Along Highway 50 in the Sierra Nevada, elevation 6,820 feet, a California winter ritual unfolded here on a recent morning. In the snow-blanketed meadow of a local homeowner’s backyard, reporters representing news organizations from across the state followed a man on skis who kept plunging an aluminum tube into the snow.

Leading the pack was Frank Gehrke, California’s chief snow surveyor, the man responsible for measuring the Sierra Nevada’s snowpack, the source of a third of this state’s water supply. Part groundhog, whose appearances signal the shift of the seasons, and part Federal Reserve chairman whose utterances on the state of the snowpack can move California’s multibillion-dollar agricultural industry, Mr. Gehrke has led the Department of Water Resources’ snowpack surveys for a quarter-century.

(See related: Californians must pull on the same oar to address water crisis)

In the state that is home to Silicon Valley, Mr. Gehrke and his team use the stick-the-tube-into-the-snow method developed by a local classics professor more than a century ago.

For more, see: In California, Reading the Snow to Tell the Future for the Water Supply