Weather Anomalies of the California Weather
People visiting California have a lot of misconceptions about it and its weather. The most famous one is that all of California is like LA, with palm trees, sub-tropical, semi-dry and that all beaches in the State look like Venice and Manhatten Beaches in the LA basin. Most think that going to Hollywood will yield fame and fortune and movie stars are just hanging out in Beverly Hills. Then there is the weather. Most tend to think that all of the State has similar balmy temps at night.
All of the above is wrong. The weather is much more predictable in the southern part from LA to Diego because the ocean influence is less dramatic and the ocean temps are much warmer than those from central California on up past SF. The ocean temps between the water around LA and San Diego can be 5-10 degrees warmer than in the SF area, which hovers around 50F in Summer and Fall.
Those visiting SF are often stunned at the coldness and foggy conditions even in July. They cannot believe they have to wear a jacket! They become equally shocked at how quickly things change just by going to Oakland or Concord and the temps reach 80s and 90s in just a few miles. That is the maritime influence as the wind chills from the water and moves onshore. The further inland you go, less maritime influence and temps start to rise rapidly.
Unlike the LA area, the SF area has so many microclimates that relying on accurate weather reports is a problem. Temps change rapidly from a cold Daly City at 60F in July (it is right on the coast) to a 90F in Walnut Creek, which is inland in the East Bay. In Sonoma county, one might have a 80F in Santa Rosa (35 miles from the coast) and if you go to Healdsburg (10 miles north) it is 90 or 95F, that is because Healdsburg is further inland. Conversely, sometimes the temp difference between Santa Rosa and Petaluma (to its south by 20 miles) will be 10 degrees colder.
More dramatic is going to Sacramento or coming from Sacramento (1.5 hrs from the bay area, about 80 miles). It is common for the following to occur if you are going to Sac:
Bay area is 60F, Fairfield is 70F, Vacaville is 80F, Dixon-Davis is 90, Sac is 100F.