FXUS66 KSGX 270357 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 857 PM PDT Sun Oct 26 2025 .SYNOPSIS... The marine layer stays deep tonight with clouds reaching the inland valleys. High pressure and periods of weak to locally moderate Santa Ana winds will bring warmer and drier weather with a shallower marine layer this week. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... Maximum wind gusts today were a bit stronger than yesterday, with the peak gusts topping out at 45 to near 50 mph. Strongest westerly winds were over mountain ridges and through the San Gorgonio Pass. Areas of low clouds and fog are expected to reach into portions of the valleys again overnight. By mid-morning Monday, weak northeasterly winds are expected to develop on the coastal mountain slopes and below passes. That wind shift will quickly clear any lingering low clouds. High temperatures on Monday are expected to be 3 to 5 degrees warmer than today in and west of the mountains, but a few degrees cooler in the deserts. From previous discussion issued at 2 PM October 26... Tuesday and Wednesday... As the tough pushes inland and begins to dig southward through Utah, allowing high pressure to increase across the Great Basin. Ensemble guidance has been hinting at this offshore wind mid week, but now within the range of high resolution guidance, confidence is increasing for a weak and possibly (30%) moderate Santa Ana Wind event. Offshore flow looks to increase late Monday, peak on Tuesday, and diminish late Wednesday. For Tuesday, strong gusts (35-45 mph) look to be largely confined to the mountain passes though 25-35 mph gusts could extend into portions of the Inland Empire below the Cajon/Banning passes. Dry desert air filtering into the inland valleys resulting from the offshore flow could lead to localized critical fire weather conditions when combined with strong winds through mountain passes on Tuesday. Meanwhile, an upper level ridge gradually builds Monday night into Tuesday, allowing thickness to increase. This combined with an eroded marine layer and compressional warming brought by the offshore winds, a substantial warming trend from Monday into Tuesday is expected. High temperatures Tuesday afternoon look to reach the low to mid 90s across portions of inland Orange County, inland San Diego County valleys, and the Inland Empire. These temperatures would run 13-18 degrees above normal for late October, leading to moderate HeatRisk. To account for the unseasonable warmth and the moderate HeatRisk, a Heat Advisory has been issued for Tuesday afternoon. While offshore flow will be weaker on Wednesday, the ridge remains overhead and similar temperatures are possible. Late week... The offshore pressure gradient relaxes late Wednesday, with onshore flow reestablished by Thursday afternoon. The ridge begins to weaken some as well, allowing temperatures to cool some for Thursday, albeit still 5-10 degrees above normal. Weak ridging remains in place into the end of the week, keeping the marginally above normal warmth in place. The marine layer looks to return, at least partially, by Thursday morning. && .AVIATION... 270330Z...Coast/Valleys...Low clouds across western San Diego County will continue to fill into parts of Orange County and the Inland Empire this evening. Clouds based near 1200-1500 ft MSL will lower overnight closer to 500-1000 ft MSL after 08Z. Confidence is low to moderate (25-40%) on any cigs 300-500 ft MSL with accompanying FG reaching KONT between 13-16Z. Vis reductions below 1sm in parts of the Inland Empire and higher coastal terrain until 16-18Z Mon as clouds clear back to the coast. Increasingconfidence that any conditions stay SCT-FEW010 Monday evening into Tuesday morning as offshore winds begin to strengthen across SoCal. Mountains/Deserts...VFR conditions expected through the TAF period. FEW-SCT high clouds AOA 20,000ft MSL through Monday morning. && .MARINE... No hazardous marine conditions are expected through Thursday. && .SKYWARN... Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...Heat Advisory from 11 AM to 7 PM PDT Tuesday for Orange County Inland Areas-San Bernardino and Riverside County Valleys- The Inland Empire-San Diego County Valleys. PZ...None. && $$ PUBLIC...CO AVIATION/MARINE...APR