Swell Matrix

Area Forecast Discussion

National Weather Service Los Angeles/Oxnard Ca

907 pm PDT Fri jul 19 2024

Synopsis

19/757 PM.

Well above normal temperatures are expected through early next week, especially across the interior areas, though some cooling is expected closer to the coast as onshore flow increases. Night and morning low clouds and areas of dense fog will continue near the coast.

Short Term

(Fri-Mon), 19/756 PM.

***UPDATE***

Heat continues to be the main forecast concern across much of Southwest California, especially away from coastal areas. Highs across the interior ranged from 95 to 105 degrees in the hottest areas today, including interior San Luis County, Woodland Hills, Santa Clarita Valley, the lower mountains and Antelope Valley. Very dry conditions developed as well in the eastern sections, with humidities in the teens to upper single digits. Overnight lows are expected to be very warm for the eastern sections as well, with upper 70s to lower 80s common over the mountains and foothills and portions of the deserts.

Onshore pressure gradients are fairly strong this evening, with gusty winds between 30 to 35 mph through Soledad Canyon into the Antelope Valley. The onshore winds are helping to keep humidities higher on the west side of the mountains, compared to the very dry conditions on the east side.

Saturday's highs are expected to increase anywhere from 2 to 5 degrees for the interior areas, with highs 100 to 110 degrees common. Coastal areas will warm up by a degree or two in most areas, except for the Santa Barbara South Coast where Sundowner Winds will bring an increase of up to 5 degrees compared to today. Highs there will be between 70 to 80 degrees. The Sundowners are expected to bring northwest wind gusts between 35 to 40 mph to the passes and canyons of Southwest Santa Barbara County.

***From Previous Discussion***

Strong high pressure across the western states is still generating well above normal temperatures across the region, but especially across the far interior where highs approaching 110 are possible each day through the middle of next week. However, closer to the coast and including the some of the valleys a 1200' marine layer and roughly a 3mb onshore flow is providing a moderating effect on the temperatures, keeping highs mostly in the 80s and 90s, except some very low 100s across the western San Fernando Valley, Santa Clarita Valley, and in the southern Salinas Valley. In addition, there have been ample overnight recoveries in those areas with lows mostly in the 60s and even some high 50s. So heat risk in those areas, especially factoring in the relatively cool overnight temperatures, while not zero, are not quite reaching criteria for advisories and warnings. Some of the higher elevations above the valleys, such as the Santa Monica Mountains above 2000 feet, where overnight lows haven't dropped much below 80, heat risk factors are much higher and advisories continue through at least Sunday.

Minimal, if any, changes are expected in this pattern through early next week. There will be slight warming across the far interior, but closer to the coast very little change. A shallow marine layer will keep a chance of low visibilities near the coast during the night and morning hours.

Long Term

(Tue-Fri), 19/156 PM.

No significant changes in temperatures early next week so it will remain dangerously hot across the far interior, and 4-8 degrees normal elsewhere. Ensemble based guidance indicates slight warming may develop Tuesday and Wednesday away from the immediate coast which may push some areas into heat advisory territory, particularly across the southern Salinas Valley and warmer parts of the LA/Ventura Valleys. Then as high pressure begins to weaken Thursday and Friday highs in all areas are expected to cool with those trends continuing into next weekend.

Lastly, increasing moisture from the southeast east next Tuesday and Wednesday may be enough to bring some thunderstorms back to at least eastern LA County. Otherwise, thunderstorm chances will be under 10% through the period.

Aviation

19/2344z.

At 23Z over KLAX, the marine layer was 900 feet deep. The top of the inversion was at 4000 feet with a temperature of 27 Celsius.

High confidence in CAVU TAFs for KPRB, KBUR, KVNY, KWJF, and KPMD.

Low confidence in all coastal sites. Minimum flight cat may vary one category at any time during the fcst period. Timing of flight cat changes may vary +/- 5 hours from fcst. There is 40% chance of VLIFR conditions at KSMX , 30% chance at KSBP, KSBA, KOXR, KCMA, and a 10% chance at KSMO, and KLAX. MVFR-VFR conditions likely at most coastal sites by 20Z.

KLAX, Low confidence in TAF. Cigs <010 expected from current time thru 18Z, when cigs should be cleared. 10% chance cigs less than 020 and/or vsbys below 1 SM between 06Z-16Z. No significant east wind component expected. Low confidence in flight cat timing, as flight cats may frequently change thru the overnight hours. Changes may occur +/- 5 hours from fcst.

KBUR, High confidence CAVU TAF with seasonal winds expected.

Marine

19/906 PM.

Moderate confidence in dense fog and visibilities under one mile being an issue through the weekend and likely through early next week in all the waters. The reduced visibilities will likely linger well into the afternoon hours.

High confidence in northwest winds increasing each day through Sunday. High confidence in at least Small Craft Advisory (SCA) winds and steep seas for the outer waters (offshore from the Central Coast to San Nicolas Island) through tomorrow afternoon and becoming low end Gale Force by Saturday night lasting through Sunday night. There is a Gale Warning in effect in the outer waters Saturday afternoon through Sunday night.

For the nearshore Central Coast waters, there is a 60 percent chance for SCA conditions Saturday and Sunday.

For the Santa Barbara Channel, fairly high confidence that SCA winds and seas will be localized to the far Western Portions Saturday afternoon to Saturday night, and Sunday afternoon to Sunday night. The winds and steep seas will expand Saturday and Sunday, with a 30 percent chance of those conditions being widespread enough to warrant a Small Craft Advisory.

For the rest of the nearshore waters, choppy seas will be building due to the gusty winds in the region, but SCA conditions are unlikely.

Good confidence in conditions falling below advisory levels by Monday afternoon and remaining below advisory levels for all waters through Wednesday morning. On Wednesday afternoon, another chance for SCA level conditions returns to the outer waters.

Watches, Warnings, Advisories

Ca, Excessive Heat Warning remains in effect until 10 PM PDT Wednesday for zones 38-344-345-353-376>383. (See LAXNPWLOX). Beach Hazards Statement in effect from Saturday evening through late Sunday night for zones 87-354-362-366. (See LAXCFWLOX). Heat Advisory now in effect until 10 PM PDT Sunday for zones 342-343-369-370-375. (See LAXNPWLOX). Heat Advisory in effect until 9 PM PDT Saturday for zones 373-548. (See LAXNPWLOX). PZ, Small Craft Advisory in effect from 2 PM Saturday to 3 AM PDT Sunday for zones 645-650. (See LAXMWWLOX). Small Craft Advisory in effect until 2 PM PDT Saturday for zones 670-673-676. (See LAXMWWLOX). Gale Warning in effect from 2 PM Saturday to 11 PM PDT Sunday for zones 670-673-676. (See LAXMWWLOX).

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