10/601 PM.
A cooling trend will affect the region Friday into the weekend with max temps dropping to below normal by Sunday. The sticky tropical air will finally exit the region by this weekend. Marine layer clouds will likely return to many coastal areas.
(Thu-Sun), 10/923 PM.
***UPDATE***
It was a mostly sunny day today, with some altocumulus cloud build ups over the mountains, and a few thunderstorms over the Eastern San Gabriel Mountains this afternoon. High temperatures across most coasts and coastal valleys were 5 to 10 degrees cooler than yesterday, while more interior areas were a couple degrees warmer. These temperatures ranged from 80s and 90s at the coasts to 90s to low 100s everywhere else, about 10 to 20 degrees above normal for this time of year.
Overnight lows will remain elevated in the 60s to mid 70s. The forecast leans toward a return of marine layer clouds tonight across the Central Coast, and possibly into the southern L.A. Coasts around Long Beach, but less confidence than normal as the first night of marine layer clouds is always tricky to forecast and models rarely handle it well. Additionally, advisory level Sundowner winds across Southwestern Santa Barbara County are expected to continue through the night and a Wind Advisory is in effect.
As for tomorrow, onshore flow is expected to increase further, while 500 mb heights will decrease by about 3 dam, and PWATs will start to decrease through the day. The combination of the three will allow widespread cooling across the region, with some locations decreasing by as much as 8 degrees. Temperatures are forecast to be in the 70s and 80s at the coast and 80s and high 90s away from the coast.
Allowed the Extreme Heat Warnings to expire on time at 8pm PDT. However, just issued Heat Advisories for the coasts south of Point Conception, including the inland coasts of Ventura and L.A. Counties due to the continued very warm overnight lows and expected highs of around 10 degrees above normal.
Otherwise forecast was in shape and no other updates were needed for this evening.
***From Previous Discussion***
The very hot and muggy weather has been the main story as of late, but today should be the last day of these truly oppressive conditions for Southwest Californians. Temperatures have generally trended down today due mainly to the positive trend in onshore flow. While the LAX-DAG gradient is near neutral, the positive trend has allowed for the onshore winds to kick in much earlier than yesterday, thus providing some relief to coastal areas. These hot and humid conditions continue to add to this multi-day high heat-illness risk event, thus the Extreme Heat Warnings in place will continue through this evening. Overnight temperatures will still remain relatively warm tonight, but cooler and less humid air will make its return tomorrow.
The upper level ridge that has trapped the remnant Marie mositure and brought very hot temps to the region will finally flatten out starting tomorrow thanks to an upper level trough swinging down into the PACNW. This will help usher in a significant cooling trend which will continue each day through the weekend, bringing the entire region to below normal for mid-September by Saturday/Sunday. Most of the region will see temps in the 70s at the coasts and 80s inland. PWATs will drastically decrease as the tropical mositure moves out of the region, bringing us to around 0.75 inches by Saturday evening down south. The combination of cooler temps and drier air will lead to significantly more tolerable weather across the region.
A slight chance of thunderstorms and showers exists this afternoon over interior mountains of LA and Ventura Counties, with the Eastern San Gabriels most favored. With any thunderstorm that forms, the air is juicy enough to produce heavy downpours along with gusty winds and lightning. The steering flow remains fairly weak from the west-southwest direction, so storms will be slow moving to the northeast. Because of this, there is a low but non-zero risk for localized flash flooding and the Bridge and Summit burn scars are within that area of risk.
As far as winds go, we're looking for onshore flow to increase each day, which will bring some breezy conditions to the region this weekend.
Expecting the marine layer to reform and many coastal areas can expect some evening and morning marine layer clouds as early as tonight, but best chances this weekend (and best chances along the Central Coast). One caveat is an expected uptick in Sundowner winds across SW SB County through Saturday night. This will help warm things up at the coasts, making it tougher for this area to cool below normal. It may also inhibit any marine layer formation from Ventura County to southern SB County. These winds will likely reach advisory levels each night through Saturday and a Wind Advisory has been issued for tonight.
(Mon-Thu), 10/219 PM.
