Swell Matrix

Area Forecast Discussion

National Weather Service Los Angeles/Oxnard Ca

614 am PDT Thu may 24 2018


24/340 AM.

Low pressure moving across the eastern Pacific will push into central California Saturday. Skies will generally be mostly cloudy through early Saturday, except partly cloudy in the Antelope Valley. There is a chance of showers north of Point Conception tonight and Friday, with patchy night through morning drizzle elsewhere. It will be quite cool through Friday, then there will be a warming trend this weekend into early next week.

Short Term

(tdy-Sat), 24/406 AM.

Very deep marine layer across the region again early this morning, and the depth has risen to 5000 feet. With the deep marine layer and some cyclonic low level flow, there could be some patchy drizzle this morning, especially in the foothills. Models show plenty of moisture lingering, so expect skies to remain mostly cloudy west of the mountains today. If there is any clearing, it would mostly likely be across the coastal plain. Max temps will be down across most of the region today, with temps as much as 10 to 15 degrees below normal in the valleys. Gusty winds will affect the mtns and Antelope Valley this afternoon and evening, but will probably remain below advisory levels.

A sharpening upper trough in the eastern Pacific will evolve into an upper low about 400 nm west of Pt Conception later this morning. This low will drift eastward, and be centered about 100 nm west of Monterey by late tonight, while taking on somewhat of a negative tilt as it does so. Some upper level diffluence and decent low and mid level lift should be sufficient to produce at least isolated shower activity north of Pt Conception late tonight and Fri. Elsewhere, deep moisture and strongly cyclonic flow will likely allow for patchy drizzle late tonight/Fri morning from the coastal slopes west and south. Have left pops out of the forecast for now, but a case could certainly be made for some slight chance pops, especially in the foothills of L.A. County. Skies will likely remain mostly cloudy west of the mountains again on Fri. Max temps will change little on Fri, except there will be several degrees of cooling in the mountains and Antelope Valley. Gusty winds in the mtns and Antelope Valley may get close to advisory levels Fri afternoon and evening.

The upper low will move across Central CA Fri night and early Sat Saturday, with a trough extending southward into the forecast area. Expect the marine layer to remain very deep, but a weakening inversion could make for a more ragged cloud field. Still, there should be a fair amount of night through morning clouds in coastal and valley areas. There could still be some patchy drizzle in coastal and valley areas of L.A. and VTU Counties. Developing N-S gradients Fri night should bring some gusty winds to the Santa Ynez Range and adjacent south coast of SBA County Fri night, which could keep skies clear there, or at least delay clouds until morning.

Expect better clearing on Sat as the trough axis moves east of the region in the afternoon. North to south offshore gradients will continue to sharpen, and there should be gusty northwest to north winds across southern SBA County and the I-5 corridor late Sat into Sat night. Max temps will likely be up a few degrees in most areas on Sat, but should still be below normal, except possibly across the south coast of SBA County due to downsloping northerly flow.

Long Term

(Sun-Wed), 24/421 AM.

The upper low will move eastward into northern Utah on Sunday, then will move very little thru Mon. Height rises and weakening onshore flow should allow for a warming trend Sun and Mon, with somewhat of a decrease in coverage and inland extent of the night thru morning low clouds and fog. By Mon and Tue, max temps should be near or a bit above normal, especially across the interior. However, latest models keep some weak troughing across the region, with a very weak upper low forming just west of the area by Tue. This may have the affect of keeping max temps down a bit, but heights will be fairly high. A more significant trough will approach the Pacific Wed, bringing cooling to the region.



At 1238Z, the marine layer depth was around 4300 feet deep at KLAX. The top of the inversion was around 4800 feet with a temperature near 12 degrees Celsius. The marine layer is expected to deepen to around 5000 ft.

Moderate-to-high confidence in the current forecast. Highest confidence in MVFR conditions at coastal and valley terminals through much of today. MVFR cigs will become VFR in many locations. Moderate confidence that valley TAF sites will stay cloudy most of the day with a 40% chance for some clearing across coastal sites S of Point Conception this afternoon.

KLAX, MVFR conditions will persist through this morning and likely become VFR late this morning or early afternoon hours. There is a 40% chance that there will be some clearing by mid afternoon.

KBUR, MVFR conditions will persist through most of this morning then become VFR and likely linger through much of the day.


24/244 AM.

For the Outer Waters, high confidence in the current forecast. Winds and seas will remain below Small Craft Advisory levels through at least Friday. There is a 60 percent chance of Small Craft Advisory level northwest winds across the southern portion of the Outer Waters from Point Conception to San Nicolas Island from Friday night through Sunday. Confidence is somewhat lower for advisory level gusts for the northern portion of the Outer Waters from Saturday afternoon through Sunday.

For the Inner Waters, generally high confidence in the current forecast. For the waters north of Point Sal, winds and seas will remain below SCA levels through Monday, except for a 40 percent chance of SCA level winds Saturday night.

For the waters south of Point Conception, winds and seas will remain below SCA levels through Friday. For Friday night through Sunday, there is a 60 percent chance of SCA level winds at times, especially across western sections of PZZ650.

A long period southerly swell will continue to move through the coastal waters through early Friday. Locally rough conditions may occur at local harbor entrances, especially those with southerly exposure.

Watches, Warnings, Advisories

Ca, Beach Hazards Statement in effect through this evening for zones 40-41-87. (See LAXCFWLOX). PZ, NONE.

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