Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 231630

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
930 AM PDT Fri Apr 23 2021

.SYNOPSIS...23/251 AM.

Weak high pressure, building in through Saturday, will bring some
warming inland, while onshore flow will continue and keep
temperatures cooler near the coast. A persistent marine layer will
continue extensive night through morning low clouds, clearing to
near the beaches in the afternoon. A weak storm system could bring
rain and mountain snow to the area between Sunday and Monday. A
warming trend is expected for the middle of next week.


.SHORT TERM (TDY-SUN)...23/929 AM.


Still a deep marine layer in place with an eddy circulation south
of Pt Conception. Clouds expected to clear a little earlier and
better today as high pressure starts to build over the area, but a
9+ mb LAX-DAG gradient might make it more difficult for some
coastal areas.

Models continue to trend weaker with the system Sunday into early
Monday. Still a good chance of rain north of Pt Conception, but
models show it weakening as it moves south and farther away from
the main upper low in northern California. Also, because the low
is so far north there is little to no southerly flow with the
front which will limit the precipitation across southern areas.
Projected rain amounts now down to a quarter inch or less in most
areas, highest across SLO County, and lowest in Ventura County
(probably under a tenth there). Eastern LA County should get a
slight bump up in amounts due to better orographics, but still
mostly under a quarter inch.

***From Previous Discussion***

The ridge aloft will move east of the region on Saturday, then a
trough of low pressure originating from the Gulf of Alaska will
drop into the region. The trough associated with the Aleutian low
will split off from the semi-permanent trough feature and drop
into the West Coast over the weekend. Global model ensemble
solutions, showing a confident stance last night, are now starting
to trend weaker with the system. The solution could be struggling
with the finer details as the system is a cutoff trough. As we
are entering the windows of the higher-resolution models and the
trough will split off today, model performance should be a bit
clearer later tonight. Though PoPs and QPF amounts have trended,
rain is still likely between Sunday and Monday. The most likely
time period for rain looks like Sunday night for areas north of
Point Conception, and Monday for areas south of the point.
Rainfall amounts have trended drier in the latest runs, now a
tenth to a quarter of an inch. Local amounts up to a half inch are
possible across the coastal slopes of the mountains. Up to an
inch snow is now possible above 6000 feet.

Gusty winds could develop across the interior portions with this
storm. Advisory level winds are possible across the mountains and
a tad more likely for the Antelope Valley between Sunday and

.LONG TERM (MON-THU)...23/328 AM.

The storm system will exit the region late Monday and high
pressure aloft will build in through Thursday. GFS and ECMWF
operational solutions both agree on a strong ridge of high
pressure settling into the region between Wednesday and Friday.
A hot air mass will likely develop for the latter half of the work
week next week. ECMWF ensemble suggest temperatures in the 90s to
near 100 degrees for the valley areas, with temperatures in the
mid 70s to mid 80s at the coast.



At 1000Z, the marine inversion at KLAX was based near 3900 feet.
The top of the inversion was 5400 feet with a temperature of
10 degrees Celsius.

Overall, moderate confidence in 12Z TAF package. Current MVFR/IFR
CIG restrictions will continue at all coastal/valley sites this
morning. For the afternoon, there is a 30-40% chance that CIGs
could dissipate. For tonight, high confidence in return of MVFR
CIGs for coastal/valley sites, but only moderate confidence in
timing of CIG return.

KLAX...Moderate confidence in 12Z TAF. There is a 30-40% chance
that MVFR CIGs could dissipate after 21Z. For tonight, high
confidence in MVFR CIGs. No significant easterly wind component is

KBUR...Moderate confidence in 12Z TAF. There is a 30-40% chance
that MVFR CIGs could dissipate after 21Z. High confidence in MVFR
CIGs tonight.


.MARINE...23/912 AM.

Patchy fog will continue across most of the coastal waters through
Saturday, then there is a chance of light rain Sunday and Monday.

Across the Outer Waters... There is a thirty five percent chance
of Small Craft Advisory (SCA) level winds near Point Conception
during the afternoon and evening hours today and Saturday. Winds
will be SCA level Monday and Tuesday afternoon and evening.
Otherwise and elsewhere, conditions will remain below SCA level.

Across the Inner Waters north of Point Sal... SCA level winds are
likely Monday and Tuesday afternoon and evening, otherwise
conditions will remain below SCA level.

Across the Inner Waters south of Point Conception... Winds will be
SCA level across the western half of the Santa Barbara Channel
Saturday afternoon and evening, then again Monday and Tuesday.
Otherwise and elsewhere, conditions will remain below SCA level.


.BEACHES...23/300 AM.

The first south swell of the Spring season is expected to arrive
Friday morning and will continue through the weekend. The swell
heights will be 3 to 4 feet, and along with periods of 18-20
seconds should produce breakers of 3 to 6 feet, highest on south
facing beaches. There may be local max sets to 7 feet, and there
is a chance of surf 7 to 8 feet on south facing beaches of
northern LA County.


CA...Beach Hazards Statement in effect through Sunday morning for
      zones 40-41-87. (See LAXCFWLOX).



Light snow accumulations in the mountains could create driving
hazards Sunday night and into Monday.



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