521 FXUS66 KSGX 231632 AAA AFDSGX Area Forecast Discussion National Weather Service San Diego CA 922 AM PDT Fri Apr 23 2021 .SYNOPSIS... A deep marine layer will gradually decrease in the depth through the weekend, but with night and morning low clouds still covering all of the coast and valleys. There will be some patchy drizzle early this morning. Inland areas will warm slowly through Saturday, then begin to cool on Sunday. Onshore flow will continue periods of stronger and gusty southwest to west winds along the desert slopes of the mountains into the deserts. A Pacific low pressure system and late season winter storm will widespread rain and high elevation mountain snow Sunday night through Tuesday morning, with Monday the most likely time for precipitation. Monday is expected to be the coolest day as well with some locations struggling to reach 60 degrees. Beyond Tuesday, a period of substantial warming will ensue for Wednesday through Friday, as high pressure aloft strengthens across California. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... Morning Update: The only forecast update was to adjust the sky cover forecast, with gradual partial clearing this morning with partly cloudy skies this afternoon except at the immediate coast which will likely remain cloudy through the afternoon. Previous forecast discussion (issued at 349 AM PDT): SHORT TERM (Today through Sunday)... The marine remains around 5500 feet deep with light measurable rainfall amounts from patchy drizzle overnight mostly across portions of San Diego County from the coast to the mountains. The marine layer will gradually decrease in depth to around 3000 feet on Sunday. Areas of night and morning coastal low clouds and fog will extend onto the lower coastal slopes of the mountains for tonight into Saturday morning and across most of the valleys for Saturday night into Sunday morning. There will be a slow warming trend for inland areas through Saturday with cooling on Sunday. Gusty southwest to west winds will continue each late afternoon through late at night along the desert slopes of the mountains into the deserts. && .LONG TERM (Monday through Thursday)... A Pacific low pressure system will move inland along the West Coast around late Sunday and Monday with chances for precipitation as early as Sunday night and as late as Tuesday with Monday the most likely time for precipitation. Ensemble guidance continues to show timing differences as well as differences in rainfall amounts with amounts having trended lower in the past 24 hours. For the latest deterministic forecast, totals range from one-quarter to one-third inch near the coast to one-half to three-quarters of an inch in the mountains with less than one-tenth inch in the deserts. Monday is expected to be the coolest day. There are differences in the timing of how quickly the system moves east on Tuesday with those differences evident in the high temperature guidance for Tuesday with less warming in the slower scenarios and greater warming if it moves east more quickly. High pressure aloft will then strengthen across California with dry weather and more substantial warming for Wednesday through Friday with high temperatures warming to above average on Wednesday and well above average for Thursday and Friday. With the warming, high temperatures for Thursday and Friday would reach the lower to mid 90s in the Inland Empire and around 100 in the lower deserts. && .AVIATION... 231545Z...Coasts/Valleys/Mountains...Widespread FEW-BKN clouds with cigs 2000-3500 FT MSL. Vis reduced 3-5 SM in some valley areas and where clouds intersect higher terrain. Valleys will clear through 19Z, with little clearing expected along the coast. Clouds will spread back into the valleys by 08Z Sat. BKN-OVC cigs with bases 1500-2500 ft MSL expected. Deserts...Mostly clear with unrestricted vis through tonight. Periods of W-NW winds with gusts 20-30 kt, isolated higher gusts to 40 kt on desert mountain slopes and east of San Gorgonio Pass after 20Z today. Mod-stg up/downdrafts and LLWS over/east of the mtns at times. && .MARINE... No hazardous marine conditions are expected through Sunday. Breezy northwest winds will develop across the outer coastal waters on Monday. && .BEACHES... South swells from 180-190 degrees of 3-5 ft with a period of 16-22 seconds will impact Southern California beaches through Sunday. Elevated to locally high surf is expected, especially on south- facing beaches in Orange County. Strong and dangerous rip and longshore currents will be generated at all beaches. A Beach Hazards Statement is in effect for Orange County through Sunday afternoon, 5- 7 ft surf expected. Surf of mostly 3-5 ft mainly across San Diego County. && .SKYWARN... Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...Beach Hazards Statement through Sunday afternoon for Orange County Coastal Areas. PZ...NONE. && $$ PUBLIC...17/JMB AVIATION/MARINE/BEACHES...CO