10/840 PM.
Onshore flow will replace offshore flow through midweek as a ridge of high pressure moves east of the region. A shallow marine layer depth will bring dense fog at times to the coast, possibly reaching the valleys by Wednesday morning. A broad trough of low pressure will approach the West Coast on Wednesday night and bring rain, heavy at times through Thursday night or Friday. Drier but cool weather is expected over the weekend.
(Mon-Thu), 10/932 PM.
Dirty ridging aloft remains in place across the region this evening. High pressure is slowly breaking down over the region as high clouds stream over the ridge. A cooling trend will develop through midweek as cyclonic flow replaces anticyclonic flow aloft, while at the surface, onshore flow replaces offshore flow. A shallow marine layer depth is in place across the coastal areas this evening, preluding a broader return of low clouds and fog to the region through Wednesday. Strong high pressure aloft continues to press down on the marine layer enough to keep it as shallow layer near the surface. Low clouds and dense fog will be possible for all coastal areas tonight and into Tuesday morning, which likely will reach the western fringes of the Santa Ynez Valley and maybe the San Gabriel Valley by daybreak. A dense fog advisory was added for the Central Coast, the Ventura County coast, and the southeastern portion of Santa Barbara County through 9 am Tuesday, but there is a high chance that this advisory will need to be expanded into the remaining coastal areas by Tuesday morning.
Temperatures will cool by about 7-12 degrees away from the coast on Veterans Day while remaining near persistence along the coast as clouds could hug the coast on Tuesday afternoon. An earlier update fixed temperatures across the Southland valleys to not cool the area quite as much, but the beaches and immediate coastal areas could end up being much cooler than what is forecast if clouds hang in longer than forecast. The next shift will be briefed about the potential for clouds hanging in along the beaches.
***From Previous Discussion***
Onshore flow is expected to resume in all areas Tue and Wed leading to 5-10 degrees of cooling each day across the inland areas.
A moderate to strong storm with PW's around 1.5" is expected to move through the area Thursday. Could see some light precip as early as Wednesday night along the Central Coast and a few post- frontal showers Friday but 90% of the rainfall should take place on Thursday. Most areas will experience around 6-8 hours of precip with the front, 1-3 hours of which could be heavy with up to 0.75" per hour and a 20% chance of as much as an inch per hour. The heaviest precip will be in the usual favored upslope areas, including the Santa Lucia's, the Santa Barbara mountains (particularly the Santa Ynez Range) into the western Ventura County mountains, the Santa Monica mountains, and the eastern San Gabriel mountains. All of those areas will be at risk for heavy rain and flooding. If models stay consistent it's likely that a Flood Watch will be issued for the most vulnerable areas, including the most recent burn scars. Projected rain amounts remains about the same with most coastal/valley areas falling into the 1-2" range and foothills and south facing mountains in the 2-4" range. But would not be surprised to see a couple 5" totals when all is said and done.
Not expecting any snow below 8000 feet with this system until the very tail end of it when there could be a few inches between 6000-8000 feet.
(Fri-Mon), 10/228 PM.
There is still some uncertainty with regard to how long showers will continue following the main cold front on Thursday. The latest ensembles place the trough right through LA County Friday morning with northwest flow developing during the afternoon and evening. There still could be some brief moderate to locally heavy showers before the trough passage Friday morning but most of the ensembles are indicating rain rates well below a half inch per hour after 4am Friday.
Dry but cool weather is expected over the weekend. There remains a small chance of a weak storm next Monday but recent model runs have backed off that system.
11/0543z.
At 0444Z at KLAX, the marine layer depth was 300 feet. The top of the inversion was near 11 feet with a temperature of 28 degrees Celsius.
High confidence in VFR conditions for KPRB, KBUR, KVNY, KWJF and KPMD. 10% chance for VLIFR conds at KPRB from 12Z-17Z.
Low to moderate confidence in all coastal sites. Timing of flight cat changes may be off +/- 2 hours, and there is a 30% chance KOXR and KLAX do not clear Tuesday. Less than 1/2SM vsbys are observed at some coastal sites, and there is a 50% chance at remaining sites once clouds are present. Low confidence in return of low clouds after 12/00Z.
KLAX, Low to moderate confidence in TAF. Cigs may arrive anytime between now and 10Z. 50% chance for vsbys less than 1/2SM when cigs arrive. Clearing may be off by +/- 3 hours, but there is a 30% chance for no clearing. No significant east wind component is expected.
KBUR, High confidence in TAF.
10/844 PM.
For the Outer Waters, moderate to high confidence in current forecast. Tonight through Wednesday, high confidence in winds and seas remaining below Small Craft Advisory (SCA) levels for most of the waters, but winds may near SCA levels near Point Conception at times. From Wednesday night through Saturday, high confidence in a combination of SCA level winds and seas. On Thursday, there will be a 20% chance of Gale force winds across PZZ670.
For the Inner Waters north of Point Sal, moderate to high confidence in current forecast. Tonight through Wednesday, high confidence in winds and seas remaining below SCA levels. For Wednesday night and Thursday, high confidence in SCA level winds with a 20-30% chance of Gale force winds Wednesday night and Thursday morning. Strongest winds look to affect the Central Coast. For Friday, there is a 30-40% chance of SCA level winds and seas. On Saturday, 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. Today through Wednesday night, high confidence in winds and seas remaining below SCA levels. On Thursday, there is a 40-50% chance of SCA level southeast winds in the morning and a 60-80% chance of SCA level west to northwest winds in the afternoon. For Thursday night through Friday night, high confidence in SCA level west to northwest winds with a 20-30% chance of Gale force winds. On Saturday, high confidence in winds and seas remaining below SCA levels.
Dense fog will continue to be an issue for all the coastal waters tonight and Tuesday morning. Visibilities of one nautical mile or less are likely.
On Wednesday night and Thursday, there will be a slight chance of thunderstorms across the coastal waters from the Santa Barbara Channel northward. Any thunderstorms that develop will be capable of producing frequent lightning, gusty and erratic winds, locally rough seas and even waterspouts.
Ca, Dense Fog Advisory remains in effect until 9 AM PST Tuesday for zones 340-341-346-347. (See LAXNPWLOX). Dense Fog Advisory in effect until 9 AM PST Tuesday for zones 350-354-355. (See LAXNPWLOX). PZ, NONE.
