The Pacific Ocean is a defining feature of the West Coast, and it plays a significant role in the climate of many local vineyards. But in some areas, the ocean creates an effect that turns basic climatic principles on their heads.
Inversion layers, where standard temperature gradients are reversed, create unique growing conditions for vintners. Under normal conditions, “air gets about five to six degrees cooler with every thousand feet of altitude,” explains Steven Burgess, the former owner of Burgess Cellars and the architect of the pending Crystal Springs of Napa Valley AVA, which sits right below an inversion layer. “That’s why there is snow in the mountains. But if there are two or more air masses, or strata, then the rule of thumb does not work.”
Whether it is affecting diurnal shifts or annual growing seasons, an inversion layer can create conditions that go against climatic norms; however, it can also lead to wines with their own distinct characters. From California to New Zealand, here’s how atmospheric inversion layers affect viticulture.
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Understanding Inversion Layers
According to the National Weather Service, “a temperature inversion is a layer in the atmosphere in which air temperature increases with height.” Cooler air on the surface level forces warm air upward in the evening hours through the early morning. As altitude increases, air density decreases, meaning heavier, cooler air remains at lower altitudes.
Many of the most dramatic inversion layers are created from cold ocean waters, such as the Pacific, which cool the surrounding air and lower its density, inhibiting normal convection patterns. Therefore, the impact of inversion layers is often pronounced in coastal sites. The air below the inversion is known as the marine layer, which is responsible for the fog that blankets vineyards in areas like the Sonoma Coast (and the reason for San Francisco’s famously chilly summers).
In mountain vineyards, an inversion layer occurs when the cold ocean air fills the valley floor, causing heat accumulated during the day to rise. As a result, nighttime temperatures on the mountain are warmer than temperatures in valley-level vineyards.
Feeling the Impact in High-Altitude Vineyards
Captûre Wines is located in the Pine Mountain-Cloverdale Peak AVA, which starts at 1,600 feet and rises to 2,866 feet in altitude, straddling both Sonoma and Mendocino counties. Winemaker Sam Teakle farms Cabernet Sauvignon and Sauvignon Blanc from vineyards located at 2,500 feet and up.
“One thing that caught me by surprise the first year I started working with the vines at 2,800 feet was how quickly the grapes ripened and were ready to harvest,” says Teakle. “Bud break is often three weeks behind that of the valley floor, but because of the inversion layer, with the cooler days and warmer nights, the vines catch up, maturity-wise.”
Mountain areas affected by inversion layers generally have small diurnal shifts; compared to the valley floor, which Teakle says can swing 50 degrees Fahrenheit in difference, he estimates there’s a 30-degree variation from day to night in his vineyards.
“We have fewer days, but more hours in the day to achieve physiological ripeness,” says Teakle. Vines at this altitude sit above the fog and “are working as soon as the sun rises,” he says. “Because of the constant breeze, they never shut down due to excessive daytime heat. Then at night when the valley is full of cool air, the mountain stays pleasantly warm allowing the vines to ripen perfectly.” Teakle says he gains physiological ripeness in his grapes without the long hang time that other Cabernet Sauvignon producers in Napa and Sonoma tout.
At Stonestreet Estate in the proposed Pocket Peak AVA in Sonoma, which is nested within Alexander Valley, these less dramatic diurnal shifts caused by the inversion layer translate into vineyards that are, on average, 1.7 degrees Fahrenheit warmer than the valley.
The entire 5,500-acre Stonestreet property, planted to Cabernet Sauvignon, Merlot, Sauvignon Blanc, and Chardonnay, ranges from 400 to 2,400 feet in elevation, with many vineyards sitting anywhere from 1,000 to 2,400 feet. “We don’t have problems ripening even in the cold vintages,” says Kristina Shideler, the winemaker at Stonestreet. “But yet in the warm vintages, these wines aren’t blown out and coming in at 30 brix. [Winemakers] always talk about the effect of the diurnal shift as being a positive thing; well, we have less of a diurnal shift up there. Maybe that’s better.”
The Cooling Effect of the Marine Layer
When it comes to coastal sites, proximity to the ocean also plays a role in inversion layer impact. For vineyards that sit within the marine layer, instead of hot summers, daytime temperatures can be downright chilly.
“The closer you are to that cold body of water, the more your air temperatures are moderated by that huge, massive cold air mass,” says Andy Peay, the cofounder of Peay Vineyards, located in the West Sonoma Coast AVA. Their vineyard location—within five miles of the cold Pacific waters, and below 1,000 feet—sits within an inversion layer. During the summer months, he says the thermometer reads 15 to 20 degrees Fahrenheit cooler than inland areas.
The air mass coming off the ocean is not just cold, it’s also saturated, which translates into fog. And fog plays its own role in contributing to consistently cool temperatures by blanketing vineyards and blocking sunlight.
The result is a style that brought Peay to the West Sonoma Coast in the first place. “The idea was to go to where we can get wines that are phenologically ripe with moderate alcohol and good acidity without having to futz with them,” he said. “That’s why we want to be in the inversion layer.” The cooler, moderate temperatures allow for longer hang time, and more phenolic development, which gives the estate’s Pinot Noirs, “silky, not grippy, tannins,” says Peay. “And not just fruit, but also floral and tea and earth [notes].”
While California’s proximity to the Pacific Ocean offers myriad instances of inversion layers, this climatic effect can be found elsewhere in the world. At Te Kano Estate in New Zealand’s Central Otago region, winemaker Dave Sutton notes the presence of a marine layer in the estate’s Waitaki vineyard, which is situated at approximately 656 feet, between a mountain range and the South Pacific Ocean. “I think that’s what they see in California,” says Sutton. “You get those kinds of fogs rolling in, basically pulling moist, cold air off the ocean and over the vineyards.” Pinot Noir from Waitaki is elegant and perfumed due to the more extended growing season, with lots of flavor development at a lower brix level.
Whether mountain or coastal, vineyards affected by an inversion layer display characteristics that speak to this element of their terroir. “These are indeed true mountain wines, full of structure and texture,” says Teakle. “But they have a distinct elegance and balance to them seldom seen in other mountain sites.”
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Shana Clarke is a wine, sake, and travel writer, and the author of 150 Vineyards You Need To Visit Before You Die. Her work has appeared in Saveur, Fortune, NPR, Wine Enthusiast, and Hemispheres. She was shortlisted for the Louis Roederer 2020 International Wine Writers’ Awards and ranked one of the “Top 20 U.S. Wine Writers That Wineries Can Work With” by Beverage Trade Network in 2021. She holds a Level 3 Advanced Certificate from Wine & Spirit Education Trust and is a Certified Sake Sommelier. She will always say yes to a glass of Champagne. Learn more at www.shanaspeakswine.com and follow her @shanaspeakswine.