Swell Matrix

Area Forecast Discussion

National Weather Service Los Angeles/Oxnard Ca

839 pm PDT Fri Mar 23 2018


23/517 PM.

A trough of low pressure will push into the West Coast this weekend, with a slight chance of light showers north of Point Conception through Saturday night. The system will push into Arizona early next week before a ridge of high pressure builds into the region later in the week. This will support breezy offshore winds to start off the week with temperatures warming to above normal later in the week.

Short Term

(Fri-Mon), 23/836 PM.


Breezy winds are affecting portions of Southwest California this evening in the wake of the recent storm system. The strongest winds are southwest to west winds affecting the Antelope Valley, with localized gusts 45 to 50 mph in the foothills near Lake Palmdale. Winds are expected to subside later this evening, and are already showing that trend at other sites in the area. Meanwhile, increasing northwest winds are noted along the Santa Barbara South Coast, west of the city of Santa Barbara. Winds are gusting to 38 mph through Refugio Canyon, with gusts up to 30 mph elsewhere in that area. Believe that the strongest winds will remain localized to the Refugio area, so will hold off on issuing a Wind Advisory, but the forecast has been updated to note the ongoing winds. Mid-level stratus clouds are expected along portions of the coast later tonight, especially in L.A. County where they may spread inland over the San Gabriel and SF Valleys. An eddy circulation is forecast by both the NAM and local WRF models, which works to push the stratus clouds inland over the coastal valleys. ***From Previous Discussion***

Should be a lot of sunshine this weekend, especially southern areas as a weak trough pushes onshore well to to the north. This trough may just have enough strength to it to spread some very light precip to areas north of Pt Conception but if it happens it may not even be enough to measure. The other weather factor this weekend is some gusty northwest winds through the Santa Ynez Range and I5 corridor, though thinking now is that speeds will generally be below advisory levels. There's also a small chance that the upslope flow on the north side of the Ventura/LA mtns could spawn a few light snow flurries especially by Sunday but again amounts shouldn't pose any significant concerns.

That same trough will evolve into a cutoff low over the Colorado River Valley late Monday with north to northeast flow developing behind it. This will keep the air mass fairly cool but too dry for any precip. Perhaps some light northeast winds Monday into Monday night but probably below advisory levels.

Long Term

(Tue-Fri), 23/123 PM.

By Tuesday there may be enough upper support and offshore surface gradients to generate some low end advisory level Santa Ana winds Tue/Wed across Ventura and LA Counties.

The trough will kick east late Wed and Thu and allow a ridge to build in from the west. This is when we'll see temperatures climbing back up into the 70s and possibly near 80 by Friday.

High confidence in dry weather continuing through the following weekend as well.



At 0000Z, at KLAX the marine inversion was 800 feet deep, and the top was at 2000 feet with a temperature of 13 degrees Celsius.

Moderate to high confidence in the 00z TAFs, with the reduced confidence in coastal sites with lower cigs related to the marine layer, including the L.A. Valley sites and KPRB. MVFR cigs are expected for these sites, but the timing is lower certainty. The highest confidence is for the L.A. sites, with lowest confidence for those north of Point Conception.

KLAX, Moderate to high confidence in the 00z TAF. MVFR cigs are expected to arrive between 06-08z and continue through around 18z, but the timing will likely differ by +/- 2 hours. Otherwise, VFR conditions will prevail through the period.

KBUR, Moderate confidence in the 00z TAF. MVFR cigs can be expected between 10Z-15Z Sat, but the timing of low cloud onset and dissipation is low confidence. Otherwise, high confidence in VFR conditions through the period.


23/118 PM.

Generally good confidence in the current forecast. For the outer waters, Small Craft Advisory (SCA) winds will affect PZZ670 thru this evening and thru at least late Sun night for PZZ673 and PZZ676. There is also a 60% chance of SCA winds Sun thru Tue for PZZ670, and Mon thru Tue for the two southern zones.

For the inner waters N of Point Conception, SCA winds will prevail this evening, with a 60% chance of SCA winds at times Sun night through Mon night. For the inner waters S of Point Conception, SCA winds are expected Sat afternoon thru Sun evening, especially western portions, with a 50% chance of SCA winds Mon into Tue.

Watches, Warnings, Advisories

Ca, NONE. PZ, Small Craft Advisory in effect until 3 AM PDT Saturday for zones 645-670. (See LAXMWWLOX). Small Craft Advisory in effect from 3 PM Saturday to 9 PM PDT Sunday for zones 650-655. (See LAXMWWLOX). Small Craft Advisory in effect until 3 AM PDT Monday for zones 673-676. (See LAXMWWLOX).

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