Duarte Weather

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FXUS66 KLOX 230358
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
858 PM PDT Sat Sep 22 2018

.SYNOPSIS...22/457 PM.

Temperatures will be around normal into next week with fair
skies, except for an overnight coastal marine layer that may
spread to some valleys each morning. An upper level trough will
brush the area Sunday into Monday for cooler temperatures,
followed by ridging and warming Tuesday through Thursday. An
approaching trough will bring another cooling trend by next
weekend.

&&

.SHORT TERM (SAT-TUE)...22/856 PM.

The latest satellite imagery shows an upper-level trough of low
pressure along the Washington State coast and stretching out to
the southwest, while an upper-level ridge of high pressure remains
anchored over the Sonoran Desert. The trough will advance on the
region through Monday, passing to the north. Southwest flow aloft
will remain in place and keep onshore flow at the surface and some
semblance of a persistent marine layer in place along the
Southern California coast. Increasing southwest flow aloft through
Sunday should bring a tad stronger onshore push on Sunday and
more developed marine layer stratus deck into Sunday morning.
Marine layer induced low clouds and fog, already pushing into the
Central Coast, should engulf the entire coastal sections by
daybreak Sunday or slightly thereafter. Some intrusion of the low
clouds and fog should also make it into the lower valley areas
such as Santa Ynez and San Gabriel Valleys. A late push cannot be
ruled out into the Cahuenga Pass late tonight or just after
daybreak Sunday. With a bit stronger onshore flow, a decent cool
down looks on tap into Sunday. The forecast has been updated to
tweak temperatures and marine layer stratus coverage into Sunday
morning.

***From Previous Discussion***

Monday we`ll see another few degree cool down before heights rise
and temps jump up a few degrees again on Tuesday.

Little change expected in the night through morning low clouds
through the short term as most areas will clear out for sunny
afternoons, all except some beach areas. As far as wind goes,
there`s nothing of note outside of the usual breezy southwest
winds each afternoon across the AV we get with our onshore flow
pattern. There`s just enough of a negative SBA-SMX pressure
gradient that there may be localized breezy north winds the
western portion of the SBA south coast.

.LONG TERM (WED-SAT)...22/121 PM.

Heights and thickness peak on Wednesday as the upper ridge axis
sits right along the west coast and to bring the warmest day of
the 7-day forecast. This will also help to limit the overnight low
clouds to the immediate coastal areas and should see rapid
clearing during the day. Cooling then kicks in on Thursday when
models break down the ridge and start moving the closed upper low
that`s currently well to our west eastward and joining up with the
broader open trough that digs into the Pacific NW on Saturday.

GFS and EC disagree slightly on the upper flow pattern by
Saturday, the cooler GFS maintaining the closed low as it moves
it into the west coast, and a deeper solution than the ensemble
mean, while the EC absorbs the closed low into the broader trough
pattern and has a weaker southwest upper flow pattern over
forecast area. But ultimately the difference in the forecast is
just a few degrees (EC not as cool as the GFS). The official
forecast splits the difference and cools temps down on Saturday,
but not as dramatic as with the operational GFS solution. Low
clouds within the coastal plain should be similar each night,
possibly a little more inland extent by Saturday as heights lower
each day from Wednesday on. No real wind issues expected in the
long term period.

&&

.AVIATION...23/0103Z.

At 00Z, the marine layer depth was around 750 feet deep at KLAX.
The top of the marine inversion was around 1600 feet with a
temperature near 27 degrees Celsius. There was another inversion
up to around 2600 feet.

Moderate to high confidence in the current forecast. Higher
confidence in categories, less confidence in timing. LIFR to IFR
conditions will spread into coastal and lower valley terminals
through 13Z. The best chance of predominant IFR conditions will be
for terminals south of KOXR. Timing could be up to 2 hours
earlier than forecast, or up to 5 hours later than forecast.

KLAX...IFR conditions will spread into KLAX as early as 03Z or as
late as 10Z. There is a 50 percent of MVFR conditions developing
as soon as 13Z or as late as 15Z. VFR conditions should develop
around 17Z, but there is a 30 percent chance that IFR to MVFR
conditions delay until as late as 21Z. Any east winds that could
develop between 10Z and 16Z should remain less than 5 knots.

KBUR...VFR conditions are expected throughout the period. There is
a 10 percent chance of IFR conditions between 11Z and 16Z. No wind
impacts are expected at this time.

&&

.MARINE...22/857 PM.

A marginal Small Craft Advisory continues for the southern two-
thirds of the outer waters through late tonight. Pockets of
advisory level winds with short- period seas should be expected
through at least evening south of Point Sal and out to 60 NM
offshore.

High confidence in marginal advisory level wind and sea
conditions developing across the outer waters off the Central
Coast Sunday and Sunday night. Winds should diminish and be below
advisory levels Monday and Tuesday.

Pockets of dense fog with visibility one mile or less will remain
through at least tonight and possibly into late Sunday morning,
especially north of Point Conception and through the Santa Barbara
Channel.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory in effect from 3 PM Sunday to 3 AM PDT
      Monday for zone 670. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PDT Monday for zone
      673. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PDT Sunday for zone
      676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (TUE-SAT).

No significant hazards expected.

&&

$$

PUBLIC...Hall/Jackson
AVIATION...Hall
MARINE...Hall
SYNOPSIS...Smith

weather.gov/losangeles

NWS LOX Office Area Forecast Discussion