Frank Gehrke glided across a field of fluffy white powder, stopping to stab an aluminum tube into the snow to extract a sample. With the help of partner Dave Hart, Gehrke weighed the tube to compute the snow's water content.
The seemingly crude measurements offer a critical assessment of the state's snowpack and help forecast how much water will flow into reservoirs later in the year.
On Thursday, the pair trekked to Phillips Station – elevation 6,800 feet along Highway 50 – for what was the season's first snow survey.
Unfortunately, nobody was paying attention. A swarm of storms brewing in the Pacific slammed into the state Thursday night and are expected to dump several feet of snow in the Sierra by the end of the weekend, making Thursday's data old news.
Gehrke, snow survey section chief for the California Department of Water Resources, wasn't deterred by the pending storm or the pending obsolescence of his data, logging his measurements like clockwork.
He said the state has performed the snow survey ritual since 1929, and the timing of the surveys is not pegged to weather. In fact, the mantra of the snow survey office might be consistency, consistency, consistency.
For nearly 80 years, the surveys have occurred near the first of every month, from January through May, at the same locations.
The key thing, Gehrke said, is to do the measurement during a "window of time," usually from the 28th day of the prior month to the third day of the current one.
In addition to 250 manual snow surveys, DWR also collects snow depth and water content data from about 130 automated sensors, Gehrke said.
"One of the things they want to do with regard to climate change is you want the same sensors in the same location over time," said Gary Estes, who coordinates the California Extreme Precipitation Symposium. "You want to make sure that what you're seeing is a variation in the climate and not a variation in where you're taking the measurement."
This month's snow survey will not generate a water forecast, Gehrke said, but results will help validate data from automated sensors.
"Sensors have problems, they fail and lose calibration … a manual system is really hard to screw up," said Estes, who also sits on the board of the American River Watershed Institute.
Historically, surveyors may have needed days or weeks to trek to the measurement points. Once they get there, surveyors take measurements using a hollow tube and techniques similar to those used by James Edward Church for a snow survey at Mount Rose in 1906. Church, who taught classics at the University of Nevada, Reno, was a life-long weather buff who pioneered a simple technique to measure the water content in snow.
"Before that, people would melt snow, which is completely impractical in a field situation," Gehrke said.
Now, after the data are collected and verified, a water forecast goes out to contractors of the State Water Project.
"You have a big pot of water and you try to divvy it out to various entities depending on the water supply," said Gehrke.
The snowpack stores water during the winter for use during the drier summer months. By comparing data on the snow's water content against stream flow, Gehrke said, they can forecast water availability.
On the day Gehrke and Hart logged their measurements, the snowpack was about 60 percent of normal, but the cold-air storm that rolled in Thursday night is adding inches to the snowpack.
That's good news for the state.
2007 was a dry year, and the state ran through the surplus gained during the previous wet year. Gehrke said the state needs a storm-filled winter to replenish the snowpack to avoid drought-like conditions later.
Estes said water forecasting is critically important to water and energy planners. In addition to DWR, federal agencies, utilities and irrigation districts also carry out or collaborate on snow surveys.
Estes said the state's "plumbing" is complex, with water and energy needs often intertwined.
During the peak energy periods of the summer, utilities rely on hydroelectric power, Estes said,
"It's easy to open the valve and let more water run out to generate power faster, with a quicker response time, than to bring on an extra gas-powered generator," Estes said.
Call The Bee's Ngoc Nguyen at (916) 321-1041.
