Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
282 FXUS66 KSGX 280412 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 912 PM PDT Wed Aug 27 2025 .SYNOPSIS... Increasing clouds and moisture from Tropical Storm Juliette will bring scattered light to locally moderate showers tonight through Thursday, as well as a 10-15% chance of thunderstorms over the mountains Thursday afternoon. Warmer and drier weather will occur Friday into the weekend with less than 10% chances for storm activity. Monsoonal moisture will slowly return early next week with a slight chance of afternoon and early evening thunderstorms for the mountains and deserts. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... Evening update... Isolated showers and thunderstorms over the mountains dissipated earlier this afternoon. The initial band of clouds associated with Tropical Storm Juliette has made it into Southern California this evening. There are some weak radar returns moving into far southeastern San Diego County, but it is likely just picking up the clouds/virga with no precip being reported at the surface. The 00Z sounding shows most of the moisture above 25000 ft with a fairly deep dry layer down to 13000 ft and then some residual monsoon moisture below that. This dry layer should saturate overnight as deeper moisture from Juliette moves in, producing light to locally moderate rainfall, with the greatest coverage over Riverside and San Diego Counties and more isolated showers northward. High res guidance shows rainfally rates mostly 0.10"/hr or less, though as the remnant upper low lifts north and into So Cal, there could be enough dynamics coupled with weak elevated instability to produce local rates of 0.25-0.50"/hr or more. Thunderstorm probabilites are fairly low, less than 5% for all areas tonight, increasing to 5-15% Thursday afternoon with the highest chances over the mountains. Otherwise thick cloud cover and the weak low moving through will bring considerable cooling tomorrow with highs in the upper 70s to upper 80s in the coastal areas, valleys, and high deserts, 60s-70s in the mountains, and low to mid 90s in the low deserts. Previous discussion... Skies will clear out by Thursday night. Friday will see a drying trend, which will limit the storm chance across the mountains to near 10 percent. High pressure over northern Mexico will grow and expand this weekend. This will bring drier, less humid air to the area with warmer temperatures. This will bring temperatures closer to near average with highs near 110 across the deserts and 90s across inland valleys west of the mountains. Cumulus clouds may build over some of the mountains each afternoon, but the threat for thunderstorms will be minimal. The area of high pressure will amplify further over the desert southwest by next Monday and Tuesday, providing a path for increased monsoonal moisture to return to our area. This will lead to increased chances for shower and thunderstorms across the mountains and deserts with mostly clear skies and near average temperatures elsewhere. Ensemble cluster models start to have larger solution spread on the high remaining in place into the middle of the week, while some others show a weaker trough forming off the coast, which would bring slightly cooler and drier weather to our region. && .AVIATION... 280345Z...Very patchy low clouds based 800-1000 ft at the immediate coast overnight tonight. Remnants from tropical storm Juliette will slide into the area from the south overnight. High cloud bases AOA 10 kft associated with this moisture will keep conditions mostly VFR. Occasional -RA/RA for San Diego/Riverside Counties from 11z Thu to 00z Fri. Gusty outflow winds possible with any afternoon shower activity. && .MARINE... Very slim chance (less than 10%) of a thunderstorm over coastal waters Thursday. If a storm develops, there could be gusty winds leading to locally rough seas, along with lightning. Otherwise, no hazardous marine conditions are expected through Sunday. && .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...SS/APR AVIATION/MARINE...KW