Acton Weather

663
FXUS66 KLOX 231311
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
611 AM PDT Wed Apr 23 2025

.SYNOPSIS...23/333 AM.

A persistent marine layer with stronger onshore flow will keep a
cooler weather pattern in place through Saturday. Night through
morning low clouds and fog with drizzle will be a staple of the
forecast with clouds struggling to clear from beaches each day.
Gusty onshore winds are possible across the interior portions of
the area through the end of the week. A warming trend is expected
for next week.

&&

.SHORT TERM (TDY-FRI)...23/440 AM.

The latest fog product imagery shows low clouds and fog extending
into the coastal slopes of the mountains across the Southland and
into the interior valleys of San Luis Obispo County. Earlier
AMDAR soundings from KLAX around 07Z indicated a marine layer
depth near 2100 feet deep, but that was several hours ago, and the
marine layer has deepened substantially since. From looks of the
satellite imagery combined with NAM BUFR time height sections, the
marine layer depth is close to 3500 feet deep currently. If NAM
BUFR time height sections play out as advertised, the marine layer
depth should top out around 4000 feet deep later this morning.
With the marine layer depth deepening substantially, drizzle is
possible as weak dynamics with a shortwave trough move over the
region and interact with the deep marine layer cloud deck this
morning. Some rain gauges in southern Santa Barbara County are
starting to pick up a few tips due to heavy drizzle.

A deep marine layer depth is likely to continue to remain in place
over the coming days as broad troughing remains anchored along
the California coast and strong onshore flow will remain intact. A
cooler pattern will linger into late week with temperatures below
seasonal normals. Weak dynamics aloft will continue to scrape the
area and bring the possibility of night through morning drizzle.

Across the interior portions of the area, stronger onshore flow
will bring much breezier to windier conditions during the
afternoons and evenings. A wind advisory was added for the western
Antelope Valley foothills for this afternoon and this evening where
gusts up to 45 mph are possible. Isolated gusts to 55 mph cannot
be ruled out near Lake Palmdale. With similar onshore pressure
gradients developing over the coming days, additional wind
advisory headlines may be needed.

By Friday, an elongating trough in the Gulf of Alaska will enter
the region while splitting off from the flow aloft. This cutoff
trough will likely deepen the marine layer depth between Friday
and Saturday to turn it into a deep moist layer up to around 7000
to 8000 feet deep on Friday night. This will be plenty deep enough
to produce night through morning drizzle or light rain across the
region. Mountain showers seems to be a high probability given the
pattern and favorable flow pattern.

.LONG TERM (SAT-TUE)...23/441 AM.

The cutoff trough will approach the California coastline on
Saturday morning as the marine layer mixes out into a deep moist
layer. The forecast ensemble members introduce a majority of the
perturbations with light rain across the area. EPS members are
the wettest relative to the GEFS and CMC ensemble members. Almost
all of the EPS ensemble members have precipitation across the
region with amounts lessening as one heads south. EPS QPF means
suggest a quarter inch or less, with a high chance of values
between 0.25 and 0.50 inch for San Luis Obispo County. Meanwhile,
GEFS and CMC keep the forecast more inline with night through
morning drizzle. Given the cutoff trough, the current forecast
generally keeps NBM values for PoPs, while skewing PoPs higher
along the coastal slopes of the mountains.

Temperatures will be much cooler than normal on Saturday with most
areas being 5-12 degrees below normal. Temperatures in the mid
50s to mid 60s will be common across the coastal and valley areas.
Experimental data analysis on the NBM forecast suggests KLAX and
KOXR potentially seeing record low maximum temperatures on
Saturday. Local records versus the forecast indicate otherwise,
but near record low maximum temperatures will be possible on
Saturday.

A warming trend for much of next week is expected as cluster
analysis still favors an upper-level ridge of high pressure
building into the West Coast. Anomalously high heights seem more
plausible across the Pacific Northwest, but the pattern will still
likely create above normal temperatures with less marine layer
low cloud coverage.

&&

.AVIATION...23/1305Z.

At 12Z at KLAX, the marine layer was 3400 feet deep. The top of
the inversion was at 4700 feet with a temperature of 14 C.

Clouds were widespread across the region, and have pushed into all
areas except for the Antelope Valley, the mountains above 4000
feet, and the far interior valleys of SLO County. Conds were
mostly MVFR to high IFR, except LIFR to VLIFR in the higher
valleys, foothills and lower mountain slopes, with local LIFR
cigs on the Central Coast and in the Santa Ynez Valley.

Expect skies to clear by late morning in the valleys and early
afternoon across interior portions of the coastal plain. Cigs will
likely linger all day the coast, especially south of Pt.
Conception. Expect widespread low clouds tonight, with MVFR cigs
in most areas, except for IFR to VLIFR conds once again in the
higher valleys, foothills and lower mountain slopes.

KLAX...Moderate confidence in TAF. There is a 30% chance that cigs
will scatter out between 20Z and 02Z. There is a 30% chance of an
east wind component of 7 to 9 kt from 10Z-17Z Thu.

KBUR...Moderate confidence in TAF. Cigs may arrive linger until as
least as 21Z today.

&&

.MARINE...23/542 AM.

In the Outer Waters, moderate confidence in the forecast. Winds
will be close to low-end Small Craft Advisory (SCA) levels at
times thru Fri night. SCA conds are likely (70% chance) in the
northern zone (PZZ670) this afternoon thru late tonight, while
there is a 40% chance of SCA level winds elsewhere. There is a 40%
chance of low end SCA level winds anywhere across the outer
waters Thu afternoon thru Fri night/Sat morning. SCA level conds
are likely (70% chance) Sat afternoon thru Sun night.

For the Inner Waters north of Pt. Sal, moderate confidence in
the forecast. There is a 40% chance of SCA level winds during the
afternoon/eve hours today thru Fri. SCA conds are likely (60%
chance) during the afternoon/eve hours Sat and Sun.

For the Inner Waters south of Pt. Conception, moderate confidence
in the forecast. There is a 40% chance of SCA level winds during
the afternoon/eve hours today thru Fri in western portions of the
Santa Barbara Channel, then SCA conds are likely there (60%
chance) during the afternoon/eve hours Sat and Sun. Otherwise,
SCA conds are not expected thru Sun night.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory in effect from noon today to 9 PM PDT this
      evening for zone 381. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect from 3 PM this afternoon to 3
      AM PDT Thursday for zone 670. (See LAXMWWLOX).

&&

$$

PUBLIC...Hall
AVIATION...DB
MARINE...DB
SYNOPSIS...Hall

weather.gov/losangeles

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