You can visit San Francisco comfortably any time of year. Possibly the best time is September and October, when the city's summerlike weather brings outdoor concerts and festivals. The climate here always feels Mediterranean and moderate—with a foggy, sometimes chilly bite. The temperature rarely drops below 40°F, and anything warmer than 80°F is considered a heat wave. Be prepared for rain in winter, especially December and January. Winds off the ocean can add to the chill factor. That old joke about summer in San Francisco feeling like winter is true at heart, but once you move inland, it gets warmer. (And some locals swear that the thermostat has inched up in recent years.)