Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000
FXUS66 KLOX 230645 AAA
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
1145 PM PDT Tue Jun 22 2021

Updated aviation section

.SYNOPSIS...22/805 PM.

A general cooling trend will continue through Thursday as onshore
flow remains in place. There will also be a slight chance of
showers and thunderstorms on Wednesday across the San Gabriel
Mountains and eastern Antelope Valley. For the weekend, high
pressure aloft will build over the West Coast, bringing a
significant warming trend to the area.

&&

.SHORT TERM (TUE-FRI)...22/804 PM.

***UPDATE***

The marine inversion early this evening ranged from around 1100
ft deep at LAX to near 2000 ft deep at VBG. Low clouds cleared off
the coast this afternoon, but some low clouds were moving to the
immediate Central Coast early this evening. There were also plenty
of mainly mid level clouds moving into VTU/L.A. Counties from the
S early this evening. The low clouds should expand along the
Central Coast and move inland overnight. S of Point Conception,
low clouds are expected to develop overnight and expand inland to
some of the adjacent vlys by late tonight, altho more mid level
clouds will likely move in and could help to disrupt the low cloud
coverage. Otherwise, skies will be clear to partly cloudy across
the region overnight. Gusty SW winds up to 30 mph or so were
noted across the Antelope Vly and portions of the coast early
this evening thanks to good onshore gradients to the N and E.
These winds are expected to diminish overnight.

***From Previous Discussion***

Overall, 12Z models in good synoptic agreement through the short
term period. At upper levels, low will continue to wobble just off
the Central CA coast through the period. Near the surface,
moderate onshore gradients will continue.

Given the upper level flow pattern, main issue in the short term
is mid/high level moisture drifting northward across Southern CA.
Main concern will be Wednesday. Models indicate an increase in
PWATs across LA county along with increasing instability. Looks
like enough moisture and instability to warrant a slight chance of
TSTMs Wednesday afternoon over the San Gabriel Mountains and
eastern sections of the Antelope Valley. Also, will need to watch
for any potential of this activity to develop across the San
Gabriel Valley, but right now that potential is below mentionable
levels. Any thunderstorms that do develop will likely produce some
brief downpours, but gusty winds and dry lightning will be main
concerns with any development.

Otherwise, the forecast through Friday is just a continued
exercise in trying to predict the marine layer stratus. H5 heights
lower a bit through Thursday which would allow for some deepening
of the marine inversion. So with the continued onshore flow, will
continue with idea of rather widespread stratus/fog across the
coastal plain and into the coastal valleys. Stratus should
dissipate nicely each day as inversion does not appear too strong.
As for temperatures, expect minor day-to-day fluctuations,
generally a little cooler Wednesday/Thursday with some warming on
Friday. Do not anticipate any significant wind issues through the
period. There will likely be some locally gusty northerly winds
across the Santa Ynez Range Wednesday night and Thursday night,
but nothing expected to approach advisory levels.

.LONG TERM (SAT-TUE)...22/202 PM.

For the extended, 12Z models continue to exhibit decent synoptic
agreement. At upper levels, strong ridge will build over the
western states. Near the surface, weak to moderate onshore
gradients are forecast to continue.

Forecast-wise, this pattern sets the stage for another round of
significant heat for the area. The center of the upper level
ridge will be centered over the Pacific Northwest through the
period. So, our area will avoid the worst heat. However, it still
is expected to be very warm with Sunday likely the warmest day. In
fact on Sunday, interior sections (valleys to the deserts) are
expected to have temperatures ranging 100-110 degrees. There is a
good chance that some heat products (advisories or warnings) will
be needed for the mountains, deserts and interior SLO county
Sunday and Monday. The continued onshore flow will keep the
coastal plain cooler, but temperatures will still be well above
seasonal normals.

As for clouds, will continue with some mention of night and
morning stratus/fog for the coastal plain, given the continued
onshore gradients. However, would not be surprised to see the
weekend stratus forecast being overdone, given the strength of the
upper level ridge. For the middle of next week, the synoptic
pattern will result in an easterly upper level flow over the area.
So, there is the potential for an easterly wave to bring a threat
of showers/thunderstorms. Too far out to have any level of
confidence in that potential, but the situation will be monitored
closely over the coming days.

&&

.AVIATION...23/0643Z.

At 05Z, the marine layer depth was around 900 feet deep at KLAX.
The top of the marine inversion was around 1500 feet with a
temperature around 24 degrees Celsius. There was another
inversion up to around 3100 feet.

Low-to-moderate confidence in the current forecast for coastal
and valley terminals. Moderate-to-high confidence in the current
forecast for desert terminals. The highest chance for any IFR to
MVFR conditions will be for terminals north of KSBA. There is a
high (60-70 percent) chance of IFR to MVFR conditions at coastal
terminals south of KSBA. There is a lesser chance for Los Angeles
County valley terminals. An earlier arrival of VFR conditions
should be expected, especially for Los Angeles County terminals.
There is a low-to-moderate (20-40 percent) chance of ceilings
between 6000 and 12000 feet at eastern Los Angeles County
terminals after 13Z.

KLAX...There is a 60 percent chance of MVFR conditions between
09Z and 16Z. VFR conditions should develop around 16Z. There is a
20 percent chance of ceilings between 6000 and 12000 feet at KLAX
between 15Z and 23Z.

KBUR...There is a 30 percent chance of IFR to MVFR conditions
between 13Z and 15Z. There is a 40 percent chance of ceilings
between 6000 and 12000 feet between 14Z and 22Z.

&&

.MARINE...22/1259 PM.

High confidence that winds and seas will remain below Small Craft
Advisory (SCA) level through Thursday morning. By late Thursday
afternoon, there is a 30-40% chance of SCA level NW winds from
Point Conception to San Nicolas Island, strongest near the Channel
Islands. NW winds are expected to strengthen across the waters on
Friday leading to moderate confidence in widespread SCA level
winds from the Central Coast to San Nicolas Island through the
weekend.

Patchy drizzle or light rain is possible across all the waters
tonight through Wednesday morning.

&&

.BEACHES...22/630 PM.

A combination of an elevated long-period south swell and higher
than normal astronomical tides will lead to minor tidal overflow,
elevated surf, and dangerous, strong rip currents across beaches
of Los Angeles and Ventura Counties this evening through Saturday.
The most likely time for tidal overflow to occur will be during
the evening hours. Each evening, high tide will range between 7
and 7.5 feet, with the highest tides expected on Wednesday and
Thursday.

A Beach Hazards Statement will remain in effect from this evening
through Thursday evening for the Los Angeles and Ventura County
beaches, with a good chance it will be extended through Saturday.
Pooling of water is possible around high tide, and there may be
minor flooding of beach parking lots. Minor tidal overflow is also
possible across beaches of the Santa Barbara County South Coast.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement in effect through Thursday evening
      for zones 40-41. (See LAXCFWLOX).
PZ...NONE.

&&

.HAZARD POTENTIAL OUTLOOK (FRI-TUE).

Hot temperatures are expected to return, and especially for inland
areas, starting Saturday and will likely continue for at least
several days beyond that. This will likely bring heat-related
illness concerns to inland areas.

&&

$$

PUBLIC...Thompson/Sirard
AVIATION...Hall
MARINE...Sweet
BEACHES...Sweet/Phillips
SYNOPSIS...RAT/Sirard

weather.gov/losangeles


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