The National Weather Service's San Diego office has issued a weather advisory outlining a cooling trend expected to continue through Thursday, accompanied by periods of stronger and gusty southwest to west winds persisting for the mountains and deserts through Friday evening.
According to the latest forecast, a deep marine layer will persist into Friday, potentially bringing light precipitation in the form of drizzle or light rain from the coast to the coastal slopes of the mountains, primarily during nights and mornings. Following this period, warmer and drier conditions are anticipated for Saturday through Monday, with high temperatures on Sunday hovering around average and Monday's temperatures spiking to about 5 degrees above average.
The weather discussion for extreme southwestern California, including Orange, San Diego, western Riverside, and southwestern San Bernardino counties, indicates that a closed low pressure system at 500mb will continue its eastward movement over the Pacific, eventually making landfall over Southern California late Wednesday night into Thursday morning. Subsequently, a second low pressure system will dig in over the western United States from Thursday through Saturday, maintaining onshore flow and leading to cooling temperatures, extensive marine layer clouds, and gusty winds over the mountains and deserts.
The morning's marine layer deepened to approximately 4000-4500 feet, with low clouds extending well inland, even reaching the Cajon Pass. Instances of drizzle were observed across much of the Inland Empire, inland Orange County, and the San Diego County Valleys. Given the persistent onshore flow over the next several days and the existing deep marine layer, there will be ongoing chances for drizzle each night through Thursday night.
Moreover, periods of gusty west to southwest winds are anticipated over the mountains and desert foothills during the afternoons and evenings. Wind speeds are expected to intensify gradually each day through Friday, possibly necessitating Wind Advisories starting Thursday afternoon and peaking on Friday afternoon and evening. Peak wind gusts of 40-60 mph are anticipated, with even higher gusts exceeding 60 mph over mountain ridgelines, below passes, and within wind-prone canyons.