738 FXUS66 KSGX 200332 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 832 PM PDT Thu Jun 19 2025 .SYNOPSIS... Low pressure moving ashore along the West Coast will bring a cooling trend into the weekend. This will usher in elevated winds to the mountains and deserts, along with a deep marine layer accompanied by extensive night and morning low clouds west of the mountains. The low pressure pattern will weaken by next week, leading to gradual warming with less wind inland. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... Update: Latest satellite imagery displays a broad collection of low clouds over the inner socal bight, which will continue to surge inland throughout the evening. There will also likely be some areas of patchy fog developing, both over the waters and for higher elevations along the coast where the clouds will intersect, and portions of the inland valleys as well. Over the course of the next couple of days as we begin to become more influenced by the trough with an associated areas of low pressure upstream. With an enhancement of the marine layer, there will likely be a more persistent extent of clouds into the further inland areas (as bases will rise) and skies will likely remain broken to overcast for the coastal areas this weekend, with only partial clearing for the inland areas. There could also be some drizzle possible for the coastal and inland areas from Saturday night into Sunday morning. Winds will also continue to increase over the high deserts, and also within the San Gorgonio Pass and for wind-proned areas of the lower deserts. Guidance still has enough coverage of wind gusts being right around, or exceeding the threshold, for the San Gorgonio Pass to warrant the need for a wind advisory. There could also be some areas of blowing dust for these locations due to the winds. Other than that, models are still on track showing the trough deepening for 1000-500 mb thickness values to drop down to 577-583 dm over the CWA, giving way to much cooler temperatures for this weekend, especially on Saturday, where the IE will likely see highs only around 75 to 80F...compared to the values being closer to around 100F in recent days. Ensemble members still indicate that the trough will weaken with slight ridging occurring over the region by later next week, with a gradual increase of temperatures through then. (Previous discussion submitted at 236 PM): An area of low pressure currently off the coast of British Columbia will push southward into the western U.S. through the weekend. The area of high pressure that brought the hot weather to our area the past couple days continues to progress into the Southern Plains. This leaves us in a weak troughing pattern as the marine layer has slightly deepened since yesterday. Low clouds are continue to fade across the beaches this afternoon, with clouds coming back ashore early this evening. The area of low pressure will move into the Pacific Northwest on Friday, further deepening the marine layer, which will help to spread greater cooling to inland areas. Expect temperatures to lower another 5 degrees or so into tomorrow as this system comes closer. As this marine layer deepens, expect low clouds to fill in much of the coastal basin each night. The tightening pressure gradient will also contribute to increased winds across the mountains and deserts each afternoon and evening. As the trough approaches, wind gusts currently across the northern mountains and deserts are close to 20-35 MPH. Winds will increase by Friday and Saturday as the area of low pressure deepens across California and the Great Basin. NBM 75th percentile winds show widespread gusts of 30-40 mph across desert regions, with gusts over 50 mph in some of the passes. West winds will funnel through the San Gorgonio Pass these days with winds near 55 mph at times along Interstate 10. This has prompted a Wind Advisory to be issued for Friday and Saturday in the pass, where people should watch for difficult driving conditions at times in the afternoons and evenings. Much more noticeable cooler weather will also be felt by this weekend with the coolest temperatures occurring on Saturday. Coastal areas will see highs up to 5 to degrees below normal, with other inland areas seeing highs 5 to locally 15 degrees below average. Highs will be in the upper 60s to lower 80s for most areas, with most spots across the lower deserts staying below the 100 degree mark. By Sunday, the main portion of the area of low pressure to the north will push further into the Northern Rockies as the flow splits aloft, where another weaker trough will hang across the area into Monday and Tuesday. This pattern will maintain a deeper marine layer and below average temperatures across the region, though less wind for the mountains and deserts as the pressure gradient weakens. Weak flow aloft is evident in ensemble models by the middle of next week with a possible ridge of high pressure building in across the Desert Southwest, which would lead to gradual warming by the end of the week. && .AVIATION... 200300Z....Coast/Valleys...Satellite shows low clouds have begun to move inland, with CIGs for San Diego County coastal sites, likely to reach Orange County by 04-06z. Bases generally 1200-1600ft MSL. Further inland spread expected 9-11z, with CIGs for the Inland Empire likely 11z-16z. VIS will be slightly improved everywhere outside of where clouds intersect terrain, generally above 4SM. Retreat of clouds to the coast by 16-18z, although clouds may linger at the beaches beyond this point. Low clouds push inland again Friday evening, possibly a bit earlier, around 01z Saturday, with slightly higher bases. .Mountains/Deserts...Clear skies and unrestricted VIS through Friday. Westerly winds with gusts 25-40 knots through mountain passes locally into deserts, producing pockets of up/downdrafts in lee of ridges through 11Z Friday. Similar but slightly stronger winds pick up again after 21Z with mod to strong up/downdrafts near mountain peaks. BLDU with VIS below 3SM possible at times through Friday evening. && .MARINE... Northwest wind gusts around 20 knots near San Clemente Island Friday afternoon and evening. Otherwise, no hazardous marine conditions are expected through Wednesday. && .SKYWARN... Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...Wind Advisory from 11 AM Friday to 11 PM PDT Saturday for San Gorgonio Pass near Banning. PZ...None. && $$ PUBLIC...APR AVIATION/MARINE...Zuber