13/219 AM.
Dense fog will continue along the coasts through late this morning and possibly into Sunday morning. Cooler temperatures today, then warming Sunday through Tuesday before a cooling trend occurs in the latter half of next week. The next chance of widespread rain is during the week of Christmas, with a low chance for light rain next weekend for northern portions.
(tdy-Mon), 13/818 AM.
***UPDATE***
Satellite imagery indicates widespread fog across our coastal sections and some valley locations this morning. Some observation sites show visibilities down to tenth of a mile. Mist and drizzle has accumulated up to 0.03" for some areas. Dense fog advisories could be extended for some locations as some guidance suggest. If anything, an early return of fog (likely dense) late this afternoon or in the evening is expected. Dense fog advisories may need to be issued early again like yesterday for some coastal areas. Most confident along the Central Coast where the ECWMF indicates east-west gradients turn onshore this afternoon thanks to upper- level low situated over the coastal waters. Otherwise, the forecast remains on track.
***From Previous Discussion***
The main focus in the short term is another warm up across Southwest California, as well as the ongoing dense fog impacting virtually all coasts and some inland coastal areas across the Los Angeles, Ventura, Santa Barbara, and San Luis Obispo counties. A Dense Fog Advisory has been issued through 10am this morning. Fog is expected to continue through the morning hours, then visibilities are expected to improve some by late morning. Another round of dense fog is forecast to return this evening and continue into Sunday morning for similar areas. Foggy conditions may prevail across the immediate coasts into Sunday Monday.
The upper level ridge that has been driving the overall warm period will continue to weaken slightly through Sunday morning before weakly strengthening starting Sunday afternoon, thus high temperatures will slightly decrease today and increase a couple degrees across coasts and valleys Sunday. Today and Sunday will feature highs in the 60s near the coasts and 70’s across most inland areas. Some of the warmer valleys in Los Angeles and Ventura County will reach the low to mid 80’s.
Monday will feature a further warm up across all coasts and valleys as the ridge of high pressure intensifies and offshore flow to the north and to the east increases. Offshore flow is forecast to remain a bit weaker than this past week, thus no wind advisories are anticipated at this time. Most coastal areas will be well into the 70’s while valleys and inland areas will be well into the 80s. Woodland Hills, typically our warmest area in this regime, may even touch 90 degrees, which would smash the current record of 85 degrees. It’s safe to say the warm December will continue with coasts 5-10 degrees above normal and inland areas 10-20 degrees above normal.
(Tue-Fri), 13/241 AM.
The warm and dry conditions continue Tuesday with little change in actual high temperatures, but overnight lows will be warmer as the offshore flow from the north and east continue. Offshore flow from the east will weaken through Tuesday, but the northerly gradients will remain fairly similar Tuesday through Thursday. Above normal temperatures will continue through the week, but some slight cooling is on the way Wednesday through Friday. Most of the forecast areas will see highs in the mid 60’s to upper 70’s by Friday.
A return of December dense fog at the coasts is possible Wednesday through Friday.
Rain is on the horizon, but likely not until next weekend at the earliest. The latest CPC 8-14 day precipitation outlook is showing “likely above normal” precipitation across the region. Almost all members of the ensembles of the GFS, EC, and EC-AI are indicating rain at some point from next weekend through a couple days after Christmas. Obviously there is a ton of uncertainty in the timing of rain and the rain totals, but there is considerable agreement that there will be some rain during that period. The GFS ensemble has a few solutions that show rain as early as Saturday afternoon for SLO County, but this is certainly the outlier compared to the remainder of the solutions across models. The current “sweet spot” with the most number of solutions favoring rain appears to be from the 22nd through the 26th, so Santa Claus may need to break out the rain coat when he visits SoCal.
13/1036z.
At 1030Z at KLAX, the marine layer was 700 feet deep. The top of the inversion was 2800 feet with a temperatures of 21 degrees Celsius.
For 12Z TAF package, high confidence in valley and desert TAFs. As for coastal sites, moderate confidence due to uncertainties in the behavior of the marine layer, especially timing of flight category changes which could be +/- 3 hours of current forecasts.
KLAX, Moderate confidence in 12Z TAF. Timing of flight category changes could be +/- 3 hours of current forecasts. There is a 30% chance of VV001 with 1/4sm FG 12Z-16Z. No significant easterly wind component is expected.
KBUR, High confidence in 12Z TAF. There is a 20% chance of MVFR VSBYs 12Z-16Z.
13/231 AM.
For the Outer Waters, moderate to high confidence in current forecast. Today through Sunday, high confidence in winds and seas remaining below Small Craft Advisory (SCA) levels. For Monday through Wednesday, there is a 50-70% chance of SCA level winds, especially from Point Conception southward.
For the Inner Waters north of Point Sal, moderate to high confidence in current forecast. Today through Tuesday, high confidence in winds and seas remaining below SCA levels. On Wednesday, 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 and Wednesday, there is a 30-40% 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 today through Sunday. The best chances for dense fog will be from the overnight through morning hours with scattered pockets likely through the afternoon and evening.
Ca, Dense Fog Advisory remains in effect until 10 AM PST this morning for zones 340-341-346-347-349-350-354-355-362-366>368-373-548. (See LAXNPWLOX). Dense Fog Advisory in effect until 10 AM PST this morning for zone 348. (See LAXNPWLOX). PZ, NONE.
