08/751 PM.
A moderate to strong Santa Ana wind event will continue developing tonight, peak on Friday and Saturday, and bring warmer temperatures to the region. Cold overnight low temperatures are expected in the interior valleys.
(Thu-Sun), 08/752 PM.
***UPDATE***
The transition from a north-wind event to a Santa Ana wind event -- described in the Previous Discussion below -- continues to progress this Thursday evening. Surface observations corroborate this relatively quick evening transition. Specifically, the LAX-Daggett pressure gradient fell by around 4 mb during the past 6 hours to almost -1.5 mb as of 03Z, and the initially strong offshore Santa Barbara to Santa Maria / Bakersfield pressure gradients weakened below 5 mb as of 03Z. Correspondingly, the observed wind gusts over 45 mph have refocused eastward -- in conjunction with the aforementioned isallobaric tendencies as facilitated by the continued eastward progression of the CONUS- full-latitude, western-states upper trough. Manifestations of these dynamic synoptic and mesoscale mass fields on the surface winds warranted the early cancellation of wind headlines in Santa Barbara County and lower elevations of Los Angeles County, and the imminent onset times of wind headlines for Santa Ana wind corridors. The latest NPWLOX addresses the updated start and stop times for the Wind Advisories and High Wind Warnings. Also of note, the Wind Advisory was expanded slightly to include the western Antelope Valley Foothills, per consensus amongst high- resolution model guidance. The latest forecast products have been updated to reflect the aforementioned headline adjustments.
Additionally, present indications are that drier air aloft, resulting from large-scale subsidence in differential anticyclonic vorticity advection on the upstream side of the aforementioned trough, is now suppressing precipitation development along the north slopes in Ventura and Los Angeles Counties. It appears that the drier air, combined with the decreasing upslope-flow component owing to the previously mentioned isallobaric tendencies, have ceased any further precipitation/snow potential including the I-5 Grapevine area. Updated forecast products reflect the removal of precipitation.
Other than a few passing high clouds over the area starting around sunrise Friday, dry conditions and sunny skies will close out the week and prevail into the weekend. Santa Ana winds will continue into the weekend, with related adiabatic warming and eventual upper ridging bringing about above above-normal temperatures by Sunday. However, chilly and areas of sub-freezing overnight temperatures in the interior valleys will continue to be a concern.
Please reference the Previous Discussion below for additional information. No other changes have been made to the ongoing forecast.
***From Previous Discussion***
Strong northerly winds have been blowing the Grapevine region down to Santa Clarita today as well as parts of the Santa Ynez Range area and the Antelope Valley as a fast moving inside slider system dropped through the Owens Valley and Nevada and is now in Utah and Arizona. We're now transitioning from a north wind event to a Santa Ana and that process will be complete by Friday morning with strong northeast winds continuing through at least mid day Sunday, strongest in the overnight and morning periods. This will be a traditional Santa Ana, creating gusty winds across much of LA and Ventura Counties (including the Channel Islands) but generally leaving out most of the LA Basin (except possibly the Long Beach area), the Antelope Valley, and all but the extreme southern portion of the Ventura mountains.
This event has plenty of cold air and winds aloft support and the rapid shift from strong onshore flow earlier today to around an 8mb offshore flow the east often tends to amplify the winds beyond what some of the models indicate. And as usual with these multi- day Santa Anas there will be some areas that experience stronger winds Friday and some that will be stronger Saturday due to the winds slowly veering to the east.
Despite the shift to Santa Anas temperatures will remain on the cool side due to all the cold air aloft that the inside slider brought to the area. Highs will be warming slightly each day as high pressure aloft slowly builds over the West coast but likely not climbing into the 70s until early next week. Overnight lows will be quite cold but tricky with the winds. In traditionally wind- free Santa Area areas like Ojai and the Antelope Valley as well as the Central Coast overnight lows will drop below freezing in many areas, some inland areas as low as around 20.
(Mon-Thu), 08/222 PM.
