California: Climate

Those unfamiliar with California assign it a two-season mediterranean climate. This is but a partial truth. Offshore ocean currents cause an intermittent fog-bank along California’s coast, creating long stretches with insufficient sunshine to ripen most grapes. These fogs do not penetrate far inland, because of the 1,000-m/3,300-ft high coastal range, leaving the San Joaquin Valley too warm and sunny—too Mediterranean if you will—to grow fine table wines. However, in the sharply convoluted in-between of the Coast Ranges, jumbled terrain, variable fog and marine breezes produce more and less perfect growing season echoes of Castellina-in-chianti, st-estèphe, beaune, and even Hattenheim in the rheingau. There is no linear pattern. Napa, 20 miles north across the bay from San Francisco, is one of the warmer, drier regions on the coast. Westerly parts of Santa Barbara County, 300 miles/500 km to the south, are cooler and foggier than any part of Napa, while much of Mendocino, nearly 80 miles north of Napa, has hotter summers. Openings to the Pacific Ocean in the Coast ranges indicate the cool spots, while mountain barriers locate the warmer ones.