California is a year-round destination, and its climate is as varied as its geography. A long coastline and two extensive mountain ranges provide moderating influences that make California both scenic and weather-wonderful. Summer is mostly dry all over, with occasional heavy showers over desert and mountain areas. Winters along the coast are generally mild. What rain there is in the state occurs most frequently and heavily October-April in the north and November-March in the south. The Santa Ana winds blow hot and dry out of the south in the winter—often hard enough (100 mph/160 kph) to close some highways. The interior areas of California, away from the coast, experience much greater extremes of temperature and season. Palm Springs, for instance, can have summer highs in excess of 110 F/39 C.
San Diego averages temperatures of 73 F/23 C in summer and 63 F/17 C in winter. San Diego's heat is moderated by ocean breezes, except during September and October, when easterly winds off the desert shoot the temperature into the 90-100 F/32-37 C range. Los Angeles enjoys relatively pleasant, mild weather throughout the year: Midday temperatures June-October average 83 F/28 C (though it can get hotter), and November-May, midday temperatures average 65 F/18 C. The thermometer seldom drops below 40 F/4 C in winter. San Francisco can be foggy and generally damp in the summer, and visitors will also encounter fog and rain on the far northern coast. Winters along the coast are generally mild.
Autumn is the best time to visit the Wine Country—that's when you can see the vines in full color and the harvest taking place. It's hotter than San Francisco in the summer, though not unbearable because there's little humidity. In winter, when harvest is over, winemakers tend to have more time to chat with visitors. In spring, the new vines are budding, and it's a popular time for bicycling through the area.
What to Wear
Sunny California's warm-weather reputation has spawned a booming tourist sweatshirt business in San Francisco—Mark Twain's famous (and unverified) line "The coldest winter I ever spent was summer in San Francisco" is frequently recited because it's all too close to the truth. The weather in California is, for the most part, mild and sunny, but expect morning (and sometimes evening) fog along the coast and cool mornings even during the summer in the Sierras. Because it lies on a peninsula surrounded on three sides by water, San Francisco can be socked in by fog for days at a time during the summer, when the warm inland weather hits the cool ocean water. San Francisco's most lovely weather is usually September and October. Southern California's weather, on the other hand, is almost monotonously perfect—morning fog followed by highs of 70-80 F/20-27 C day after day. Summer in the deserts, though, can top 100 F/38 C regularly, so if you're heading to Death Valley, Palm Springs or Joshua Tree in summer, carry plenty of water, strong sunscreen and a hat.
Wear layers, and don't forget a light sweater or jacket, and sunscreen.
California culture is generally laid-back, and conservative business attire is rare outside of the banking or insurance industries. Casual Fridays have expanded to most of the week in many California corporations, and most dress codes only draw the line at flip-flops or exposed navels—if there is a dress code at all.
