Geology of the National Parks - Death Valley
Death Valley's Incredible Weather
Why is Death Valley a Desert?
Any area that receives less than 10 inches/year of precipitation and has a high evaporation rate is considered a desert. Death Valley averages less than 2 inches each year and tops the list as the hottest, driest spot in North America. A major factor contributing to Death Valley's extraordinarily dry weather is the rain shadow effect.
Catching the Clouds: The Rain Shadow Effect
Water-laden storms sweep onto the western coast of North America from the Pacific Ocean. Why doesn't Death Valley get its share of this watery abundance? To answer that question, we have to start at the coast and work our way east.
Prevailing winds travel northwest to southeast in this part of the world, storms follow this track too. While some of the water carried in the storm clouds is dumped onto coastal communities, much of the moisture remains in the clouds until the reach the mighty Sierra Nevada mountain range.
When clouds encounter the Sierras, there's nowhere to go but up. As the clouds rise, the air cools. Cold air cannot hold as much water as warmer air, so the water condenses from the clouds and drops as rain or snow on the western flanks of the Sierras.
This precipitation supports luxuriant vegetation on the west side of the range as well as glaciers and snow fields on the higher peaks. Not a lot of moisture remains by the time the storm reaches the eastern side of the Sierras. On encountering the warmer air of the continental interior, any remaining clouds warm up and can retain their moisture without dropping it on the parched earth below.
Weather & Climate
Death Valley is famous as the hottest, driest place in North America. Even though summers are extremely hot, temperatures are cooler at higher elevations by 3 to 5 degrees F with every thousand vertical feet. Clear skies and mild temperatures in fall, winter, and spring make these seasons the most pleasant time to visit.
Weather data was compiled from the park's daily records and from National Weather Service summaries for the years 1911 through 1998 for Furnace Creek in Death Valley, California.
Temperatures in Fahrenheit / precipitation in inches 1911 to 1998
The longest summersThe greatest number of consecutive days with a maximum temperature of over 100°F was 134 days in the summer of 1974. The summer of 1996 had 40 days over 120°F, and 103 days over 110°F.
The highest ground temperaturesThe highest ground temperature recorded was 201°F at Furnace Creek on July 15, 1972. The maximum air temperature for that day was 128°F. Ground temperature on the valley floor is about 40% higher than the surrounding air temperature.