why is san francisco foggy in the summertime
San Francisco fog Under normal summertime conditions, a daily pattern of fog and low clouds occurs. Morning sun heats the ground which in turn heats the marine layer over the land areas. This creates convective turbulence within the marine layer as well as evaporation of any clouds within it. The marine layer clears back toward the coast, usually by noon. By mid-afternoon, inland areas have heated sufficiently to decrease the air pressure and increase the onshore flow. By late afternoon, the wind increases and begins to cool the onshore marine layer, allowing the fog and low clouds offshore to progress inland without evaporating. Cloudiness streams in over the Bay and through the various gaps. How far the clouds can penetrate inland depends on the depth of the marine layer and the strength of the cooling winds. As night falls and inland areas cool down, the winds usually decrease, but the fog and clouds remain wherever they have blown in until the following morning when the cycle repeats.[7]
Climate of the Tampa Bay area The dry season often begins in early November and can last into early May. The local weather during these months is normally sunny, mild, and quite dry, with a general cooling trend through the fall and a slow increase in temperatures starting in February. Highs during the coolest part of the winter average around 70 °F (21 °C), usually with sunny skies. The occasional passage of a cold front will bring rain followed by a few days of cooler temperatures.[2] Lows rarely reach freezing 32 °F (0 °C), an occurrence which happens, on average, once every other year in areas away from the water and less frequently in areas on Tampa Bay or the Gulf of Mexico.[2] While deep freezes are very infrequent, serious cold snaps are a significant concern due to the diverse range of freeze-sensitive agriculture and aquaculture industries in the area as well as tropical landscaping such as coconut palms and royal palms.