26/714 PM.
Marine layer stratus with patchy fog will reoccur each night from the coasts to the coastal valleys, expanding over the interior valleys through the weekend. Temperatures will very gradually cool through Monday before stabilizing. Expect below normal temperatures through late next week, trending toward normal by next weekend.
(Fri-Mon), 26/743 PM.
***UPDATE***
The main weather concern continues to be extensive marine layer clouds during the overnight to morning/early afternoon hours, gusty winds and cooler than normal temperatures. Last night low clouds advanced well inland over the coasts and coastal valleys, and into interior San Luis Obispo County, the Santa Clarita Valley and up the lower coastal slopes. This is expected to recur tonight into Saturday. Today LA County cleared more slowly than the Ventura coast and valleys, and the HREF low cloud cover forecast indicates that this is likely again on Wednesday. Over portions of Ventura County, clearing may be delayed or limited tomorrow. This deep marine layer with extensive low cloud cover and slow/limited clearing is likely to persist through early next week.
As for winds, the Wind Advisories for SW Santa Barbara County (NW winds) and the Antelope Valley and Foothills (SW winds) are increasing slowly, with a chance of falling short of Advisory levels (45 mph). Saturday afternoon and night appear more likely to reach Advisory levels in SW SBA County, with stronger surface pressure gradients between KSBA and KSMX.
A persistent upper trough over the West Coast along with continued strong onshore flow and an extensive marine layer will result in a cooling trend for the area through Sunday. Highs along the coast will change little, but away from the coast cooling of 2 to 6 degrees is expected on Saturday, especially over the far interior. Weaker cooling of 2 to 3 degrees is expected going into Sunday.
***From Previous Discussion***
Troughing over CA well into next week will mean a fairly stable forecast between now and then. Offshore flow at the surface and deepening of the marine layer will keep low stratus/fog along the coasts and coastal valleys during the evenings and mornings/early afternoons well into next week.
This, along with increasing clouds, will result in below normal temperatures and gradual cooling through Sunday or Monday. Daytime temperatures will begin to stabilize after that but continue to run below climatological norms. Highs will largely run in the 70s, with locations further inland reaching the 80s, and coastal locations generally warming into the mid- to upper-60s.
As the pressure gradient tightens, winds will begin to increase this evening, peaking on Saturday. A WIND ADVISORY is in effect for the Antelope Valley and Western Antelope Foothills through 5 AM PDT Sunday for gusts to around 50 mph. The NBM 24-hour max wind gust for these two regions for the rest of today and Saturday is up to 50 mph with a much broader area of max gusts to 40 mph. Additional WIND ADVISORIES are in effect for the Santa Barbara SW coast and the Santa Ynez Western Range for sundowner winds 5 PM PDT this evening through 3 AM PDT tomorrow and again Saturday night into Sunday morning. Offshore northwest winds winds will reach 30 mph with gusts up to 50 mph. The Santa Barbara beaches will experience breezy onshore winds during these same timeframes, with gusts ranging 25 to 35 mph.
A secondary low will drop into northern CA early Monday and continue rotating southward before lifting northeastward into Nevada early Tuesday. More on that below.
(Tue-Fri), 26/1152 AM.
Another low dropping into northern CA early Monday will continue southward and eventually lift northeastward into Nevada early Tuesday. Persistent troughing over CA will mean a continuation of onshore flow and the resultant daily low stratus and fog. Still not forecasting any precipitation, although some very light mist or drizzle falling out of the stratus deck cannot be ruled out. Temperatures will remain very stable and run up to 10 degrees below climatological norms throughout next week but will trend toward normal heading into late next weekend. At this point, flow aloft will turn zonal before an area of high pressure builds in over the Southwest during the weekend.
27/0111z.
At 1629Z at KLAX, the marine layer was 2600 ft deep. The top of the inversion was at 3500 feet with a temperature of 18 C.
High confidence in VFR TAFs for desert airfields (KPMD & KWJF).
Moderate confidence in the remainder of the TAFs. Timing of flight cat changes could be off +/- 2 hours and CIG heights +/- 300 ft.
KLAX, Moderate confidence in TAF. Arrival of MVFR CIGs around 012 expected to arrive around 02Z. 15-25% chance CIGs initially arrive IFR around 008. Similar to previous overnight periods, the low clouds are expected to gradually lift toward 015 then 020 and 025 after dawn. 25% chance east wind component reaches 7-8 kts 12Z-16Z on Saturday. KBUR, Moderate confidence in TAF. Arrival of IFR CIGs around 008 should be accurate within +/- 2 hours of current forecast. CIGs should lift to MVFR 010-015 around 13Z. No wind issues expected.
26/812 PM.
Small Craft Advisory (SCA) level wind gusts have expanded to the inner waters focused across the western and southern Santa Barbara Channel and north of Point Sal today, peaking Saturday before gradually diminishing through Monday. Local gusts may approach 35 kt near Point Conception with a 30% chance of Gale conditions across the central part of the Santa Barbara Channel Saturday evening. There is a 30-50% chance of SCA conditions expanding into the southern inner waters along and south of Point Mugu/Malibu Saturday afternoon to evening.
Seas will near 8-10 ft Saturday evening through at least Monday focused across the outer waters. Beyond, conditions look to quiet down a bit through mid next week.
Ca, Wind Advisory remains in effect until 3 AM PDT Saturday for zones 349-351. (See LAXNPWLOX). Wind Advisory in effect from 5 PM Saturday to 3 AM PDT Sunday for zones 349-351. (See LAXNPWLOX). Wind Advisory remains in effect until 5 AM PDT Sunday for zones 381-383. (See LAXNPWLOX). PZ, Small Craft Advisory in effect until 3 AM PDT Sunday for zone 645. (See LAXMWWLOX). Small Craft Advisory in effect until 3 AM PDT Saturday for zone 650. (See LAXMWWLOX). Small Craft Advisory in effect from 11 AM Saturday to 3 AM PDT Sunday for zone 650. (See LAXMWWLOX). Small Craft Advisory in effect until 9 AM PDT Monday for zones 670-673-676. (See LAXMWWLOX).
