FXUS66 KSGX 041835 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 1000 AM PST Wed Dec 4 2024 .SYNOPSIS... High pressure aloft and developing weak offshore flow will bring well above average high temperatures in inland areas through this weekend. Areas of night and morning low clouds and fog, locally dense, will occur in coastal areas through Friday morning. A low pressure system from the northwest will bring cooling early next week with gusty west to northwest winds in the mountains and deserts. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... Low clouds and fog had mostly cleared western San Diego County by 10 AM but were still covering many parts of Orange County. Skies should clear back to the coast in Orange County by noon, and temperatures will generally be deg F above normal this afternoon inland, though near or a little below normal near the coast. With the marine layer getting more shallow tonight then, there could be a little bit of dense fog over higher coastal terrain, and perhaps near the immediate coast Thursday night before the marine layer will likely become minimal. A closed low aloft will likely remain over Arizona through Friday and then only very slowly drift to the east as a high pressure ridge extends from the East Pacific through California and the Great Basin. This will be an offshore flow pattern, though high-resolution models indicate any Santa Ana winds to be weak to locally moderate. Through Thursday night, most of the winds appear to be along the mountain ridges, but some of the gusty winds could come down into the valleys, especially the Inland Empire, Friday through Saturday. Current gust potential is to around 40 MPH in the windiest locations south of Cajon Pass. Humidity will be low with some 10-15 percent values mainly Saturday for elevated to locally near critical fire weather conditions. It should be quite mild across the region with highs Friday-Saturday around 80 or even a little above at most lower elevation locations away from the immediate coast. A cooling trend will occur early next week with a long-wave trough moving southeast from the Pacific coast off of British Columbia through much of the western US. This should be a dry trough for SoCal, but it could be accompanied by a moderate Santa Ana wind event due to a surface high pressure center developing in the Great Basin and cold air advection from the northeast. && .AVIATION... 041700Z....Coasts/Valleys...Low clouds based around 800-1200ft MSL are starting to retreat in southern San Diego County, but should hold on for another hour or so in Orange County before eventually clearing by 19z. VIS reductions to 3-5SM remain possible in the western valleys and higher terrain until the clouds clear. VFR prevails through the afternoon until low clouds move back ashore after 01z. These clouds should only reach about 5-10 miles of inland extent tonight, with lower bases around 500-1000ft MSL. Reduced VIS 1-5SM possible, especially on mesas and higher coastal terrain. Otherwise...VFR and mostly clear skies prevails through Thursday morning. && .MARINE... No hazardous marine weather 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...Maxwell AVIATION/MARINE...Munyan