Swell Matrix

Area Forecast Discussion

National Weather Service Los Angeles/Oxnard Ca

914 pm PDT Fri Sep 30 2022

Synopsis

30/753 PM.

Temperatures will cool through the weekend with increasing night to morning low clouds and fog. A slow warming trend is expected to begin Sunday and run through Thursday. Light to moderate winds and mostly clear skies will prevail away from the coast.

Short Term

(Fri-Mon), 30/725 PM.

***UPDATE***

A deep marine layer has already allowed for stratus to March across the Central Coast early this evening. Clouds should then move into the Santa Ynez Valley very shortly. Stratus is more disorganized south of Point Conception, but should fill in as the evening goes on. Expecting low clouds to cover all the coasts and coastal valleys tonight through Saturday morning. Gradients are trending a bit more onshore than this time last night, and 500 mb heights are expected to continue lowering. As a result, could see low clouds try to push into the Santa Clarita Valley by early morning as well as up the lower coastal slopes. Patchy drizzle will be possible during the early morning, especially around the foothills where weak southerly (orthogonal) flow may generate enough lift. Clearing will likely be fairly slow on Saturday with the deep marine layer in place and some west-facing beaches may struggle to clear at all. There will be continued cooling with most of the population 2 to 4 degrees below normal (closer to 4 to 8 degrees below normal for the Central Coast). The Antelope and Cuyama Valleys, however, will remain 3 to 5 degrees above normal. Other than breezy southwest winds across the Antelope Valley and through the Highway 14 corridor, no wind issues are expected. The current forecast for the immediate short term looks good and no updates are planned.

***From Previous Discussion***

Synoptically, the area is under a fairly weak (582 dam) upper level ridge extending along the coast up to the Canadian border. The feature remains essentially stationary during through Thursday, with an upper level low off to the northwest and a CONUS-spanning trough to the east. The ridge will build a bit on Sunday (maybe 588 dam by Tuesday) leading to some warming in the area. By Wednesday afternoon the models bring a slug of moisture into the US southwest, most likely fed from remnants of Tropical Storm Orlene which is currently forecast to make landfall on Mexico's west coast next Monday. This moisture should stay east of our area, but tropical tracks introduce a lot of uncertainty into the extended forecast. Currently the NBM puts about a ten percent chance of precipitation in the eastern San Gabriel mountains beginning next Friday.

Sunday will get off to a similar start, with low clouds and stratus along the coast and coastal valleys. The onshore flow will be slightly weaker and the ridge will begin to slowly build so temperatures should at least stop falling, and likely rise a degree or two. Aside from the coastal stratus the skies should be mostly clear again.

Monday will warm a couple of degrees again as the heights build. Onshore flow throughout the weekend will keep the highs moderate along the coast. Warmer areas like Woodland Hills and the Antelope Valley will be in the low to mid 90s. Skies will be clear except for the morning coastal stratus.

Long Term

(Tue-Fri), 30/117 PM.

In the longer range, deterministic models and their respective ensembles maintain the general position of the ridge and drop the 500 mb heights slightly beginning next Saturday. Onshore gradients gradually weaken through the period and go neutral to weakly offshore by Friday which should result in less widespread stratus/fog coverage. It should also make Friday the hottest day of the next 7 at about 5 degrees above normal in downtown LA. Aside from the morning stratus, skies will otherwise remain mostly clear. There could be increasing cloudiness later in the week over Los Angeles County if moisture from Orlene makes it this far north. Any increase in the clouds would help keep it a bit cooler. October generally brings the start of the Santa Ana Wind season and increased fire weather risk, but no signs of that yet in the extended.

Aviation

01/0412z.

At 0405Z, the marine inversion at KLAX was based at 2000 feet. The top of the inversion was 3800 feet with a temperature of 21 degrees Celsius.

Overall, moderate to high confidence in 06Z TAF package. For coastal and valley sites, high confidence in CIG/VSBY restrictions through Saturday, but only moderate confidence in timing of flight category changes. High confidence in CAVU conditions for desert TAFs.

KLAX, Overall, moderate confidence in 06Z TAF. High confidence in CIG/VSBY restrictions, but only moderate confidence in timing of flight category changes through TAF period (could be +/- 2 hours of current forecasts). No significant easterly wind component is expected.

KBUR, Overall, moderate confidence in 06Z TAF. Timing of dissipation of MVFR conditions could be +/- 2 hours of current 1730Z forecast.

Marine

30/758 PM.

High confidence in the current forecast of winds below Small Craft Advisory levels through the weekend, along with diminishing seas. By Monday winds will begin to increase some, especially during the late afternoon to evening hours.

SCA level NW winds will be possible across the outer waters by Monday evening into the middle of next week.

Widespread patchy fog expected to develop across the waters, especially later tonight into Saturday morning.

Watches, Warnings, Advisories

Ca, NONE. PZ, NONE.

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