Winter may have officially ended two months ago, but its cold, wet weather has returned.
California was hit this week by a storm of epic proportions — for the month of May, at least — and more water is on the way. According to Turlock Irrigation District, the Tuolumne River watershed since Wednesday has accumulated two inches of precipitation, with the current forecast indicating another four to five inches over the next 16 days. The historical average amount of rainfall in the watershed during the month of May as a whole is 1.59 inches.
The late rainfall comes on the heels of one of California’s wettest winters in years, which saw a majority of the season’s months exceed the historical average for precipitation. Storms in February alone produced nearly 14 inches of rain in the watershed, and statewide, California’s snowpack surged to 152 percent of its historical average, leaving the state drought-free for the first time in nearly a decade.
According to TID, this week’s storm was part of a cooler weather system, which dropped freezing levels and lowered the total amount of runoff from the large snowpack into Don Pedro Reservoir. During this week’s storm, the Sierra Nevada range received an additional eight to 15 inches of powder since Wednesday, extending the season at some ski resorts until July. Another eight to 15 inches is expected over the weekend.
With a massive snowpack in the Sierra Nevada range already and more powder on the way, TID is keeping a close eye on Don Pedro’s water level.
TID has increased releases to the Tuolumne River to approximately 6,800 cubic feet per second to accommodate for the influx of precipitation and runoff, Communications Specialist Brandon McMillan said, and the agency anticipates holding releases near this level through the weekend.
McMillan said TID works closely with the Airborne Snow Observatory — an aerial snow monitoring program developed by NASA — to manage water storage, flood protection, generation and recharge opportunities. The ASO measures the snowpack and also helps balance competing demands on water releases, he added, and LiDAR technology provides precise measurements of depth for every square meter of snow in the watershed.
Combined with more conventional snowpack surveys, ASO provides a complete and precise picture of snow water content.
“This data is used to determine when and how much water will be released from Don Pedro Reservoir based on anticipated precipitation and runoff, and is extremely helpful during off-season storms such as those we are currently experiencing,” McMillan said. “Having more precise measurements of the snowpack prevents TID from making unnecessary releases and increasing flood risks.”
TID Chief Hydrologist Wes Monier described the ASO program as having “created new reservoir space and water supply without any impacts to the current physical or environmental paradigms.”
Given the size and water content of this year’s snowpack, McMillan said TID will likely maintain releases around the 6,000 CFS mark until July.
