Swell Matrix

Area Forecast Discussion

National Weather Service Los Angeles/Oxnard Ca

409 pm PST Mon Nov 28 2022

Synopsis

28/125 PM.

Significantly cooler week ahead, coldest Wednesday morning with areas of near to sub-freezing temperatures. Localized light rain chances through Wednesday, then moderate widespread rain likely at times Thursday through Sunday. Gusty northerly tonight, with light offshore flow Tuesday through Wednesday.

Short Term

(tdy-Thu), 28/218 PM.

Stratocumulus clouds dot the skies over Ventura and LA Counties this evening, with marine layer moisture lingering while marine inversion weakens. This moisture, coupled with moderate onshore flow could spit out some accumulating drizzle on the San Gabriel foothills, otherwise it should all scatter out later tonight.

Gusty onshore flow over the interior areas will turn to northwest to north tonight and focus over southern Santa Barbara County and the I-5 Corridor. Gusts between 35 and 50 mph are expected in those favored areas. The Santa Monica Mountains could also see some locally gusty winds. There is some moisture embedded in these winds, which could result in light rain or snow showers over the northern mountain slopes later tonight. Snow levels will also lower to around 4500 feet, and some of the mountain roads could see up to an inch accumulation.

The winds will turn northeasterly on Tuesday and weaken, but will remain locally breezy through Wednesday especially over the mountain areas of all 4 counties and some valleys. This will help coastal and valley areas bump up a few degrees, but keep mountains and interior areas cool. This will also keep skies clear and dry out the air mass. These two ingredients will allow Wednesday morning to be the coldest of the week, with sub-freezing temperatures possible in the Santa Ynez Valley, and likely for the interior valleys.

Attention then turns to the first of two storms expected later this week. A weak low, currently over northern British Columbia, will strengthen and dip south into northern California Thursday afternoon. A cold front associated with the low will sweep through the West Coast. Before that front moves through the southern half of the state Thursday night and Friday, some moist southwest flow may result in light pre-frontal showers during the day on Thursday especially Santa Barbara and southward. For the rest of the storm, read on..

Long Term

(Fri-Mon), 28/229 PM.

A cold front will move through the southern half of California Thursday Night through Friday morning, plus or minus 6 hours. With moderate southerly flow and precipitable water readings near 1.2 inches, expecting widespread moderate rain over the region and locally heavy rain possible. The EPS ensemble system is in good agreement with 80% of its members showing 1 to 2 inches of rain. There are some lighter outliers, but even those show some rain. The majority of the GEFS ensembles however show light amounts generally in the 0.10 to 0.50 inch range, with only about 20% showing over an inch. With that said, confidence is high for widespread rain. Amounts are trickier, but leaning toward the usually better European model with 1 to 2 inches in general the more likely scenario. This would also result in higher amounts in the mountain and foothills. Sticking with 2 to 4 inches at this point there, but could see those amounts up to double that if the forecast holds. With the southerly flow, snow levels will be well above 7000 feet for the bulk of the precipitation, but could lower to 6000 feet on the back side of the front. As such, a healthy amount of snow is expected at the resort levels, with little below that.

After a short break, moderate confidence for another storm coming after sometime over the weekend. The EPS and GEFS are at odds again, with the EPS favoring a weaker system than the first (about half the rain amount) while the GEFS favoring a wetter solution. Regardless, more rain is looking favorable with lower snow levels.

Aviation

29/0008z.

At 2350Z, the deep moist layer at KLAX was 4300 feet deep. The top of the inversion was at 6500 feet with a temperature of 7 degrees Celsius.

Overall, low to moderate confidence in 00Z TAF package. Marine layer has deepened and clouds are widespread in coastal, valley, and coastal slope locations of LA/Ventura counties. For the most part, conditions were MVFR to VFR in coastal and valley areas, and IFR to LIFR in the foothills and mountains. Skies should clear in coastal areas this afternoon, and clouds may linger through the day across the LA/Ventura county valleys. There could be a few showers across eastern L.A. County this afternoon and evening, and on northern slopes tonight into early Tue. Expect MVFR to VFR cigs in coastal/valley TAFs of LA county tonight, but developing northerly flow should cause clouds to scour out in the valleys late tonight, and on the coastal plain early Tuesday morning.

KLAX, Overall, low to moderate confidence in 00Z TAF. Expect SCT-BKN030 conditions to continue through tonight, and likely exit after sunrise as light northerly flow develops. There is a 20 percent chance of north winds reaching 10 knots on Tuesday morning.

KBUR. Overall, low to moderate confidence in 00Z TAF. BKN025-035 conditions expected to continue through much of the night, then will likely scour out after 12z as light northerly flow develops.

Marine

28/120 PM.

No updates to the marine forecast in the afternoon issuance.

For the Outer Waters, moderate confidence in the forecast. Small Craft Advisory (SCA) levels winds in the northern zone (PZZ670) have overspread the outer waters this morning. Winds are expected to increase to Gale Force this afternoon and persist through late tonight. SCA winds are then likely Tue morning, but should fall below SCA levels in the afternoon. However, seas may remain above SCA levels through Tue afternoon. Expect conditions to be below SCA level Tue night thru Wed night. SCA level S winds are expected Thu and Thu night. There is a 30% chance that SCA level winds will continue into Fri.

For the Inner Waters N of Pt. Sal, moderate confidence in the forecast. Winds and seas will likely increase to SCA levels this afternoon, then winds will drop below SCA levels by late tonight. There is a 30% chance that seas will remain above SCA levels thru mid morning Tue. There is a 30% chance of SCA level winds Tue afternoon/evening. SCA conds are not expected Tue night thru Thu morning, then SCA level S winds are likely Thu afternoon and Thu night, with a 30% chance that SCA level winds will linger into Fri.

For the Inner Waters south of Point Conception, moderate confidence in the forecast. SCA level W to NW winds are likely across western portions of the SBA Channel this afternoon through late tonight, with a 30-40% chance of SCA level winds across northwestern portions of the southern zone (PZZ655). Otherwise, SCA conds are not expected thru Wed night. There is a 40% chance of SCA level SE-S winds Thu into early Fri.

Watches, Warnings, Advisories

Ca, Wind Advisory in effect until 6 AM PST Tuesday for zones 53-54-349-351-352. (See LAXNPWLOX). Wind Advisory in effect until midnight PST tonight for zone 59. (See LAXNPWLOX). PZ, Small Craft Advisory in effect until 3 AM PST Tuesday for zones 645-650. (See LAXMWWLOX). Gale Warning in effect until 6 AM PST Tuesday for zones 670-673-676. (See LAXMWWLOX).

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