420 FXUS66 KSGX 092026 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 126 PM PDT Mon Jun 9 2025 .SYNOPSIS... Shallower marine layer each morning through mid-week with well above normal temperatures for inland areas and deserts, peaking Tuesday and Wednesday. A slight cool down is expected for the end of the week before temperatures increase again for the weekend. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... Light drizzle was observed this morning for parts of San Diego County but satellite showed the marine layer quickly burned off for valleys and inland areas, much quicker than previous mornings. While the coming days will feature a shallower marine layer with less inland extent as high pressure builds in, low clouds will persist along the immediate coastline likely through at least mid week. Water vapor imagery shows a shortwave trough over the southern half of California with amplifying high pressure to the southwest. This troughing is helping to limit the influence of the high, with temperatures this afternoon expected to be very similar to Sunday. The shortwave won`t hang around for long as it moves down into southwest New Mexico on Tuesday, and high pressure builds over SoCal. Once again, the marine layer will moderate temperatures along the coastline for Tuesday with strong onshore flow, but further inland areas will experience a decently quick warm up. The valleys and even the mountains may reach close to 10 degrees above normal, while the deserts will see highs potentially encroaching on or exceeding 110F in some desert spots. Moisture from the southeast may move up into the Coachella Valley and lower deserts both Tuesday and Wednesday, and depending on if it is mixed out in time, may curb some of the warm up with the height increases. While the pattern still favors significant warming in these areas, the influence of the moisture may place a ceiling on highs both afternoons. In any case, temperatures for the Coachella Valley and lower deserts peak both Tuesday and Wednesday, with the inland areas and mountains likely to peak Tuesday. Late Wednesday an upper level low along the coast of Canada looks to move southward towards Graham Island, flattening the high a bit and zonal flow aloft looks to prevail over the region Thursday and Friday. Around the same time, the weaker high will slowly move eastward into Baja before reaching the Four Corners early Saturday, with ridging quickly rebuilding. A slight cool down is expected for the latter half of the week, but a return to ridging this weekend looks to push highs back to well above normal, potentially even warmer than earlier in the week. This pattern looks to holdover into early next week with no meaningful cooldown or precipitation in sight, a significant shift from just a few days ago where it seemed troughing would prevail for the weekend. && .AVIATION... 092022Z....Coast/Valleys...Low clouds reached into the western and southern parts of the Inland Empire last night. Clouds have cleared inland areas, but only partial and/or intermittent clearing at the immediate coast. Probability of BKN-OVC clouds all day today at KSAN is around 80-90%. Clouds will push inland after 01Z tonight into Tuesday, but not as far inland as this morning. Bases would be around 500-1000 feet MSL with some vis reduced over higher coastal terrain. Mountains/Deserts...Mostly clear skies and unrestricted VIS today and tonight. && .MARINE... No hazardous marine conditions are expected through Friday. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...None. && $$ PUBLIC...Zuber AVIATION/MARINE...Small