Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
815 FXUS66 KSGX 031048 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 348 AM PDT Wed Sep 3 2025 .SYNOPSIS... Monsoonal moisture will remain in place through Thursday with chances for afternoon and early evening thunderstorms for the mountains, deserts, and inland valleys. Greater drying will occur for Friday and Saturday with a slight chance of thunderstorms for the mountains and deserts for Friday afternoon. The drying will continue into early next week along with a cooling trend with high temperatures for next Tuesday a few to around 5 degrees below average. Night and morning coastal low clouds will gradually return through the weekend and spread locally into the far western valleys late each night for next week. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... .SHORT TERM (Today through Friday)... Greater monsoonal moisture will remain in place through Thursday followed by a drying trend into early next week. Chances for showers and thunderstorms will persist for the mountains, deserts, and inland valleys during the late morning through early evening with the greater chances for today and Thursday. The greatest HREF 90th percentile hourly rainfall for today is around one-half inch and is around one inch on Thursday as there may be some increase in lower level moisture into the lower deserts on early Thursday. High temperatures will slowly cool with around 5 degrees of cooling through Friday. Friday high temperatures will be near average at the coast to around 5 degrees below average for the lower deserts with high temperatures ranging from the 70s near the coast to the upper 80s to mid 90s for the Inland Empire with the upper 90s to 102 for the lower deserts. && .LONG TERM (Saturday through Tuesday)... The drying will continue into early next week. NBM daily chances for measurable rainfall in the mountains falls below 10 percent on Saturday and below 5 percent for Sunday into next week. A large closed low pressure system well off the West Coast will begin to bring dry southwest to west flow across the area beginning on Saturday. This will persist through at least the middle of next week as that low pressure system moves slowly into the western states on Tuesday and Wednesday. With the drying, nights will be gradually cooler. While there is an overall cooling trend in high temperatures for early next week, there is greater spread in the NBM high temperature guidance on when the greater cooling occurs due to differences in the timing and strength of the low pressure system as it moves into the western states. With the cooling, high temperatures on Tuesday will be a few to around 5 degrees below average with high temperatures on Tuesday ranging from the 70s near the coast to the upper 80s to mid 90s for the Inland Empire with 100 to 104 for the lower deserts. Night and morning low clouds will spread inland across coastal areas and sometimes in the far western valleys late each night. && .AVIATION... 030930Z...Coast...Patchy and intermittent low clouds and fog with CIGs 600-900 feet MSL and vis 2-5SM through 15Z. Similar low cloud bases, coverage and timing tonight after 07Z into Thursday. Valleys/Mountains/Deserts...Mostly clear through 19Z and after 01Z. Clouds building over mountains with bases 9000 feet MSL and a chance of SHRA/TSRA 19-01Z. TSRA tops to 35000 feet. Gusty and erratic winds, low visibility, and lightning will accompany any TSRA, along with lower bases 6000-9000 feet MSL. && .MARINE... 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...17 AVIATION/MARINE...MM