SAN DIEGO (FOX 5/KUSI) -- Soak up the sunshine and seasonal Southern California weather because a storm system will bring much different weather heading into the weekend. Temperatures were widespread in the 70's for beaches and valleys Wednesday afternoon with mostly clear skies. High pressure aloft is contributing to the pleasant, yet dry weather middle of this week. Changes, however, are on the way and could arrive as early as Thursday evening as a trough of low pressure to the north will sweep through California the second half of this week.  Onshore flow will start to strengthen with the return of gusty west to southwest winds accompanied by much cooler weather. The best chances of light rain showers begin Thursday night into Friday morning, but there is another slight chance for overnight Friday into Saturday. The remainder of the weekend looks mostly dry.  Models have trended much drier with this system so we are looking at roughly a tenth inch of rain for the coast and valleys with up to a quarter inch of rain for mounains.