People often quote Mark Twain as having said "the coldest winter I ever spent was a summer in San Francisco." Those people are wrong. Mark Twain never said that. Whoever DID say it, however, was getting at a true and important point: San Francisco can be chilly in the summer. August is generally the warmest month, but it can be rather un-summery at times. Plan to be happy you brought a sweater for the evening and more traditional summer clothes for the day. The weather can swing twenty degrees in as many hours, but it's no problem if you prepare. And now you know. To know more, go to www.weather.com and type "94103" into the zip code field.