Orographic precipitation

Orographic precipitation forms when terrain forces moist air upward, cooling it until water vapor condenses and falls as rain or snow. It often creates wetter windward slopes and drier leeward regions.

Orographic lift: The forced upward movement of air over elevated terrain. This lifting initiates the cooling that produces orographic precipitation.
Atmospheric moisture: Water vapor and liquid or ice particles present in Earth's atmosphere. A supply of atmospheric water vapor is required for terrain-triggered precipitation.
Orographic enhancement: An increase in precipitation caused by terrain-induced ascent of moist air. Forecasts account for extra precipitation where terrain forces stronger uplift.
Cascade Range: A volcanic mountain range extending from British Columbia through Washington and Oregon to Northern California. Pacific moisture produces heavy windward precipitation and a pronounced lee-side dry zone.
Frontal precipitation: Precipitation produced when air is lifted along a boundary between contrasting air masses. Frontal boundaries lift air, unlike the terrain that forces orographic ascent.
Adiabatic process: A change in a system's state without heat transfer to its surroundings. Rising air expands and cools approximately adiabatically as pressure decreases.
Atmospheric stability: The resistance of an air parcel to vertical displacement relative to its surroundings. Stability affects how readily forced ascent continues and how clouds develop.
Orographic precipitation model: A numerical representation of precipitation changes caused by airflow over terrain. These models estimate how topography modifies rainfall and snowfall.
Sierra Nevada: A mountain range in eastern California and western Nevada. Its western slopes receive substantial Pacific-driven orographic precipitation.
Convective precipitation: Precipitation generated when buoyant air rises, cools, and forms clouds. Convection is driven chiefly by buoyancy rather than airflow meeting terrain.

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