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000
FXUS66 KLOX 060304
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
804 PM PDT Wed May 5 2021

.SYNOPSIS...05/715 PM.

A broad area of low pressure will approach the West Coast
tonight. Increasing onshore flow will bring a deeper marine layer
and cooling trend to the area into the weekend. Onshore flow will
weaken early next week and a slight warming trend is expected.

&&

.SHORT TERM (WED-SAT)...05/802 PM.

***UPDATE***

After a day of limited clearing for the beaches south of Point
Conception, the marine layer is already moving onshore from the
Santa Barbara South Coast and southward to the LA Coast. The split
channel satellite product (highlighting night fog) shows low
clouds pushing onto the Central Coast beaches as well, although not
showing at the airports yet. With a shallow, strong marine
inversion, expect to see dense fog in some areas during the
overnight hours into Thursday morning.

An elongated trough of low pressure over the Eastern Pacific will
approach the West Coast fairly quickly tonight into Thursday.
This will lower heights aloft, and cause onshore pressure
gradients to increase strongly across SW California. Expect
limited to no clearing for the beaches tomorrow. The valleys and
interior areas will be clear and a few degrees cooler, anywhere
from 3 to 8 degrees down from today`s highs. Look for a similar
amount of cooling on Friday, bringing highs closer to seasonal
normals. In addition, southwest to west winds will increase each
afternoon to evening period through interior canyons and the
Antelope Valley. These areas will likely see gusts between 35 to
45 mph, strongest in the usual places such as Lake Palmdale.

***From Previous Discussion***

With the cooling aloft associated with the trough and increasing
onshore flow the marine layer will deepen through the end of the
week. Probably not much tonight but certainly Thursday night and
Friday with clouds expected to push well into the valleys.
Following the trough passage Friday west to northwest winds will
kick up, especially Central Coast, southern SB County, and the
Antelope Valley. Low end wind advisories possible in any of those
areas Friday and Saturday. Clearing at the coast will continue to
be slow or non-existent, though better clearing is likely Friday
afternoon when the trough moves through.

.LONG TERM (SUN-WED)...05/203 PM.

There`s a fair amount of model disagreement with the upper level
pattern over the weekend into early next week, though impacts
either way are fairly minimal. Some of the ECMWF ensembles are a
little warmer with a more progressive pattern and faster height
rises over the West Coast while the GFS ensembles favor more of a
troughy pattern with a deeper low over the Idaho. The official
forecast leans towards a slightly warmer ECMWF solution but could
certainly see this going either way. In any case, no big heat
waves coming in the next week to ten days and overall a pretty
quiet pattern.

&&

.AVIATION...05/2356Z.

At 2300Z, the marine layer at KLAX was 1300 feet deep. The top of
the inversion was at 2300 feet with a temperature of 24 degrees C.

Moderate confidence overall in the coastal TAFs, with high
confidence for the valley and desert sites. For the Central Coast
sites, there is a 30% chance that VFR conditions will continue
through the period, otherwise timing of IFR cigs could be off by
+/- 2 hrs from TAF times. Similar concerns with timing differences
further south. There is a 20% chance cigs could lift to MVFR,
especially for the LA County sites.

KLAX...Moderate confidence in the 00Z TAF. Timing of IFR cigs
could differ by +/- 2 hrs from TAF time of 03Z. There is a 20%
chance cigs could lift to MVFR after 10Z. East wind component is
expected to remain below 5 kt.

KBUR...Moderate to high confidence in the 00Z TAF. There is a 20%
chance that IFR cigs will occur between 06Z to 15Z.

&&

.MARINE...05/653 PM.

For the Outer Waters, moderate to high confidence in forecast.
Conditions expected to remain below Small Craft Advisory (SCA)
levels through midday Thu. Good confidence in SCA level NW winds
spreading from N to S across the outer waters Thu afternoon and
evening, then continuing with at least at SCA levels thru Sun.
There is a 60-70% chance of Gale Force winds late Fri afternoon
through late Fri night, and a Gale Watch has been issued for that
time period. Winds will continue through the weekend with a chance
of Gale force gusts, especially Sun.

For the Inner Waters N of Pt. Sal, moderate confidence in
forecast. Winds and seas will remain below SCA levels thru Thu
morning. There is a 40% chance of SCA level winds Thu afternoon
and evening. SCA level winds are expected much of the time Fri
afternoon thru Sun, with a 30% chance of Gales force gusts Fri in
the late afternoon and evening.

For the Inner Waters S Pt. Conception, moderate to high confidence
in forecast. Expect winds and seas to remain below SCA levels
through Sun, except SCA conds are likely across the western SBA
Channel Fri afternoon thru Fri night, and there is a 30-40% of SCA
level winds there Sat afternoon into Sat evening.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory in effect from 2 PM Thursday to 5 PM PDT
      Friday for zones 670-673. (See LAXMWWLOX).
     Gale Watch in effect from Friday afternoon through late
      Friday night for zones 670-673-676. (See LAXMWWLOX).
     Small Craft Advisory in effect from 11 PM Thursday to 5 PM
      PDT Friday for zone 676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (SAT-WED).

No significant hazards expected.

&&

$$

PUBLIC...MW/Smith
AVIATION...Smith
MARINE...Smith
SYNOPSIS...MW/Smith

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