Not much change through Wednesday, with zonal flow continuing at the upper levels. Temperatures will remain below seasonal normals. Weak to moderate onshore flow will continue with light northerly offshore flow each night through morning. There will likely be some morning low clouds each day with the greatest coverage across the Central Coast. Skies, otherwise, will be mostly clear.
By Thursday, deterministic models and ensembles suggest the ridge will begin to build back west, which would bring warmer temperatures to the area once again. Onshore flow to the east is also forecast to trend weaker slightly weaker Thursday morning. The greatest question is how progressive this westward movement of the ridge is, so while temperatures are likely to begin to increase, to what extent and how quickly remains uncertain. What does appear to be more clear is that any warming trend will likely not be nearly as warm as the last couple of days.
No significant wind issues are expected, although there will be the usual gusty southwesterly winds each afternoon across the mountains and deserts and the typical near advisory level evening gusts across the SW corner of SBA county.
11/0059z.
At 0029Z at KLAX, there was no marine layer. The top of the inversion was at 2800 ft with a temperature of 30 C.
High confidence in VFR conditions for all sites except for KSMX (60% chc of LIFR), KSBP (20% chance of LIFR) and the LA Coastal sites, where there is a 20% chance of IFR/MVFR conds at KSMO and a 40% chance of no CIGs at KLAX and KLGB.
KLAX, MOderate confidence in the 00Z TAF. There is a 40% chance that no CIGs affect the site, and if CIGs do occur, the timing could be off by +/- 2 hours. There is a 30% chance that east wind component reaches 8 kts Fri 11/09Z-16Z.
KBUR, High confidence in th 00Z TAF.
10/738 PM.
Conditions are expected to become increasingly hazardous across the outer waters into the weekend. A Gale Watch (50-60% chc) has been issued for PZZ676/673 Saturday evening into Monday morning. The coastal Jet may develop across PZZ670 Saturday evening causing winds to increase there as well, but confidence in winds reaching Gale force is low at this time. Otherwise, SCA winds are expected across the outer waters through Saturday afternoon or longer. Small Craft Advisory (SCA) conditions are expected to reach into the nearshore waters along the Central Coast and the Santa Barbara Channel at times (especially during afternoon/eve hours) through early next week.
10/823 PM.
The potential for moderate coastal flooding will continue through this evening, mainly around evening high tide for south facing shores. Even though the south swell from post tropical cyclone Marie is subsiding, the tides remain very high. The actual observed tides have been running about 6 to 8 inches above predictions, with the evening tides near or exceeding 7 feet.
While impacts will not be as extreme as the past few days, possible impacts include continued beach erosion, flooded sandy beach areas, bike paths, and parking lots, as well as low-lying roads. Some areas that may continue to see impacts are: the Alamitos Peninsula in Long Beach, Avalon on Catalina Island, and Oxnard to Malibu (including the Pacific Coast Highway near Point Mugu).
Beach Hazards Statements (BHS, CFWLOX) are in effect through this evening for the beaches of Los Angeles, Ventura, and southern Santa Barbara Counties due to these very high evening tides.
Ca, Beach Hazards Statement in effect until midnight PDT tonight for zones 87-349-350-354-362-366. (See LAXCFWLOX). Heat Advisory in effect until 6 PM PDT Friday for zones 349-350-354-355-362-366>368. (See LAXNPWLOX). Wind Advisory in effect until 6 AM PDT Friday for zones 349-351. (See LAXNPWLOX). PZ, Small Craft Advisory in effect from 3 PM to 9 PM PDT Friday for zone 645. (See LAXMWWLOX). Small Craft Advisory in effect until 3 AM PDT Friday for zone 650. (See LAXMWWLOX). Small Craft Advisory in effect from 3 PM Friday to 3 AM PDT Saturday for zone 650. (See LAXMWWLOX). Small Craft Advisory in effect until 9 AM PDT Monday for zone 670. (See LAXMWWLOX). Small Craft Advisory in effect until 6 PM PDT Saturday for zones 673-676. (See LAXMWWLOX). Gale Watch in effect from Saturday evening through Monday morning for zones 673-676. (See LAXMWWLOX).
