FXUS66 KSGX 272053 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 153 PM PDT Mon Oct 27 2025 .SYNOPSIS... Offshore flow and strengthening high pressure aloft will bring warming through Wednesday with periods of gusty Santa Ana winds along and below the coastal slopes of the mountains for tonight into Wednesday with the stronger gusts to 35 to 45 mph. High temperatures 15 to 20 degrees above normal expected Tuesday and Wednesday afternoon. Weak onshore flow will bring less hot conditions inland for Thursday and Friday with high temperatures for next weekend at least a few degrees warmer as high pressure aloft strengthens and another weak offshore event appears possible. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... Today through Wednesday... As the trough currently over Idaho digs southeastward today, building high pressure across the Great Basin will strengthen the offshore pressure gradient. North to northeasterly flow is set to begin this afternoon across the deserts and desert slopes, while onshore flow prevails today for the coasts and valleys. This will likely inhibit the marine layer, with only a few clouds possible along the coasts tonight. As inland high pressure builds, the offshore gradient is set to peak on Tuesday, resulting in in weak to locally moderate strength Santa Ana winds, with strong gusts primarily focused within and below main mountain passes. Wind gusts here could gust up to 35 to 45 mph on Tuesday afternoon, with 25-35 mph gusts stretching into the Inland Empire, the Santa Ana Mountains, and the inland valleys of San Diego County. High pressure in the Great Basin slides east heading into Wednesday, and while offshore flow should persist through late Wednesday, wind gusts should be notably weaker than Tuesday. Meanwhile, a building ridge paired with the compressional effects of the downslope, offshore winds and a lack of a marine layer will culminate in a substantially warmer day on Tuesday compared to today. Afternoon temperatures are expected to soar into the low to mid 90s across inland portions of Orange/San Diego counties and the Inland Empire, coming in about 13-18 degrees above normal for late October. Despite weaker offshore flow Wednesday, continued dry conditions and the upper level ridge keeps temperatures hot, even a degree or two warmer than Tuesday. With this, widespread moderate HeatRisk is still expected across Orange County inland, San Diego County valleys, and the Inland Empire, and the Heat Advisory currently in effect for Tuesday into Wednesday remains on track. The offshore flow brining in the hot and dry desert air will also send afternoon humidity into the low teens Tuesday and Wednesday afternoon. This when combined with the Santa Ana winds will bring elevated fire weather conditions, and locally critical conditions during the periods of strongest winds in the afternoon within wind- prone mountain passes. Thursday into Late Week... The offshore pressure gradient relaxes late Wednesday into Thursday, with onshore flow reestablished for the coasts and valleys by Thursday afternoon. The absence of offshore flow allows 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. Another weak offshore wind event is possible this weekend, which could bring another period of warmer and drier conditions. && .AVIATION... 262000Z...Coast/Valleys...Mostly clear through the afternoon hours with lingering HZ and vis 3-5sm across the Inland Empire. Confidencenow moderate to high of BKN cigs near 800-1200 ft MSL returning to VCTY KSAN/KCRQ 06-16z Tue. Cigs becoming more intermittent after 12Z Tue. Lower confidence in these cigs impacting VCTY KSNA. N/E winds with gusts 20-30 kts increasing across parts of the Inland Empire downwind of the Cajon / Banning Passes after 12Z Tues will lead to MOD UDDFS at times. Mountains/Deserts...Clear and VFR conditions today and tonight. N/E wind gusts 20-35 kts around coastal facing slopes and passes after 12Z Tue, leading to MOD UDDFS. && .MARINE... No hazardous marine conditions are expected through Friday. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...Heat Advisory from 11 AM Tuesday to 7 PM PDT Wednesday for Orange County Inland Areas-San Bernardino and Riverside County Valleys-The Inland Empire-San Diego County Valleys. PZ...None. && $$ PUBLIC...Munyan AVIATION/MARINE...APR