Occurs when air is forced to rise and cool due to terrain features such as hills or mountains. If the cooling is sufficient, water vapor condenses into clouds. Additional cooling results in rain or snow. It can cause extensive cloudiness and increased amounts of precipitation in higher terrain.
Where the flow of air is forced up and over barriers such as highlands or mountains. Moist air being forced aloft begins to cool, consequently condensation forms, and rain or snow begins to fall. By the time the air reaches the leeward side of the barrier, it sinks and warms, resulting in decreasing relative humidity, cessation of precipitation, and the dissipation of clouds. May be called an orographic uplift.
Ascending air flow caused by mountains. Mechanisms that produce the lifting fall into two broad categories: 1) the upward deflection of horizontal larger-scale flow by the orography acting as an obstacle or barrier; or 2) the daytime heating of mountain surfaces to produce anabatic flow along the slopes and updrafts in the vicinity of the peaks. The first category includes both direct effects, such as forced lifting and vertically propagating waves, and indirect effects, such as upstream blocking and lee waves. Even though this term strictly refers only to lifting by mountains, it is sometimes extended to include effects of hills or long sloping topography. When sufficient moisture is present in the rising air, orographic fog or clouds may form.