175
FXUS66 KLOX 011237
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
537 AM PDT Wed May 1 2024

.SYNOPSIS...01/319 AM.

Ridging aloft building into eastern Pacific Ocean will continue
to bring a general warming trend through Thursday. The warming
trend may be muted across the southern coastal areas as onshore
flow strengthens slightly. Stronger troughing over the West Coast
over the weekend will bring some cooling along with a chance of
rain. Otherwise, night through morning low clouds and fog will
continue at times, remaining mostly intact for the southern
portion of the area.

&&

.SHORT TERM (TDY-FRI)...01/439 AM.

The latest water vapor imagery shows a shortwave trough digging
south in zonal flow this morning as ridging aloft is building
across the eastern Pacific Ocean. Onshore flow is strengthening
across the southern portion of the area due to an eddy circulation
in place near San Nicolas Island, but some weakening is starting
to take place north of Point Conception. A low cloud field is
stretching from Santa Barbara to the southeast into the San Pedro
Channel and pushing into the Los Angeles and Ventura County
valleys this morning, but the cloud field is quite disorganized
with breaks in the clouds across the area.

A quite complex pattern is setting up over the next several days
in the zonal flow. The latest forecast ensembles offer up a range
of solutions with a wider spread as one heads south and farther
inland. This will make for a difficult forecast over the coming
days as offshore flow will wage a battle against the onshore
regime. The most likely outcome will be the ridge aloft
to the west asserting some influence for areas north of Point
Conception. Onshore flow could end up being replaced by offshore
flow on Thursday and bring some warming to San Luis Obispo and
Santa Barbara Counties.

To the south, onshore flow will likely stay wedged in. Although it
will be less classical of a synoptic pattern for May, it is very
plausible that onshore flow could strengthen. Any offshore push
will not be strong enough to dislodge the eddy circulation off the
coast. With the ridge aloft adding some heating to the interior
areas outside the marine influence, onshore pressure gradients
will likely increase through the period. With 500 mb heights
increasing into Thursday and onshore pressure gradients
strengthening, clouds could end hugging the beaches over the
coming days. The latest tabular forecast guidance and EPS ensemble
members buy into this idea and keep Los Angeles and Ventura
coastal terminals near persistence over the coming days. The
forecast keeps a mention of low clouds across the South Coast of
California into Friday.

By Friday morning, the marine layer induced low cloud field could
end up becoming more entrenched as troughing along 160W ejects
over the top of the ridge and drops down into the region. The
marine layer depth should become more organized and deepen as
onshore flow strengthens. The forecast ensembles agree that a
cooling trend should take shape, establishing on Friday.

.LONG TERM (SAT-TUE)...01/435 AM.

The latest forecast ensemble agree a cooling trend will continue
into Sunday as the semi-permanent Aleutian low pressure system
kicks out an upper-level trough that will dig into the West Coast.
EPS, GEFS, and CMC ensemble members are leaning more toward an
inside slider type trough of low pressure to affect the area over
the weekend. The latest PoPs break away from NBM values to
emphasize the highest rain chances for the northern areas and
along the northern slopes Saturday night through Sunday morning.
Temperatures also break away from NBM values on Sunday to buy into
better cooling, but EPS and GEFS ensemble means also lean toward
Monday being equally as cool. Rainfall amounts will be light, on
the order of a quarter of an inch or less, but there is a 15-20
percent chance that amounts could be higher than that in
northwestern San Luis Obispo County, highest near Rocky Butte.
Snow levels should be above 6000 feet with this system, but there
is still a great amount of uncertainty with the colder air mass
aloft. Any changes to the west, and the system could be wetter and
more cold air could be transported into the region. The latest
forecast ensembles give the Interstate 5 Corridor a 20 percent
chance of seeing accumulating snowfall between Sunday and Sunday
night.

