Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
747 FXUS66 KSGX 120424 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 824 PM PST Tue Nov 11 2025 .SYNOPSIS... Low clouds will spread a little farther inland tonight as the marine layer deepens slightly but the fog is less likely to be dense. For Wednesday and Thursday, onshore flow will strengthen spreading greater cooling inland. A low pressure system from the northwest will bring additional cooling for Thursday night and Friday along with showers and a slight chance of thunderstorms. There could be another round of widespread showers on Saturday. Chances for showers are less on Sunday with additional precipitation possible for early next week. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... This evening, the marine layer is marginally deeper than yesterday and low clouds are likely to spread farther inland but fog is less likely to be dense. Widespread mid and high clouds continue to cover the region downstream from the low pressure system to the west. Inland temperatures were once again well above seasonal averages and six climate sites tied or exceeded the previous record high temperature for this date. From previous discussion... A low pressure trough deepening south of the Gulf of Alaska will merge with the low to our west and intensify as it moves east toward the coast. This will bring stronger onshore flow and cooling to the region with highs 10 degrees cooler in the western valleys. Highs will remain near 90 degrees again across the lower deserts on Wednesday, before becoming much cooler. By Thursday, the storm system will move closer to the region with most areas seeing another 5 degrees of cooling. South to west winds will be strongest on Thursday and Thursday night, with widespread gusts 25-45 MPH, locally over 50 MPH in the passes. Model guidance is still struggling some with exact timing of the onset of precipitation, though hi-res models show a slower scenario with precip beginning sometime early Friday morning across the LA basin and surrounding mountains. NBM shows precip coming in as early as Thursday afternoon. Confidence becomes higher as to when the heaviest precipitation will be, which will occur from north to south on Friday morning into the early afternoon. Rain rates will likely be over 0.50"/hr, locally near 0.75"/hr. As this moves through, there will be an increased risk of traffic incidents, flooding, and debris flows/mudslides from local area burn scars. Snow levels will remain rather high during this event as the system pulls in moisture from the subtropics. Snow levels will be near 9,000 feet to start on Thursday with levels dropping near 7,000 feet by Friday with a slushy accumulations under one inch in places near these levels. We continue to watch where the exact path of this area of low pressure will go as it moves inland over the weekend. This will dictate where (or if) the wrap-around moisture (the rain/snow on the north side of the low pressure system) from the weather system goes. In a scenario like this, precip will move over the area from east to west, but confidence on where the precipitation sets up and how much falls is still in question. If the system moves further south, there will be a better chance for a greater amount of the area to get rain vs. if the low pressure center moves further north, keeping the southern half of our area not as wet. The system will exit on Sunday, leaving 20-30% chances of precip in the forecast. A secondary trough will move over the West Coast by early next week, keeping the weather pattern unsettled. The strength and how far south this system will go remains to be seen, but chances (20-30%) for light precip are in the forecast for the entire region, along with cooler weather. && .AVIATION... 120415Z...Coasts/Western Valleys...Low clouds 700-900 ft MSL are covering areas west of I-15 in San Diego County and 5-10 miles inland in Orange County. Valleys around I-15 currently experiencing VIS down to 1/4-2SM due to FG, with VIS improvements anticipated overnight as bases lift to 1000-1200ft by 09-12z. Clouds will spread further into inland valleys and perhaps western portions of the Inland Empire (25-35% chance of occurrence after 08z), reducing VIS to 0-5SM in those areas. Scattering back to the coasts and VIS improvements everywhere around 18-19z Wednesday. Patchy cloud cover may linger through the afternoon within 5 miles of the coast, then move inland after 23z, remaining FEW-BKN in coverage as it does so with bases rising to 1500-2000 ft MSL by Wednesday evening. Otherwise...VFR conditions will continue through Wednesday with SCT-BKN high clouds AOA 20 kft. && .MARINE... A storm system will bring strong winds and elevated seas late Thursday through Friday as a front passes through the coastal waters. Wind gusts 20-25 kts expected in the outer waters, closer to 15 to 20 kts for the nearshore waters. A swath of moderate to heavy precipitation will accompany the cold front with a slight chance of thunderstorms Thursday night through Friday. && .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...Westerink