ST. HELENA -- Napa Valley winegrape growers are drawing on a number of measures to limit water usage and protect vines that are beginning to bud more than a month early, as California's drought has turned normally wet, chilly winter days into a stretch of warm, dry days that could ultimately lead to a smaller 2014 crop, according to local industry experts.

Though showers are in the forecast later this week and into the next, growers of the highest-priced winegrapes are looking for rain -- and a lot of it -- in the next few months, Jennifer Putnam, executive director of Napa Valley Grapegrowers, said at a press conference in the 670-member trade association's St. Helena offices on Tuesday.

Southern Napa Valley should have received almost 15 inches so far in the July-to-June rain season, but the accumulation in that area was 2.98 inches, she said. The valley faced a similar drought situation four decades ago.

"If February and March were wet, we would be in a good position," she said. The valley would have to get 8 to 9 more inches of rain to get to that point.

A key challenge for winegrape growers in drought conditions is figuring out how much of the yet-to-be-seen crop can make it to harvest, given available water, according to Domenick Bianco of Renteria Vineyard Management.

"If we continue to see drought conditions, we will see a smaller crop," Mr. Bianco said at the news event. "If we get 80 percent of the water of the previous year, we could have 80 percent of the crop of the past year."

The effect of rainfall that's one-fifth of normal by this point in the season is noticeable because of the absence of a common vineyard cover crop -- yellow-flowered mustard, which beneficially competes with vines for resources, keeps soil in place and fixes nitrogen in soil. This may call for growers to use compost or fertilizer to provide vine nutrients, Mr. Bianco said.

Growers are concerned about what they are seeing -- vines waking up too early from their winter naps. Usually, dormancy lasts until late February or early March. But buds have been seen on about 10 percent of chardonnay vines on the hills of Los Carneros appellation straddling southern Napa and Sonoma counties, and vines also are starting to bud in the Rutherford and Stag's Leap viticultural areas of Napa Valley, Mr. Bianco said.

"Growers and managers are taking very proactive steps," he said.

Crews usually are busy in the vine rows in January beginning pruning, but the warm weather this season has allowed vineyard teams to progress much further by now and to take a number of measurements to determine, he said. Suckering, or removing of vine shoots, will likely start three to four weeks earlier than the typical April start. Usually done to allow the vine to concentrate its physiology on developing the best fruit, shoot thinning this year will take on new importance by limiting the foliage and clusters the vine needs water to support. Yet there's a balance, because removing too much foliage can lead to on hot days vine shutdown of activity and "sunburn" of exposed fruit.

So tools growers are bringing to the drought fight include the simple -- fixing leaking hoses and pipes -- to high-tech neutron probes that measure soil moisture and irrigation models based on evapotranspiration, or ET, or the water needs of a plant based on environmental conditions. These tools help with critical timing of irrigation, if a vineyard is has it, and "precision irrigation," or watering portions of a vineyard block at certain times, rather than the entire property.

One thing certain areas of Napa Valley have going for them this year are ample aquifers so far, yet the wine industry is monitoring groundwater closely to see how it's affecting surface water such as major waterways, according to Hal Huffsmith, director of vineyard operations for Trinchero Family Estates.

"We'd prefer to avoid the situation in Paso Robles," he said. Vineyard and other agricultural irrigation is blamed for a significant drop in the water table in that area.

Two years ago, vintners and growers approached the county of Napa to form a Groundwater Resource Advisory Committee that would oversee a program in which growers would agree to have their well performance logged twice annually to help with policy-making.

So far this year, Trinchero's wells throughout Napa Valley, except for some on the hillsides, have adequately performing wells, Mr. Huffsmith said.

"I suspect that even if the drought persists for a couple of years, we will continue to have consistent crops in Napa Valley," he said.

Challenges with adequate water on hillsides to water cover crops is posing challenges with compliance with county of Napa hillside erosion-control guidelines, and growers and public officials are pursuing solutions, according to Mr. Bianco.