Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
513 FXUS66 KSGX 140403 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 903 PM PDT Wed Aug 13 2025 .SYNOPSIS... Fair and slightly cooler weather is expected today through the weekend as a low pressure trough hangs over the West. The marine layer will send coastal clouds into parts of inland valleys each night and morning. Temperatures will remain a little below normal. Next week, high pressure rebuilds over the Southwest, which will bring a modest warming trend to Southern California, with temperatures returning to around average. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... Evening Update: The latest GOES-18 Night Fog imagery shows that the marine layer has infiltrated nearly all of Orange County and all of the coastal areas and extending inland to around 5 to 10 miles within San Diego County. This will continue to do so throughout the night, and some of these low clouds will likely make it into portions of the Inland Empire again, especially in the vicinity of Ontario and at the mouth of the southern end of the IE. The marine layer tomorrow will also likely hug the coast throughout the day and periodically go broken to overcast for some areas throughout the afternoon hours tomorrow. Overnight lows should be slightly cooler tonight from where they were last night, and tomorrow will be a smidgen cooler for some locations as the ridge continues to break down and the trough upstream over the East Pac waters slowly advances towards the region. This will result in the gradual cooldown into the early part of the weekend. Afternoon winds will also become gusty for the wind-prone areas. This gradual cooldown will be followed by a gradual warmup to return beginning Sunday through the middle of next week as the ridge over the desert southwest begins to shift back towards the west and builds as it does. From previous discussion... As we suspected, coastal clouds have struggled and failed to fully clear from the coast so far today. The strong marine inversion and the coastal eddy are doing their job of juicing the marine layer. A weak but deepening trough of low pressure over the Pac NW and our local coastal eddy have contributed to this deeper marine layer trend. This trough will drive our general cool pattern through the weekend, with cooler weather in all areas and low clouds and fog reaching into parts of the inland valleys each night and morning. Temperatures will continue a few degrees below normal west of the mountains through Thursday, while temps continue a few degrees above average in the mountains and deserts. That is especially true today as we head into the final hours of our Extreme Heat Warning for our lower deserts. A cooler air mass Friday and Saturday will bring the entire region below average those days and through the weekend at least. Next week we`re fairly confident that the high pressure ridge over the Southwest will strengthen and expand into SoCal, eventually centering over the four corners area. This will bring a warming trend for all areas and of course a shallowing of the marine layer. That will mean less extensive coastal cloudiness and less duration next week. It won`t be a rapid or significant warming trend, as temperatures will take a few days to get back to average, maybe not until Wednesday. For the past month or so we`ve been teased by model guidance showing some increase in monsoon moisture about a week into the future. But we`re not offended by the bullying tease, so we have no meaningful chances of precipitation in our forecast. There are some hints late next week that the ridge will weaken slightly, hinting at a cooling trend. && .AVIATION... 140330Z...Coasts/Valleys...Low clouds have pushed inland nicely this morning, full through about 10-15 miles inland and based 900-1200ft MSL. Bases will likely settle down to 700-1000ft MSL by 09z Thursday, with inland extent reaching through 15-20 miles. 60% chance CIGs reach KONT for 10-15z Thursday. Vis restrictions to 3-5 SM in BR near higher coastal terrain and locally within valleys. Clouds scatter back to the coasts 17-19z Thursday morning with partial and interment clearing expected along the immediate coast. Clouds likely push back ashore by 00-02z Friday with slightly higher bases. Mountains/Deserts...Mostly clear with VFR conditions through Thursday evening. && .MARINE... No hazardous marine conditions are expected through Tuesday. && .BEACHES... A 14-16 second southwesterly (200-220 degree) swell will bring elevated surf and a high rip current risk to southwest facing beaches. Surf of 3 to 5 feet, with sets to 6 feet, are expected through Thursday, with surf lowering 2 to 4 feet by Friday. Strong rip currents could continue into Friday for some beaches. Consult a local lifeguard if you`re at the beach. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...None. && $$ PUBLIC...Stewey AVIATION/MARINE/BEACHES...Munyan