Officials will trek into the mountains on Thursday to measure California’s snowpack again, in the hopes that recent storms have added to the state’s water supply. The California Department of Water Resources will perform the second survey of the season in the Sierra Nevada. Winter snow provides drinking water for much of the state as it melts in the spring and summer and flows into reservoirs for storage. The Sierra snowpack was 67 percent of normal in this winter’s first manual measurement earlier this month. The amount of snow is measured monthly through the winter at more than 260 locations to help water managers plan for how much they can deliver to customers later in the year.