14/241 AM.
Areas of dense fog will continue through later this morning, then visbilities are expected to improve. Temperatures will trend warmer through Tuesday, then cool Wednesday as onshore flow to the east kicks in. Thursday will warm again as winds flip offshore, then temperatures will gradually cool into the weekend. Low chance for light rain across northern areas next weekend, followed by a chance for widespread rain during Christmas week.
(tdy-Tue), 14/241 AM.
Areas of dense fog are currently impacting portions of the forecast area, namely the Ventura County coast and western and southern Santa Barbara County, including the Santa Ynez Valley. A Dense Fog Advisory has been issued though 10am for these areas, but there is a chance the Dense Fog Advisory will be cancelled early if visibilities begin to improve. Aside from the marine layer clouds across the coasts and lower coastal valleys, high clouds will stream overhead through at least this afternoon, especially over Los Angeles and Ventura counties. As far as tonight, confidence is low in if and where low clouds will develop. Expecting less coverage as winds will trend offshore overnight, likely limiting development especially south of Point Conception. Current thinking is the Central Coast will see another round of low clouds with dense fog, and best chances down south will be near the Long Beach area. Not expecting much in the way of low clouds or fog Monday night into Tuesday as winds will be solidly offshore.
The aforementioned offshore winds from the north to northeast will become common across typically windy areas by Monday morning and continuing into Tuesday. There is some upper level support beginning Monday night from the north-northeast, but directionally upper level winds will shift to the north-northwest late Tuesday. At this point Wind Advisories are unlikely, but some localized gusts to 45 mph are possible across portions of the western San Gabriel, Santa Susana, and Santa Lucia mountain ranges.
Today will feature fairly similar temps compared to yesterday, although coastal areas will warm up a few degrees as onshore flow is expected to be limited, if not completely muted in the afternoon. Expecting immediate coasts to remain in the 60’s today while coastal valleys will reach the 70’s to low 80’s. The increasing offshore flow combined with the strengthening upper level ridge will lead to coasts and coastal valleys increasing up to 5 to 10 degrees in some areas on Monday. Interior portions will cool slightly. Coasts will top out near 70 degrees, while coastal valleys will reach the upper 70’s to mid 80’s with warmest areas threatening 90 degrees. 500 mb heights will peak around 588 dam (December normal is 571 dam) on Tuesday, leading to an overall warming of the entire region, most noticeable across interior portions. Coast and valley temperatures south of Point Conception may need to be bumped up a few degrees as the NAM is showing 950 mb temps reaching 23-24 degrees C, which will likely put the inland coasts comfortably into the 70’s. Some records will be threatened, notably Downtown Los Angeles on Monday where the record is 85 and we are forecasting 83. Woodland Hills will also close in on records through Tuesday. For Tuesday and Wednesday, coasts will be 5-10 degrees above normal and inland areas 10-20 degrees above normal.
In addition to warming max temps, overnight lows will also warm up Monday and Tuesday, but lows aren’t expected to be quite as warm as last week.
(Wed-Sat), 14/241 AM.
Wednesday will feature a flip to onshore flow to the east, and northerly gradients will weaken some. This will bring several degrees of cooling to coasts and valleys, especially in conjunction with the upper level ridge beginning to weaken.
Winds will quickly turn back offshore to the east and the northerly gradient will re-strengthen. Northwest to northeast winds are on track to peak very late late Wednesday night into Thursday evening, with Sundowner winds common across southern Santa Barbara County through the remainder of the forecast period, peaking Wednesday and Thursday night. Upper level winds will generally be from the north-northwest, with strongest upper level support occurring Thursday, hence the peak of the winds. Although winds generally look sub advisory during the period, there is a low to moderate chance for Wind Advisories on Thursday. Temperatures will increase again Thursday as the offshore flow strengthens, then drop a few degrees (save for the Antelope Valley) Friday and Saturday as winds flip back to onshore the upper level pattern flattens out and becomes more zonal. Upper level troughing will begin Saturday, turning the upper flow slightly southwesterly, marking the beginning of the overall pattern change.
The pattern change may bring some light rain to northern San Luis Obispo County as early as late Saturday, but the main focus for any rain of significance shifts to Christmas week as an upper level trough approaches the West Coast. Virtually every model and AI ensemble member brings rain to the 4-county forecast area. Rain is still favored to begin in SLO County around the 22nd, working down south with some solutions showing rain into the weekend following Christmas. The timing of the mean of the ensembles is in the 23rd through Christmas Day timeframe. There is still quite a wide range of outcomes for the Christmas week storm system, so keep monitoring the forecast for updates.
14/1021z.
At 1000Z at KLAX, the marine layer was 1100 feet deep. The top of the inversion was 2800 feet with a temperatures of 20 degrees Celsius.
For 12Z TAF package, high confidence in KPMD and KWJF, but only moderate confidence in coastal and valley sites. Lower confidence for this sites is due to uncertainties with respect to the marine layer. Through this afternoon, timing of flight category changes could be +/- 3 hours of current forecasts.
KLAX, Moderate confidence in 12Z TAF. Timing of flight category changes through this afternoon could be +/- 2 hours of current forecasts. Timing of flight category changes tonight could be +/- 3 hours of current forecasts. No significant easterly wind component is expected.
KBUR, Moderate confidence in 12Z TAF. Timing of VFR conditions could be as early at 16Z this morning and there is a 30% chance of IFR/LIFR conditions 12Z-17Z. High confidence in VFR conditions this afternoon through tonight.
14/221 AM.
For the Outer Waters, moderate to high confidence in current forecast. Today through Monday morning, high confidence in winds and seas remaining below Small Craft Advisory (SCA) levels. From Monday afternoon through Thursday, there is a 50-70% chance of SCA level winds, especially across PZZ673/676.
For the Inner Waters north of Point Sal, moderate to high confidence in current forecast. Today through Monday, high confidence in winds and seas remaining below SCA levels. For Tuesday through Thursday, there is a 30% chance of SCA level winds in the afternoon and evening hours.
For the Inner Waters south of Point Conception, moderate to high confidence in current forecast. Today through Monday, high confidence in winds and seas remaining below SCA levels. For Tuesday through Thursday, there is a 30-50% chance of SCA level winds across the western half of the Santa Barbara Channel with high confidence in winds and seas remaining below SCA levels elsewhere.
Areas of dense fog with very low visibility will affect much of the coastal waters this morning.
Ca, Dense Fog Advisory in effect until 10 AM PST this morning for zone 343. (See LAXNPWLOX). Dense Fog Advisory remains in effect until 10 AM PST this morning for zones 346>348-354-355. (See LAXNPWLOX). PZ, NONE.
