23/723 PM.
Dry conditions are expected through at least Friday with temperatures rising to near or slightly above normal. Gusty Santa Ana winds will impact the region at times Tuesday through Thursday.
(Sun-Wed), 23/912 PM.
High pressure aloft in place over the region through the weekend is breaking down this evening. Stronger westerlies aloft with a weak shortwave trough will weaken offshore flow, reversing the flow pattern to weakly onshore across the Southland. A return of low clouds and fog is occurring, and low clouds should continue to establish across the coastal sections and lower coastal valleys tonight and into Monday morning. Low clouds and fog are broken up initially and difficult to form as a weak marine inversion is in place this evening. An eddy circulation spinning up in the southern California bight tonight and into Monday morning should permit the clouds to regroup for the southern areas. While the marine layer depth will be deeper south of Point Conception and likely keep dense fog more patchy in nature, there is higher concern for areas north of Point Conception where the marine layer depth is thinner. The latest NAM-BUFR time height sections and boundary layer relative humidity suggest a little more coverage over the interior valleys tonight as trapped low-level moisture will stream into interior San Luis Obispo County out of the Central Valley. As a result, this will need to watched closely for dense fog development.
Some cooling will develop across the coastal sections on Monday as onshore pressure gradients develop. There is some concern that low clouds and fog could hug the coast into the afternoon as the eddy circulation and low Sun angle could inhibit mixing enough to keep the marine inversion in place. Thus, the morning low clouds and fog could hang around a little longer and possibly all day long.
After the shortwave trough exits the region, an offshore flow pattern will get underway again on Monday night.
***From Previous Discussion***
The most notable potentially impactful weather in the short term will be the offshore winds across the region from San Luis Obispo County south to Los Angeles County beginning Monday night and continuing into Thanksgiving day, especially the weak to moderate Santa Ana wind event Tuesday through Thanksgiving morning. The recent wetting rains have greatly mitigated the wildfire threat in the area. However, the soils soaked by the rains allows for trees to more easily be knocked over by winds. Always be cautious parking under trees, and be sure to secure those outdoor Thanksgiving decorations.
Moderate northerly winds 20-30 mph will kick things off in LA County Monday afternoon through the I-5 Corridor and into the Santa Clarita Valley. While maintaining a healthy LAX-BFL northerly gradient (5.0-6.0 mb), winds will begin to tilt to the northeast as the LAX-DAG gradient strengthens to around -6mb by Wednesday morning. While upper support will be somewhat limited, the peak surface gradients are enough to warrant a moderate chance for wind advisories to be issued for late Tuesday into Wednesday afternoon across Santa Ana Wind prone areas, although winds may not surface down to the Oxnard plain in this event. In addition to Santa Ana Wind prone areas being impacted, the northerly winds look strong enough to pose a low to moderate chances for wind advisory issuances on the coastal side of the Santa Monica Mountains from Point Mugu to Santa Monica.
As far as winds go in SLO and Santa Barbara counties, the Santa Lucia Winds will be strongest across the Santa Lucia Range and into the interior mountains beginning Monday night and continuing through the week, peaking Tuesday and Wednesday. Winds in the 25-35 mph range will be common, with isolated gusts to 45 mph.
Temperatures will climb to 5-10 degrees above normal in many areas Tuesday and Wednesday, with widespread temperatures in the 70s, even in the coastal areas. Warmest valley locations may even touch the low 80s.
(Thu-Sun), 23/221 PM.
Thanksgiving will begin with Santa Ana winds continuing into the early afternoon hours, albeit a skosh weaker than Wednesday’s peak, peaking in the 20-30 mph range and tapering off by Turkey time. Santa Lucia winds will continue across the aforementioned mountain areas through Friday. As far as high temperatures go, highs will decrease slightly, but most folks across Southwest California will experience highs in the 70s and clear skies.
There is quite a bit of uncertainty regarding the forecast for next weekend as a potential storm system may arrive as early as Saturday. While there is still considerable disagreement amongst the GFS and the EC/ECAIFS plus their ensembles, the EC and the ECAIFS have both trended the upper level trough considerably further to the southwest, resulting in a majority of their ensemble members showing at least some precipitation at some point next weekend. At this point, potential rain totals look quite low due to low PWATs as the upper level trough meandering across the Western CONUS before dropping southwest. On the other hand, the GFS and its ensembles remain much drier, which would certainly result in a dry Santa Ana pattern.
24/0558z.
At 0514Z at KLAX, there was no marine layer nor an inversion.
Overall, moderate confidence in 06Z TAF Package. Timing of CIG/VSBY restrictions may be off +/- 2 hours, with flight cats off by one when CIGs are present. 20% chc of LIFR CIGs at KSBP from 10 to 16Z Monday.
KLAX, Moderate confidence in TAF. Arrival and departure times of CIGs may be off +/- 2 hours. Expect IFR to low-MVFR conds when CIGs are present - BKN/OVC 007-012 with 3 to 6SM VSBYs. No significant east wind component expected.
KBUR, LIFR to IFR conditions may arrive as early as 10Z, or as late as 14Z. However, there is a 20% chance of no arrival. VFR conditions expected around 17Z thru end of fcst period. No wind impacts are expected at this time.
23/727 PM.
For the Outer Waters, high confidence in current forecast. A combination of Small Craft Advisory (SCA) level winds and seas will continue through Monday afternoon. From Monday night through Thursday, winds and seas should remain below SCA levels. On Friday there is a 40% chance of NW winds increasing to SCA levels.
For the Inner Waters north of Point Sal, moderate to high confidence in current forecast. Through midnight there is a 30% chance of SCA level gusts. For Monday through Thursday, high confidence in winds and seas remaining below SCA levels.
For the Inner Waters south of Point Conception, moderate to high confidence in current forecast. Through Monday night, high confidence in winds and seas remaining below SCA levels. For Tuesday, there is a 30% chance of SCA level northeast winds from Ventura south to Santa Monica, increasing to a 60% chance Tuesday night into Wednesday. On Thursday, high confidence in winds and seas remaining below SCA levels for all of the southern Inner Waters.
Ca, High Surf Advisory in effect until 3 AM PST Monday for zones 340-346. (See LAXCFWLOX). PZ, Small Craft Advisory in effect until 3 PM PST Monday for zones 670-673-676. (See LAXMWWLOX).
