Earth's spin and the latitudinal gradient in solar energy input both contribute to prevailing wind patterns at Earth's surface. These surface winds—the northeast trades, the southeast trades, the westerlies, and the easterlies—blow primarily in certain directions at certain latitudes around the globe. For example, the westerlies are prevailing winds that blow from west to east at latitudes between 30 and 60 degrees north or south of the equator. Most of North America receives weather from the westerlies.

Regional climates on Earth are influenced by prevailing surface winds, the spatial arrangement of water and land, and by land topography. In the accompanying animation, we examine the causes of a rain shadow, which is a region of low precipitation on the leeward (wind-protected) side of a mountain range.


In North America, the Great Basin of Nevada and Utah is a classic rain shadow. This rain shadow occurs because the prevailing surface winds are westerlies that blow from the Pacific Ocean onto the California coast. As the air moves eastward it rises over the towering Sierra Nevada, which runs north and south along the eastern edge of California. Much of the water vapor in the rising air condenses and falls as precipitation on the western side of this mountain range. Far less rain and snow fall to the east of the crest of the Sierra Nevada. As a consequence, the lands to the east are part of the Great Basin Desert.

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Textbook Reference: Concept 41.2 Solar Energy Input and Topography Shape Earth’s Physical Environments