The extreme climate of Death Valley is attributable to its location on the leeward (downwind) side of the Sierra Nevada Mountains in central California. Air that has been warmed and moistened by its passage over the Pacific Ocean is driven up over the Sierras as it is carried eastward by the prevailing southwesterly winds of the northern mid-latitudes.
As the air rises up over the mountains, it expands and cools, triggering condensation that forms clouds and causes precipitation on the windward (west facing) slopes. At the same time, the latent heat stored in the water vapor in the air is released by the condensation process, adding measurable heat to the air As the now warmer and drier air continues its eastward journey over the peaks and begins its descent into the valleys on the leeward side of the range, its temperature rises as it is compressed under the higher atmospheric pressure of the lower elevations. The fact that Death Valley lies below sea level causes even more compression of the descending air, creating a very hot and dry “rain shadow desert” in Death Valley.