08/929 PM.
There will be cooler weather through Monday as light onshore flow returns as well as areas of low clouds and locally dense fog. Then late Monday into Wednesday a strong and damaging Santa Ana wind event is expected across parts of Los Angeles and Ventura Counties. Fire weather concerns will be high with the winds and low humidity.
(Sun-Wed), 08/928 PM.
***STRONG AND DAMAGING SANTA ANA WINDS WITH VERY LOW HUMIDITIES EXPECTED TO BRING PARTICULARLY DANGEROUS RED FLAG WARNING CONDITIONS TO MANY AREAS OF LOS ANGELES AND VENTURA COUNTIES MONDAY NIGHT INTO TUESDAY***
***UPDATE***
Generally quiet wx across the region this evening ahead of the upcoming major Santa Ana wind event. Low clouds and fog have developed along much of the coast S of Point Conception this evening and have spread inland even to as far as some of the adjacent vlys. Overnight, the low clouds should spread to all coastal areas S of Point Conception and expand only slightly further inland thanks to pressure gradients tuning offshore later tonight. Areas of dense fog has already developed int he southeastern VTU County vlys and a Dense Fog Advisory has been issued for this area overnight into Mon morning. Patchy dense fog will be possible in other areas later tonight. Otherwise and elsewhere, mostly clear skies with a few hi clouds at times can be expected thru the night.
Taking a look at the 00Z NAM and some hi res model data, it looks like the major wind event is on track. The latest NAM forecast pressure gradients for 12Z Tue from LAX-DAG is -9.3 mb, with the 24-hour offshore trend of -8.2 mb, which are exceptional numbers.
Widespread damaging northeast winds are likely to occur across portions of VTU/L.A. Counties including the western San Gabriel Mtns thru the Santa Clarita and San Fernando Vlys, the eastern VTU County vlys, Santa Monica Mtns and many coastal areas of VTU County and the Malibu coast. The High Wind Watches have been upgraded to High Wind Warnings this evening, with gusts to 65 mph expected in lower elevations, and gusts up to 70 to 80 mph in the higher elevations. Please see the latest Non-Precipitation Weather Message (LAXNPWLOX) for the latest info on the High Wind Warnings. ***From Previous Discussion***
Low clouds will continue into the morning hours but clear rapidly as the next Santa Ana wind event begins around noon in the LA Mountains and mid to late afternoon across the San Fernando, Santa Clarita, and interior Ventura County Valleys.
A very strong Santa Ana wind is expected across portions of LA/Ventura Counties later Monday into at least Tuesday, with some lingering winds into Wednesday. Now that we're within 48 hours of the onset it's within the window of our high res models and the wind forecast looks quite similar to the last very strong event on Nov 5-6 and highlighting most of the same areas that received 40-80 mph winds, namely the Santa Susana, San Gabriel, and western Santa Monica mountains and even parts of the San Fernando, Santa Clarita, and Ventura coast and valleys. Forecast gradients this morning have come down slightly but still very strong with again strong upper level support and good cold advection. Winds will push well out over the coastal waters between Pt Dume to Ventura, as well as off the OC coast, easily reaching the Channel Islands, including Catalina, Anacapa, Santa Cruz, and San Miguel. The combination of these strong winds and rapidly lowering humidity into the single digits in some areas will lead to very dangerous fire weather concerns. Given the lack of rain in these areas over the last several months as well as several days of very low humidities, any fire starts would be expected to have extremely rapid spread.
On Wednesday much of the upper level support is gone but offshore gradients are expected to be in the 5-6mb range so there will be continued gusty winds and extremely high fire danger through at least early afternoon.
With strong cold air advection high temperatures will be on the cooler side, especially inland. Highs at lower elevations expected to be around 70, and warmest at the coast. Then warming slightly each day through Wednesday as the cold advection shifts east and high pressure builds aloft. Overnight temperatures will be modified in areas that are getting the Santa Ana winds. However, outside those areas, with extremely low humidities, temperatures will fall rapidly and well below freezing in some areas, especially in the Antelope Valley where lows in the high teens are possible in the colder areas. May need a freeze watch there with the possibility of freezing pipes.
