precipitation extremely unlikely. Due to global weather patterns certain regions are affected by global circulation patterns of air movement. Particularly notable are bands of desert on the western coast of continents in the sub-tropical regions in which air masses are nearly always descending. Other major factors are latitude and altitude, polar latitudes being cold, particularly in winter, and high altitude land masses providing lift as air masses move over them resulting in precipitation.