Duarte Weather

000
FXUS66 KLOX 190309
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
809 PM PDT Thu Apr 18 2019

.SYNOPSIS...18/710 PM.

An upper level low approaching the area will bring low clouds to
the coast tonight. Strong onshore flow will knock a few degrees
off of high temperatures Friday, but it will remain quite warm.
There will be a slight chance of a thunderstorm over the
mountains. Much cooler temperatures are expected Saturday as a
robust marine layer develops.

&&

.SHORT TERM (THU-SUN)...18/809 PM.

***UPDATE***

Overall, a very quiet evening across the forecast district. Latest
satellite and surface observations indicate partly cloudy skies
under some cirrus with low clouds/fog over the coastal waters.
Latest sounding data indicates marine inversion based around
600 feet.

Forecast-wise, main issue in the immediate short term will be the
potential for low clouds and fog. Latest model data still
indicates a weak eddy circulation developing overnight along with
weak onshore gradients. Additionally, H5 heights do lower a couple
of DMs overnight. So, will expect the stratus to develop across
the coastal plain overnight with the best chances for development
across the LAX coast and along the Central Coast. Do not
anticipate any significant deepening of the inversion, so stratus
will be confined to the immediate coast. With the inversion
expected to remain shallow, dense fog will be a concern. At this
time, not confident in the areal extent of dense fog and will not
issue any advisories at this time. However, a Dense Fog Advisory
may be needed overnight and Friday morning.

Otherwise, the immediate short term is unremarkable. Winds will
not be an issue overnight and overnight lows will be seasonable
for this time of year.

Current forecast looks good in the immediate short term. So, no
updates are planned at this time.

***From Previous Discussion***

A warm day across the area under light offshore flow and sunny
skies. Gradient trends are starting to reverse however and visible
imagery is showing what appears to be a shallow marine layer
approaching the outer channel islands and even the backside of
Catalina. Given the weak gradients and forecast soundings showing
a low inversion it looks like a decent set up for some dense fog
over some of our coastal waters and adjacent coastal zones (mainly
Central Coast and LA County).

Onshore trends continue Friday with models now showing close to
7mb LAX-DAG by afternoon so coast/valley temps should be cooler by
3-6 degrees, perhaps more on the Central Coast. An upper low that
is currently about 600 miles southwest of LAX is expected to
slowly move towards the coast Friday into Friday night. Models
ramped up instability parameters over the mountains, particularly
Ventura and SB Counties. However, moisture is seriously lacking
below 500 mb so whatever develops will be very high based. Can`t
rule out a stray thunderstorm so low pops have been introduced
into the forecast for our mountain areas bordering the Kern County
line. Main threat would be dry lightning given the lack of
moisture as well as gusty winds.

Even more cooling expected Saturday as a trough will move through,
creating a coastal eddy circulation and deepening the marine layer
to probably around 3000`, if not higher. LAX-DAG gradient expected
to increase to as much as 9mb by afternoon so it will probably be
a very slow clearing day south of Pt Conception with temps mostly
in the 60s. Possibly near advisory level winds in the Antelope
Valley.

Northwest flow will increase behind the trough Saturday and set up
a little Sundowner for srn SB County Saturday night. This may keep
the marine layer away from that area overnight but low clouds
should return elsewhere. With less of an eddy circulation Sunday
and weaker onshore flow low clouds should clear earlier with
maybe a couple degrees of warming, especially if clouds linger
through the afternoon Saturday.

.LONG TERM (MON-THU)...18/208 PM.

A ridge will build over the area Monday through Wednesday with
light offshore flow by Tuesday. Warmest days will be Tuesday and
Wednesday with highs again back into the 80s and possibly lower
90s. Cooling expected Thursday as we transition back to onshore
flow but still about 5 degrees above normal.

&&

.AVIATION...18/2308Z.

At 2300Z, the marine inversion at KLAX was based at 300 feet.
The top of the inversion was 1400 feet with a temperature
of 25 degrees Celsius.

Overall, low to moderate confidence in 00Z coastal TAFs and high
confidence in valley/desert TAFs. For tonight/Friday morning,
50% chance VLIFR/LIFR conditions at KLAX/KSMO/KLGB/KSMX and a 20%
chance at KSBA/KOXR.

KLAX...moderate confidence in 00Z TAF. There is a 50% chance of
VLIFR/LIFR conditions 10Z-17Z and MVFR conditions 17Z-20Z.

KBUR...high confidence in 00Z TAF with CAVU conditions expected.

&&

.MARINE...18/809 PM.

High confidence in winds staying below Small Craft Advisory (SCA)
through Friday afternoon, although local gusts to 20 KT are likely
in the San Pedro Channel in the afternoon hours. Moderate
confidence in dense fog with visibility under one mile becoming
more expansive tonight through Friday, especially along the Los
Angeles and Orange County coast lines.

West to northwest winds and short period seas will be increasing
Friday night through Sunday night. There is a 30 percent chance
for Gale Force winds between Point Conception and San Nicolas
Island Saturday afternoon and Sunday with Sunday looking more
likely than Saturday. Otherwise, widespread SCA conditions are
likely in most or all zones sometime over the weekend.

&&

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

&&

.HAZARD POTENTIAL OUTLOOK (SUN-THU).

No significant hazards expected.

&&

$$

PUBLIC...MW
AVIATION...RAT
MARINE...Kittell/RAT
SYNOPSIS...Stewart

weather.gov/losangeles

NWS LOX Office Area Forecast Discussion