(Thu-Sun), 08/217 PM.
Still a lot of uncertainty with the specifics later next week as a couple fast moving troughs pass through the state, though overall weather conditions are expected to be very low impact. Onshore flow will return Thursday as the first trough quickly moves through. A few of the ensemble solutions show some light rain across northern areas. After a brief period of weak ridging Friday the next trough arrives along the west coast Friday night into early Saturday. A few solutions show some very light rain as far south as LA County, but most are quite a bit farther north and event there amounts are mostly under a quarter inch. For most areas, temperatures will be near normal (60s to low 70s) with no significant winds.
09/0557z.
At 0543Z at KLAX, the marine layer was 600 ft deep. The top of the inversion was at 5500 ft with a temperature of 15 C.
Moderate confidence in TAFs overall. Timing of cig/vsby restrictions may vary +/- 2 hours. There is a 30% chance of no flight cat restrictions developing for KVNY and KBUR.
Winds speeds may be off by 5-10 kt during peak winds for KBUR, KVNY, KOXR, KCMA, KSMO, KPMD, and KWJF. UDDFS is possible over and near to hier trrn starting 18Z Mon, and LLWS is possible for KCMA, KOXR, KVNY, and KBUR starting 21Z Mon.
KLAX, Low-to-moderate confidence in TAF. Timing of cig/vsby restrictions may vary +/- 2 hours. There is a 10% chance of the east wind component reaching 6 to 8 kt from 07Z-17Z Mon, and there is a 30% chance of a 15 kt east wind after 03Z Tue.
KBUR, Moderate confidence in TAF, except there is a 30% chance of no flight categories restrictions developing overnight. LLWS and lgt-mdt turbc is possible starting 21Z Mon.
08/909 PM.
For the Outer Waters, our biggest concern in the near term is strong Northeast winds from the Santa Ana wind event. The NE winds should stay confined to the extreme southern portion of PZZ673, near the Channel Islands. The timeframe is Monday night through mid- day Tuesday. Winds will be more widespread and stronger for PZZ676 and the southern half of PZZ673, where a GALE Watch has been issued.
For the Inner Waters, a STORM Watch has been issued from Monday evening through Tuesday morning. The winds will be strongest for the Coastal Waters from Ventura to Malibu, extending to the Channel Islands. The San Pedro Channel will be another hot spot for winds during the same timeframe. Wind-driven waves of 4 to 6 ft with local sets to 8 ft are expected.
East facing harbors will likely see significant impacts with gusty northeast winds, short period seas, and breaking waves in and near harbor entrances. During the peak of the winds, east facing harbors such as Avalon and Two Harbors on Catalina Island, and Smugglers Cove on Santa Cruz Island should NOT be considered safe harbor. Some of our strongest Santa Ana winds have a maritime history of creating dangerous and life threatening conditions in east facing harbors. Please see MWSLOX for more details for east facing harbors.
08/804 AM.
High astronomical tides approaching 7 feet during the early morning hours will bring a chance of moderate coastal flooding to southwest California shores late this week and for the upcoming weekend. Normally dry beach walkways and parking lots may see tidal overflows and minor coastal flooding. There is a chance that beach erosion may occur. Rip current activity may increase during the run up to high tide.
Ca, High Wind Warning in effect from 10 PM Monday to 1 PM PST Tuesday for zones 88-354-355-358-362-370>372-374. (See LAXNPWLOX). High Wind Warning in effect from 4 PM Monday to noon PST Wednesday for zones 369-375-379. (See LAXNPWLOX). Dense Fog Advisory in effect until 9 AM PST Monday for zone 374. (See LAXNPWLOX). Red Flag Warning in effect from 10 AM Monday to 6 PM PST Wednesday for zones 288-358-369>380-548. (See LAXRFWLOX). Red Flag Warning in effect from 10 PM Monday to 10 PM PST Tuesday for zone 345. (See LAXRFWLOX). Red Flag Warning in effect from 2 PM Monday to 2 PM PST Wednesday for zones 354-355-362. (See LAXRFWLOX). PZ, Gale Watch in effect from Monday evening through Tuesday morning for zones 673-676. (See LAXMWWLOX).
