Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 281147

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
447 AM PDT Sun May 28 2023

.SYNOPSIS...28/446 AM.

A strong onshore flow pattern will keep a persistent and deep
marine layer in place through the week. Night through morning low
clouds and fog with limited afternoon clearing will continue as
well. Local drizzle is possible each morning across coastal and
valley areas. Temperatures will be cooler than average for most of
the week.


.SHORT TERM (TDY-TUE)...28/401 AM.

Deep marine layer (about 4000 feet deep) across the region again
this morning. Low clouds were widespread in all coastal and valley
areas with the exception of the Cuyama Valley. Once again clouds
have pushed well into the coastal slopes. There could be some
local drizzle this morning, especially in the foothills of L.A.
County. With strong onshore gradients in place, expect a slow
burnoff of clouds today, with skies possibly remaining mostly
cloudy all day in some coastal areas. Models show some decent
instability across the mountains, especially the Ventura County
mountains this afternoon and evening, but very little mid level
moisture. Therefore just expect some buildups across the Ventura
County mtns this afternoon. There may be some cooling today,
especially in the interior valleys, mtns and deserts. Max temps
will remain well below normal, especially in the valleys.

An upper low off the coast of central and northern California
will drop slowly southward tonight and Mon, to a position about
200 nm west of Point Conception Monday afternoon. It will then
drift slowly eastward or southeastward depending on which
deterministic solution one believes. The GFS takes it across
southern L.A. County Tue, while the EC still has it west of Point
Conception. The WRF is somewhere in between, but closer to the
solution shows by the EC.

In general, this pattern favors a very deep marine layer to
continue the Tue, with night through morning low clouds and fog in
all coastal and valley areas. Increasingly cyclonic flow will
likely increase the chance of drizzle late each night through the
morning, especially south of Point Conception. There could even
be some light amounts of measurable rain, particularly in the
foothills. Very strong onshore gradients will continue, making
for slow clearing, and skies may well stay mostly cloudy each
afternoon in coastal and valley areas. There will be some gusty
winds during the afternoon and evening hours in the Antelope
Valley. Lowering heights should lead to some cooling each day in
the mtns and deserts, with mostly minor changes west of the
mountains. Once again, there will likely be some buildups each
afternoon in the mtns, especially in Ventura County and possibly
L.A. County. However, the chance of thunderstorm activity is
still only 10 percent as moisture will remain somewhat limited.
There may be a slight better chance of convection on Tue, so that
will have to be monitored.

.LONG TERM (WED-SAT)...28/444 AM.

The upper low will move east of the region Wed, but another upper
low will form just off the coast, then linger there through Thu.
The marine layer will remain deep, with night thru morning low
clouds and fog in coastal and valley areas, pushing into the
coastal slopes. There still could be some drizzle, and a few
ensemble members show some measurable rain Wed into Thu. Onshore
gradients will remains quite strong, with slow and limited
clearing expected west of the mountains. Temperatures will remain
well below normal through Thu.

Once that second upper low moves east of the region late Thu, a
very weak ridge will try to build into the region Fri thru Sat.
This may be strong enough to reduce the marina layer depth enough
to keep clouds out of the mountain slopes. There may also be
somewhat better clearing west of the mtns Fri and Sat, with some
warming likely, especially away from the coastal plain.



At 0734Z at KLAX, the marine layer was 1700 feet. The top of the
inversion was 5000 feet with a temperature of 15 degrees C.

Moderate confidence in TAF package. There is a 40% chance of
clearing in the afternoon at all coastal sites, similar to
yeasterday`s pattern. Timing of flight categories chances may be
off by +/- 3 hours.

KLAX...Moderate confidence in TAF, due to uncertainty in CIG
changes timing. High confidence any east wind will be under 8 kts
and will last no more than 3 hours.

KBUR...Moderate confidence in TAF, due to uncertainty in CIG
changes timing. Timing of clearing of CIGs today may be off by
+/- 3 hours.


.MARINE...28/257 AM.

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 night widespread SCA level
winds, and borderline SCA level seas will spread over the outer
waters and the western portion of the Santa Barbara Channel.


.BEACHES...28/202 AM.

Long-period south swell originating from the Southern Hemisphere
will move into the coastal waters through Tuesday. Strong rip
currents and elevated surf of local 3 to 5 feet will be possible
over the Memorial Day holiday weekend. There will be the potential
for hazardous rip currents and a Beach Hazards Statement may be
needed later this weekend.






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