Swell Matrix

Area Forecast Discussion

National Weather Service Los Angeles/Oxnard Ca

224 pm PDT Thu Mar 28 2024

Synopsis

28/129 PM.

An unseasonably cold and vigorous storm system will move into the region late Friday through the weekend with periods of heavy rain and mountain snow along with a slight chance of thunderstorms. A warming and drying trend will develop next week.

Short Term

(tdy-Sun), 28/211 PM.

All systems go for yet another strong weekend storm. Ensembles have more or less held steady with the most likely outcomes with regard to rain amounts and timing so very little change has been made to those. Rain expected to begin along the SLO County coast by noon Friday, then working its way southeast through the area, reaching southern Santa Barbara County and Ventura County later in the afternoon and into LA County shortly thereafter. Periods of heavy rain will develop mainly during the evening and overnight hours Friday night into Saturday morning as the main frontal band moves through followed by a temporary decreasing in shower coverage through the rest of Saturday morning and afternoon.

Models show a secondary front coming through Saturday evening into early Sunday that will ramp up precipitation once again. This one could be even more impactful than the first as the upper low will be much closer to the area at that time with greater instability, leading to possible thunderstorms with higher rain rates on top of heavy rainfall from earlier Saturday. Showers and isolated thunderstorms will continue through Sunday, greatest in coverage and intensity across LA/Ventura Counties.

Rain totals are holding steady in the 1-3" range for coast/valleys/lower foothills and 3-6" for higher foothills and mountains. Areas south of Pt Conception are expected to generally have higher rain amounts due to the favorable upslope flow and likely greater coverage of post-frontal showers and storms on Sunday. Flood watches have been issued for most areas through the weekend due to expected periods of heavy rain that will result in frequent and widespread road flooding as well as additional mud and rock slides. Thunderstorms Sunday could produce small hail, gusty winds, frequent lightning, and possibly even a small tornado or waterspout.

Significant snow accumulations are expected in the mountains, especially above 6000 feet where 1-2 feet are possible, and locally even higher at the highest peaks. A winter storm watch has been issued for the mountains from Santa Barbara County through LA County from late Friday through Sunday afternoon. Chances for snow on the Grapevine remain slim as snow levels are expected to stay mostly at or above 4500 feet through the storm, but can't rule out a dusting at pass level (10-20%).

Precip expected to taper off by Sunday evening but could linger across eastern LA County as late as early Monday morning.

Long Term

(Mon-Thu), 28/223 PM.

There's a small chance the upper low will linger into early Monday across LA County, otherwise dry and warmer conditions are expected next week with highs back into the 70s across the valleys and inland coastal plain areas by Tuesday. Models in good agreement on a strong high pressure ridge developing across the area through Wednesday with highs possibly into the lower 80s in the warmer valleys by Tuesday.

A potential big change later next week as the highly amplified swings back to a deep trough along the West Coast. Roughly 80% of the model clusters favor this scenario. Most of those solutions favor the trough taking a more inland trajectory which is a drier pattern for southern California, but potentially very windy and much colder Thursday into Friday.

Aviation

28/1830z.

At 18Z at KLAX, there was no marine layer nor inversion.

Good confidence in TAFs through 08Z, then moderate confidence in all coastal TAFs and LA Valley TAFs. High confidence in desert TAFs There is a 30% chance of CIGs remaining VFR after 08Z for KSBA, Ventura, and LA TAFs coastal/valley TAFs. Timing of flight cat changes may be off by +/- 3 hours.

KLAX, Moderate confidence in TAF. Timing of flight cat changes may be off by +/- 3 hours with a 30% chance of conds remaining VFR through the period. There is a 20-30% chance of an east wind component of 8-10 kt from 13Z-18Z Sat.

KBUR, Low to moderate confidence in TAF. There is a 30% chance that conds remain VFR through the period.

Marine

28/1228 PM.

