Orographic lift

Orographic lift is the upward deflection of airflow by terrain such as a mountain range. Rising air cools, which can form clouds and produce precipitation.

Adiabatic process: A change in a system’s temperature caused by expansion or compression without heat exchange with its surroundings. As air rises over terrain, lower pressure makes it expand and cool without exchanging much heat.
Atmospheric pressure: The force per unit area exerted by the weight of the atmosphere. Pressure decreases with altitude, allowing rising air to expand and cool.
Numerical weather prediction: Forecasting atmospheric conditions by solving mathematical equations with computer models. Models represent terrain and airflow to estimate where orographic precipitation will fall.
Cascade Range: A volcanic mountain range extending from northern California through Oregon and Washington into British Columbia. Moist Pacific air rises over the Cascades, producing heavy windward precipitation and a drier interior.
Lapse rate: The rate at which an atmospheric variable, usually temperature, changes with altitude. The environmental lapse rate determines whether lifted air stays buoyant or becomes stable.
Atmospheric stability: The atmosphere’s tendency to resist or enhance vertical displacement of air. Stability governs whether terrain-lifted air continues upward or returns toward its starting level.
Mountain meteorology: The study of atmospheric processes and weather in mountainous regions. Orographic lift is one of the central processes shaping mountain weather.
Sierra Nevada: A mountain range in eastern California and western Nevada. Pacific storms rise over the Sierra Nevada and deliver substantial rain and snow to its western slopes.
Orographic precipitation: Precipitation enhanced when moist air is forced over elevated terrain. It is the common precipitation outcome when terrain-driven ascent cools moist air to saturation.
Relative humidity: The ratio of water vapor in air to the maximum amount possible at the same temperature. Cooling increases relative humidity, bringing lifted air closer to cloud formation.

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