What weather forecasters called the biggest storm in three years raised a below average Sierra Nevada snow pack to levels above normal, according to automated readings from the California Department of Water Resources. Arthur Hinajosa, department hydrology branch chief, called it “a much needed helping of snow.” Statewide, automated precipitation monitoring stations showed that the average snow pack on January 8 stood at 109 percent of normal for this time of year. Snow pack in the northern Sierra stood at 112 percent of normal, in the central area at 101 percent, and in the south at 128 percent. The levels were up from the department’s January 3 manual snow survey. It showed snow levels in the Sierra Nevada ranging between 61 and 70 percent of normal. Reservoir levels, the department said, remain well below average because last year the snow pack reached only 40 percent of normal by the end of winter. Snow pack not only is a key supply of water for the state, but also a key determinant of the availability of hydropower. The department will release its next findings in February.