Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
708 FXUS66 KSGX 041646 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 946 AM PDT Sat Oct 4 2025 .SYNOPSIS... Weak offshore winds this morning will give way to the typical sea breeze west of the mountains in the afternoon. Temperatures this afternoon will be warmer than yesterday outside of the immediate coast and low deserts, but still near to below the daily average. Daily marine layer clouds will likely make a comeback early Sunday morning, with more widespread low clouds early next week. Little change in temperatures through Monday, followed by a gradual warming trend into the middle/latter part of next week. There is the potential for tropical moisture to move into the area late in the week, bringing a slight chance of showers, mostly over the mountains. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... .SHORT TERM... The upper level low that brought cooler temperatures and breezy winds to the region yesterday has moved to the northeast into the Intermountain West this morning, leaving us in broad, weak troughing. As a result, winds are calm outside of a few typically windy gaps like the Banning Pass into the northern Coachella Valley and through the In-Ko-Pah Gorge just east of the San Diego County line, which are still seeing gusts to 20-30 mph. Elsewhere, the movement of the low has resulted in weak offshore (generally north to northeast) flow. This is contributing to the mostly clear skies in the area, outside of a scattering deck around 1500 feet in the more sheltered Inland Empire and northern Orange County. More typical, mild SoCal weather is expected today into early next week. Winds will shift to the west starting at the coast early this afternoon as the sea breeze develops, then move inland into the late afternoon. High temperatures today will be a few degrees (2-4 F) above yesterday`s outside of the immediate coast and low deserts, where temperatures will be about the same as yesterday to even a tad cooler. Despite this mild warmup, temperatures remain near (along the coast) to 5 to 10 degrees below the daily average temperature. A broad trough remains over the western U.S. into early next week, and a shortwave digging down the western side of the trough will develop into a weak low off the south-central California coast. This will result in a very subtle cooling trend Sunday through Monday for most of southwest California, but in practice temperatures will still be very similar to today. However, it will shift the flow to a more onshore regime, which will bring nightly and morning low clouds back to our coastal areas. Low clouds will struggle to form most of tonight, but an eddy circulation developing early Sunday morning will moisten things up enough to get at least patchy low clouds along the San Diego and likely northern Orange County coastline. Low clouds Sunday and Monday nights will be earlier to develop and more widespread. && .LONG TERM... The weak closed low will open into the broader trough and move to the northeast late Tuesday into Wednesday as the west end of a broad high over the southern U.S. nudges into the area. This will result in a warming trend Tuesday through the mid to latter half of next week. Meanwhile, a large low pressure system will drop south out of the Gulf of Alaska and make its way down the West Coast. Simultaneously, a developing tropical system south of Baja California will gradually make its way northwest through next week, likely leading to some amount of remnant moisture moving into Southern California by late Thursday/Friday. There is significant differences in model output for where the low from the northwest will set up, as well as the track of the tropical system along with how much moisture from it will advect into the area, leading to a low confidence forecast for both temperatures and possible convective rainfall for the latter part of next week. For now, the forecast is for near zero chances for rainfall increasing to a small chance (10-15%) by late Thursday, then with slight chances (15-20%) over the mountains and parts of the deserts and less than 15% chances elsewhere Friday and Saturday. Moisture would be fairly high-based, resulting in those higher chances over the mountains, but if we get strong enough forcing from troughing nearby, showers west of the mountains would not be out of the question, as indicated by a handful of ensemble members. Currently instability appears too weak to include any thunderstorms in the forecast. && .AVIATION... 041600Z....Coasts/Valleys...Patchy low clouds with bases 1500-3000 ft MSL will scatter or clear by 17Z. Patches of low clouds may develop after 03Z Sun. Less than 30% chance for cigs at coastal TAF sites before 12Z Sun. Any clouds that develop will be patchy in coverage with bases 1500-2500 ft MSL. Mountains/Deserts...VFR conditions will prevail into Sun. && .MARINE... No hazardous marine conditions are expected through Wednesday morning. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...None. && $$ PUBLIC...CSP AVIATION/MARINE...CO