Fog. It’s what defines the Russian River Valley.

While other American Viticultural Areas have traditionally been defined by geologic markers, the Russian River Valley in California’s Sonoma County follows the regular intrusion of cooling fog from the Pacific Ocean a few miles to the west.

Much like the tide, that fog ebbs and flows through the Petaluma Wind Gap and the channel cut by the Russian River. It usually arrives in the evening, often dropping the temperature 35 to 40 degrees from its daytime high. The fog retreats to the ocean the following morning.

This natural air conditioning allows the grapes to develop full flavor maturity over an extended growing season — often 15 to 20 percent longer than neighboring areas — while retaining their life-giving natural acidity. Add in the region’s amazing complexity of soils, and the valley is perfect for growing Pinot Noir — as the 2012 bottling from Parnell Estate deliciously demonstrates