882 FXUS66 KSGX 140400 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 839 PM PDT Sun Apr 13 2025 .SYNOPSIS... Minor cooling Monday followed by more significant cooling for the second half of the week, with daytime temperatures down to 10-20 degrees below normal on Friday. Low clouds and fog will continue across the coastal areas and western valleys each night and morning through the middle of the week, with marine layer drizzle possible Tuesday morning. There is a 10 to 15 percent chance of light precipitation over the mountains Monday night, and then a 15 to 30 percent chance for the mountains westward at times Thursday night through Saturday. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... This evening...Surface pressure gradients have trended much weaker onshore which, along with a weaker inversion, could explain why today cleared better at the coast than yesterday. Low clouds are forming along the coast but the coverage and inland extent is significantly less than at this time yesterday. The afternoon sounding shows the marine layer deeper than yesterday afternoon and high-resolution models, however still show marine layer low clouds extending into the inland valleys by sunrise Monday. From previous forecast... Temperatures hold fairly steady for tomorrow with weak ridging building in and highs generally near normal to slightly above normal west of the mountains, and 5-10 degrees above normal for areas east of the mountains. AM low clouds and fog are once again expected on Monday with similar inland extent and visibility restrictions as seen this morning. After Monday, a cooler trend sets in as a series of lows move across the region along with increasing moisture in the lower and mid levels. For early week, a low off the coast of San Diego will become an open trough, sweeping across Baja and up through Southern California, bringing the first chance for some precipitation early Tuesday morning. At this time, chances remain low for meaningful precipitation outside of the mountains where about a 10-20% of some light rain and/or snow showers will be possible at the highest elevations given snow levels above 8000ft. Elsewhere, a deepening marine layer may lead to some morning drizzle, especially for the coastal and valley areas. As the trough moves up and out on Tuesday the cooler weather arrives, with highs 5-10 degrees below normal west of the mountains and slightly above normal for the deserts. On Wednesday, a low off the coast will begin to push across Central California, transitioning to a positively tilted trough on Thursday. This trough will bring significantly cooler temperatures, 15-20 degrees below normal for some spots, as well as push some moisture into the area. At the same time, a deep low pushes down from the north, arriving in southern Nevada by early Friday morning. Models are in much better agreement today on this next low, with better agreement on precipitation chances for late week. Lows both Thursday and Friday in the low to mid 60s along the coast and in the valleys, 40s and 50s in the mountains, and 60s to low 80s in the deserts. Snow levels will fall to around 6000-6500ft for both days, paving the way for some light snow accumulations in the mountains. While models are in better alignment with the upper level pattern for late week, QPF amounts have generally trended down with the latest model runs, indicating a higher-confidence in a lower-impact event at this point. Quite a few things still need to be ironed out with the upcoming system and how far south it manages to go, but currently the highest chances (25-35%) for accumulations will be in the mountains. As the low moves out of the area, a slow warming trend sets in with weak ridging building and highs look to return to near or slightly below normal by early next week. && .AVIATION... 140400Z...Coasts/Valleys...Low clouds based 1200-1700 ft MSL are starting to slowly fill in but remain fairly patchy at this hour after some efficient clearing that occurred this afternoon. Still, expecting clouds to continue fill in across the coastal basin over the next few hours, bringing CIGs to all coastal TAF sites (KSAN/KCRQ/KSNA) by 05-06z. With tops near 2500-3000ft MSL, clouds will continue to spread inland overnight, eventually reaching the Inland Empire and KONT/KSBD by 10/11z. VIS reductions limited to the higher elevations and localized inland valleys. Low clouds scatter out in the inland valleys first after 15-16z, with the coasts clearing out by 18-19z Monday. Elsewhere...Mostly clear skies with VFR conditions. Local west wind gusts 25-35 kt over the mountains into the passes and deserts this evening, waning by 08-09z. && .MARINE... No hazardous marine conditions are expected through Thursday. && .BEACHES... Surf 3-5 feet is expected through Sunday with sets to 6 feet along west facing beaches, bringing a high risk for rip currents. && .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...PG AVIATION/MARINE/BEACHES...Munyan