"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.