Rain Shadow Deserts

Moisture for storms comes from large bodies of water, primarily oceans, and are pushed over the continents by massive global air currents. When this moist air comes over a continent and hits a mountain it is forced up the range where it cools, condenses and often falls as rain. Mountains often receive much more precipitation than the areas around them. As this air pushes over the top of the mountain and down the other side it can again expand, although it has now lost much of its moisture. This "Rain Shadow" effect can be so strong that the area behind a mountain is a desert. In fact, all the deserts of North America are influenced by this "Rain Shadow" effect.

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