Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
403 FXUS66 KSGX 050407 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 907 PM PDT Thu Sep 4 2025 .SYNOPSIS... Additional chances for afternoon showers and thunderstorms over the mountains and deserts tomorrow, followed by drying through early next week. A large low pressure system moving inland into the western states next week will maintain dry conditions. There will be a cooling trend through Wednesday with high temperatures for some inland areas cooling to 8 to 12 degrees below average by Wednesday of next week. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... Earlier this afternoon, a few thunderstorms developed over the San Diego and Riverside county mountains. All thunderstorm activity diminished by 7 PM, and dry conditions are expected overnight. Patchy low clouds are developing along the coast and are expected to remain patchy in coverage overnight. Low clouds should quickly clear Friday morning. Highs Friday will be a few degrees cooler than today, with additional chances of thunderstorms over the mountains and deserts Friday afternoon. From previous discussion issued at 2 PM September 4, 2025... Tomorrow through this weekend... For tomorrow, the mid-level steering flow will not be as good so that most of the showers/storms that form will likely remain over the far eastern extent of the mountain ranges in San Diego and Riverside counties. There could also be a storm or two developing over the San Bernardino Mountains tomorrow afternoon. As more troughing continues to slowly advance towards the region, a slight cooling trend will occur into Saturday, and then temperatures will remain nearly steady going into Sunday. There will also be a drying trend each day, and the marine layer will continue to thicken and become more persistent, especially for the coastal areas, as onshore flow becomes more predominant. Early through mid part of next week... During this period in the forecast, models are still strongly indicating that the region will become influenced by troughing over the east Pacific waters, which will allow for temperatures to be much cooler and slower to the seasonal average (and even slightly below average) by next Tuesday and Wednesday. This will also keep mid-level flow southwesterly with drier air advection to help to thwart off convection development (thunderstorm activity) throughout the week for our mountains and deserts. Afternoon winds will also become more gusty for locations prone to higher winds. Conditions are expected to remain dry, however, it also can not be ruled out with the troughing overhead that there could be a few areas of drizzle possible for some of the coastal and inland valleys during the early morning hours for each day. && .AVIATION... 050315Z...Coast...Low clouds based 800-1200 ft MSL have started to develop along the northern San Diego coastline, and will continue to spread along the coast and inland 10-15 miles. Local vis reductions over higher coastal terrain 2-5 SM. Clouds clear to beaches 15-17Z, redeveloping after 06/06Z with similar bases. Valleys/Mountains/Deserts...Isolated SHRA/TSRA expected over San Diego County and southern Riverside County mountains again Fri 19- 01Z, with slighter chances (15-20%) for more northerly mtns and deserts/desert foothills. CB bases of about 10000 feet MSL with TSRA tops to 35k feet. Gusty, erratic winds, blowing dust with low visibility, lightning, and lower bases 6000-9000 feet MSL will occur with any TSRA. && .MARINE... No hazardous marine conditions are expected through Monday. && .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...CO/Stewey AVIATION/MARINE...CSP