Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 031054

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
354 AM PDT Sat Jun 3 2023

.SYNOPSIS...03/353 AM.

High pressure aloft will bring a warming trend with better
clearing of morning low clouds and fog today, then a weak upper-
level low pressure system will bring slight cooling on Sunday. A
stronger low pressure system will bring much cooler weather Monday
through Wednesday, along with a slight chance of showers and
thunderstorms Monday through Wednesday afternoon. A cooler air
mass is likely to remain through the rest of next week with
extensive low clouds.


.SHORT TERM (TDY-MON)...03/348 AM.

The latest satellite imagery shows low clouds and fog well-
entrenched along the Central Coast of California, while low clouds
are struggling to form across the Southland this morning. A much
thinner marine layer depth is in place over the northern areas,
evident by cloud ceilings early this morning. To the south, a
remnant deep marine layer depth and a weak marine inversion is
contributing to lack of low cloud coverage this morning. The
latest AMDAR sounding from KLAX indicate a 2500 foot deep marine
layer depth across the Southland, down from around 3600 feet deep
a few hours earlier. While ridging aloft is starting to clamp
down on the marine layer and thin it, the marine inversion will
remain weak for the current time. It should tighten and strengthen
as the morning progresses. Better coverage should start to form
and take shape as we move towards daybreak.

With ridging aloft in place, onshore flow should continue to
weaken today. Areas outside of the marine layer depth will likely
warm several degrees over yesterday`s values. Some coastal valley
areas will warm to just near normal to a few degrees above normal
today, while the interior valleys, mountains, and desert will
warm to about 3-6 degrees above normal for this time of year.
Clearing should still be decent for most areas today, except
clouds may hug the beach areas into the afternoon.

After the ridge axis moves over the region later today, onshore
flow should start to strengthening again and set up a cooling
trend into early next week. An upper-level trough near 34N and
143W will advance toward Point Conception through Monday. Slight
cooling is expected for Sunday, but a deepening marine layer and
much stronger onshore flow will bring more significant cooling for
Monday. NAEFS ensemble pressure gradients strengthen KLAX-KDAG
and KSMX-KBFL pressure gradients through Monday, then there some
uncertainty beyond that. Low clouds and fog will become well-
entrenched across the area and struggle to clear from the land
mass each day. Night through morning drizzle will be part of the
forecast, possibly measuring or turning into light rain across
portions of the area.

With the trough position and the amount of instability with around
the trough circulation, there is a non-zero chance of showers and
thunderstorms just about everywhere in the area from Sunday
afternoon into midweek next week. PoPs were nudged a little higher
as the latest EPS solutions increase precipitable water means to
between 150 and 200 percent of normal for this time of year, or to
almost three standard deviations above the mean. 1000-500 mb
lapse rates tighten to near 7-8 degrees Celsius per kilometer,
while K-index values approach 40 degrees Celsius during Sunday
afternoon and evening, and again on Monday afternoon and evening.
Showers and thunderstorms were expanded into some of the coastal
and valley areas primarily north of the Los Angeles-Ventura
County line as a difluent flow pattern develops for periods of
time across the area. With the slow steering flow, there is a
chance that some of the storms could be slow-moving and increase
the potential for flooding.

.LONG TERM (TUE-FRI)...03/350 AM.

The deterministic solutions indicate that the low pressure system
will be slow to move over the region, wobbling around the
southwest California into midweek. Some of the ensemble members
solutions maintain the threat a deep marine layer depth with drizzle
and isolated showers and thunderstorms over the area. Pattern
recognition would suggest a similar premise. A cooler weather
pattern with a deep marine layer depth will likely remain in
place. While there is some uncertainty in strength of the flow
pattern, there is a high chance that strong onshore flow will
remain intact. Clouds will likely struggle to clear from the land
mass each day through at least Wednesday.

NAEFS surface pressure gradients seem to keep strong onshore flow
in place toward late week despite the upper-level trough vacating
the region. Ensemble members keep a cooler air mass with lower
heights across the region into late next week. All this should
lead to cooler than normal temperatures with a continued deep
marine intrusion. A June Gloom pattern is likely to continue with
clouds struggling to clear each day.



At 0900Z, the marine inversion at KLAX was based at 2400 feet.
The top of the inversion was 4100 feet with a temperature of
17 degrees Celsius.

Overall, moderate confidence in 12Z coastal/valley TAFs and high
confidence in desert TAFs. Lower confidence for coastal/valley
sites due to uncertainty in marine layer behavior south of Point
Conception. There is a 30-40% chance of IFR to MVFR CIGs
developing from KSBA southward 12Z-18Z.

KLAX...Moderate confidence in 12Z TAF. There is a 30-40% chance of
MVFR or IFR CIGs 12Z-17Z. For tonight, high confidence in return
of IFR CIGs, but only moderate confidence in timing (could be +/-
2 hours of current forecast). No significant easterly wind
component is expected.

KBUR...Moderate confidence in 12Z TAF. There is a 20% chance of
IFR CIGs 13Z-17Z. For tonight, there is a 20% chance of IFR CIGs
after 10Z.


.MARINE...03/334 AM.

For the Outer Waters, high confidence in current forecast. Small
Craft Advisory (SCA) level winds will continue through tonight
(with the strongest winds this afternoon and evening). For Sunday
through Wednesday, winds and seas will remain below SCA levels.

For the Inner Waters north of Point Sal and the Inner Waters south
of Point Conception, high confidence in current forecasts. Today
through Wednesday, winds and seas are expected to remain below SCA

For Monday afternoon and evening, there is a slight chance of


PZ...Small Craft Advisory in effect until 3 AM PDT Sunday for
      zones 670-673-676. (See LAXMWWLOX).




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