-- Discussion containing changed information from previous version are highlighted. --
819
FXUS66 KLOX 222053
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
153 PM PDT Sun Sep 22 2024

.SYNOPSIS...
-- Changed Discussion --
22/153 PM.

Warm and dry conditions can be expected through Monday as high
pressure aloft builds over the region. The warmer air mass will
likely remain in place through much of the week away from the coast,
with the hottest daytime temperatures forecast for Monday and
Tuesday. It should turn cooler late this week into next weekend.
Mostly clear skies can be expected through the period except for
night and morning coastal low clouds and fog.
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&&

.SHORT TERM (TDY-WED)...
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22/150 PM.

Low clouds persisted along much of the immediate coast early this
afternoon with little change expected the rest of the day.
Elsewhere, mostly sunny skies will prevail across the region thru
the afternoon. Breezy onshore winds will prevail as well. Temps
will top out a few degrees below normal for the coast and adjacent
vlys, and a few degrees above normal for the interior vlys, mtns
and deserts. Much of the inland coast and vlys will be in the 70s
and 80s this afternoon, except the warmest vlys will likely reach
into lower 90s.

A dry northwest flow aloft with H5 heights around 584-585 dam
will prevail through tonight. The upper level flow will turn more
northeast on Mon as an upper level low develops several hundred
miles off the SW CA coast with the forecast area under a col area
aloft between the upper level low off the coast and a broad upper
level trof over the Great Basin. The upper level low will edge
slowly N Mon night thru Wed, and by Wed will weaken and become a
broad upper level trof. H5 heights over SW CA will be in the
585-586 dam range thru Tue then fall to 581-584 dam by Wed with
the upper level flow turning to the S and SW.

The marine layer will shrink through tonight thanks to
significant warming between about 900 mb and below. By early Mon
morning, the inversion should be around 800 ft or so S of Point
Conception and possibly near surface-based on the Central Coast.
Little change in the inversion depth is expected thru Tue, then it
should increase only slightly for Tue night into Wed and be about
1000 ft or less.

A marine layer pattern with night and morning low clouds and fog
mainly along the coast followed by clearing back to or off the
coast during the late morning and afternoon hours can be expected
tonight through Wed. Due to the shallow marine inversion
developing, patchy dense fog is possible with the low clouds
especially later at night into the morning hours thru Tue.
Elsewhere and otherwise across the forecast area, mostly clear
skies are expected thru Wed, with breezy onshore winds each
afternoon.

Pressure gradients to the N and E are forecast to trend offshore
tonight into Mon morning which will allow temps to warm
considerably. Highs on Mon are forecast to be 5-10 deg above
normal except along the immediate coast. Weak pressure gradients
will support continue significantly above normal temps into Tue,
especially away from the immediate coast. Also of note, overnight
lows will be quite a bit above normal for many areas, with temps
likely remaining in the 70s for the foothills and lower mtns. By
Tue night and Wed, temps should start to trend cooler as onshore
flow increases. Highs on Wed are expected to be a few degrees
below normal to near normal for the coast and vlys, and 3-7 deg
above normal for interior areas including the mtns and deserts.

.LONG TERM (THU-SUN)...22/152 PM.

The GFS and EC ensembles and deterministic are in generally good
agreement thru the extended period. An upper level low is forecast
to develop about 500 miles SW of the fcst area by Thu then
meander well off the coast thru next Sun. Upper level ridging will
linger generally over the southern Great Basin into SE CA thru
the period. H5 heights over the forecast area should be in the
586-588 dam range thru the extended period altho the EC
deterministic does increase the H5 heights to 590-592 dam next
weekend.

The marine inversion should remain relatively shallow Thu and Fri
then increase some to about 1000-1500 ft or so Sat and Sun. Night
thru morning low clouds and fog mainly for the coast can be
expected Thu thru Sat, then expand some inland on Sun. Otherwise
and elsewhere, mostly clear skies can be expected thru the period.

Temps Thu and Fri should be from a few degrees below normal for
the coast and vlys to a few degrees above normal for interior
areas, then cool several degrees over the weekend as onshore flow
increases. By Sun, temps should be several degrees below seasonal
norms for most areas, but remain a few degrees above normal in the
far interior vlys and deserts.
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&&

.AVIATION...22/1745Z.

Around 1636Z, the marine layer depth was around 1700 feet deep at
KLAX. The top of the marine inversion was around 4100 feet with a
temperature near 23 degrees Celsius.

High confidence in TAFs for KPRB, KPMD, and KWJF. There is a 10%
chance for VLIFR-LIFR cigs/vsbys at KPRB between 10Z and 15Z.

Low confidence in KBUR and KVNY. There is a 40% chance cigs do not
reach, and VFR conds prevail. Otherwise, VLIFR-LIFR conds are
slightly more likely.

Low confidence in LA coastal TAFs. There is a 10% chance for
VLIFR conds at KLAX/KSMO between 04Z and 15Z. However, there is
also a 10% chance that conds remain IFR-MVFR during this period.

Low confidence in remaining coastal TAFs north of LA county. There
is a 30% chance cigs don`t burn off at KSBA today. There is a 40%
chance of VLIFR conds at KSMX and a 30% chance at KSBP. At other
sites, minimum flight cat may be off by one cat at any point after
cigs arrive.

Arrival of cigs may be off by +/- 4 hours from current forecast at
all sites with cigs in TAFs, with greatest uncertainty south of Pt
Conception.

KLAX...Low confidence in TAF due to uncertainty in arrival time
and cat of cigs. There is a 30% chance of cigs arrive as early as
00Z or as late as 04Z. There is also a 10% chance for cigs
OVC001-OVC002 between 04Z and 15Z, and a 10% chance of cigs
remaining OVC005 or higher during this period. There is a 30%
chance for MVFR conds by 18Z.

KBUR...Low confidence in TAF. There is a 40% chance cigs don`t
reach KBUR, and VFR conds prevail thru the period. If cigs do
arrive, there is a 30% chance for cigs OVC001-OVC002 and/or vsbys
1/2SM or lower.

&&

.MARINE...
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22/1225 PM.

High confidence in the current forecast through Wednesday, then
moderate confidence thereafter. Winds and seas will remain below
Small Craft Advisory (SCA) levels through at least Wednesday,
except for 30-40% chance of local low end SCA level wind gusts
near Pt Conception and the San Pedro Channel thru this evening.
There is also a 20-30% chance for SCA level winds in the inner
waters off the LA and OC Coasts in the afternoon thru evening
Wednesday.

Then, moderate to high confidence in winds and seas increasing to
SCA level Thursday thru Friday, with highest confidence in the
Outer Waters (Central Coast south to San Nicolas Island) Friday.
There is also a 20-30% chance for Gale Force winds Friday
afternoon thru late night in the Outer Waters, with highest
confidence from Pt Conception north.
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&&

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

&&

$$

PUBLIC...Sirard
AVIATION...Lewis
MARINE...Lewis/Hall
SYNOPSIS...Sirard

weather.gov/losangeles

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