399
FXUS66 KLOX 151535
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
835 AM PDT Sun Sep 15 2024

.SYNOPSIS...15/216 AM.

An extended period of cooler weather is expected for the upcoming
week. Clouds will likely struggle to clear from the beaches the
next couple of days. A weak and dying cold front will bring a
chance for light rain to most of the area Monday morning. Another
slight chance of rain will develop on Wednesday. A warming trend
will begin on Friday and continue into the weekend.

&&

.SHORT TERM (TDY-TUE)...15/834 AM.

***UPDATE***

The forecast is well on-track, and no changes have been made to
the ongoing forecast.

***From Previous Discussion***

What a difference a week makes. Weak troffing and moderate to
strong onshore flow in both direction have lifted the marine
layer to near 3800 ft. Marine layer stratus covers all of the
coasts and vlys and extends into the mtns passes. A 9 mb onshore
push to the east this afternoon will delay clearing inland and
will likely keep the low clouds over the coasts (and esp the
beaches) all afternoon long. The weak lift provided by the
troffing will allow for some morning drizzle esp near the
foothills. Most areas will cool 3 to 6 degrees today and max
temps will end up 8 to 12 degrees blo normal. Max temps across the
csts will mostly be in the 60s and the vlys in the 70s. The strong
onshore push to the east will bring advisory level gusts to the
western Antelope Vly and foothills.

One more day of smoke from the Bridge Fire is likely for the
Santa Clarita Valley and the San Gabriel Mountains (see the Air
Quality Alert for more details).

A cold early season upper low will rotate out of the PAC NW and by
Monday morning it will be centered over the Bay Area with a 558
central hgt. A trof and weak cold front will rotate around the low
and through Srn CA. Hgts will fall to 568 dam. The hgts falls and
pva from the upper low will further deepen the moist layer to
between 5000 to 6000 ft. The deep marine layer and weak lift will
combine to bring widespread drizzle and a chance (30 to 40
percent) of measurable light rain in the morning. The exception to
this will be the San Gabriel Vly and the coastal foothills of the
eastern San Gabriel mtns where rain is likely (75 to near 80
percent chance) The next highest chance of light rain will be
across the northwestern portion of San Luis Obispo County, which
will be closer to center of the low pressure system. Rain totals
of around 0.25 inches will be possible for both these locations.

Clouds, rain, onshore flow and lowering hgts will all mix together
and lower max temps 2 to 4 degree across the csts, 3 to 6 degrees
in the vlys and rather spectacular 10 to 15 degrees across the
interior. Max temps will end up 10 to 20 degrees blo normal. Most
max temps across the csts/vlys will only be in the mid 60s to
lower 70s.

There is a chc that the cool air from the upper low will weaken
the inversion enough to create a reverse clearing episode where
the coasts clear but a strata CU deck cooks up over the vlys
keeping them mostly clear.

Cold air advection and moderate onshore flow to the east will
likely bring advisory level wind gusts to portions of the SBA
County south coast, the coastal plains of VTA County and the
Malibu area as well as the San Gabriel mountains.

The upper low will push off to the east on Tuesday and hgts will
rebound to about 576 dam. There will be 3 to 6 degrees of warming.
Despite the warming max temps will come in 6 to 12 degrees blo
normal. There will be less marine layer clouds in the morning and
it possible if there was enough cool air advection and mixing
Monday that there will be no morning low clouds at all.

.LONG TERM (WED-SAT)...15/326 AM.

The unseasonable weather will continue into the extended period.
On Wednesday another cool upper low will rotate into Srn CA and
lower hgts down to 567 dam or so. The system does not look very
moist and it will only bring a 20 to 30 percent chc of rain with
the best chc`s again in the San Gabriel foothills and NW SLO
county. 2 to 4 degrees of cooling will keep most cst/vly temps in
the mid 60s to mid 70s.

Look for a little warming on Thursday as the low slowly moves out.
Some EC solutions show a much slower exit resulting in a chance
for some morning rain or drizzle as well little to no warming.

Weak ridging builds in for Fri and Sat and hgts are forecast to
rise to 586 dam. The onshore flow weakens considerably and this
should keep most of the morning low clouds away. Look for 4 to 8
degrees of warming on Fri and 3 to 6 additional degrees on Sat.
This warming will bring Saturday`s max temps to 2 to 4 degrees
above normal.

&&

.AVIATION...15/1049Z.

Around 0715Z, the marine layer depth was around 2700 feet deep at
KLAX. The top of the marine inversion was near 4700 feet with a
temperature around 19 degrees Celsius.

