Source: Nature: "Life in Death Valley"
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Death Valley's deep, narrow shape and its relative position to four major mountain ranges contribute to its extreme weather conditions. Low elevations, lack of moisture and an average of 300 days of sunshine result in an annual evaporation rate of 150 inches. Due to the rain-shadow effect of the mountains surrounding the valley, fewer than two inches of rain falls annually. In this video segment from Nature, learn about the rain-shadow effect and air circulation in Death Valley.
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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.
Death Valley roasts in triple digits for up to 8 months of the year. No place else in the Western world comes close to being this hot – for this long. The Valley works like a huge convection oven. Hot air crawls up the steep rock walls, cools slightly and sinks back down. Compressing as it descends, it heats even more.
Masses of superheated air take ground temperatures up to two-hundred degrees Fahrenheit.
But heat is only the beginning.
A mere inch-and-a-half of rain falls each year, condemning this place to perpetual drought.
Convection clouds taunt the desert with rain. Most of the time, they don’t even bring shade.
Storms blowing in from the Pacific slam into the mountains to the west, leaving Death Valley in a barren rain shadow.
The trivial amount that does make it past the peaks is often stolen back up to the skies in the form of a Virga – rain that evaporates before even hitting the ground.
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