Fairly complex marine forecast, with rapidly changing conditions, and moderate confidence thru the weekend

For today thru Fri morning,

Small Craft Advisory (SCA) level W-NW winds continue developing in the SBA Channel affecting PZZ650 and eastern portions of PZZ673, spreading to the remainder of the waters through this afternoon. Winds will drop below SCA levels in most areas late tonight, except early Fri in the SBA Channel and the southern inner waters. However, seas will remain above SCA levels in the outer waters and the inner waters N of Pt Sat thru Fri, so a SCA will remain in effect for those areas into Fri afternoon.

From Fri afternoon into the weekend,

Winds will shift to S and increase ahead of a cold front Fri. In the northern two outer waters zones (PZZ670/PZZ673) and in the inner waters N of Pt Sal, winds are expected to reach gale force Fri afternoon thru Fri night, so a GALE WARNING is in effect. SCA level S-SW winds are likely Sat/Sat night, with SCA level seas thru early Sun.

In the southern outer waters, high end SCA level S winds are expected Fri afternoon thru Sat morning, with a 40% chance that winds will remain at SCA levels thru Sat night. Seas will remain at or above SCA level thru early Sun.

In the SBA Channel and in southern inner waters, SCA level SE-S winds are likely (60% chance) Fri evening, and there is even higher confidence in SCA conditions Sat thru Sat night.

Conds are expected to be below SCA level across all waters Sun afternoon thru Mon.

There is a 20-30% chance of thunderstorms late Fri night in northern areas and across all of the waters Sat thru Sun.

Beaches

28/1227 PM.

On W and NW facing beaches on the Central Coast, high surf is expected to continue developing, then continue thru at least Sun morning and possibly thru the day Sun. Surf heights of 8 to 12 ft with local sets to 15 ft are expected.

On W facing beaches of Ventura County, high surf is expected to continue developing this afternoon, then continue thru at least Fri afternoon. Surf heights of 5 to 7 ft with local sets to 8 ft are expected. There is a 40-50% chance that high surf will continue thru the weekend, and the High Surf Advisory will have to be extended.

On any beaches with a westerly exposure on the south coast of SBA County, and on the beaches of L.A. County, surf of 3 to 6 feet is expected later today thru the weekend. There is a 50% chance that surf will reach High Surf Advisory levels Fri thru Sat, especially on the beaches of L.A. County late Sunday into Monday.

Strong and dangerous rip currents are expected on all beaches thru the weekend.

Watches, Warnings, Advisories

Ca, Flood Watch in effect from Friday evening through Sunday afternoon for zones 38-88-344-345-354>358-362-366>375-378>383-548. (See LAXFFALOX). High Surf Advisory in effect until 9 AM PDT Sunday for zones 340-346. (See LAXCFWLOX). Wind Advisory in effect from 3 PM Friday to 6 AM PDT Saturday for zones 340-341-343-344-346-347. (See LAXNPWLOX). Flood Watch in effect from Friday afternoon through Sunday afternoon for zones 340>343-346>353-376. (See LAXFFALOX). High Wind Watch in effect from Friday afternoon through late Friday night for zones 342-345. (See LAXNPWLOX). Winter Storm Watch in effect from Friday afternoon through Sunday afternoon for zones 353-376>380. (See LAXWSWLOX). PZ, Small Craft Advisory in effect until 3 PM PDT Friday for zones 645-673. (See LAXMWWLOX). Gale Warning in effect from 3 PM Friday to 3 AM PDT Saturday for zones 645-673. (See LAXMWWLOX). Small Craft Advisory in effect until 9 AM PDT Friday for zones 650-655. (See LAXMWWLOX). Small Craft Advisory in effect from 11 PM Friday to 5 PM PDT Saturday for zones 650-655. (See LAXMWWLOX). Small Craft Advisory in effect until noon PDT Friday for zone 670. (See LAXMWWLOX). Gale Warning in effect from noon Friday to 3 AM PDT Saturday for zone 670. (See LAXMWWLOX). Small Craft Advisory in effect until 9 AM PDT Sunday for zone 676. (See LAXMWWLOX).

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