FXUS66 KSGX 021557 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 857 AM PDT Fri May 2 2025 .SYNOPSIS... A low pressure system will move into Southern California this weekend. It will keep our marine layer deep and the clouds pervasive and bring cooler weather, especially Sunday. It will also bring strong winds Saturday afternoon through Sunday along with scattered showers including snow in the higher mountains. A smaller chance of showers continues through Tuesday. Dry and warmer weather expected Wednesday and Thursday. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... The coastal basin is filled almost to the brim with clouds this morning. Clouds extend to 3,500-4,000 feet up the coastal slopes, where true fog is found. The inversion is stronger today and the cloud is thicker, so clearing will be late and partial or not at all near the coast. A trough off the NorCal coast will amplify and drop southward, eventually cutting off from the jet stream and dropping into SoCal by Saturday evening. Initially, this will enhance our marine layer even further for Saturday, featuring a pretty robust eddy. Strong onshore winds come next Saturday afternoon. Gusts of 35-50 mph will be common across the mountains and deserts, with isolated gusts through mountain passes into deserts reaching or topping 65 mph. Finally, the showers arrive Saturday evening, but not for everyone, and continue through at least Sunday. The trough axis moves east of our area, but rotating lobes of vorticity and moisture contine to drop south through SoCal through Tuesday. That will keep small chances of showers in the forecast, but with a more emphasis inland. There is a slight chance of thunderstorms Sunday afternoon in the high desert and mountains. Precipitation amounts are not impressive: near zero near the coast, ramping up to about one-third inch in the mountains, but locally higher where any thunderstorm occurs. Model trends have stepped back on the cold air and instability of this system. Snow levels are now bottoming out at around 6,000 feet and widespread thunderstorm chances have been trimmed back. Snowfall still looks like 1 to 3 inches, but only accumulating above 6,500 feet. Winds drop off some Sunday afternoon and evening. High temperatures on Sunday will flirt with low max temp records with upper 50s to lower 60s in the coastal basin, 40s and 50s in the mountains, 60s in the high desert and 70s in the low desert. Yeah, that's cold for May, 15-20 degrees below normal for some inland areas. Isolated to scattered showers will continue on Monday and Tuesday, but the best chances will be in the mountains. Finally, the pulses of energy from the north will stop and the trough continues to weaken and move east. That will bring dry and warmer weather Wednesday and especially Thursday. The longwave ridge amplifies quite well over our region Wednesday and beyond, but there is some weak shortwave troughing that dampens it. The warming trend should be enough to bring temperatures above normal Thursday and Friday. 70s at the coast and 80s inland might feel good for a change. Meanwhile, the marine layer should rebuild quickly to reestablish our seasonal nocturnal cloud pattern near the coast. && .AVIATION... 021545Z....Coasts/Valleys...A deep marine layer has filled the coastal basin with bases 2000-2500 feet and tops around 3500 feet. Clearing will be slow to occur with inland areas scattering from 16- 18z and later for coastal areas. There is a 25% chance that parts of the San Diego County coast remain BKN through the afternoon. Regardless, low clouds will surge inland over San Diego County as early as 0z this evening and eventually spread to the rest of the coastal basin. Bases and tops should remain around 2000-2500 feet and 3000-3500 feet, respectively. Areas of DZ possible along the coast Saturday morning. Slow clearing once again for inland areas on Saturday and coastal areas will likely remain broken through the day as a low pressure system approaches. Mountains/Deserts...ISO TSRA possible from Idyllwild to Big Bear 20Z Fri-03Z Sat. Otherwise, SKC through tonight until SCT/BKN high clouds move over Southern California on Saturday. Increasing winds for the deserts and desert slopes Saturday with widespread 20-30kts and 40kts through mountain passes by 0z Sunday. && .MARINE... Gusty west to northwest winds will develop over the coastal waters Saturday, strongest late Saturday afternoon into early Sunday morning. Sustained winds 15-20 kts for inner coastal waters and 20- 30 kts for outer coastal waters. There is an 40% chance of wind gusts exceeding 34 kt near San Clemente Island in the outer coastal waters and a less than 5% chance over the inner coastal waters early Sunday morning. A Gale Watch remains in effect from Saturday afternoon through Sunday morning. Combined seas of 8-11 feet in the outer coastal waters and 6-8 feet in inner coastal waters with steep, wind-driven waves are expected. Wave heights peak Sunday morning and gradually lower Sunday afternoon into Monday. && .BEACHES... 8-11 foot swell with a 6-9 second period from the west will bring elevated surf conditions on Sunday. Elevated surf of 3-6 ft is most likely with sets to 7 ft in southern San Diego County. Elevated surf may continue into Monday morning. Surf and a high risk of rip currents will create hazardous swimming conditions at all beaches Sunday. Swell and surf will lower later on Monday. && .SKYWARN... Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...Gale Watch from Saturday afternoon through Sunday morning for Waters from San Mateo Point to the Mexican Border Extending 10 to 60 nm out including San Clemente Island. && $$ PUBLIC...MM AVIATION/MARINE/BEACHES...KW