Synopsis
Santa Ana winds will continue through Saturday, with the strongest winds expected today. Hot and dry conditions expected for the coastal basin with moderate to locally major HeatRisk for coastal areas. Santa Ana winds weaken by Sunday, allowing the coastal basin to cool off. Further cooling expected region-wide for next week with widespread rain as a low pressure system moves in from the northwest.
Discussion
FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES...
Upper-level northeasterly flow has combined with a strong offshore surface pressure gradient to produce moderate to locally strong Santa Ana winds. Thus far, the winds have been primarily out of the northeast with the typically windy corridors north of San Diego County being more favored. Upper level winds will turn due east across the region this morning as an upper cut-off low moves to the south. Concurrently, the strong surface high over the northern Plains will migrate southward over the next day. As a result, winds will turn easterly and strengthen in favored zones (San Diego County, southern OC, and the eastern Inland Empire) and weaken slightly elsewhere.
Wind gusts today will peak around 50-65 mph along coastal slopes and adjacent foothills (locally higher for east-facing slopes and downwind of the Banning Pass). For the valley, corridors of wind gusts 35-55 mph expected, especially in eastern San Diego County. Winds slowly weaken tonight into Saturday as the easterly flow aloft and the surface pressure gradient both weaken. Gusts on Saturday are expected to peak around 40-55 mph along coastal slopes and foothills (locally higher for east-facing slopes. Corridors of gusts 30-45 mph will continue for the valleys. Santa Ana winds weaken further Saturday night and diminish entirely by Sunday.
Elevated to near-critical fire weather conditions will continue through Saturday, though relative humidity values will be slightly higher than they were on Thursday. Some influx of moisture from the south will keep RH values mainly above 15% through the remainder of the event. In fact, there is a slight chance of light showers for southern San Diego County Saturday morning, though there is an even lower chance (5-10%) for any wetting rainfall.
Looking forward to next week, the return of onshore flow on Monday will bring cooler weather for the coastal basin. Patchy fog is expected Mon/Tue mornings as the marine layer rebuilds itself. Models continue to become better aligned regarding the strength and track of a robust upper-low pressure system expected to swing through the region mid-next week. This will bring a widespread cooling trend starting next Tuesday and widespread precipitation next Wed-Thu. Precipitation will likely remain light to moderate due to lack of any notable moisture source, though model guidance has trended wetter since yesterday. There is still some disagreement on precipitation amounts and extent of cooling at this time. Elevated winds are also expected for mountains, deserts, and coastal waters. Model solutions diverge by next weekend, though the mean of the guidance leans slightly toward upper troughing.
Aviation
160540Z...SKC and VFR today. Northeast winds will remain elevated through tonight, when the strongest and most widespread winds are expected. For the mountain foothills peak gusts of 45 to 55 kt are expected. For the valleys, gusts 30 to 45 kt, locally higher near mountain foothills are likely. Coast and Coachella Valley will also see elevated winds with gusts 20 to 30 kt. There is a potential for gusts of 50 kt to occur at KONT early this morning, increasing around 10Z Fri. Winds will weaken from north to south by 18-22Z. Areas of MOD-STG up/downdrafts in lee of (south and west of) mountains along with areas of LLWS where strong winds do not surface. East winds continue into Sat.
Marine
Isolated northeast gusts could exceed 20 knots today into early Saturday. Otherwise, no hazardous marine conditions are expected through Monday.
Beaches
A south swell from 190 to 200 degrees at 3 to 4 feet with a 15-17 second period will generate elevated surf of 3 to 6 feet, with local sets to 7 feet. There is an increased risk of strong rip currents.
Skywarn
Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions.
Sgx Watches/Warnings/Advisories
CA...Heat Advisory until 8 PM PDT Saturday for Orange County Coastal Areas-Orange County Inland Areas-San Diego County Coastal Areas.
High Wind Warning until 8 PM PDT Saturday for San Bernardino and Riverside County Valleys-The Inland Empire-San Diego County Valleys.
High Wind Warning until 8 PM PDT Friday for San Bernardino County Mountains.
High Wind Warning until midnight PDT Saturday night for Riverside County Mountains-San Diego County Mountains-San Gorgonio Pass near Banning.
High Wind Warning until noon PDT Saturday for Santa Ana Mountains and Foothills.
Wind Advisory until noon PDT Saturday for Orange County Inland Areas.
PZ...None.
PUBLIC...KW AVIATION/MARINE/BEACHES...Castro