902
FXUS66 KLOX 021603
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
903 AM PDT Sun Jun 2 2024

.SYNOPSIS...02/332 AM.

Temperatures cooler than normal will linger today due to strong
onshore flow and a persistent marine layer. A warming trend will
establish through Thursday due to high pressure aloft building in
and weakening onshore flow. The warming trend will be most
pronounced away the coast into the interior valleys. Closer to
the coast, night through morning low clouds and fog with persist
with moderate to strong onshore flow continuing. Clouds may
continue to struggle to clear from the beaches.

&&

.SHORT TERM (TDY-TUE)...02/903 AM.

***UPDATE***

A weak trough passing through the region lifted and squeezed out
measurable rain across much of coastal Ventura into portions of
LA County this morning. Otherwise, low clouds and patchy fog was
prevalent except for elevations above about 3000 feet for southern
areas and 2000 feet up north. Gusty but mostly sub-advisory
northwesterly winds will continue through tonight for prone areas
mentioned in detail in the previous discussion.

Forecast challenge of today will be assessing competing factors in
the building ridge and interior heat through mid week with a
stubborn marine layer closer to the coast. The greatest
uncertainty in the upcoming heat impacts is the coastal valleys,
which are near the margin of these two competing factors. Although
being further inland and higher in elevation, the Antelope Valley
Excessive Heat Watch is also largely dependent on these competing
factors, leading to only moderate confidence of reaching
excessive heat criteria there. Will take a closer look at current
heat products with the afternoon package, but a quick look
suggests the current Excessive Heat Watch covers the region with
the greatest risk for excessive heat.

***From Previous Discussion***

The latest satellite imagery indicates low clouds and fog pushing
well into the coastal slopes of the mountains early this morning
as strong onshore flow and a persistent deep marine layer depth
remain in place. An eddy circulation continues to spin just
northwest of Santa Catalina Island, deepening the marine layer
depth to between 3000 and 3500 feet deep south of Point
Conception. To the north, the marine layer depth is closer to
around 2000 feet deep this morning as clouds are pushing into the
interior valleys of San Luis Obispo County. Patchy drizzle is
possible this morning and there is a good chance that an update
will issued to the forecast as some rain gages are starting to
pickup drizzle and ceilings at area airports are falling
slightly. A cooler weather pattern will linger today across much
of the coastal and valley areas, and these areas are likely below
to slightly below normal. Across the interior, temperatures will
start to warm as downsloping effects continue and onshore flow
starts to wane.

Gusty Sundowner winds are weakening across southern Santa Barbara
County this morning, but the northerly surface pressure gradient
will tighten over the coming days, potentially bringing another
couple rounds of Sundowner winds. With the gradient progged to be
slightly weaker today, wind advisory headlines were tabled for
this afternoon and tonight, but the gradient will tighten on
Monday night and could bring another round of advisory level
Sundowner winds. Gusty northerly winds will also develop through
the Interstate 5 Corridor and a wind advisory will likely be
needed for this area, as well. Marginally gusty winds could
possibly also extend into portions of the far western Antelope
Valley.

A warming trend will take shape over the coming days as 500 mb
heights climb. The developing northerly surface pressure gradient
and climbing heights will weaken the onshore push each day and
thin the marine layer depth some. The warming trend will become
more pronounced between Tuesday and Wednesday across the interior
portions as hot temperatures will develop across interior valleys
and adjacent foothills, but closer to the coast, a persistent
moderate to strong onshore push will remain and keep the warming
trend more moderate along the coast. The likely scenario will be
for a June Gloom pattern to keep low clouds and fog hugging the
beaches each afternoon, then the clouds will push back in during
the evening.

.LONG TERM (WED-SAT)...02/437 AM.

Temperatures will warm closer to critical levels for excessive
heat across the Antelope and San Luis Obispo Interior Valleys on
Wednesday. NBM solutions are suggesting a greater than 95 percent
chance of 100 degree high temperatures for KPMD and KWJF on
Wednesday, and high chance of temperatures reaching 105 degrees.
Chances for very hot temperatures are lower elsewhere but still
near excessive criteria across the Carrizo Plain. Given it will be
a close call, an excessive watch was added for Wednesday
afternoon and evening for Antelope and San Luis Obispo Interior
Valleys and adjacent foothill areas to highlight the potential for
excessive heat. As it is a marginal case, it would not be
surprising to see the watch either dropped or converted to an
advisory or warning. With the southeast flow aloft developing with
the ridge building into southeast California, it is possible that
this watch could also be extended into Thursday.

