Mendocino County Wine - Climate and Geography

Climate and Geography

Mendocino County has a wide range of viticultural mesoclimates that are influenced by the county's diversity in climatic and geography. On the eastern borders of the county is the Mayacamas Mountains separating it from nearby Lake County and the influences of the large Clear Lake. Within the county, the Mendocino Range segment of the larger California Coast Ranges essentially divides the region into two climatic spheres. The land to the west of the ranges, closest to the coast tend to have more maritime climate that includes more cooling and rain influences from the Pacific ocean. Among the wine regions in this cooler area are the Mendocino Ridge, the Anderson Valley and the Yorkville Highlands AVAs. East of the ranges, the climate turns warmer and more Mediterranean around Ukiah and along the path of the Russian River as it makes it way southward to Sonoma County. Among the Mendocino wine regions in this warmer area are the Redwood Valley, Potter Valley, Cole Ranch, McDowell Valley, Covelo, Dos Rios AVAs as well as most of the large general area Mendocino AVA. In this eastern region, the ranges serve as a type of rain shadow and barrier to the cool Pacific fog which leaves the climate during the growing season much drier and warmer with ratings of Region III and IV on the Winkler scale.

In the west, the Pacific fog plays a dominant role in the climate of the Anderson Valley. Following the path of the Navarro River from the Pacific, the fogs drifts in an blankets the valley with low hanging cool air. Vineyards in these areas are often planted with cool-climate varieties like Pinot noir, Chardonnay, Gewürztraminer and Riesling. At high elevations in Anderson Valley and nearby Mendocino Ridges beyond the fog's reach, these warmer pockets of lands will usually be planted with more warm climate varieties like Zinfandel. With the nearby Pacific bringing in a steady stream of moisture, rain during the harvest months can be an issue in this part of the county.

Around Ukiah, in the center of the large Mendocino AVA to the east of the Mendocino Ranges, the climate can get very hot warm during the growing season with mean July temperatures during the peak ripening month often in excess of 73°F (23°C). The average annual rainfall of 38 inches (964mm) is mostly consolidated in the winter months, which means that drought is a common viticultural hazard that often requires supplemental irrigation. The warm allows this part of the county develop full bodied and very ripe red wines from Cabernet Sauvignon, Merlot, Petite Sirah and Zinfandel.

The vineyard soils of the region are mostly deep alluvial soils. Near the Russian and Navarro Rivers, the soil becomes more gravelly-loam while the vineyards planted on the surrounding slope contain more thin scree. North of Ukiah and to the west, vines are often planted with an eastward orientation while further south in Mendocino Valley, vineyards are often planted with a westward orientation in order to prevent heat stress. In generally the climate in Mendocino county promotes a shorter growing season of around 268 days compared to the 308 days that is an average growing season in neighboring Sonoma.