FXUS66 KSGX 090442 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 842 PM PST Wed Jan 8 2025 .SYNOPSIS... Much lighter Santa Ana winds and dry air across southern California. Warmer temperatures on Thursday but the offshore northeast to east winds increase significantly on Thursday and reach moderate to locally strong Thursday night and early Friday before decreasing Friday afternoon. Light winds for the weekend but another Santa Ana wind period is possible early next week, increasing Sunday night and Monday. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... The Santa Ana winds are much lighter all areas. Only gusts to 40 mph this evening are the most wind prone areas, Cajon Pass of San Bernardino mountains and the Santa Ana mountains canyons. This will continue tonight as we are in between surges. Please see the LSRSGX (local storm reports) and the PNSSGX products for summaries of highest wind gusts and impact in our region of Socal. The large closed upper low that made this a strong wind event has shifted far south in the Baja Mexico and warming aloft is moving across Socal while the surface pressure gradient from the Great Basin is weaker, 10 mb pressure gradient from Salt Lake City to San Diego which was 20 mb during Tuesday evening peak strength. Winds are going to be light offshore on Thursday morning but another short wave trough drives north to south from Utah to Arizona on the front side of the amplified jet stream pattern. This system is forecast to merge with the old closed upper low from northern Mexico, and this will increase a new surge of Santa Ana winds again for all areas by midday Thursday and into Thursday evening with primarily strongest for the San Diego mountains (peaking Friday early morning), and for the favored canyons and passes across the San Bernardino, Santa Ana and Riverside county mountains. Due to northeast to easterly wind flow prevailing these areas should get gusts 50 to 75 mph, so continuation of red flag conditions down into the foothills and inland valleys as well as Inland Empire. Other areas along I-5 and I-15 gusts 15 to 30 mph. Brief short wave ridging aloft for Friday and Saturday, so another decrease to light offshore flow but remaining a dry air mass. More cold polar air mass enters the Great Basin on Monday and Tuesday with potential strong surface high for development of another Santa Ana winds. However, the upper air pattern phasing is uncertain on the latest guidance so the strength is not confident for early next week but at least moderate Santa Ana is there based on the surface high settling over Utah around 1048 mb. && .AVIATION... 090330Z...Northeast winds will continue to diminish overnight, with breezier winds confined to foothills through mid AM Thursday. N winds restrengthen along SBD Co coastal slopes, in the Inland Empire and Orange County 16Z-20Z Thu with gusts 25-40 kts. Northeast winds increasing across RIV/SD Co mts late Thursday morning, with stronger winds expanding to the west into valleys Thursday evening into Friday morning. Winds during this time will be highest across parts of SD County, in the western foothills into the eastern valleys, with moderate confidence in wind gusts over 50 kts along coastal slopes and mountains. Winds will be somewhat erratic and intermittent in strength. Breezy NE winds will make it locally into coastal areas 04-07Z Fri, including KSAN, with moderate confidence in timing of the wind change to easterly. These winds will generate areas of BLDU with reduced vis 3-5SM, along with areas of LLWS and MOD to locally strong up/downdrafts in lee of mountains. && .MARINE... Winds will continue to decrease this evening to 10 kts or less by around midnight. Northeast winds pick up again Thursday afternoon, with areas of winds 10-15 kts with gusts up to 20 kts through Friday morning. Winds tapering off and becoming more northerly by Friday afternoon. No additional hazardous marine conditions are expected Friday afternoon into the weekend. && .FIRE WEATHER... Red flag warning continues and extended through Friday except coastal areas and deserts not included. && .CLIMATE... Most climate sites are now in first place, others top 3, for driest start to a water year (October 1). San Diego passing 2018 and 1963. && .SKYWARN... Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...Red Flag Warning until 6 PM PST Friday for Orange County Inland Areas-Riverside County Mountains-Including The San Jacinto Ranger District Of The San Bernardino National Forest-San Bernardino County Mountains-Including The Mountain Top And Front Country Ranger Districts Of The San Bernardino National Forest-San Bernardino and Riverside County Valleys -The Inland Empire-San Diego County Inland Valleys-San Diego County Mountains-Including The Palomar And Descanso Ranger Districts of the Cleveland National Forest-San Gorgonio Pass Near Banning-Santa Ana Mountains-Including The Trabuco Ranger District of the Cleveland National Forest. High Wind Warning until 2 PM PST Friday for Riverside County Mountains-San Diego County Mountains-San Diego County Valleys-San Gorgonio Pass Near Banning. PZ...None. && $$ PUBLIC/FIRE WEATHER...Tardy AVIATION/MARINE...Westerink/CSP