 The influence of the ocean generally moderates temperature extremes, creating warmer winters and substantially cooler summers in coastal areas.The cool California Current offshore, enhanced by upwelling of cold sub-surface waters, often creates summer fog near the coast, creating a warm-summer Mediterranean climate (Köppen climate classification "Csb").Further inland, the climate becomes more continental, with some areas turning semi-arid (Köppen "BSk"), with colder winters and markedly hotter summers.