OROGRAPHIC PRECIPITATION is caused or enhanced by one or more of the effects of mountains on the Earth’s atmosphere. These effects include the upward or lateral motions of air directly caused by mountains acting as a barrier as well as the thermal effects of the mountains that cause them to be elevated heat or cold sources. Mountains can generate both stratiform precipitation, which takes place in a statically stable atmosphere, and convective precipitation, which results from the release of static instability. The most obvious effect of mountains is that they can cause the air encountering them to rise. Rising air cools adiabatically, and if it is sufficiently humid, condensation and perhaps precipitation can occur. Precipitation formed by this mechanism is widely referred to as upslope precipitation. It is widely recognized that the slope on the upwind side of the prevailing wind (the windward side) generally receives more precipitation than the leeward side. In contrast, some of the world’s deserts are on the leeward side of mountain ranges. Because of interactions with other processes, however, there is no general rule about the location on the mountain slope where the maximum upslope precipitation will occur.