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000
FXUS66 KLOX 191122
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
422 AM PDT Fri Apr 19 2024

.SYNOPSIS...19/253 AM.

Strong onshore flow in place will bring a cooling trend into
today. Extensive low clouds and fog will struggle to clear today
as a deep marine layer depth remains in place into tonight. A
warming trend is expected over the weekend as weak ridging builds
in aloft, then a weak trough will dig south into the region
through late next week. A cooling trend is forecast with a very
deep marine layer. There is a slight chance of showers or drizzle
late next week.

&&

.SHORT TERM (TDY-SUN)...19/423 AM.

A deep marine layer depth is in place across the region this
morning as a weak upper trough of low pressure sits west of Point
Conception. Clouds are extending well into coastal slopes north
of Point Conception and are making a run down the Cuyama Valley
this morning. South of Point Conception, most coastal and valley
locations are cloudy at this time, and clouds are starting to
enter the Santa Clarita Valley from the west. Very patchy drizzle
has developed across portions of the area this morning as weak
dynamics with the trough interact with the deep marine layer
depth.

The latest AMDAR soundings from KLAX indicate the marine layer
depth has deepened to near 2300 feet deep, and some additional
deepening is likely to occur as a weak upper-level trough remains
upstream from the area. The trough, currently sitting near 34.7N
and 123.3W, or about 150 miles west of Point Conception, will
continue to move over the region through today. With low clouds
well-entrenched this morning, clouds will struggle to clear from
the land mass and keep a cooler maritime air mass in place today.
At best, only partial afternoon clearing will occur at the coast.
The beaches will likely be shrouded in clouds throughout today.

A deep marine layer depth will likely remain intact through
tonight then slowly shrink into Saturday. A reverse clearing day
looks to be setting up for Saturday with cold air advection
developing across the northern areas. Clouds may not completely
clear from the Southland, but the clouds will break up some and
give a bit more sunshine. Some semblance of a marine layer depth
or a remnant moist layer will likely linger into Saturday night
and Sunday and keep some low clouds and fog in the forecast for
the current time. EPS ensemble member cloud means agree with this
idea in clearing out the northern areas for Saturday night and
Sunday but keep some clouds lingering from Santa Barbara to the
southeast into the South Coast Basin.

With less clouds and a retracting marine layer depth for Saturday
and Sunday, a warming trend should take shape. Almost all members
of the EPS, GEFS, and CMC ensembles agree with warming for the
weekend. A significant warm up is taking shape for Sunday,
especially across the valleys of the Southland and into the
Antelope Valley. Of note, portions of the Antelope Valley could
see its first 90 degree day of 2024. Typically, Palmdale and
Lancaster see their first 90 degree days around April 30th. EPS
members suggest high temperatures having a no chance of KPMD and
KWJF hitting the first 90 degree mark, but NBM solutions indicate
a 10 percent chance of a 90 degree on Sunday for Lancaster, and a
30 percent chance of highs hitting 90 degrees at Palmdale. The
forecast maintains NBM values at 88 degrees for both for now, but
it worth also noting that ECMWF tabular forecast guidance suggest
90 and 91 degrees for Lancaster and Palmdale respectively.

.LONG TERM (MON-THU)...19/418 AM.

The ridge axis will slowly drift over the area between Sunday and
Monday while flattening. Southwest flow aloft redevelops on Monday
and onshore flow should strengthen through Thursday. All ensemble
members have a cooling trend establishing by Tuesday across the
region, with significant cooling forecast for the Antelope Valley
and interior portions of the area between Monday and Wednesday as
an upper-level trough digs into the region.

Fairly high confidence exists in cooling for the period with a
deepening marine layer depth. The main question seems to be if
enough instability and moisture makes it into the region for
precipitation to develop in the period. EPS precipitable water
means approach 0.80 inch for KVBG and KLAX, which is more than
ample to produce precipitation. EPS 500 mb height means do not
dip quite as low as historical values for KLAX, but GEFS and CMC
height means are closer to the climatological values of 564
decameters. For the current time, the forecast breaks away from
NBM values after Wednesday night to emphasize a slight chance of
showers by Thursday. Run-to-run ensembles continue to trend wetter
with each model run, but EPS and CMC ensemble members seems to
wetter relative the GEFS solutions. Heavy measurable drizzle or
light rain cannot be ruled out. The most probable amounts would be
a tenth of an inch or less.

&&

.AVIATION...19/1014Z.

At 0900Z, the marine inversion at KLAX was based at 2300 feet.
The top of the inversion was 4100 feet with a temperature of
16 degrees Celsius.

Overall for 12Z TAF package, moderate confidence in coastal and
valleys TAFs, but high confidence in desert TAFs. For coastal and
valley sites, timing of flight category changes could be +/- 3
hours of current forecasts. There is a 30% chance that current
MVFR/IFR conditions may not dissipate this afternoon for coastal
sites.

KLAX...Overall, moderate confidence in 12Z TAF. Timing of
dissipation of MVFR conditions could be +/- 2 hours of current 21Z
forecast with a 30% chance that MVFR CIGs will not dissipate at
all this afternoon. For tonight, high confidence in return of MVFR
CIGs, but moderate confidence in timing (could be +/- 2 hour of
current 02Z forecast). No significant easterly wind component is
expected.

KBUR...Overall, moderate confidence in 12Z TAF. Timing of
dissipation of MVFR conditions could be +/- 2 hours of current 19Z
forecast with a 15-20% chance that MVFR CIGs will not dissipate
at all this afternoon. For tonight, high confidence in return of
CIG restrictions, but only moderate confidence in timing (could
be +/- 2 hour of current 06Z forecast) and flight category (40%
chance of IFR CIGs instead of MVFR CIGs).

&&

.MARINE...19/306 AM.

For the Outer Waters, high confidence in current forecast. Through
Saturday morning, winds and seas will remain below Small Craft
Advisory (SCA) level. For Saturday afternoon through Sunday night,
combination of SCA level northwest winds and seas are expected.
For Monday and Tuesday, winds and seas will remain below SCA
levels.

For the Inner Waters north of Point Sal, high confidence in
current forecast. Today through Saturday morning, winds and seas
will remain below SCA levels. From Saturday afternoon through
Sunday evening, SCA level winds can be expected in the afternoon
and evening hours. For Sunday night through Tuesday, winds and
seas will remain below SCA levels.

For the Inner Waters south of Point Conception, moderate to high
confidence in current forecast. Other than a 50-70% chance of SCA
level winds across the western half of the Santa Barbara Channel
Sunday afternoon/night, winds and seas are expected to remain
below SCA levels for the souther Inner Waters through Tuesday.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...NONE.

&&

$$

PUBLIC...Hall
AVIATION...RAT
MARINE...RAT
SYNOPSIS...Hall

weather.gov/losangeles

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