The USGS Water Science School
This picture shows a common sight seen during fair-weather days where there are mountain and ridges in the landscape. Maybe you've wondered why big, puffy clouds seem to like to hang out near mountain ridges and above mountain peaks. The mountains are not putting out more humid air than other areas, but the process of condensation is taking place because of the mountains. In the United States, since weather moves generally west to east, this is more easily seen when moving air from the west hits higher terrain and is pushed up by the landscape as the air travels eastward.
Although you don't see the water vapor in the clear air approaching and moving upward and above the mountain ridge, vapor is present and the potential for clouds are present, too. As the air is pushed up by the landscape, the higher-altitude air is cooler than the moving air, so condensation occurs and clouds form. Often this is responsible for rain on the windward sides of mountain ranges, such as the Sierras in California, and much drier air on the leeward side of the mountains, as in Nevada.
Back to The water cycle: Precipitation | Condensation | Atmosphere
Credit: Bureau of Land Management