Swell Matrix

Area Forecast Discussion

National Weather Service Los Angeles/Oxnard Ca

1006 am PST Fri Dec 1 2023


01/904 AM.

Cool and breezy conditions are expected through at least Saturday, with the strongest winds in the mountains. Some light rain showers will be possible in and around the Grapevine early this morning. A warming trend will start Saturday and continue through the middle of next week, with breezy Santa Ana winds.

Short Term

(tdy-Sun), 01/922 AM.


The upper level trough that brought a few showers earlier this week, has dug deep into the interior southwest states. This allowed the northwesterly 90 knot jet stream to the west of the trough to dip over California, as well as build surface high pressure over the northern half of the state. These two ingredients mean northerly winds for our region, and while they took their sweet time to materialize last night, they are upon us now. The most impactful winds are over LAX airport, where northerly cross winds gusted to 43 mph and cause some aborted landings. Modified the slate of Wind Advisories to all end at 10pm, and trimmed off some areas of Santa Barbara and Ventura Counties where the winds do not look strong enough to warrant inclusion in the advisory. Temperatures will be a mixed bag today, with interior and mountain areas well below normal, but coastal areas staying rather mild thanks to the warming effect of the downsloping north flow. Clouds will bank against the north slopes into the afternoon, with a stray shower or two possible. Snow levels are around 4500 feet. Thin mountain wave clouds are also affecting much of Ventura and Los Angeles Counties thanks to the north flow, and very unsure how they will evolve over the course of the day.

***From Previous Discussion***

The mtn winds will continue into this evening but should subside around midnight. The cool dry airmass and clear skies will allow for ample radiational cooling in the wind sheltered area and many interior areas will have freezing or near freezing overnight lows.

Hgts rise from 566 dam this afternoon to 572 dam Saturday afternoon. These hgts rises combined with sunny skies and 2 to 4 mb of offshore flow will bring 4 to 8 degrees of warming to most of the area. This warming will bring most max temps back up to normal. The offshore flow from both the N and E will generate some canyon winds in the morning, but with limited upper support no advisories are anticipated.

Again there will be some areas of freezing temps across the interior late Saturday night/Sunday morning.

Chamber of Commerce day on tap for Sunday as offshore flow persists and hgts rise to 582 dam. Like Saturday, there will be some morning canyon winds but with no upper level support they will be of the 15 to 25 mph variety. 2 to 3 degrees of warming for most of the area will bring max temps into the upper 60s and lower 70s for most of the csts/vlys.

Long Term

(Mon-Thu), 01/310 AM.

Srn CA is looking at 4 days of ridging and offshore flow in the xtnd period. Monday may be a mostly cloudy day as a grip of mid and high level clouds moves overhead. That and some Central Coast morning clouds should be the only exceptions to mostly clear skies.

The ensemble pressure gradients from the NAEFS show that there should be about 4 to 5 mb of offshore flow from the N and 1 to 2 mb of offshore flow from the east. These offshore gradients result from a fairly static sfc high sitting over the great basin and xtndg into ID. These grads are little more biased to the north than a usual Santa Ana and the morning winds will be strongest through and below the more N/S oriented canyons. With zero upper level or thermal support wind advisories are very unlikely.

Look for 2 to 5 degrees of warming each day Mon and Tue which will bring max temps across the coasts and vlys up into the mid 70s to lower 80s on Tuesday or 6 to 12 degrees above normal. Not much change in temps on Wed. There will be some cooling on Thursday as the offshore flow relaxes and and hgts fall as the ridge begins to break down.



At 1726Z at KLAX, there was no marine inversion or marine layer.

Moderate to high confidence in TAFs due to northerly winds. Timing of wind direction changes could be +/- 3 hours. Light turbulence and LLWS possible over the mountains and foothills through this morning.

KLAX, Moderate to high confidence in VFR TAF. There is a 20% of northerly winds up to 20 kt through 05Z. Good confidence that any east wind component is less than 6 kt.

KBUR, High confidence in VFR TAF.


01/917 AM.

For the Outer Waters, moderate to high confidence in current forecast. Through tonight, high confidence in combination of Small Craft Advisory (SCA) level winds and seas for the entire area with a 60-80% chance of Gale Force winds through this afternoon from Point Sal south to San Nicolas Island. For Sunday through Monday, there is a 50-70% chance of SCA level winds continuing, especially from Point Sal south to San Nicolas Island, lowering to a 30% chance of SCA level winds on Tuesday.

For the Inner Waters north of Point Sal, moderate to high confidence in current forecast. For today, there is a 60-80% chance of SCA level winds, especially this afternoon and evening. For tonight and Saturday, there is a 30-50% chance of SCA level winds. For Sunday through 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. For this morning, moderate to high confidence in SCA level winds, especially across western portions of the waters. By late tonight, winds should diminish below SCA levels. For Saturday, there is a 30-40% chance of SCA level winds across the western half of the Santa Barbara Channel again. For Saturday night through Monday, there is a 20-30% chance of SCA level northeast winds from Ventura south to Santa Monica, especially in the overnight and morning hours. For Tuesday, high confidence winds and seas remaining below SCA levels.

Watches, Warnings, Advisories

Ca, Wind Advisory in effect until 10 PM PST this evening for zones 88-352-353-372-376>379-381. (See LAXNPWLOX). PZ, Small Craft Advisory in effect until 9 PM PST this evening for zones 645-650-655. (See LAXMWWLOX). Small Craft Advisory in effect until 3 AM PST Saturday for zone 670. (See LAXMWWLOX). Gale Warning in effect until 3 PM PST this afternoon for zones 673-676. (See LAXMWWLOX).

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