As the holiday season approaches, Southern California is experiencing a spell of unseasonably warm weather, but a shift in the atmosphere promises changes leading up to Christmas Eve. According to NWS San Diego, temperatures have been well above average, particularly for inland areas west of the mountains with coastal areas ranging from 62 to 74 degrees. The western valleys and inland Orange County saw temperatures between 75 and 80 degrees, while inland valleys reached 75 to 81 degrees. The temperatures drop as you go higher with mountain areas between 4000 ft and 7000 ft experiencing 58 to 67 degrees, high desert areas at 66 to 70 degrees, and the low desert at a warm 77 to 81 degrees.
However, a low pressure trough is expected to bring rain to the region on Christmas Eve with "chance of rain will range from 10 to 50 percent across the region," NWS San Diego reported. They also anticipated light rainfall during this period. The conditions ahead are a mixed bag, with the onset of the marine layer bringing cooler temperatures, coastal fog, and the potential for light precipitation.
In the meantime, offshore breezes are decreasing, ushering in higher humidity and areas of coastal fog. Fog is expected to be an issue again tonight and could extend farther inland over the weekend due to a deepening marine layer. "A cooling trend will begin at the coast and western valleys today, but not yet inland, it will be cooler regionwide each day Friday through Sunday," explained the NWS San Diego's Area Forecast Discussion. The moisture and fog bring visibility concerns particularly for coastal and valley areas.
Christmas Eve is primed for a slight holiday twist, with the system expected to deliver westerly winds and a chance of showers. "It looks like the rain will arrive right about the time we get a visit from Santa Claus on Christmas Eve," according to the discussion from NWS San Diego. The mountains and deserts will see the strongest winds during this period, with no significant cold front accompanying the rain, meaning snow levels should stay primarily above 8,000 feet. Despite the rain's brevity, its timing could affect last-minute holiday travel and plans.
For mariners and beachgoers, conditions are also noteworthy. Areas of dense fog have prompted visibility warnings near the coast, with the possibility of persisting patchy fog through Friday morning. Additionally, a long period west swell late Saturday is expected to create seas of 8-11 feet through Wednesday for outer coastal waters and near San Clemente Island. "A high risk of strong rip currents and dangerous swimming conditions, with additional coastal impacts possible," warns NWS San Diego's Marine and Beaches section. Fire weather conditions remain elevated for the inland valleys and peninsular mountain ranges with low humidity and local east winds. A transition to onshore flow on Friday should spread higher coastal humidity inland and reduce fire weather concerns."
