In a good sign for California’s water supply, the Sierra Nevada has been blanketed by heavy snow thanks to a series of recent storms. The snowpack measured 106% of average, according to the state’s snow survey taken late last week. That’s more than double the 47% of average measured on the same day last year. The Sierra Nevada is a key source of water for California, which is still recovering from years of drought conditions. Two storms beginning on Thanksgiving brought up to 2 feet of snow in parts of the northern Sierra, said Emily Heller, a meteorologist with the National Weather Service.