Swell Matrix

Area Forecast Discussion

National Weather Service Los Angeles/Oxnard Ca

922 am PST Fri Feb 23 2024

Synopsis

23/910 AM.

Offshore flow will continue through Saturday, keeping warmer and drier conditions in place. Breezy Santa Ana winds will continue through the early this afternoon. A cooling trend will begin Sunday with light rain and mountain snow expected Monday into early Tuesday. Gusty northerly winds are possible Tuesday through Wednesday.

Short Term

(tdy-Sun), 23/921 AM.

***UPDATE***

Light to moderate offshore gradients are producing some breezy Santa Ana winds across the usual favored areas, most notably western LA County, southern Ventura County, and the Santa Lucias along the Central Coast. Winds are mostly below 40 mph but there have been a couple sites in the mountains with gusts to around 45. The offshore flow is generating some downslope warming off the mountains and temperatures are already approaching 70 in some areas at 9am. This will be the first day since late January that southern California has been in the 70s. The upper low that is still close to 1000 miles west is dragging up lots of high clouds so it won't be a perfectly sunny day but still quite nice.

Speaking of the upper low, models continue to downplay the rain amounts (quarter to half inch at most) and it's now also looking slower, such that most of Monday may remain dry.

***From Previous Discussion***

A large elongated upper low extended from about 800 nm W of San Francisco to about 950 nm west of Pt. Conception this morning. The upper low will become more compact later today and tonight and will be located around 1000 nm west of Pt. Conception early Sat morning. Both the operational runs of the GFS and the EC show a piece of short wave energy rotating around the eastern side of the upper low Sat, causing it to elongate once again, this time in a more east to west fashion by late Sat. Ahead of this slow moving system, a decent upper level ridge will persist across the forecast area tonight and Sat.

Low level gradients will remain offshore, probably strongly enough to continue to produce some locally gusty NE winds thru and below passes and canyons in the mtns and valleys of L.A./VTU Counties late tonight/Sat morning, but winds will remain below advisory levels. Gradients will turn weakly onshore Sat afternoon. Do not expect any organized low clouds tonight/Sat morning, but bands of high clouds should continue to push into the region. Due to developing onshore flow, max temps will probably be down slightly Sat, at least in coastal areas, while there may be little change inland, and slight warming in the mtns and deserts. Temps will be dependent upon how thick the cloud field is on Sat.

The upper low will continue to wobble around Sat night and Sun, but finally begin to translate eastward during the day Sun. There may be some night/morning low clouds and fog in coastal areas Sat night/Sun morning, but high cloudiness may disrupt any low cloud formation. Onshore gradients will increase Sun. Expect conditions to remain dry Sun, but it should be a partly to mostly cloudy day. There will likely be several degrees of cooling across the area Sun, especially in coastal and valley areas, with little change in the mtns and deserts.

Long Term

(Mon-Thu), 23/454 AM.

The large upper low will move slowly eastward Sun night and Mon. The deterministic run of the GFS places it about 200 nm WSW of Pt. Conception Mon afternoon, while the EC is about 150 miles to the southwest of that location. Both the GFS and EC now show the upper low weakening and tracking fairly far to the south of the region Tue, then into northern Baja Tue night. Deepening moisture and lift will bring a slight chance or chance of rain to SLO/SBA Counties by late Sun night or early Mon, and to the entire region Mon morning or afternoon into Tue morning. There is a chance that showers will linger into Tue afternoon/evening, but they should be limited after Tue morning. There is a decent amount of spread with respect to the timing of the best chance of rain and rainfall totals from this system, but the operational runs of the GFS and EC, and most of their ensembles are continuing to trend toward less rain from this system. Overall, expect rainfall totals to average one tenth to one half of an inch in most areas, unless future runs show the system holding together better and tracking farther to the north. Snow levels will be fairly high through the bulk of this event, with a few inches of snow possible above 7000 or 7500 feet. It should be noted that storm systems arriving from the south of the latitude of southern CA are typically handled poorly by the models.

Once the upper low tracks into northern Mexico, broad and mostly dry west to northwest flow aloft will set up across the region, making for a partly cloudy, cool and dry day on Wed. Heights will rise a bit Wed night and Thu, so expect a few degrees of warming, perhaps to near normal, with dry weather continuing.

Aviation

23/1633z.

At 1630Z, there was a surface-based inversion at KLAX. The top of the inversion was 800 feet with a temperature of 18 degrees Celsius.

Overall, high confidence in 18Z TAF package. VFR conditions are expected for all sites through the period. Weak offshore flow will generate some light turbulence and LLWS across the foothills and mountains through 22Z.

KLAX, High confidence in 18Z TAF. No significant easterly wind component is expected.

KBUR, High confidence in 18Z TAF.

Marine

23/833 AM.

For the Outer Waters, moderate to high confidence in current forecast. Today through Sunday, high confidence in winds and seas remaining below Small Craft Advisory (SCA) levels. On Monday, there is a 30-40% chance of SCA level southeast winds. For Tuesday, there is a 60-80% chance of SCA level northwesterly winds and SCA level seas.

For the Inner Waters north of Point Sal, moderate to high confidence in current forecast. For this morning, there is a 20% chance of SCA level northeast winds. From this afternoon through Sunday, high confidence in winds and seas remaining below SCA levels. For Monday, there is a 30-40% chance of SCA level southeasterly winds. On Tuesday, there is a 60-80% chance of SCA level northwesterly winds and SCA level seas.

For the Inner Waters south of Point Conception, moderate to high confidence in current forecast. For this morning, there is a 30% chance of SCA level northeast winds from Point Mugu to Santa Monica. Otherwise, high confidence in winds and seas remaining below SCA levels through Sunday afternoon for the southern Inner Waters. On Sunday night, there is a 30% chance of SCA level northwest winds across the western half of the Santa Barbara Channel. On Monday, there is a 20-3% chance of SCA level southeasterly winds then a 40-50% chance of SCA level west to northwest winds on Tuesday.

Watches, Warnings, Advisories

Ca, Wind Advisory in effect until 3 PM PST this afternoon for zones 88-375>379. (See LAXNPWLOX). Wind Advisory in effect until noon PST today for zones 354-355-358-362-369-372-374. (See LAXNPWLOX). PZ, NONE.

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