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000
FXUS66 KLOX 191621
AFDLOX

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

.SYNOPSIS...19/914 AM.

Strong onshore flow in place will continue the cooling trend into
today. Extensive low clouds and fog will struggle to clear as a
deep marine layer depth remains in place into tonight. A warming
trend is expected over the weekend as weak high pressure develops.
Significant cooling along with a deep marine layer are expected
next week as low pressure moves into the area. In addition, there
is a slight chance of showers or drizzle late next week.

&&

.SHORT TERM (TDY-SUN)...19/923 AM.

***UPDATE***

The marine layer has deepened to 2500 feet across the LA Basin,
sloping down to around 1700 feet along the Central Coast in
response to a weak trough over the area. Low clouds have poured
into the Santa Clarita Valley and up through some of the canyons
leading into the south facing mountains. With onshore flow up to
5.4mb to the east, at the very least it`s going to be a very slow
burnoff today, and possibly not clearing at all in some areas.
Needless to say temperatures today will be much cooler, especially
for inland areas that have been in the 70s and 80s recently.

Better clearing expected tomorrow as the trough is replaced by a
weak ridge through the weekend.

***From Previous Discussion***

A deep marine layer 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...19/1554Z.

At 15Z over LAX, the marine layer was 2500 feet deep with an
inversion top at 5200 feet and 15 degrees Celsius.

Moderate to high confidence in generally persistence forecast
(similar flight categories and timing for the next 24 hours as the
previous). While ceilings will be most common over the next 24
hours, low confidence on timing and coverage of any clearing.

KLAX...Moderate confidence in OVC015-025 being most common through
Saturday 18Z. Low confidence on when and if clearing will occur
today, but the window for that is 20-02Z. 30 percent chance of no
clearing in that window, 40 percent chance of 2-4 hours of
clearing, and 30 percent chance of 5+ hours of clearing. Southeast
winds of 4-6 knots is likely through 19Z today, and 10-18Z
Saturday, but the chance of exceeding 8 knots is less than 20
percent.

KBUR...Moderate confidence in OVC012-020 being most common
through Saturday 18Z. Moderate confidence on 3-6 hours of
clearing today in the 19-06Z window, with a 20 percent chance of
any clearing lasting less than 3 hours.

&&

.MARINE...19/855 AM.

High confidence in winds staying below 20 knots through Saturday
morning, except for winds locally to around 20 knots this evening
between Point Conception and Santa Rosa Island. Seas will remain
small as well.

High confidence in Small Craft Advisory (SCA) winds and choppy
seas forming quickly Saturday afternoon for the Central Coast
offshore waters down to San Nicolas Island. These winds will
persist through the weekend. There is a 40 percent chance of SCA
winds for the nearshore Central Coast waters and a 20 percent
chance for the western half of the Santa Barbara Channel. All
areas will see building short period seas from these winds.

Winds will weaken Monday and Tuesday, but will stay near SCA south
of Point Conception with choppy seas over most areas continuing.

&&

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

&&

$$

PUBLIC...MW/Hall
AVIATION...Kittell
MARINE...RK
SYNOPSIS...MW/Hall

weather.gov/losangeles

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