Moderate-to-high confidence in the current forecast. IFR to MVFR
conditions will persist through at least 17Z. There is a
moderate-to-high chance of conditions dropping one category
through 16Z, especially with drizzle. MVFR conditions will
struggle clear again on today, possibly not clearing at all along
at immediate coastal terminals such as KOXR and KSBA. An early
return of IFR to MVFR conditions should be expected this evening.

KLAX...There is a 50 percent chance of conditions dropping to IFR
in drizzle through 16Z, otherwise MVFR conditions are expected
through at least 20Z. VFR conditions should develop between 20Z
and 22Z, but there is a 30 percent chance of MVFR conditions
lingering through this afternoon. If VFR conditions develop as
forecast, MVFR conditions will spread back into KLAX as soon as
02Z or as late as 06Z. There is a 40 percent of light rain or
drizzle tonight after 06Z.

KBUR...There is a 60 percent chance of conditions dropping to IFR
in drizzle through 16Z, otherwise MVFR conditions are expected
through at least 20Z. VFR conditions should develop between 18Z
and 20Z, but there is a 30 percent chance of MVFR conditions
lingering through Sunday afternoon. If VFR conditions develop as
forecast, MVFR conditions will spread back into KBUR as soon as
05Z or as late as 08Z. There is a 40-50 percent of light rain or
drizzle tonight after 06Z.

&&

.MARINE...15/335 AM.

For the northern waters offshore of the Central Coast, chances
for Small Craft Advisory (SCA) level winds will increase through
the day to 50-80 percent by this afternoon and to 70-100 percent
by this evening. The highest chances will be for areas beyond 10
NM offshore. The chances for SCA level winds will decrease late
tonight through early Monday morning. There will be a moderate
(30-50 percent) chance of SCA level winds each afternoon and
evening through Wednesday.

For the southern waters from Point Sal south to San Clemente
Island and southwest through northwest of the Channel Islands,
there is a 10-30 percent chance of SCA winds this morning
increasing from northwest to southeast to 60-90 percent by this
evening. Winds will decrease some but still remain at or near SCA
levels late tonight through early Monday, then the chances for SCA
level winds will increase southeast to northwest on Monday. The
chances for SCA levels will increase to 10-30 percent across the
northwest portion and to 70-90 percent across the southeast
portion by Monday evening. There will be a high-to-likely (50-70
percent) chance of SCA level winds Tuesday through Thursday,
highest during the afternoon and evening hours.

For the Santa Barbara Channel, winds and seas will remain below
SCA levels through this afternoon, then winds will increase from
this evening through Monday afternoon. There is only a 10-30
percent chance for SCA conditions this evening increasing to a
30-60 percent chance early Monday morning. Winds will increase
further on Monday and SCA conditions are virtually certain and
affecting a vast majority of the channel. By Monday afternoon,
there 80-100 percent chance of SCA level winds across the entire
channel with 40-60 percent chance of GALES. The highest chances
for GALES will be for the eastern half of the channel. Steep seas
will also build, with a high chance of waves reaching 7 feet on
Monday night and lingering into Tuesday morning. The chances for
SCA level winds will decrease to moderate-to-high (30-50 percent)
chance on Tuesday and Wednesday afternoons and evening, highest
across the eastern portion.

For the inner waters from Point Mugu to San Mateo Point, winds and
seas will remain below SCA levels through Monday, then increase
through the day from northwest to southeast to 50-80 percent,
highest near Point Mugu and the Anacapa Passage. There is a 30
percent chance of local gale level gusts from near Point Mugu
south to Point Dume. Choppy seas will also develop on Monday
night, lingering into Tuesday morning. Winds and seas will drop
below SCA levels for Tuesday through Thursday.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory remains in effect from 3 PM this afternoon to 9
      PM PDT Monday for zones 381-383. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect from 3 PM this afternoon to 3
      AM PDT Monday for zone 645. (See LAXMWWLOX).
     Gale Watch in effect from Monday afternoon through Monday
      evening for zone 650. (See LAXMWWLOX).
     Small Craft Advisory in effect from noon Monday to 3 AM PDT
      Tuesday for zone 655. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PDT Monday for zone
      670. (See LAXMWWLOX).
     Small Craft Advisory in effect from 3 PM this afternoon to 9
      AM PDT Tuesday for zones 673-676. (See LAXMWWLOX).

&&

$$

PUBLIC...Rorke/Cohen
AVIATION...Hall
MARINE...Hall
SYNOPSIS...Gomberg

weather.gov/losangeles

Experimental Graphical Hazardous Weather Outlook at:
https://www.weather.gov/erh/ghwo?wfo=lox