Recent rainstorms have Sonoma County grape growers feeling more optimistic about being able to protect their crops from killer frost as full-blown bud break appears imminent.

"Right now we seem to be doing pretty good for frost protection. Most people have what they need," said Doug McIlroy, director of winegrowing at Rodney Strong Wine Estates.

Farther north in Mendocino County, however, growers are still being warned that they probably won't have any water for frost protection this season because of low reservoir levels and flow in the Russian River.

"Very limited, if any," said Sean White, general manager of the Russian River Flood Control District.

North Coast growers have been anticipating bud break with dread because of the lack of rain. Many have taken out crop insurance as a hedge against major crop loss.

But in Sonoma County, recent gully washers have filled farm reservoirs and increased flows on the Russian River as tiny buds popping out on vines signal the start of the 2014 growing season.

"We're in good shape," said Chris Bowen, vineyard manager for Hunter Farms in Sonoma Valley.

Bowen said buds are breaking out all over in one of the winery's chardonnay vineyards off Arnold Drive. The buds will gradually shoot into leaves and vines and, finally, clusters of plump grapes.

Full-bore bud break has yet to happen on the North Coast. But that could accelerate quickly with high temperatures expected to climb into the mid-70s to low 80s later in the week. No rain is predicted through Sunday.

"At least for the next week, it's going to be nice, unfortunately, because we could probably use the water," said Diana Henderson, a meteorologist with the National Weather Service.

The good news for grape growers is that overnight lows are predicted to be in the 40s through the end of the week. Henderson said longer-range forecasts show more of the same.

When temperatures fall below freezing, vineyard managers spray tender buds with water to form a protective ice shield on the grapes. The frost protection season generally runs from March 15 to May 15.

Sonoma County Agricultural Commissioner Tony Linegar said conditions have "certainly improved" as a result of recent storms.

It rained 9.33 inches in Santa Rosa during February, the 13th-wettest February on record. Average rainfall for the month is 6 inches.

Linegar said growers still need to manage their water use wisely so that they have enough on hand for irrigation later in the year.

McIlroy echoed that sentiment, saying "it's still a drought."

Still, Sonoma County growers generally are feeling much better about things than they were a month ago when the conversation mainly was about managing crop loss. Many growers decided to prune their vines differently to reduce fruit or canopy in an effort to reduce future water use.

Then the rains came. At Hunter Farms, Bowen said a reservoir fed by a winter stream is at capacity and should be enough to last the winery through the growing season.

In years past, the winery could purchase supplemental water from the Sonoma County Water Agency. But the agency in February notified the winery the service would not be available this year because of the drought. The agency has about 25 such contracts, mostly tied to the agricultural industry.

Lake Sonoma, which fell to about 65 percent capacity, is up to 73 percent with recent storms, said Brad Sherwood, a spokesman for the water agency.

River flows at Dry Creek southwest of Healdsburg were at 899 cubic feet per second on Monday. Under state rules, those flows can't dip below 25 cfs, Sherwood said.

"We'd be in a much different scenario if we hadn't received those rains," he said.

River flows at Hopland in Mendocino County were dropping rapidly Monday as the effect of rains diminished. Early in the day the flow was 1,600 cubic feet per second but by evening it had dropped to about 840, according to the state Department of Water Resources.

White said Lake Mendocino near Ukiah, which as of Monday was a litle over 50 percent of capacity, is still on track to run dry by November, something that has never happened. The reservoir provides nearly all the water in Russian River during the traditional dry months.

He said growers have been calling him constantly for updates. But his message to them has remained constant: without river flows above 100 cfs, they won't be able to use water for frost protection.

Some growers rely on fans for frost protection.

David Cook, a Sonoma councilman who owns a vineyard management company, said the cost to operate the fans runs between $50 and $100 an hour, which can add up quickly. There are nine fans for the 450 acres he manages in Sonoma Valley and Carneros.

"You don't want to fire up a fan unless you have good cause to," Cook said.

Like growers and vineyard managers everywhere, he'll be closely monitoring weather forecasts and temperature gauges in coming weeks for signs of impending frost.

"We'll definitely be on frost patrol by March 15, no matter what the weather does," he said.

You can reach Staff Writer Derek Moore at 521-5336 or derek.moore@pressdemocrat.com. On Twitter @deadlinederek.