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439
FXUS66 KLOX 220438
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
938 PM PDT Tue May 21 2024

.SYNOPSIS...
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21/937 PM.

Increasing onshore flow with a persistent marine layer will
likely bring a return of May Gray at the beaches on Wednesday.
Night through morning low clouds and fog will continue across the
coastal and valleys, struggling to clear from the beaches during
the afternoon. An upper-level trough of low pressure will dig
south through Friday bringing a deepening marine layer, stronger
onshore flow, and night through morning drizzle Thursday and
Friday. Some clearing and warming is possible over the holiday
weekend.
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&&

.SHORT TERM (TUE-FRI)...
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21/936 PM.

Broad upper-level troughing remains intact over the West this
evening. The latest water vapor imagery indicates a weak boundary
moving south across central California this evening. Cold air
advection is scouring some clouds away from the Central Coast,
but it appears there is not enough strength in the advective
pattern to completely scour the marine layer stratus. Clouds
continue to cling to the central California coast this evening and
confidence is waning in more clearing on Wednesday. The latest
model solutions suggest the cold air advective pattern fading away
overnight. With onshore flow increasing on Wednesday and 1000-500
mb thickness values climbing across the area, signs point toward a
return of clouds hugging the coast on Wednesday. The forecast
trends a little more pessimistic for the low clouds coverage for
Wednesday and now keeps a mention of low clouds partially
clearing at the beach areas.

With low clouds and fog likely holding more firmly across the
area, temperatures were nudged slightly cooler along the coast and
closer to persistence. It would not be shocking to see a bit more
cooling introduced into the forecast at the coast as the latest
NAM-WRF solutions suggest a 3 mb onshore trend in the pressure
gradients.

*** FROM PREVIOUS DISCUSSION ***

Thursday, the wide upper level trough will intensify, and onshore
gradients will increase. Marine layer clouds will likely linger
longer into the day, especially near the coast, and this will
cause temperatures to trend downward by around 1 to 3 degrees.
Highs will be 3 to 6 degrees below normal, locally up to 10
degrees.

Friday a shortwave trough, embedded in the larger troughing
pattern, will quickly pass over the region. This disturbance may
support night to morning marine layer drizzle for coastal areas
and a 5-10% chance of afternoon showers/thunderstorms for interior
mountains. Significant onshore flow and a cooling airmass aloft
will drop temperates to 6 to 10 degrees below normal (locally up
to 13 degrees). Friday will likely be the coldest day of the
forecast period, with daytime highs in the low- to- mid 60s for
coasts, around 65-70 for valleys, and mid 70s for deserts.

.LONG TERM (SAT-TUE)...21/226 PM.

The GFS and ECMWF are in good agreement for the weekend into
early next week. By Saturday, the shortwave trough will have
exited the region, with the board upper level trough remaining.
Typical deep marine layer clouds are likely to extend across the
coasts and valleys, with minimal chances of clearing for coastal
areas. Onshore gradients will maintain gusty winds across the
interior areas during afternoon and evening, particularly for the
Antelope Valley and foothills.

Sunday through Tuesday, upper level heights are expected increase,
resulting in a weak ridging pattern. The marine layer clouds will
lower in height, due to the higher pressure, and will not reach
as far inland. The warm airmass aloft combined with the reduction
in the influence of marine layer clouds, will result in a general
warming trend for all areas, excluding near coastal locations.
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&&

.AVIATION...22/0035Z.

At 2343Z at KLAX, the marine layer was 1400 ft deep. The top of
the inversion was at 4800 feet with a temperature of 16 C.

High confidence in KPMD, KWJF, and KPRB TAFs.

High confidence elsewhere through 03Z, then low confidence.
Timing of cigs may be off by 3 hours and off by 1 flight cat.
There is a chance that VFR conditions prevail for KBUR(30%),
KVNY(30%), KCMA(20%), KOXR(20%), and KSBA(30%). There is a 20%
chance of no clearing at KLAX and KSMO through the period.

KLAX...High confidence in TAF through 03Z, then low confidence.
There is a 20% chance that cigs tonight will hold off until at
least 09Z. There is a 20% chance of no clearing through the
period Good confidence that any east wind component will be 5
knots or less.

KBUR...High confidence in TAF through 07Z, then low confidence.
There is a 30% chance that conds will remain VFR tonight.

&&

.MARINE...
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21/909 PM.

Moderate confidence in forecast, except low-moderate confidence
for the inner waters N of Pt. Sal and in the western SBA Channel.

In the outer waters, Small Craft Advisory (SCA) level winds and
seas will continue much of the time thru Sat. There may be a lull
in the winds during the very late night thru morning hours,
especially Thu night/Fri morning. For the waters north of Pt. Sal,
there is a 30% chance of gale force wind gusts Wed afternoon/eve.

In the inner waters N of Pt. Sal, there is a 40-50% chance during
the afternoon/eve hours Wed. Then, SCA level winds are likely
during the afternoon/eve hours Thu and Sat.

In the inner water S of Pt. Sal, there is a 30% chance of SCA
level winds in western portions of the SBA Channel this
afternoon/eve, then a 40-50% chance during the afternoon/eve
hours Wed thru Sat. Otherwise, SCA conds are not expected.

A long period south to southwest swell will continue to subside
through Wed. The risk of larger than normal breaking waves
nearshore and stronger currents near most harbor entrances will
start to subside during this timeframe.
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&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement in effect through Wednesday afternoon
      for zones 87-362-366. (See LAXCFWLOX).
PZ...Small Craft Advisory in effect until 3 AM PDT Friday for
      zones 670-673-676. (See LAXMWWLOX).

&&

$$

PUBLIC...Hall/Schoenfeld
AVIATION...Lund
MARINE...DB/Lund
SYNOPSIS...Hall

weather.gov/losangeles

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