033
FXUS66 KLOX 240611
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
1111 PM PDT Mon Sep 23 2024

.SYNOPSIS...23/523 PM.

Low clouds and fog will affect coastal areas through the week
with near normal temperatures. Dense fog is likely near the coast
through at least Tuesday. Inland temperatures will remain above
normal through the week, warmest through Tuesday. Otherwise,
quiet weather is expected through the week.

&&

.SHORT TERM (MON-THU)...23/846 PM.

***UPDATE***

In response to visibilities dropping across the region this
evening, the Dense Fog Advisory has been extended to cover all
beaches through the coastal plains, into the eastern San Fernando
Valley and across the San Gabriel Valley. The shallow marine layer
and areas of dense fog will advance inland overnight, and will
yield hazardous driving conditions into Tuesday morning.

Light onshore flow maintained clouds at many coasts for much of
the day. Thus there was a dramatic temperature difference between
the beaches (highs upper 60s to low 70s) and the valleys (highs in
the upper 80s up to 103).

Besides the expanded Dense Fog Advisory, there were no other
major changes to the forecast with this update.


***From Previous Discussion***

Low clouds and fog remain parked along the coast this afternoon,
with webcams showing very low visibilities still on the Central
Coast. With no clearing trend apparent to the north, and little
change expected to the onshore push and marine layer depth
tonight, went ahead and issued a Dense Fog Advisory for the
Central Coast and Santa Ynez Valley for later this evening through
Tuesday morning. Other coastal areas may need to be added based
on how the marine layer evolves tonight. Inland of the coasts,
temperatures are up 5 to 10 degrees, with a handful of 100 degree
readings already around the current hot spot around the Santa
Clarita Valley.

Temperatures should be very similar on Tuesday compared to today
with little change to the upper level pattern and an onshore
pressure trend holding off until later in the day. Over the
coastal areas, any trends tomorrow will be based on the
unpredictable behavior of the marine layer. There is good reason
to believe however that temperatures will lower further from Santa
Barbara to Malibu as an the south-to-north pressure trends up,
which usually spells little to no cloud clearing for that area.

A weak low pressure area, currently about 250 miles west of the
Central Coast will change little through tomorrow, then pull
closer towards San Fransisco on Wednesday, before settling back to
just off the coast by Thursday. This will result in some cooling
to the region, most noticeable over the mountains and valleys.
This should also kick off some Sundowner winds with gusts in the
25 to 40 mph range. The change in the upper level pattern and the
Sundowner winds will modify the low cloud pattern and behavior.
Expecting the marine layer to deepen, which will limit some of the
dense fog threat, but the winds will likely bring more hours of
clearing and a later arrival from Santa Barbara to Malibu.

.LONG TERM (FRI-MON)...23/220 PM.

The weak low just off the coast will push further off the coast
on Friday, as a peak-a-boo high to the east pushes closer to
California. This, along with some indications of weaker onshore
flow may bring a few degrees of warming to inland areas.

While fairly benign conditions will continue Saturday into next
week, some of the finer details are a bit muddled. All of the
projections show a trough moving through the Pacific Northwest,
which would pull the weak low parked just off our coast through
southwest California and to the east. A fair amount of the
projections (mix of EPS and GEFS solutions) have this all
happening sometime over the weekend, while the slim majority (mix
of EPS GEFS Canadian) keep the status quo through the weekend with
the change happening Monday or Tuesday. Until that happens,
expected little change to the conditions on Friday, with near
normal temperatures and breezy Sundowners. After that shift
happens, expect further cooling, marine layer expansion, and gusty
onshore flow over the interior areas.

&&

.AVIATION...24/0558Z.

At 0450Z at KLAX, the marine layer was 1200 ft deep. The top of
the inversion was near 2200 ft with a temperature of 31 deg C.

High confidence in desert and KPRB TAFs.

Moderate confidence in remainder of TAFs LIFR conds are likely
through 15Z-16Z. Intermittent 1/4SM vsbys are likely at most
sites. VFR conds may arrive +/- an hour from fcst time. There is
a 20 percent chc of a few more hours of VFR conds in the afternoon
than forecast and a 30 percent chc that there will be no clearing
(except for KCMA and KLGB where there is good confidence in VFR
conds in the afternoon).

KLAX...Moderate confidence in TAF. TAF VIS will reflect sfc vis
not tall tower vis. Intermittent vis of 1/4SM is likely (60
percent) through 15Z. There is a 30 percent chc of no clearing and
a 20 percent chc of SCT conds lasting to 23Z. High confidence in
no significant easterly wind component.

KBUR...Moderate confidence in TAF. There is a 30 percent chc of
1/4SM FG conds through 15Z. Good confidence that SCT-SKC conds
will arrive by 1630Z.

&&

.MARINE...23/813 PM.

High confidence in the current forecast through early Thursday,
then moderate confidence thereafter. Winds and seas will remain
below Small Craft Advisory (SCA) levels through early Thursday,
except for a low-to-moderate (20-30 percent) chance of local SCA
level W-NW wind gusts in the vicinity Point Conception, near Point
Dume and into the San Pedro Channel each afternoon and evening
through Wednesday. There is a moderate (40-50 percent) chance of
SCA level winds Thursday afternoon through Friday for the waters
beyond 10 NM offshore along the Central Coast southeast to San
Nicolas Island. Additionally, there is a 30 percent chance of SCA
level seas across the outer waters building over the weekend,
especially over the northern outer waters where models indicate
seas building to around 10 feet Saturday night into Sunday.

A shallow marine layer over the coastal waters is expected to
bring areas of dense fog to the coastal waters tonight into
Tuesday morning, with at least patchy dense fog possible again
Tuesday night through Wednesday morning. A marine weather
statement is currently in effect through noon Tuesday.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Dense Fog Advisory in effect until 10 AM PDT Tuesday for
      zones 340-341-346>350-354>356-362-366>368-373-548. (See LAXNPWLOX).
PZ...NONE.

&&

$$

PUBLIC...Kittell/Schoenfeld
AVIATION...Rorke
MARINE...Hall/Lund/Smith
SYNOPSIS...Kittell/Smith

weather.gov/losangeles

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