15/428 AM.
Multiple periods of light to moderate rain are expected this coming week. Dry conditions will prevail through Today, with the next round of wet conditions set for tonight into Monday night, followed by more rain chances Wednesday night into Thursday night. The risk of significant impacts and flooding exists with the second storm system, as moderate to heavy rain will be possible. Temperatures will remain at or below normal. Very large surf will bring coastal impacts well into the coming week.
(tdy-Tue), 15/1057 AM.
The latest satellite imagery showed scattered cumulus over the waters to southern coastal mountain ranges with perhaps a few stray sprinkles making it to the surface. The extreme (for this time of year) water temperatures still 70-75 degrees F across much of the adjacent ocean is fueling this activity. Added slight chance showers to the forecast for southern coastal areas to some coastal slopes by this evening as increasing onshore flow ahead of the next system should spawn a bit more shower activity and drive it ashore.
While the system overall is pretty meager it does have a somewhat favorable overlap of cooling/falling 500 mb heights with weak cyclonic flow coupled with the very warm water temperatures to support a slight chance of thunderstorms focused across far southeast LA County including coastal to coastal valley areas. Otherwise rain intensity and amounts tonight through Monday night will be light and some areas will probably go rain free. Snow levels are generally above 7000 feet, but could drop to 5000-6000 feet Monday night, supporting a 20-30 percent chance of snow showers with little to no accumulation focused across higher mountains near the I-5 and into eastern LA County. Gusty northwest to north winds are expected across interior mountains to southwest Santa Barbara County and possibly filtering into some valleys and mountains near the Ventura County/ LA County border behind this system Monday night into Tuesday morning with a 20-30 percent chance of reaching advisory levels.
Near normal temperatures through Monday will fall into Tuesday and remain cool into Wednesday with frost/freeze concerns for interior and sheltered coastal valleys.
We have moderate confidence in a widespread significant storm beginning as early as Wednesday, especially for the Central Coast. See long term discussion for details.
(Wed-Sat), 15/416 AM.
For the extended period, models are in generally good agreement with yet another low pressure system from the northwest sweeping through southern California Wednesday evening to Thursday night. This system looks quite cold, with 500 mb temperatures as cold as -24 C, so along with the additional clouds and rain, thunderstorms are possible. Snow levels on the back side of the system could fall to as low as 5,500 - 6,000 feet, and mountain snow appears likely. The main front will move slowly through the forecast area Wed night thru Thu, then there will be lingering showers behind the main front Thu night.
The main front will move slowly through the forecast area Wed night thru Thu, then there will be lingering showers behind the main front Thu night. Still seeing potential for significant widespread rainfall. Looking at QPF amounts, this particular frontal passage could be a bit more impressive with deterministic models indicating rainfall totals in the 1-3 inch range, with local amounts of 3-5 inches not out of the question along favored south-facing slopes. Ensemble forecasts also seem to be leaning towards a bit more impressive frontal system than previous ones. Given the potential for some decent southerly flow, orographic effects could easily generate such totals across the foothills. Of course, a lot could change between now and then, so expected totals could change noticeably. On Friday, there may be some lingering showers in the morning hours, but most of the day should still be dry. Weak upper level ridging will bring dry conditions to the area for Sat. Temps will remain well below normal for Fri with only a slight warm-up for Sat.
High temperatures should range 5-10 degrees Wednesday, with further cooling Thursday, followed by a gradual warming trend Friday into Saturday. Overnight lows are becoming quite cold, and frost/freeze products may be needed for interior areas and possibly some valleys on the coldest nights.
15/1837z.
At 1824Z at KLAX, there was no marine layer nor an inversion.
Moderate confidence in the TAFs. Rain chances start around 08-12Z Monday with higher confidence in sites north of Point Conception. Rain should be fairly light and spotty, especially south of Point Conception.
KLAX, Moderate to high confidence in TAF. Any rain should be light and spotty. Any east wind component expected to remain below 8 kts.
KBUR, High confidence in CAVU 12Z TAF. There is a 10-20% chance of light and spotty rain starting 12Z Mon. No wind issues expected.
15/917 AM.
For the Outer Waters, moderate confidence in current forecast. Through Wednesday, high confidence in a combination of Small Craft Advisory (SCA) level winds and seas. Swell models over the past event were under-predicting wave heights, especially for locations near and south of Point Conception, so forecast leans toward slightly higher wave heights for the next event tonight through Monday. While seas are around 12-19 feet and still diminishing, a secondary peak of 13-20 feet is expected on Monday, then another Wednesday through Thursday. Additionally, there is a 30-50% chance of Gale force winds on Monday and Thursday, most likely south of Point Conception.
For the Inner Waters north of Point Sal, high confidence in the combination of SCA level winds and seas. Although models continue to underdo the wave heights, the swell is expected to lower some through today, with a secondary peak arriving on Monday (11-16 feet). SCA winds are likely Monday through Wednesday with a chance of Gales Wed night through Thursday night.
For the Inner Waters south of Point Conception, moderate confidence in current forecast. Seas at the mid channel buoy are currently around 10 feet, so the SCA continues through tonight. For Monday through Thursday, high confidence in SCA level winds developing with a 40-60% chance of SCA level seas. Additionally, there is a 30-40% chance of Gale force winds Tuesday night and Thursday night.
There is a continuing threat of dangerous breaking waves at Ventura and especially Morro Bay harbor entrances. Refer to the Marine Weather Statement which has been issued (MWSLOX) for more details.
Periodic rain can be expected through the middle of next week with a small chance of isolated thunderstorms Monday and again Wednesday into Thursday.
15/852 AM.
A series of very large, long period west-northwesterly swells will impact the coastline of southwest California through this week, creating large surf and dangerous conditions across the coasts. The largest surf will be focused along exposed west to northwest facing shores. The surf will decrease some through today, then a potential secondary increase is likely on Monday, with a third increase Wednesday night through Thursday. Shallow tidal overflows may affect some low- lying beach walkways and parking lots, especially in the morning hours near high tide. Large surf will continue to create dangerous rip currents, along with strong long- shore currents, potential sneaker waves, and large shore pound. Impacts will be less for south- facing shores.
The highest surf-related risks will be for the Central Coast as large surf between 15 to 18 feet continues, gradually lowering to 10 to 15 feet today. A High Surf Warning continues to be in effect into this afternoon for the Central Coast, then a High Surf Advisory goes into effect and will likely persist through the week. A secondary swell will arrive later tonight into Monday, likely bumping up surf heights again to 16-18 feet, with another large swell arriving Wednesday night through Thursday.
For west-facing beaches in LA/Ventura counties, high surf advisories are in effect with high surf expected to continue through at least Tuesday. There may be a relative "lull" in the surf today before the second swell arrives, but surf and rip currents will still remain hazardous.
Ca, Beach Hazards Statement in effect through Tuesday afternoon for zones 87-349-350. (See LAXCFWLOX). High Surf Warning in effect until 4 PM PST this afternoon for zones 340-346. (See LAXCFWLOX). High Surf Advisory in effect from 4 PM this afternoon to 3 PM PST Tuesday for zones 340-346. (See LAXCFWLOX). High Surf Advisory in effect until 3 PM PST Tuesday for zones 354-362-366. (See LAXCFWLOX). PZ, Small Craft Advisory in effect until 3 AM PST Wednesday for zones 645-670-673-676. (See LAXMWWLOX). Small Craft Advisory in effect until 3 AM PST Monday for zone 650. (See LAXMWWLOX).
