240 FXUS66 KSGX 051009 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 309 AM PDT Thu Jun 5 2025 .SYNOPSIS... There is a slight chance of showers and thunderstorms for this afternoon for the San Bernardino Mountains and adjacent high desert areas. A deep marine layer will continue into Friday morning with patchy night and morning drizzle. The marine layer will become shallower for the weekend into next week with night and morning coastal low clouds not spreading as far into the valleys. There will be a gradual warming trend through the weekend, continuing into early next week for the mountains and deserts, followed by a cooling trend for the middle of next week. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... .SHORT TERM (Today through Saturday)... Moisture over the mountains and deserts will continue to decrease today with a slight chance of afternoon showers and thunderstorms for the San Bernardino County Mountains and adjacent high desert areas. The marine layer is around 3500 feet deep with the saturated cloud layer below the base of the marine inversion around 2000 feet deep. There has been patchy drizzle since Wednesday evening with the light measurable amounts mostly for the coast and valleys of San Diego County and in southern Orange County near the coastal foothills of the Santa Ana Mountains. The marine layer will remain around 3000 to 3500 feet deep into Friday morning with slow or limited afternoon clearing for the San Diego County coast. The marine layer will decrease to around 2000 to 2500 feet during the weekend with night and morning coastal low clouds not spreading as far into the valleys. A slow warming trend will continue into the weekend, and continue into early next week for the mountains and deserts. High temperatures on Saturday will be around average near the coast to a few to around 5 degrees above average for inland areas. High temperatures on Saturday will range from around 70 near the coast to the 80s and lower 90s for the Inland Empire with 103 to 107 for the lower deserts. && .LONG TERM (Sunday through Wednesday)... The gradual warming trend is expected to continue for the mountains and deserts through Tuesday with high temperatures for the mountains and deserts for Monday and Tuesday 5 to 10 degrees above average. There remains the spread in the guidance in whether a weak low pressure system off the California coast will move into southern California for early next week or instead weaken and move to the west with high pressure to the south beginning to expand into southern California. The scenario with the weak low pressure system moving into southern California would result in a deeper marine layer with cooling for the coast and valleys. The scenario with high pressure expanding northward into the area would be warmer with the marine layer becoming shallower. && .AVIATION... 050930Z....Coast/Valleys...Low clouds based 800-1800 feet MSL fill the entire coastal basin with tops pushing into mountains up to 3500 feet. Vis 0-5SM over higher coastal and inland terrain and in -DZ. Scatter out 16-18Z for inland areas, 18-21Z for Orange County, and only partial if any clearing at all for San Diego County coastal areas. Low clouds push inland again after 00Z with very similar coverage, bases, vis, and patchy -DZ overnight into Friday. Mountains/Deserts...Mostly clear today and tonight. Except for cumulus and ISO SHRA/TSRA based at 10000 feet MSL 18-01Z over mountains and high desert. && .MARINE... No hazardous marine conditions are expected today through Monday. && .SKYWARN... Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...None. && $$ PUBLIC...17 AVIATION/MARINE...MM