567
FXUS66 KLOX 311756 AAA
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
1056 AM PDT Fri May 31 2024

.SYNOPSIS...31/903 AM.

A cooler than normal weather pattern will continue across much of
the area through the weekend as a persistent marine layer remains
in place with strong onshore flow. A warming trend is expected
next week, especially for the interior portions of the area
Wednesday and Thursday as onshore flow weakens.

&&

.SHORT TERM (TDY-SUN)...31/908 AM.

***UPDATE***

The marine layer has deepened by around 500 feet compared to
yesterday and clouds have responded by pushing farther inland and
higher up the coastal mountain slopes. Onshore gradients are
stronger as well so all signs are pointing towards a cooler day
for coast and coastal valleys with slower (if any) clearing of
low clouds. Farther inland across the mountains and interior areas
it will sunny and warm with highs in the upper 80s to mid 90s
with some breezy late afternoon winds.

***From Previous Discussion***

The latest local 3-km WRF time height sections suggest the marine
layer deepening additionally tonight into Saturday morning, and
Saturday night into Sunday morning as broader troughing aloft will
reinforce strong onshore flow. As the latest model solutions have
not handled the modeling of the marine layer depth well, the
forecast trends a little more aggressive with the low cloud field
over the coming days. Weak omega values in the mixed layer in the
latest 3-km local WRF solutions suggest the threat of drizzle
could be higher over the next couple of mornings, but high-
resolution multi-model ensemble solutions downplay the drizzle
threat to some extent. Considering there are a few locales with
drizzle this morning, the forecast may need to lean more toward
the deterministic solution of the local 3-km WRF. Future shifts
may need to add drizzle mentions to the forecast for Saturday
morning and again for Sunday morning if this signature continues
into the coming model runs.

With strong onshore flow in place and strengthening additionally
today, a cooling trend will develop through the weekend as clouds
will struggle to clear from the land mass each day. The forecast
goes with clouds hugging the beaches and immediate coast each day,
but with KLAX-KDAG surface pressure gradients progged to approach
8 mb onshore, there is a moderate chance that clouds may linger
longer across some interior coast and valleys today.

Marginally gusty winds will develop across the interior valleys,
such as the Antelope Valley and adjacent foothills each afternoon
and evening. The latest forecast guidance suggest winds increasing
to near advisory levels, but the forecast holds off on issuing any
advisories at this point to wait for more data. The latest NAM-WRF
solutions trend closer to advisory level winds developing across
the Antelope Valley foothills on Saturday afternoon and evening,
but the latest forecast ensemble members still lean toward the
winds being more on the marginal side.

.LONG TERM (MON-THU)...31/450 AM.

A warming trend will establish on Monday as high pressure aloft
starts to build in over the region. A developing northerly
surface pressure gradient will develop gusty northerly winds, most
likely affecting the Interstate 5 Corridor on Monday night into
Tuesday. EPS solutions bring wind gust means to near 50 mph at
KSDB, likely producing the strongest winds at sites like Whitaker
Peak and Poppy Park. Gusty Sundowner winds cannot be ruled out
either as pattern recognition in some of the deterministic
solutions suggest a wind event could develop across southern Santa
Barbara County.

EPS ensemble members continue to suggest a warming trend turning
more significant for Wednesday and Thursday as a cutoff upper-
level trough sits south of the border off the Baja California
coast and ridging aloft noses into southeast California.
Confidence is high for a hot weather pattern developing away from
the coast but lower for the coastal areas due to the persistence
of onshore flow. NBM solutions give about an 80 percent chance of
KPMD and KWJF hitting 100 degrees for the first time this year.
Temperatures break away from NBM solutions, going warmer for the
middle portion of next week across the interior portions of the
area.

&&

.AVIATION...31/1755Z.

At 17Z at KLAX, the marine layer was 2500 ft deep. The top of the
inversion was at 3800 feet with a temperature of 19 deg C.

Moderate to hi confidence in the 18Z TAFs. Low clouds over the
coast and adjacent vlys will clear to near the coast by late this
morning, with MVFR conds likely persisting thru the afternoon at
KOXR, KCMA, KSMO and KLAX. IFR/MVFR cigs will likely spread back
inland tonight and affect all coast and adjacent vly airfields and
continue into late Sat morning. The timing of the dissipation and
onset of low clouds may be off +/- an hour or two, with the
largest uncertainty of the onset of low clouds tonight for KBUR
and KVNY.

For KPRB, KWJF and KPMD, there is hi confidence VFR conds will
continue thru the TAF period. Gusty SW winds will affect the
desert airfields for most of the fcst period.

KLAX...Moderate to hi confidence in the 18Z TAF. MVFR cigs will
likely persist this afternoon with only a 20% chance of the low
clouds scattering out. There is a 50% chance of IFR cigs early
this evening, otherwise MVFR cigs will continue tonight thru Sat
afternoon. No significant east wind expected.

KBUR...Moderate to hi confidence in the 18Z TAF. VFR conds are
expected for the most part into this evening, then IFR cigs should
move in by 07Z. The cigs will improve to MVFR by 11Z and continue
into late Sat morning. The timing of the onset of the low clouds
and changes in flight cats tonight may be off +/- an hour or two.

&&

.MARINE...31/849 AM.

In the northern outer waters zone (PZZ670), winds and seas are
expected to reach Small Craft Advisory (SCA) levels (80% chance)
this afternoon thru early Sat afternoon. Elsewhere in the outer
waters, winds and seas are expected to remain below SCA levels
thru early Sat afternoon, with just a 20% chance of SCA level
gusts in the central zone (PZZ673) this afternoon and evening.

There is a 50% chance of gales in the northern zones (PZZ670/673)
Sat afternoon thru Sun night. A Gale Watch has been issued. SCA
level winds are likely (70% chance) in the southern zone (PZZ676)
Sat afternoon thru Sun night, with just a 20% chance of gales.
SCA conds are likely (70% chance) in the outer waters Mon-Tue.

In the inner waters N of Pt. Sal, there is a 30% chance of SCA
level winds this afternoon/evening. SCA conds are likely
(60-70% chance) during the afternoon/eve hours Sat thru Mon.

In the inner waters S of Pt. Sal, there is a 40% chance of SCA
winds in western portion of the SBA Channel Sat afternoon/eve.
SCA level winds are likely there (60-70% chance) Sun
afternoon/eve. Otherwise, SCA conds are not expected.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory in effect from 3 PM this afternoon to 3
      PM PDT Saturday for zone 670. (See LAXMWWLOX).
     Gale Watch in effect from Saturday afternoon through late
      Sunday night for zones 670-673. (See LAXMWWLOX).

&&

$$

PUBLIC...MW/Hall
AVIATION...Sirard
MARINE...DB/Sirard
SYNOPSIS...Hall

weather.gov/losangeles

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