222
FXUS66 KLOX 041052
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
352 AM PDT Tue Jun 4 2024

.SYNOPSIS...04/350 AM.

High pressure aloft over the region will continue a warming trend
through Wednesday, most pronounced away from the coast. Weakening
onshore flow will thin the marine layer depth some and keep clouds
confined to coastal and valley areas. A hot air mass will remain
in place across the interior valleys for much of this week, with
temperatures well above normal for this time of year. Closer to
the coast, the warming trend will be moderated due to persistent
night through morning low clouds and fog and a moderate to strong
onshore flow.

&&

.SHORT TERM (TDY-THU)...03/825 PM.

Weak upper level impulse bringing considerable high clouds to
the region this evening, disrupting the low cloud field
underneath. This upper level impulse bringing some upper level
northwest wind support tonight, brining stronger and more
extensive northwest winds to the region. Areas under a wind
advisory through tonight include the I-5 corridor, northern
Ventura county mountains, Antelope Valley western foothills, and
southwest Santa Barbra county. These areas have seen wind gusts in
the 40 to 50 mph range this afternoon and evening, and expected
to continue through much of the night, but weakening by morning.
By Tuesday morning, the upper level wind flow will shift to the
northeast with northeast winds mostly confined to the mountains,
deserts, and interior valleys. The strongest northeast winds on
Tuesday morning will be focused across the LA county mountains
where gusts of 25 to 40 mph can be expected. The breezy conditions
will coincide with hotter and drier weather, leading to an
increased risk for grass fire activity on Tuesday across the
interior.

The combination of upper level ridging and weakening onshore flow
will lead to a decreased marine layer depth across much of the
region. However, it will remain relatively deeper across LA
county due to an eddy circulation. As a result, marine layer
low clouds generally expected to be confined to coastal and
coastal valley locations. Current warming trend on track for
Tuesday, then heat peaking on Wednesday and Thursday. This early
season heatwave will be confined to the interior, with coastal
plan and coastal valley locations being modified by the
persistent onshore wind flow and marine layer influence. Current
excessive heat watches for the Antelope Valley and San Luis Obispo
County interior valleys will likely be converted to warnings.

*** From previous discussion.

Temps will turn several degrees warmer than yesterday for many
areas, with afternoon highs a few degrees above normal for much of
SLO/SBA Counties and into the Antelope Vly, but remain a few
degrees below normal elsewhere. Highs in the in the inland coast,
vlys and lower mtns will range from the mid 70s to mid 80s over
SLO/SBA Counties to the 70s to around 80 for VTU/L.A. Counties,
except in the upper 80s to lower 90s in the lower mtns and
Antelope Vly.

Flat upper level ridging will prevail over the forecast area
through tonight, with H5 heights around 585-586 dam. Upper level
ridging will build strongly into srn CA on Tue, with H5 heights
rising to 589 dam, then rise further thru Wed to around 590 dam.
The upper level ridging will linger over srn CA Wed night and Thu
with H5 heights continuing around 590 dam.

The high clouds will continue to move over the region tonight
into Tue with partly cloudy skies overall. However, marine layer
low clouds should still affect the Central Coast although will
likely clear out Tue morning as NE flow sets up. S of Point
Conception, marine layer clouds and fog will affect the coast and
into some of the adjacent vlys, but not quite as far inland as the
last few nights. For Tue night and Wednesday, low clouds and fog
will affect the coast S of Point Conception with little inland
penetration to the adjacent vlys. On Wednesday morning, low
clouds should move from the S and affect parts of the Central
Coast as well. Low clouds and fog will move to coastal areas
rather quickly Wed evening, then spread just a little inland Wed
night into Thu morning. Due to an expected shallow and strong
marine inversion below 1000 ft, it looks like patchy dense fog
will be possible with the low clouds. Otherwise, mostly clear
skies overall can be expected across the region thru Thu, except
low clouds may linger at the beaches especially on Wed and Thu.

As a side note, the upper level flow is forecast to turn E-SE for
Wed and Thu, with some mid-level moisture possibly moving into the
area. It would not be out of the question for some afternoon cu
buildups to occur over the mtns, especially the VTU County mtns.
There is even a non-zero chance of a shower or thunderstorm on Thu
for the mtns but is not reflected in the fcst due to the low chance
(10 percent or less).

Breezy to gusty offshore flow will is expected night and morning
hours mainly over SLO/SBA Counties Tue night thru Thu morning.
Otherwise, normal diurnally driven breezy winds are expected
overall Tue thru Thu.

