Swell Matrix

Area Forecast Discussion

National Weather Service Los Angeles/Oxnard Ca

358 am PDT Mon Oct 15 2018

Synopsis

15/356 AM.

Offshore flow developing today will bring warmer and drier conditions through much of this week. Gusty Santa Ana winds will be strongest today, then linger into Tuesday. Winds will weaken for Wednesday and Thursday, then increase late in the week or next weekend.

Short Term

(tdy-Wed), 15/357 AM.

, STRONG DAMAGING SANTA ANA WINDS WITH VERY CRITICAL RED FLAG FIRE WEATHER CONDITIONS EXPECTED ACROSS SOUTHWEST CALIFORNIA TODAY,

The latest satellite imagery shows offshore flow continuing to develop this morning as a cold air mass settles into the Great Basin behind an exiting trough of low pressure. The upper-level trough over northwest Arizona will continue to dig south into the lower Colorado River Basin through tonight. Stratus clouds over the coastal waters are being pushed farther to the west this morning as the offshore flow pattern settles in. Most pressure gradient parameters are now offshore. KLAX- KDAG surface pressure gradient values have an impressive -7 mb offshore trend, hovering near -5 mb currently. Warm Springs RAWS is already hitting into high wind warning criteria with sustained winds of 41 mph gusting to 54 mph in the previous hour. Gusty Santa Ana winds will only get stronger through this morning, peaking after daybreak and into the late morning hours. Strong and damaging winds are expected in the mountain areas, although isolated to local damaging wind gusts cannot be ruled out in the foothill areas. 06Z NAM-WRF solutions show 950 mb winds peaking near 55 knots across eastern Ventura County later this morning. Local gusts to 75 mph look reasonable for the mountains, including the western Santa Monica mountains. A high wind warning is in effect for the Los Angeles and Ventura County mountains, including the Santa Monica range. Coastal and valley areas of Los Angeles and Ventura Counties are under wind advisories through this afternoon. Some locales in the advisory areas could exceed advisory thresholds, including Porter Ranch, Saugus, and Sylmar.

Winds will weaken some tonight. Wind advisories will likely need to issued for the Los Angeles and Ventura County mountains and may need to be extended for the eastern Ventura County Valleys, and the San Fernando and Santa Clarita Valleys. Winds should be about 10-15 mph lighter late tonight and into Tuesday versus what is expected to occur later today.

Much warmer and much drier conditions will develop throughout today and remain warmer and drier than normal for much of the week. Today and Tuesday will likely be the warmer days of the week relative to middle and latter part of the week. With the stronger offshore flow developing this morning, today will be warmer along the coast versus the valleys and interior areas. Compressional heating processes will be much more efficient today as strong subsidence aloft combines with descending air down the coastal slopes of the mountains. Temperatures 80s to near 90 will be common for most areas in the South Coast Basin. Along the Central Coast, temperatures in mid 70s to mid 80s look on track for the next couple of days. Temperatures should be a bit more mixed for Tuesday, with the warmer valley areas likely seeing the warmest temperatures.

In the wind-sheltered areas, overnight low temperatures will be chilly and very Fall-like. Clear skies and less wind will allow for radiative cooling to be much more efficient tonight. Patchy frost was added to the Antelope Valley for tonight and into Tuesday morning. Temperatures could reach the freezing mark in areas such as Lancaster and Saddleback Butte tonight. If you have sensitive plants or livestock in the Antelope Valley, take measures to prepare for the onset of colder overnight temperatures, if you have not already done so. In other winds sheltered areas, such as the Central Coast and the Ojai and Santa Ynez Valleys, temperatures were tweaked accordingly for the next several mornings but look to remain above frost advisory criteria for now.

Long Term

(Thu-Sun), 15/357 AM.

An offshore flow pattern will persist into late week and keep a warmer and drier weather pattern in place. Model solutions remain consistent with a trough to the east, retrograding west back into southern California. The timing is still uncertain, but sometime between Friday and Monday, offshore flow should reassert itself as the trough moves west. Model solutions do agree that Saturday will be a day where offshore flow and gusty Santa Ana winds will be prevalent. Both ECMWF and GFS solutions remain consistent in suggesting at least advisory level winds will develop sometime between Friday and Saturday, then linger into Sunday or Monday. The finer details are still uncertain, such as how much moisture could move back west should the trough tap into subtropical moisture. For now, higher confidence exists in an continued offshore flow pattern with another round of gusty Santa Ana winds.

Aviation

15/1010z.

At 1010Z at KLAX there was no marine layer nor any inversion.

Overall, high confidence in CAVU conds for the next 48 hours. Strong offshore flow today will bring significant winds and areas of LLWS across LA/Ventura counties between 12Z and 22Z. Strong mountain wave activity is likely after 12Z.

KLAX, High confidence in CAVU TAF. High confidence in LLWS and turbulence issues 12Z-22Z. There is a 30 percent chc that east winds will remain under 12kt.

KBUR, High confidence in CAVU TAF. High confidence in LLWS and turbulence issues 12Z-23Z. There is a 30 percent chance of 35 kt gusts 15Z-22Z.

Marine

15/258 AM.

Outer Waters, moderate confidence in current forecast. For PZZ670/673, winds and seas are expected to remain below Small Craft Advisory (SCA) levels through Friday although there is a 30% chance of SCA level winds Tuesday afternoon/evening. For PZZ676, high confidence in SCA level northeast winds today with a 20% chance of SCA level northeast winds tonight and Tuesday.

Inner Waters north of Point Sal, high confidence in current forecast. Winds and seas are expected to remain below SCA levels through Friday.

Inner Waters south of Point Conception, high confidence in forecast. SCA level northeast winds are expected today from Ventura southward with a 40% chance of Gale Force gusts. Tonight and Tuesday, there is a 60% chance for another round of SCA level northeast winds that will be a little weaker than today's winds. Boaters should be aware of rough seas especially in and around east facing harbors (including Avalon). Avalon Harbor will likely see northeast winds gusting to between 20 and 25 knots today with 2 to 4 feet wind waves.

Watches, Warnings, Advisories

Ca, Wind Advisory in effect until 3 PM PDT this afternoon for zones 40-41-44-45-88-547. (See LAXNPWLOX). High Wind Warning in effect until 3 PM PDT this afternoon for zones 46-53-54. (See LAXNPWLOX). Red Flag Warning in effect from 9 AM this morning to 8 PM PDT Tuesday for zones 238-251-252. (See LAXRFWLOX). Red Flag Warning in effect until 8 PM PDT Tuesday for zones 240-241-244>246-253-254-288-547-548. (See LAXRFWLOX). PZ, Small Craft Advisory in effect until 3 AM PDT Tuesday for zones 650-655-676. (See LAXMWWLOX).

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