Winery Group Analyzes Monterey's Climate

Vintners & Growers Association touts "Blue Grand Canyon" and "Thermal Rainbow" as essential to the wine region's diversity

by Kate Lavin
Blue Grand Canyon Thermal Rainbow Monterey wine
Diagram of The Blue Grand Canyon and The Thermal Rainbow courtesy of the Monterey County Vintners and Growers Association.
Monterey, Calif.  -- With more than 30 tasting rooms located an hour or so from California’s Silicon Valley, the Monterey County winegrowing region already is popular with visitors. Now the Monterey County Vintners and Growers Association is shedding light on two climatic features that differentiate the area.

The Blue Grand Canyon

According to Rhonda Motil, executive director of MCVGA, a submarine canyon exists beneath the surface of the Monterey Bay. Dubbed the Blue Grand Canyon, the feature is 60 miles long and a mile deep (it reaches two miles beneath the water’s surface), making it the largest and deepest submarine canyon on the West Coast and comparable in depth to the Grand Canyon in Arizona.

“The Blue Grand Canyon is the dominant influence in our viticultural area,” Motil told Wines & Vines. “It determines annual rainfall (10 inches), and it determines water temperature (50?F),” Motil said.


Vineyards in Monterey County generally aren’t affected by frost due to the region’s coastal climate; thusly, bud break here occurs about two weeks before other growing regions. In spite of this head start, harvest often continues well into mid-November. The California Current, a Pacific Ocean current, moves south along the West Coast during summer and spring. Additionally, the Gabilan and Santa Lucia mountain ranges on either side of the Monterey AVA create a wind tunnel that significantly slows the ripening of grapevines.

Steve Lohr, executive vice president and COO of J. Lohr Vineyards & Wines, explained that stomata in grapevines (which are similar to pores in the skin) respond to the wind by closing up, slowing the intake of carbon dioxide and oxygen, which halts photosynthesis and delays ripening. Grapegrowers cite the region’s long hangtime as a real asset for winemaking.

“If we didn’t have these great winds, we might be picking two to three weeks earlier,” Lohr said, adding, “I can set my watch to 12:30, and those 15-20 mph winds come screaming through the vineyard.”

The Thermal Rainbow

Mark Greenspan of Advanced Viticulture performed a climate evaluation for the MCVGA, and concluded that the ocean surface in Monterey Bay “has a relatively steady temperature of about 55°F.” As winds blow from the northwest off the bay and down through the Monterey AVA and sub-AVAs, temperatures go from a cool 50°F near the bay and climb past 100°F in Hames Valley and San Antonio Valley, the sub-AVAs farthest from the water’s cooling effects. The variation is what the MCVGA calls the Thermal Rainbow.

Only two sub-AVAs break from this pattern, Chalone and Carmel Valley. “Chalone’s elevation brings it outside of the coastal influence,” Greenspan said, and Motil explained that there is a mini-thermal rainbow effect in Carmel Valley, which is protected from ocean winds by its surrounding hillsides.

Motil told Wines & Vines that there is no way to calculate one set of degree days in Monterey County, because the Thermal Rainbow can create variations in temperature of up to 55°F at any one time in July or August. For example, Carmel Valley has just 1,932 degree days per year, while the San Antonio Valley experiences nearly twice as many -- 3,741.

Rainbow influences planting
The variability in temperature and wind throughout Monterey County play a role in growers’ planting decisions, because while growers in the San Bernabe AVA may see fog coming off the bay, nearby San Antonio Valley is not as impacted by winds until later in the day.

Overall, Pinot Noir and Chardonnay are the most popular varieties, with about 40% of the region’s harvested acres planted to Chardonnay and 15% planted to Pinot Noir.

Varieties sensitive to changes in temperatures will perform better in locations with the smallest variation in temperature from day to night, such as the Santa Lucia Highlands, Greenspan said. “A specific example is Pinot Noir, which performs best where temperatures do not swing dramatically from day-to-day.”
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