Looks like weak to moderate offshore flow will continue for the next week at least, however support aloft for Santa Ana winds will drop off early next week. With high pressure continuing to build into the region daytime temperatures will be warming steadily, with some valley areas reaching the lower 80s by next Tuesday and even some coastal areas in the mid to upper 70s. A slower recovery for interior areas however. Chilly overnight lows will continue at least through the middle of next week but slowly climbing each day as the upper high builds.
Ensemble solutions maintain a dry pattern across the area through at least the end of next week with above normal temperatures.
09/0536z.
At 0455Z at KLAX, there was no marine layer. There was a sfc based inversion with a top of 400 ft and temperature of 15C.
High confidence in CAVU TAF.
Strong northeast winds will generate lgt-ocnl mdt turbc and LLWS over and near to hier trrn.
KLAX, High confidence in CAVU TAF. Good confidence thar any east wind component will be under 8 kt. Lgt LLWS possible between 015 and 025 AGL.
KBUR, High confidence in CAVU TAF. Lower confidence in wind speed and direction which could change frequently. Lgt-ocnl mdt turbc and LLWS possible up to 060 AGL.
08/758 PM.
For the Outer Waters, moderate to high confidence in current forecast. Through this evening, high confidence in Gale force winds and Small Craft Advisory (SCA) level seas. Overnight and through Friday, high confidence in SCA level seas for all the Outer Waters. SCA level northeast winds will affect PZZ676 with a 40% chance of Gale Force gusts Friday morning. For Saturday through Sunday, high confidence in winds and seas remaining below SCA levels. For Monday through Tuesday, high confidence in winds remaining below SCA levels, but there will be a 30% chance of SCA level seas.
For the Inner Waters north of Point Sal, moderate to high confidence in current forecast. Tonight through Friday, high confidence in SCA level seas and SCA level winds (northwest this evening, shifting to the northeast overnight). For Saturday and Sunday, high confidence in winds and seas remaining below SCA levels. For Sunday night and Monday, there is a 20-30% chance of SCA level northeast winds. For Monday and Tuesday, high confidence in winds and seas remaining below SCA levels.
For the Inner Waters south of Point Conception, moderate to high confidence in current forecast. Through this evening, high confidence in SCA level northwest winds across all the southern Inner Waters. For Friday through Saturday, there is a 60-80% chance of SCA level northeast winds from Ventura south to Santa Monica and across the San Pedro Channel, with a 40% chance of Gale force gusts Friday morning. For Sunday through Monday, there is a 30-40% chance of SCA level northeast winds from Ventura south to Santa Monica. For Tuesday, high confidence in winds and seas remaining below SCA levels.
08/759 PM.
A large, long period northwest swell will begin to diminish late tonight into Friday and through Friday night. This swell will generate high surf conditions along the Central Coast with wave heights peaking in the 10-15 foot range. For the beaches of Ventura and Los Angeles county, elevated surf conditions of 3-6 feet with local sets to 7 feet are expected. These surf conditions will generate dangerous rip currents along the beaches.
A HIGH SURF ADVISORY remains in effect for the Central Coast and a BEACH HAZARDS STATEMENT remains in effect for the Ventura and Los Angeles County beaches. The statements are in effect through Friday evening.
Ca, Freeze Warning remains in effect until 9 AM PST Friday for zones 38-348-357-381-382. (See LAXNPWLOX). Beach Hazards Statement in effect through Friday evening for zones 87-354-362-366. (See LAXCFWLOX). Wind Advisory remains in effect until 1 PM PST Sunday for zones 88-354-355-358-362-370>372-374-376>378-381. (See LAXNPWLOX). High Surf Advisory in effect until 9 PM PST Friday for zones 340-346. (See LAXCFWLOX). High Wind Warning remains in effect until 3 PM PST Friday for zone 369. (See LAXNPWLOX). High Wind Warning remains in effect until 1 PM PST Sunday for zones 375-379-380. (See LAXNPWLOX). PZ, Small Craft Advisory in effect until 3 PM PST Friday for zone 645. (See LAXMWWLOX). Small Craft Advisory in effect until noon PST Saturday for zone 655. (See LAXMWWLOX).
