Weather San Francisco is fairly mild most of the year. In other words it never gets really hot or really cold. Truly the best Weekend Getaway any time of year.
January is coldest with an average high of 56 degrees and low of 46 degrees.
October is warmest with an average high of 68 degrees and low of 56 degrees in September (warmest nights).
As you will note there is only an eight degree difference between the warmest and coldest months. Wow! That sounds great to this girl from the Northern Midwestern states with our hot summers and freezing cold winters. San Francisco is the perfect spot for a weekend getaway at any time of year.