Amid record-setting heat in the state’s south, California’s water managers will measure the Sierra Nevada snowpack, which supplies water to millions. Department of Water Resources officials will trek to the mountains Thursday to check the snow depth, one gauge of the state’s water supply. Electronic sensors show snow levels are about one-third of normal. At the peak of California’s recently ended five-year drought, Gov. Jerry Brown ordered 25 percent water conservation in cities and towns and declared a drought emergency.