Acton Weather

537
FXUS66 KLOX 020511
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
911 PM PST Sun Dec 1 2024

.SYNOPSIS...01/909 PM.

Offshore flow in place over the weekend will break down on Monday
as a weak upper-level trough moves into the region. Onshore flow
will establish on Monday as the trough advances toward the
California coast. Varying amounts of high clouds can be expected
through Tuesday for most areas, but night through morning low
clouds and fog are possible each night and morning through
Tuesday. A cooling trend will bottom out on Tuesday or Wednesday,
the a warming trend will establish for late week.

&&

.SHORT TERM (SUN-WED)...01/905 PM.

An offshore flow pattern clings to the area this as the flow
regime continues to gradually break down. Weak upper-level ridging
aloft remains east of the area this evening as a weak upper-level
trough advances toward the region near 29N and 131W. As the trough
approaches the California coast through Tuesday, an onshore flow
pattern should develop and bring some cooling. Patchy stratus
cannot be ruled out entirely for tonight and into Monday morning,
but the main cloudiness should come from middle and high level
cloudiness streaming over the region through Monday evening.
Monday will be cooler than today across many coastal and valley
areas with the largest amount of cooling expected along the
Central Coast. Only slight cooling is expected across the
Southland on Monday.

There is slight concern for isolated mountain showers and
thunderstorms across the southern mountains on Tuesday. 850-500 mb
lapse rates do steepen to between 7 and 8 degrees Celsius per
kilometer on Tuesday afternoon. The latest model solutions and
forecast ensembles tend to keep the air mass dry, but based upon
the trough`s source region and experience, there will likely some
moisture to work with on Tuesday afternoon. A few lightning
strikes were already observed on satellite imagery earlier today,
so it stands to reason that the air mass is marginally unstable,
as well. With 500 mb height dropping as the system comes ashore,
it would be surprising to see a few pop up showers, especially
over the mountains.

An update to the forecast was sent previously to tweak
temperatures and cloud cover. Otherwise, no additional updates
are planned.

***From Previous Discussion***

Upper level ridging will nose into nrn CA from late Tue thru Wed.
This upper level pattern will result in a NE flow aloft Tue night
and Wed.

Marine layer low clouds and fog are expected to develop along
portions of the Central Coast and L.A. County coast Mon night into
Tue morning, and for much of the coast Tue night into Wed
morning, possibly extending into the southern parts of the San
Gabriel Vly. It would not be out of the question to see some
patchy dense fog as well, especially along the Central Coast.
Otherwise, varying amounts of mid and hi level clouds are expected
to move back into swrn CA later tonight thru Tue morning for
partly to mostly cloudy skies. Mostly clear skies should then
prevail Tue afternoon thru Wed.

Onshore pressure gradient trends will continue tonight thru Wed,
altho the actual pressure gradients are forecast to remain light
offshore to the N and E especially night and morning hours. Breezy
offshore flow can be expected for the inland foothills and mtns
each night and morning. Otherwise, a light to breezy diurnal wind
pattern is forecast for the coast and vlys each day.

High temps will continue to be about 5-10 deg above normal away
from the coast Mon thru Wed. The warmest vlys should reach into
the 70s each day, with mid 60s to around 70 for the inland coastal
areas, lower mtns and deserts.

.LONG TERM (THU-SUN)...01/157 PM.

The EC and GFS deterministic have some minor disagreements while
the mean ensembles are in generally good agreement thru the
extended period. Either way, dry conditions will persist across SW
CA Thu thru Sun. Upper level ridging over nrn and central CA into
Thu is forecast to slowly move S and into SRN CA Fri thru Sat.
The ridge should then break down some Sat night and Sun as an
inside slider upper level trof moves into the Great Basin.

There may be some low clouds and fog along the L.A./VTU County
coast Wed night into Thu morning, otherwise clear to partly cloudy
skies can be expected Thu thru Sun. Offshore pressure gradients
to the N and E can be expected, with gradients trending more
offshore each day thru Sat. Pressure gradients to the E should
trend onshore into Sun, while gradients to the N are expected to
increase. Breezy to gusty NE flow is expected each night and
morning in the wind prone areas, but should be strongest Fri night
into Sat morning when winds could approach Advisory levels as
times.

Temps will turn warmer for Thu thru Sat, peaking on Sat with
highs about 7-14 deg above normal. Temps should then cool back a
few degrees on Sun but still be 6-12 deg above normal. The warmest
inland coast and vlys for Fri and Sat should have highs in the
70s, with low 80s in the western San Fernando Vly, and 60s to
lower 70s closer to the coast.

&&

.AVIATION...02/0034Z.

At 0003Z at KLAX, there was no marine layer. There was a surface
based inversion with a top at 1250 ft and a temperature of 18 C.

Overall, moderate to high confidence in the 00Z TAF Package.

There is a 20-30% chance of coastal fog affecting the Central
Coast sites, KOXR, and the LA Coastal sites between 06z to 16z.
Otherwise, expect VFR conds thru the pd.

KLAX...Moderate confidence in the 00Z TAF. There is a 20% chance
of fog impacting the site from 06Z to 16Z. If realized, flight
cats could fall to IFR with a 10% chance of LIFR conds. No
significant east wind component expected.

KBUR...High confidence in 00Z TAF with VFR conds thru the pd.

&&

.MARINE...01/825 PM.

Winds and seas will very likely (80 to 90% chance) remain below
Small Craft Advisory (SCA) levels across the entire waters thru
early Wed. There is a 30% chance of SCA level winds in the outer
waters Thu night thru Friday.

There is a 30 to 40% chance of low clouds and fog in portions of
the coastal waters late tonight/Mon morning, but will be more
likely Mon night/Tue morning.

&&

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

&&

$$

PUBLIC...Hall/Sirard
AVIATION...Smith
MARINE...Black/Smith
SYNOPSIS...Hall

weather.gov/losangeles

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