First off what a stupid thread, you should've made this a random comment. To explain, you have to realize SF is a peninsula which is surrounded by water(obvious); and that water is the result of currents from alaska which is cold as fuk. Cold water = cool and moist layer of air near the surface.
'When you have colder air near the surface and warmer air above it, you will have a stable environment. During the warm season, the air well above the surface will warm up significantly with the change in seasons. However, the ocean temperature will still remain relative cool. This will result in a the formation of a very stable layer near the surface also known as the coastal marine layer. Because this layer is so stable, the cool and moist air is stuck near the surface and can not mix with the drier and warmer air above. This will result in the formation of a thick low cloud layer that usually cover the coast during the morning hours. If the marine layer is deep enough, the low overcast skies may not break up at all. Without any sunshine, the summer high temperatures may barely reach 60 degrees, while the inland areas will bake in the summer heat The low clouds may even be thick enough to produce very light precipitation in the form of drizzle or sprinkles in patchy coastal areas.'
I wouldn't tell anyone not to come to the bay because its cold, only sf is cold, and oakland is a bit cold too. But outside that all the rest of the inland is hot as fuk. I live in San Jose and its always hot as hell here.