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000
FXUS66 KLOX 240335
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
835 PM PDT Tue Apr 23 2024

.SYNOPSIS...23/749 PM.

Strong onshore flow and a deep marine layer will maintain much
cooler than normal temperatures across much of Southwest
California through at least Friday. Areas of night through
morning fog and drizzle are expected across the coast, valleys,
and foothills, with only partial afternoon clearing. Warmer
weather is expected by the weekend into early next week.

&&

.SHORT TERM (TUE-FRI)...23/834 PM.

***UPDATE***

The only real forecast challenge for the evening update is the
evolution of the marine layer clouds and potential for drizzle.
With fairly widespread drizzle from the coast and inland to the
interior mountain slopes last night into this morning, see no
reason why that will not happen again. Heights aloft will lower
overnight as a closed low system approaches the coast, and
onshore flow will continue, so expect good inland progression of
low clouds in the deep marine layer. With the added boost of good
lift over the hills, expect to see drizzle fairly widespread
again, with patches of heavy drizzle likely.

Clearing potential for Wednesday is another interesting issue.
Today we saw reverse clearing, with coastal areas scattering out
while clouds lingered over the valleys and hills. Would not be
surprised to see another day of reverse clearing Wednesday, with
gusty onshore winds through the interior passes and canyons into
the Antelope Valley. There is also a small chance that the marine
layer will deepen enough that the layer falls apart, with clearing
everywhere. As for winds, the 00Z gradients from LAX to Daggett
will be somewhat stronger Wednesday afternoon so expect gusts
between 35 to 45 mph to be common, and 50 mph at Lake Palmdale.

***From Previous Discussion***

There is low confidence in how the marine layer will behave
Wednesday now that the it`s so deep. The most likely outcome is
another day very similar to today, with (not so) low clouds
reforming overnight in most areas then another reverse clearing
pattern tomorrow. Most of the high res forecast models favor this
scenario along with some pockets of drizzle, especially near the
south facing foothills. However, the next upper low will be
quickly approaching the area Wednesday with an arrival expected
Wednesday night into Thursday. So some additional cooling aloft is
expected that could either reinforce the marine layer or
potentially weaken it enough to where it clears out more
completely in the afternoon. In any case, temperatures will
remain well below normal with some breezy but again sub-advisory
level winds across interior areas.

With the arrival of the upper low Wednesday night into Thursday
morning, chances for more widespread drizzle or light rain
increase. But with northwest flow following the trough passage
Thursday afternoon that should help generate better clearing.
Increasing west to northwest winds expected in the afternoon and
evening with wind advisories possible for some coastal areas and
interior areas as well.

Yet another trough quickly follows for Friday, though models
have been tracking this one more inland. Temperatures will remain
on the cool side with some gusty west to northwest winds but
minimal chances for precip, except possibly across the northern
mountains and interior SLO County. Still low confidence in the low
cloud coverage but the most likely outcome is for less clouds
across coast and valleys. Temperatures will remain below normal
but should be 3-6 degrees warmer than Thursday.

.LONG TERM (SAT-TUE)...23/153 PM.

The warming trend that started Friday is expected to continue into
early next week with weakening onshore flow and minimal, if any,
marine layer stratus. Temperatures should be back to normal
levels over the weekend and sneaking a few degrees above normal by
Monday. Some cooling then expected Tuesday that will likely
continue through the rest of next week as yet another cold upper
low drops out of the Pac NW.

&&

.AVIATION...24/0229Z.

At 00Z at KLAX, the marine inversion was based at 3200 feet. The
top of the inversion was 6200 feet with a temperature of 11 C.

Low to moderate confidence for coastal/valley TAFs and high
confidence for desert TAFs. Lower confidence for coastal/valley
sites due to uncertainties in timing of flight category changes.
Expecting cigs to eventually return to the coasts/valley sites and
to

KLAX...Moderate confidence, due to uncertainty in timing of cig
arrival and dissipation. No significant easterly wind component
is expected.

KBUR...Moderate confidence, due to uncertainty in timing of cig
arrival and dissipation.

&&

.MARINE...23/236 PM.

For the Outer Waters, moderate to high confidence in current
forecast. Today through Wednesday night, high confidence in winds
and seas remaining below Small Craft Advisory (SCA) levels. For
Thursday through Sunday, high confidence in combination of SCA
level winds and seas. Across the two southern outer water zones
(PZZ673/676), there is a 50-60% chance of Gale force winds
Thursday and Friday afternoon/night.

For the Inner Waters north of Point Sal, moderate to high
confidence in current forecast. Today through Wednesday night,
high confidence in winds and seas remaining below SCA levels.
For Thursday through Friday, there is a 60-80% chance of SCA level
winds, especially in the afternoon and evening hours. For
Saturday and Sunday, there is a 40-50% chance of SCA level winds,
especially in the afternoon and evening hours.

For the Inner Waters south of Point Conception, moderate to high
confidence in current forecast. Today through Wednesday morning,
high confidence in winds and seas remaining below SCA levels,
expect for a 60% chance of SCA level winds for the SBA Channel
this evening/night. Wednesday afternoon/night, there is a 60-80%
chance of SCA level winds for all the southern inner waters. Winds
will pick back up Thursday morning for the SBA channel (with a
20-30% chance of Gale force winds on Thursday), and reaching the
waters south of Point Mugu Thursday afternoon. SCA wind or seas
will last much of the time Thursday through Saturday.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory in effect until 9 AM PDT Wednesday for
      zone 650. (See LAXMWWLOX).

&&

$$

PUBLIC...MW
AVIATION...Phillips
MARINE...RAT/Schoenfeld
SYNOPSIS...MW/Smith

weather.gov/losangeles

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