10/223 PM.
Extreme heat and humidity will continue today with a high risk for heat illness. Cooling will start Friday and continune into the weekend with max temps dropping to below normal. The sticky tropical air will finally exit the region by this weekend. Marine layer clouds will likely return to many coastal areas.
(tdy-Sun), 10/219 PM.
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.
10/1733z.
At 1645Z at KLAX, the marine layer was 1200 ft deep. The top of the inversion was at 2300 ft with a temperature of 30 C.
High confidence in VFR conditions for all sites except for KSMX (60% chc of LIFR), KSBP & KLGB (30% chc of LIFR) from Fri 11/10Z-16Z.
KLAX, High confidence in VFR TAF. There is a 30% chance that east wind component reaches 8 kts from Fri 11/09Z-17Z.
KBUR, High confidence in VFR TAF. No wind issues expected.
10/1253 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 but confidence is too low if winds will reach Gale strength at this time. 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).
Ca, Extreme Heat Warning in effect until 8 PM PDT this evening for zones 38-87-88-340>358-362-366>375-548. (See LAXNPWLOX). Beach Hazards Statement in effect until midnight PDT tonight for zones 87-349-350-354-362-366. (See LAXCFWLOX). Wind Advisory in effect until 6 AM PDT Friday for zones 349-351. (See LAXNPWLOX). PZ, Small Craft Advisory in effect until 11 PM PDT this evening 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 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).
