John Clendenen lifted his muddy leather boot and gave a swift kick to a cabernet grapevine tucked away in the rolling ridges between Windsor and Chalk Hill. A light shower fell from the vine onto the already water-logged soil.

?Here?s problem A,? said the veteran Healdsburg vineyard manager, pointing to a cluster of dark purple grapes marred by bunch rot. ?The cabernet ... it?s just anyone?s call at this point. I was surprised to see so much rot.?

The heavy rains that drenched the North Coast this week didn?t last long. Few, however, expected a week of unrelenting moisture, fog and overcast skies that, when coupled with Thursday?s temperatures in the high 60s and low 70s, created textbook conditions for what is technically known as botrytis rot.

?Seventy degrees and moist ? it doesn?t get any better for mold,? said Ron Vann, who owns the vineyard Clendenen was reviewing Thursday afternoon.

Clendenen said ripe grapes don?t know when to stop taking water. They?ll continue to absorb moisture, diluting sugar levels and increasing the possibility that softer-skin varieties, such as chardonnay and zinfandel, literally split open.

?Here?s a grape that wants to split,? he said, pointing to a dark line that ran across the surface of the grape, resembling the ?linea nigra? pregnant women get below their belly button.

?Actually the rotten berries don?t taste bad,? he said after trying a grape not yet covered by the grayish mold.

Clendenen said he would be out Friday ?leafing? Vann?s crop, yanking vine leaves away from the bunches to increase ?air movement? and allow grapes to dry out and prevent further rot. For vineyard owners, that process is a cost they would not have incurred had it not rained.

?You try not to let it bother you but you hate to see good grapes go to waste,? said Vann. ?But one thing you can?t control is the weather.?

The dreary, humid weather that hung over the North Coast on Thursday was a unique phenomenon in the state, said Steve Anderson, a forecaster for the National Weather Service.

?Everywhere else it was sunny and beautiful,? he said.

On the beaches of Santa Cruz, it was 82 degrees and Sacramento had a high of 77. Only Marin, Napa and Sonoma counties experienced continued residual moisture from Monday?s storm.

Duff Bevill, a Dry Creek vineyard manager, said he had also hoped to see the sun finally come out Thursday afternoon.

?We were hoping to get something going for this afternoon, but that didn?t materialize,? he said Thursday.

Just before the rainstorm hit the North Coast on Monday night, winery owners hurried to get batches of grapes processed. By Thursday, after three days of inclement weather, wineries were on their second fermentation cycle and some were eager to get their hands on newly picked grapes.

Saralee McClelland Kunde, a Russian River Valley grape grower with a total of 400 acres at five different vineyard sites, said she was shocked to see yet another wet day Thursday.

?The weatherman was calling for blue skies and we certainly didn?t see it,? she said. ?We always get rain about now, but we don?t get a January storm.?

Kunde said about 5 percent of her crop is still on the vine, mostly syrah and merlot, but she has detected no unwanted rot. For late harvest wines, such as light riesling and gewurztraminer, rain and botrytis are ideal.

?The more the merrier,? she said, adding, however, that such varietals are ?a minute part of business.?

For the red grapes that are still out, ?it?s hurry up and wait,? she said.

David Beckstoffer, president of Beckstoffer Vineyards, also said he had yet to see rot in the company?s 1,000 acres in Napa, Mendocino and Lake counties.

One-third to a quarter of Beckstoffer?s cabernet grapes in Napa, about 1,000 tons, have yet to be picked. Also, up to a quarter of the company?s chardonnay grapes in Lake County, about 800 tons, and 5 percent of its cabernet grapes in Mendocino County are still on the vine.

?It?s not ideal but it could be a lot worse,? said Beckstoffer. ?We?re watching the ground much more than the grapes. We want to know when we can get the equipment out there on the vineyards.?

Nick Frey, president of the Sonoma County Winegrape Commission, said while there?s some chardonnay and other white varietals still in the fields, most of what?s left to be harvested are cabernet grapes.

He said once bunch rot appears, the fungus tends to grow exponentially.?

?If it?s there, once it starts it kind of doubles every day,? he said, adding that it?s too early to tell what the economic impact will be on the industry.

Thursday night?s and Friday morning?s lingering clouds are expected to finally burn off and give way to sunshine this afternoon, Anderson said. A high of 75 is expected, he said.

As Clendenen, the vineyard manager, made his way through Vann?s vineyards Thursday, his boots collected more and more mud.

?I could get a crawler tractor through here,? he said. ?But what we need is some dry weather.?