Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 05/30/23

Area Forecast Discussion...UPDATED

National Weather Service Los Angeles/Oxnard CA

 902 PM PDT Mon May 29 2023

.SYNOPSIS...29/839 PM.

A strong onshore flow pattern will maintain the deep and
persistent marine layer for most of this week. Night through
morning low clouds and fog, with limited afternoon clearing, will
also continue. Areas of drizzle or light rain are expected during
the night and morning hours through Tuesday. There will be a
slight chance of thunderstorms in the mountains Tuesday afternoon
and evening. Temperatures will be below normal much of the week,
with some warming possible for late week into the weekend.

&&

.SHORT TERM (MON-THU)...29/846 PM.

Slightly better clearing today for some areas but many areas
still remained mostly cloudy. Current satellite imagery showing
low clouds into portions of the coastal slopes and foothills of
the Antelope Valley. Current ACARS data showing a deep moist
layer to around 4000 feet. This combined with the strong onshore
flow pattern (LAX-Daggett peaking at +8 mb) resulted in cooler
temperatures and gusty onshore winds today across the interior,
with the Antelope Valley only climbing to the mid 70s. Wind gusts
between 30 and 40 mph occurred across the Antelope Valley this
afternoon and evening, with isolated gusts around 50 mph near Lake
Palmdale. Some mid level moisture and instability also generated
some afternoon buildups over the local mountains, but no storms
detected on radar.

Closed upper level low pressure system off the Central Coast
will drift southeastward across the forecast area on Tuesday.
This pattern will maintain the strong onshore flow pattern and
deep moist layer to around 5000 feet as depicted by the 00z NAM
cross sections. As a result, there will likely be areas of drizzle
late tonight into Tuesday morning. With many of the high resolution
models and HREF ensembles showing some light QPF, there is a
slight chance (15-20%) of measurable rain late tonight into
Tuesday morning for much of the region, especially the foothills
and coastal slopes.

With the closed low pressure system moving over the region on
Tuesday, there will be an influx of colder air aloft with 500 mb
temperatures falling to around -18 degrees Celsius near the core.
This will lead to increased instability over the mountains,
especially Santa Barbara and Ventura Counties, where lifted index
values are between -4 and -7, and CAPE values range between
400-700 J/kg. As a result, there is a slight chance (15-20%) of
thunderstorms over the mountains on Tuesday afternoon/evening,
with the highest chances over Ventura and Santa Barbara counties.
There is also a 5-10 percent chance of showers and thunderstorms
over non-mountain areas on Tuesday afternoon. With fairly weak
flow aloft, storms will likely be slow moving, increasing the
chances for heavy downpours. There is also the chance of small
hail and gusty winds with thunderstorms.

***From previous discussion ***

Wednesday stratus forecast a tricky one with a much weaker marine
inversion and the upper low east of the area by that time. Will
continue to with the gloomy forecast with the possibility of
drizzle but could also see earlier clearing happening with the
weaker inversion in place and being on the back side of the low.

Consensus models indicate a couple degrees of warming Thursday,
though this may be overdone. Models indicate a weak trough over
the area and still 8-10mb of onshore flow. With those factors
it`s hard to see much clearing from the coast/valleys. The
pattern certainly favors a below normal temperature day with slow,
if any clearing.

.LONG TERM (FRI-MON)...29/152 PM.

There does appear to be good consensus in a warming trend by
Friday and continuing through at least Saturday as ensembles have
been advertising a ridge developing over California. Temperatures
are expected to rise 5-10 degrees by Saturday, finally getting
back to with a degree or two of normal for the first time in
several days. There`s also a corresponding decrease of onshore
flow by around 2mb which should help temperatures climb and allow
the marine layer to clear sooner. By Sunday and Monday models show
a weak upper low undercutting the ridge and bringing cooler
temperatures. This solution is supported by virtually all of the
model clusters, though around 30% of them are weaker with the
trough. Models also show increasing onshore flow at this time as
well so there is good confidence in a cooling trend for early next
week.

&&

.AVIATION...29/2337Z.

At 2335z at KLAX, the marine layer 4000 ft deep. The top of the
inversion was 4800 feet with a max temperature of 11 degrees C.

For coastal and valley sites, moderate confidence in latest TAFs
with most areas seeing vfr/mvfr cigs tonight through Tuesday,
however onset of cigs could be +/-2 hours from TAF timing.
Low pressure system and deep moist layer will bring areas of
drizzle and a 15-20 percent chance of measurable rain to
coastal/valley areas later tonight into Tuesday. There is
also a 20 percent chance of thunderstorms on Tuesday afternoon
across the local mountains, with a 10 percent chance being
in the vicinity of KWJF and KPMD.

KLAX...Moderate confidence in TAF. VFR/MVFR cigs expected
tonight through Tuesday, with a 20 percent chance of SCT
conditions by Tuesday afternoon. There is a 15-20 percent
chance of light rain late tonight into Tuesday. No significant
easterly wind component is expected.

KBUR...Moderate confidence in TAF. VFR/MVFR cigs expected
tonight through Tuesday, with a 20 percent chance of SCT
conditions by Tuesday afternoon. There is a 15-20 percent
chance of light rain late tonight into Tuesday.

&&

.MARINE...29/857 PM.

For all waters, high confidence in current forecast through
Wednesday. For this period winds and seas are expected to remain
below Small Craft Advisory (SCA) levels.

Moderate confidence that Wednesday afternoon widespread SCA level
winds, and borderline SCA level seas will spread over the outer
waters and the western portion of the Santa Barbara Channel. The
gusty SCA winds and choppy seas are expected to persist through
Thursday night, then beginning to subside Friday into Saturday.

&&

.BEACHES...29/858 PM.

Long-period south swell originating will continue across the
coastal waters through Tuesday. Strong rip currents and elevated
surf of local 3 to 5 feet will be possible through Tuesday. There
will be the potential for hazardous rip currents and a Beach
Hazards Statement may be needed.

&&

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

&&

$$

PUBLIC...Gomberg/MW
AVIATION...Gomberg
MARINE...Smith
BEACHES...Sweet/Smith
SYNOPSIS...DB/SMITH

weather.gov/losangeles

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