San Francisco is characterized by its Mediterranean climate with mild moist winters and dry summers. The water that surrounds the city acts as a moderator to the climate, so that there is very little variation in seasonal temperature.
In any season of the year, one must accept that it is very probable that the city will be covered by a characteristic fog formed by the combination of cold water from the ocean with the heat from the Californian peninsula.
The summer in San Francisco is not too exhausting since is not too warm, to the point that, at nightfall, you may need some kind of light jacket. During this time the temperatures tend to oscillate between 50 and 70ºF.
The winters in San Francisco are quite cold, especially during the months of January and February when the temperature of the city can get down to 41ºF and only reach a maximum of 57ºF. This temperature, along with the humidity and abundant rain, makes winter not the best time to visit the city.
When traveling to San Francisco, we like the summer. The best months to visit the city are between May and September since they are the least cold (without being too warm) and the least rainy.
During all of these months, while during the day it may be quite warm, at night it gets a lot cooler, so light summer clothes are not practical.