The main story could end up being the winds with this system as
all of the EPS solutions suggest a gusty wind pattern developing
across the mountains and desert and into some of the coastal
areas, as well. Based upon the EPS wind gust means at terminals
and the areal extent, the pattern seems to suggest gusty west to
northwest winds on Saturday and Sunday, shifting to northwest to
north into Monday.

Zonal flow should redevelop on Monday and a warming trend is
looking to establish for early next week.

&&

.AVIATION...01/1236Z.

At 12Z at KLAX, the marine layer was 2600 ft deep with an
inversion top at 4500 ft with a temperature of 14 C.

Low to moderate confidence in coastal TAF sites and L.A. Valley
sites, with high confidence elsewhere. Cigs are starting to
become patchy and scatter out, but could reform over the
coastal/valley TAF sites through 18Z Weds. Otherwise, timing of
flight cat changes could be off by +/- 2 hours.

KLAX...Low to moderate confidence in TAF, however high confidence
19-05Z. Cigs may scatter out early this morning, but remain
possible through 18Z. BKN010-015 conds possible as early as 06Z
Thurs. There is a 30% chance of an east wind component reaching 7
kts through 18Z Wed, otherwise good confidence in any east wind
component remaining less than 7 kt.

KBUR...Low to moderate confidence in TAF. Timing of flight cat
changes may be off by +/- 2 hours.

&&

.MARINE...01/410 AM.

For the outer waters, winds will likely drop below Gale levels
this morning, but are expected to restrengthen by the afternoon,
so decided to extend the Gale Warnings through late tonight.
Swell will continue to be steep and choppy through Thursday night.
After gales subside, Small Craft Advisory (SCA) conds are
expected for the outer waters through Sunday. However, there is a
40-50% chance of gale force wind gusts again Thursday afternoon
and evening, and again Sunday afternoon through evening (and
possibly through much of next week).

For the inner waters N of Pt. Sal, SCA level winds are likely
through tonight. Then, there is a 60% chance of SCA winds during
the afternoon and evening hours through Friday. Seas will start to
diminish below advisory levels late tonight.

For the Santa Barbara Channel, SCA level W-NW winds are expected
across the extreme western portion this afternoon/evening, but not
far enough into the channel to warrant issuing an advisory. Then,
there is a 20-30% chance of SCA winds each afternoon/evening
Thursday and Friday across the extreme western portion. Winds will
likely remain below SCA levels for eastern portions of the
channel through Friday night. Saturday afternoon through Sunday,
there is a 40-50% chance of widespread W to NW SCA level winds
across the entire inner waters, with a 20% chance of gale force
wind gusts on Sunday.

For the southern inner waters, there is a 20% chance of SCA level
W to NW winds near Anacapa Island Wednesday evening. Otherwise,
good confidence in conds remaining below SCA levels through Friday
night. Saturday afternoon through Sunday, there is a 40-50%
chance of widespread W to NW SCA level winds across the entire
inner waters, with a 20% chance of gale force wind gusts on
Sunday.

&&

.BEACHES...01/1203 AM.

Persistent strong winds and outer water swell heights of 10-15
feet with a 10 second period will lead to high surf along the
Central Coast (7-11 feet) and Ventura County beaches (4-7 feet).
Surf will be highest across west- and northwest-facing beaches.
There is a 40% chance of high surf advisory criteria lingering
through the evening. NO coastal flooding is expected.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory in effect until 2 PM PDT this afternoon
      for zones 340-346-354. (See LAXCFWLOX).
     Wind Advisory in effect until 9 AM PDT this morning for zone
      376. (See LAXNPWLOX).
     Wind Advisory remains in effect until 9 AM PDT this morning
      for zones 378-381-383. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 3 AM PDT Thursday for
      zone 645. (See LAXMWWLOX).
     Gale Warning in effect until 3 AM PDT Thursday for zones
      670-673-676. (See LAXMWWLOX).

&&

$$

PUBLIC...Hall
AVIATION...Lund
MARINE...Lund/Phillips
BEACHES...Lund
SYNOPSIS...Hall

weather.gov/losangeles

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