"If we continue to see drought conditions in 2014 we will see a small crop," Bianco said.
The Napa Valley has received about 3 inches of rain this winter, compared to the 15 inches it normally would have at this time, said Jennifer Putnam, executive director of the Napa Valley Grapegrowers.
"We're coming off a very dry base," Putnam said. "The last time we saw levels like this was in 1976 and 1977."
In Sonoma County, grape growers have had about 2 inches of rain since July, only 13 percent of the normal amount.
While the situation on the North Coast may be dire, grape growers on the Central Coast have even worse water problems.
"This is not just a local problem, it's a statewide problem," said Doug McIlroy, director of winegrowing at Rodney Strong Wine Estates.
Vineyard managers and wineries alike are taking steps to curtail water use.
At Constellation Brands, executives are having serious conversations about water conservation in the wineries, said Steve Smit, vice president of vineyards and grape management. A winery typically uses about 1 to 4 gallons of water for each gallon of wine it produces, primarily on cleaning tanks and pipes, Smit said.
"Conservation has always been in the forefront, but this is just one more squeeze," Smit said.
Wineries are looking for new ways to collect and conserve water. For example, wineries that aren't already collecting rain water could start. But that won't help in this situation, Smit said.
"Assuming we stay dry, we're figuring we're going to have a crop loss, just due to the drier vines," Smit said.
Vineyards that have access to wells will likely be in better shape than those that draw from reservoirs, because reservoirs rely heavily on rainfall and runoff. Sonoma County may be in a better position than Napa County because of the prevalence of wells, McIlroy said.
"Those relying on direct diversions from tributaries, they're going to be in trouble, because there's no water in the tributaries," Linegar said.
But in Sonoma County, some wells are starting to run dry, and many new wells have been added in the past year, Linegar said.
"Our groundwater supply is very, very low, and a lot of wells have been extended over the past year," Linegar said. "I'm as concerned really almost about our groundwater situation as surface water, because it's equally as bad."
In the Russian River watershed, about 76 percent of the grape growers rely on well water to protect their crops from frost, and only 7 percent rely on direct diversions from rivers or streams.
As an alternative, vineyard managers have been flocking to buy wind machines, the tall, windmill-like structures that can move warm air from higher in the air to the ground level.
At Garton Tractor, the Turlock-based company with an office in Santa Rosa, wind machines are sold out until April, said Gary Petersen, sales consultant. Sales of the Sentinel Wind Machine, which cost about $30,000 for a portable version, have doubled over the past year, while rentals of the machines quadrupled, Petersen said.
"I just hung up the phone with another guy," Petersen said. "I was caught a little off guard with this."
Grape growers are buying the maximum levels of crop insurance, with some anticipating total crop loss, Linegar said.