There is good amount of uncertainty for Thursday and Friday as EPS
and GEFS solutions offer up quite a bit of spread for high
temperatures. The chances for 100 degree temperatures fall in NBM
solutions into Thursday. There is a low chance that an early
start to the Southwest Desert Monsoon could develop across
southern California. This could cut into temperatures by
increasing cloud cover across these areas. In hinting at the
possibility, EPS cloud cover means do increase some between
Thursday afternoon and into next weekend.

With the ambient southeast flow aloft, PoPs and chance for
thunderstorms are non-zero for Thursday and Friday, but PoPs
still remain below mentionable levels during the afternoon and
evening. Pattern recognition would suggest the pattern consistent
with the monsoon developing but forecast ensemble and
deterministic solutions do not have a good handle on it. Stay
tuned for updates on this.

A cooling trend should develop for next weekend as troughing digs
into the region.

&&

.AVIATION...02/1231Z.

At 12Z at KLAX, the marine layer was 3500 ft deep. The top of the
inversion was at 5300 feet with a temperature of 18 deg C.

Almost a repeat of yesterday morning at this time. Low clouds and
fog in all coastal/valley areas, except the Cuyama Valley. Clouds
were affecting the coastal mountain slopes as well. There will be
local drizzle again this morning. The one difference is that cigs
are a bit higher today. Conds were mostly MVFR in coastal and
lower valley areas of L.A./VTU Counties and IFR to LIFR in the
remainder of the region in which it is cloudy. There will likely
be some VLIFR conds in the foothills and lower mountain slopes.
Clearing will likely be slow again today, with clouds scattering
out by late morning in the valleys and early afternoon across the
coastal plain. Clouds may linger thru the day at some beaches,
especially S of Pt. Conception thru the day. Low clouds and fog
will spread inland this eve, reaching the valleys (except the
Cuyama Valley) overnight. Conds should be mostly low MVFR to high
IFR, except LIFR/VLIFR in the foothills/mtns.

KLAX...Moderate confidence in 12Z TAF. There is a 20-30% chance
that there will be no clearing this afternoon. There is a 20%
chance of IFR cigs from 09Z-15Z Mon. There is a 20% chance of an
east wind component of 7-8 kt from 09Z-15Z Mon.

KBUR...Moderate confidence in 12Z TAF. There is a 20% chance that
cigs will not scatter out until 21Z or 22Z. There is a 20-30%
chance that cigs will arrive as early as 06Z Mon.

&&

.MARINE...02/855 AM.

In the northern outer waters zone (PZZ670), Small Craft Advisory
(SCA) level winds will likely increase to gales this afternoon
(70-80% chance), then continue into tonight. For the two southern
outer water zones (PZZ673/676) gale force wind gusts have
developed this morning and the Gale Warning is in effect for
these areas through later tonight. For all the outer waters zones,
SCA conds are expected late tonight thru Tue night. For the
northern two zones, there is a 50% chance of SCA conds Wed mainly
due to seas, then SCA conds are not expected Wed night/Thu. In the
southern outer waters, SCA conds are unlikely Wed thru Thu.

In the inner waters N of Pt. Sal, SCA level winds are likely
(70-80% chance) during the afternoon/eve hours today and Mon, with
a (40-50% chance) Tue afternoon/eve. Though winds will drop off
tonight/Mon morning, seas will likely remain near or at advisory
levels so the SCA is in effect thru Mon night. SCA conds are not
expected late Tue night thru Thu.

In the inner waters S of Pt. Sal, there is a 40% chance of SCA
winds in western portion of the SBA Channel during this
afternoon/eve, and a 50-60% chance Mon afternoon/eve. Otherwise,
conds over the inner waters should be below SCA levels thru Thu.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Excessive Heat Watch in effect from Wednesday morning through
      Wednesday evening for zones 344-381>383. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 3 AM PDT Tuesday for
      zone 645. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 PM PDT this afternoon
      for zone 670. (See LAXMWWLOX).
     Gale Warning in effect from 3 PM this afternoon to 3 AM PDT
      Monday for zone 670. (See LAXMWWLOX).
     Gale Warning in effect until 3 AM PDT Monday for zones
      673-676. (See LAXMWWLOX).

&&

$$

PUBLIC...Hall/Munroe
AVIATION...DB
MARINE...DB/Sirard
SYNOPSIS...Hall

weather.gov/losangeles

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