After a summer-like pattern of high pressure and offshore flow prevailing through at least Thursday in Southern California, much cooler conditions and a thicker marine layer will begin to return Friday and over the weekend into early next week, the National Weather Service said.  While this may be the last cooler and wetter interlude of the season in Northern California, as UCLA climate scientist Daniel Swain points out, it may help to temporarily tamp down the presently above-average wildfire risk.