Yes, San Francisco is known for its cool temps and fog. But don't necessarily let that guide how you dress and prepare for your hike. The weather conditions you'll encounter will all depend upon the trail you're on and the season in which you're hiking. In addition, Bay Area weather varies dramatically from mile to mile, as the region is full of microclimates, or small pockets of weather [source: Grant's San Francisco Travel Guide]. In one area, it might be 70 degrees Fahrenheit (21 degrees Celsius) with little wind, while a few minutes away, it's 58 degrees Fahrenheit (14 degrees Celsius) and damp.
Nevertheless, there are some things to keep in mind regarding Mother Nature. The rainy season is from November to March; there's little or no rain the rest of the year. And despite the wild weather variations mentioned above, overall the average year-round temps range from about 40 to 70 degrees Fahrenheit (4 to 21 degrees Celsius), so the weather is never extreme [source: Grant's San Francisco Travel Guide]. What does all of this mean for hiking?
Because the weather can change fairly dramatically from region to region, no matter which trail you select, it's best to carry a few basics with you when hiking, such as a hat, water-resistant jacket, light rain or wind pants, gloves, an extra pair of socks, and an emergency space blanket. And layers are always a good idea, especially for longer hikes [source: Hiking Guide]. You may start out in chilly, foggy weather, then end up with sunny, warm temps that will leave you sweating profusely if all you have are a long-sleeved shirt, pants and a thick coat.