Temps will heat up thru Wed thanks to the building upper level
high pressure system. For Tue, hi temps should be 3-13 deg above
normal for many areas, increasing to 5-15 deg above normal Wed
except 14-17 deg above normal for the Antelope Vly and SLO County
interior vlys, where there is an Excessive Heat Watch in effect.
Altho temps will cool a couple of degrees on Thu, they will remain
well above normal and the Excessive Heat Watch will continue for
the SLO County interior Vlys and Antelope Vly. The hottest temps
will be in these areas with highs expected to be in the 95-108
range overall. Please see the latest Non-Precipitation Weather
Message (LAXNPWLOX) for further details on the expected heat and
for the current Wind Advisories.

.LONG TERM (FRI-MON)...03/223 PM.

The GFS and EC mean ensembles are in fairly good agreement for
the extended period. The western periphery of an upper level high
over AZ/NM will linger on Fri over srn CA, then should weaken some
on Sat before some upper level troffiness moves into the area Sun
and Mon.

There will still be a non-zero chance of an afternoon shower or
thunderstorm in the mtns on Fri, otherwise dry weather will
prevail during the extended period. Marine layer clouds will
affect the coast and some adjacent vlys each night and morning Fri
thru Sun, then the marine inversion should deepen enough for Sun
night and Mon for widespread low clouds to move well inland over
the region and up to the coastal slopes. Otherwise, mostly clear
skies can be expected thru the period.

A cooling trend is expected Fri thru Mon. Temps will still be a
few degrees above normal Fri, then cool to several degrees below
normal by Mon, except still a few degrees above normal for the
interior vlys and deserts.

&&

.AVIATION...04/0021Z.

At 2355Z at KLAX, the marine layer was 2800 ft deep. The top of
the inversion was at 4500 feet with a temperature of 22 deg C.

Considerable high clouds disrupting the low cloud field this
afternoon. Expect a shallower marine layer tonight, with clouds
likely confined to coastal and lower valley areas. An eddy
circulation will likely keep marine layer depth relatively
higher across LA County where cigs will most likely in MVFR
category (with 20% chance of IFR category). Otherwise, looking
for IFR to LIFR cigs at other coastal/valley TAF sites, with
20% chance of VLIFR conditions at KSMX.

KLAX...Moderate confidence in the 00Z TAF. MVFR cigs likely
to impact KLAX much of tonight into Tuesday morning, with
a 20% chance of IFR cigs. There is a 20% chance of an east wind
component of 7-8 kt from 09Z-17Z Tue.

KBUR...Moderate confidence in the 00Z TAF. Most likely that
MVFR cigs will return late tonight and early Tuesday morning,
with a 20% chance of IFR cigs and also a 20% chance that
skies will remain clear.

&&

.MARINE...04/351 AM.

In the outer waters, Small Craft Advisory (SCA) level winds and
seas are expected to drop below SCA levels in the southern zone
(PZZ676) this evening, the central zone (PZZ673) late tonight, and
the northern zone (PZZ670) Wed evening. There is a 30% chance that
SCA conds will linger into Wed in the central zone (PZZ673). From
late Wed night thru Sat, SCA conds are not expected. However, in
the northern zones (PZZ670/673), there is a 20-30% chance of
advisory level seas Thu/Thu night, and SCA level winds Sat.

In the inner waters N of Pt Sal, SCA level NW winds are expected
(80% chance) this afternoon/eve. Then, SCA conds are not
expected late tonight thru Fri.

In the inner water S of Pt Sal, SCA conds are not expected thru
Sat. There will be SE winds late each night and morning thru Fri,
with isolated winds to 15 kt thru passages and channels, and
between islands.

Steep, choppy seas will affect the outer and northern waters thru
at least Wed night, pushing into western portions of the SBA
Channel at times.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory in effect from 10 AM Wednesday to 8 PM PDT
      Thursday for zones 343-344. (See LAXNPWLOX).
     Excessive Heat Warning in effect from 10 AM Wednesday to 8 PM
      PDT Thursday for zones 381>383. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect from 3 PM this afternoon to 9
      PM PDT this evening for zone 645. (See LAXMWWLOX).
     Small Craft Advisory in effect until 9 PM PDT Wednesday for
      zone 670. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PDT Wednesday for
      zone 673. (See LAXMWWLOX).
     Small Craft Advisory in effect until 9 PM PDT this evening
      for zone 676. (See LAXMWWLOX).

&&

$$

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

weather.gov/losangeles

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