California’s 2017 wine harvest is under way, and it feels, in a sense, remarkably normal.

Compared with the last two vintages — freakishly early, hot and small — this year has seen many early-ripening varieties like Pinot Noir begin harvest at the end of August, with later ripeners like Cabernet Sauvignon and Syrah expected to remain on the vine until mid-to-late September. Yields look about average.

If the grapes themselves signal a return to relative normalcy, however, the human flurry surrounding them is anything but. Vineyard labor, an increasingly endangered resource, has reached a shortage this year that, according to vineyard owners, could be approaching a crisis.

That pinch looks especially dire in Sonoma County.

Historically, Jake Bilbro, owner of Limerick Lane Vineyard in Healdsburg, could give a vineyard management company a couple of days’ notice when he needed a picking crew to show up. But with the management companies increasingly short-staffed, Bilbro said that the timing has been stretching out further and further. “Last year in the heat, we were making calls pushing a week out. This year, we’re making calls two weeks out.

“We’re prepaying (the vineyard management company) in order to keep the crew there through the end of the pick,” Bilbro continued. “I’ve never heard of that in my life.”

Whereas five years ago, some Sonoma County growers charged wineries around $125 to $150 per ton for labor, those figures have now nearly doubled, to $275 to $300. In Napa, it can reach $400. That’s because vineyard workers’ wages have risen considerably as they’ve become harder to find.

It also means fewer people are doing more work. “The pickers are gearing up for three shifts, 18 hours a day,” Bilbro said.

Other California wine regions don’t seem to be feeling the pinch so acutely. In Monterey County, where the wine industry shares workers with other crops, grape grower Steve McIntyre said he’s seeing a surplus of labor this time of year.

“Activities in many annual crops starts to taper off, and operations move south,” McIntyre said. And 95 percent of his grapes are machine-harvested, which further reduces labor needs, unlike in Sonoma or Napa, where higher-end wineries demand hand harvesting.

Certainly, those higher-end wineries can afford to pay workers more — and they are. Workers for Napa’s Silverado Farming Co., for instance, which farms for wineries like Dana Estates and Lail Vineyards, are now earning as much as $45 an hour during the peak of harvest.

But when you’re charging $475 for a bottle of wine, as Dana does, you’re in the 1 percent. For most of the state’s vintners, the labor situation has become untenable. “Almost 80 percent of wine grapes in California are harvested by machine,” said Peter Nissen, owner of Napa’s Nissen Vineyard Services Inc. and the president of the California Farm Labor Contractor Association. “As labor tightens, you’re just going to see more and more machines.”

“We are in completely uncharted territory,” said Limerick’s Bilbro.

It’s uncharted territory, too, for our era’s ever-erratic weather patterns. While 2017 marked the official end of California’s five-year drought, the wetter winter didn’t quite have the effect that many had hoped.

“We had so much rain this past winter that we didn’t think the irrigation demand was going to be so great,” said Jed Steele, a winemaker in Lake County. “But the summer was too hot. The heat was excessive to the point where it actually slowed ripening.”

And while you might think a rainy winter would bode well for yields, the crop size is merely average. Still, that’s a big relief compared with the last two years: In 2015, a freakishly short crop year, some coastal Pinot Noir vineyards were down by about 50 percent.

It’s not just winter rain that affects crop size; it’s also rain in the springtime, when the plants flower. “Spring is a really important time for root flush growth,” said Cam Mauritson of Mauritson Wines in Dry Creek Valley. “When you have not as much spring rain, you’re getting a smaller root system. Over time, that has an effect.

“The drought is still taking its toll,” Mauritson said.

June hailstorms this year wrecked the crop loads at some vineyards in Contra Costa County and on Napa’s Atlas Peak. Evangelho Vineyard in Antioch was down 80 percent in some blocks; Atlas Peak’s Mead Ranch was about 70 percent diminished, according to Turley winemaker Tegan Passalacqua.

Though vintners are harvesting about 10 days to two weeks later than last year, it’s still not exactly a late harvest.

“This would have been considered, a decade ago, on the earlyish side,” said Adam Lee, owner of Clarice Wine Co. “But the fact that I’m looking at my calendar and can see the month of September makes it seem like we’re in a more normal range.”

Last week’s heat hastened ripening considerably, and with temperatures expected to exceed 100 degrees in some regions this week, it could be a mad rush to get the fruit off the vine.

Where there are heat spikes, there’s a risk of dehydration. “You don’t want to overwater the plants this close to harvest,” said Fred Delivert, winemaker for Tolosa Winery in San Luis Obispo. “But we had to irrigate ... to avoid dehydration.”

Heat in its most extreme form — fire — threatened vineyards in Santa Barbara, Mendocino and Lake counties this year. In July, the Alamo Fire burned dangerously close to Santa Maria’s 650-acre Bien Nacido Vineyard.

“The fire came within a few feet of our vines,” said Michael Brughelli, Bien Nacido’s director of sales. Luckily, it didn’t come in contact with any plants, and the smoke didn’t linger: “The fuels were fairly light, and the smoke was blowing up and away, not settling. There was really no ash fall.”

Meanwhile, farther north, Masut Wines owner Jake Fetzer watched as 1,000 acres burned in July next to his vineyard in Mendocino’s Eagle Peak AVA. “We were cutting trails around the vineyard so that the fire wouldn’t burn us up,” he said.

Fetzer knows well what fire can do to grapevines: In 2008, extreme fires led to high levels of smoke taint in his vineyards — and there was no hiding it. “You could smell the grapes,” he said. “They were almost like a smoked ham when you delivered them.”

None of this year’s fires presented any such danger. “We’ve been testing for smoke taint pretty extensively since the fire,” said Brughelli. “We haven’t found any trace amounts.”

Though it’s too soon to say, the 2017 vintage’s quality looks promising. Acids are a little bit lower, in general, but color is more stable than in the last few years.

“The flavors are fascinating,” said Dominic O’Reilly, winemaker at Topa Mountain Winery in Ojai. “The vines have just gotten a lot more nutrients with the rain down into the roots, and more foliage on the vines has translated to more character in the grapes as well.”

Hotter summers, earlier harvests, fewer workers: Even when we call it “normal,” California’s wine harvests seem to be moving toward extremes.

Jake Bilbro is grateful, at least, that the extreme conditions have brought all hands on deck. Last week, when he was in a pinch, friends like Cam Mauritson and vineyard manager John Grace lent him trucks, forklifts and tractors. “If it weren’t for them,” he said, “we wouldn’t make it when unforeseen issues such as labor shortages and 110-degree weather come at you.”

Esther Mobley is The San Francisco Chronicle’s wine, beer and spirits writer. Email: emobley@sfchronicle.com Twitter: @Esther_mobley Instagram: @esthermob

Annual yield

Recent harvests in thousands of tons for Lake, Mendocino, Marin, Sonoma and Napa counties

2011

380

2012

556

2013

567

2014

334

2015

256

2016

322

Avg*

412