SAN FRANCISCO WATHER AND CLIMATE

San Francisco's climate is characteristic of California's Mediterranean climate with mild, wet winters and dry summers. Since San Francisco is surrounded on three sides by water, San Francisco's climate is strongly influenced by the cool marine currents of the Pacific Ocean which moderates temperature swings and produces a remarkably mild climate with little seasonal temperature variation that many people desire. The cool and dry period of May to October is mild to warm, with average high temperatures of 64-70°F (17-21°C) and lows of 51-56°F (10-13°C). The moist rainy period of November to April is cool with high temperatures of 56-64°F (13-17°C) and lows of 46-51°F (7-10°C). On average, temperatures exceed 75°F (24°C) 28 days a year.

The combination of cold Pacific Ocean water and the desert heat of the California mainland create the city's characteristic marine layer fog that can cover the western half of the city all day during the spring and early summer. The San Francisco fog is less pronounced in eastern neighborhoods, in the late summer, and during the fall, which are the warmest months of the year. Due to its sharp topography and maritime influences, San Francisco exhibits a multitude of distinct seaside microclimates. The high rolling hills in the geographic center of the city are responsible for a 20 percent variance in annual rainfall between different parts of the city. These hills also protect neighborhoods directly to their east from the foggy and cool conditions experienced in the city's Sunset District and for those who live on the eastern side of the city, San Francisco is sunnier, with an average of 260 clear days, and only 105 cloudy days per year. Annual precipitation is in the form of rainfall and represents about 20.4 inches (510 mm) which occurs mainly during the cooler months of November through April. On average, there are 67 cool, rainy days a year.

This Mediterranean climate is ideally suited for vineyards in the rain or fog shadow of the coastal topography. Virtually all of the valleys just in land from San Francisco are filled with vineyards and wineries. These vineyards are bathed in sun and at the same time benefit from the moist Pacific air masses. In addition to producing some of the world's best wines, the inland areas just beyond the marine layer and coastal mountains also are home to the vegetable, fruit and nut basket of the United States. The central valley of California produces a significant portion of the nation's green foods.