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000
FXUS66 KLOX 220402
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
902 PM PDT Sun Apr 21 2024

.SYNOPSIS...21/853 PM.

Strengthening onshore flow and a deepening marine layer will
bring low clouds and fog to the coast and coastal valleys through
this upcoming week. High temperatures will cool significantly
to below-normal readings by Tuesday as a series of low pressure
systems track across the area this week. There will be a chance
for drizzle or very light rain this week with the passage of
these systems.

&&

.SHORT TERM (SUN-WED)...21/906 PM.

***UPDATE***

Low clouds and fog returning to all coastal areas from Pt
Conception south with some patchy dense fog in the Santa Barbara
area. With the transition from weak ridging to weak troughing
tonight, cooler air aloft should begin to lift the marine layer
overnight with less dense fog near the coast but some chances of
dense fog as the stratus rolls into the valleys overnight. Onshore
gradients continue to trend stronger tonight which will assist in
pushing the marine layer well into the valleys with significant
cooling there Monday.

Low clouds also expected to fill in along most of the Central
Coast tonight, at least up to around Morro Bay or so, then fill in
the rest of coastal SLO County Monday into Monday night. Much
cooler there as well Monday where it was a "balmy" 73 in Pismo
Beach Sunday and in the low 80s in SLO.

***From Previous Discussion***

Surface pressure gradients will remain decidedly onshore and
strengthen through the middle of this week, as midlevel ridging
across portions of the Intermountain West focuses the strongest
surface heating over the central Great Basin. Diurnally enhanced
onshore gradients for LAX-DAG are forecast to reach 8-9 mb by
Monday and remain similarly strong through mid-week, as a midlevel
low progresses eastward over the East Pacific toward the southern
California coast. This will reinforce and the marine layer over
coastal areas and coastal valleys into mid-week.

Widespread low clouds and fog are expected to accompany the
deepening marine layer, which will also bring a significant
cooling trend. By Monday, high temperatures are expected to have
cooled to the 60s over the beaches and the 70s across coastal
valleys. Then by Tuesday and Wednesday, temperatures are expected
to remain in the 60s in most areas, except rising into the 70s
over the Antelope Valley away from the marine layer. These
correspond to temperatures falling by 5-10 degrees each day
through Tuesday. In addition, significant deepening of the marine
layer to depths over 2500-3000 feet Monday night into Tuesday will
support the potential for light drizzle over many areas. However,
measurable precipitation will be unlikely through the middle of
the week, as the mid and upper troposphere remains dry, and
large-scale forcing for ascent remains weak.

.LONG TERM (THU-SUN)...21/216 PM.

The aforementioned midlevel low is forecast to track eastward
across the region on Thursday. Temperatures aloft will cool in
conjunction with the passage of this disturbance, which will also
be followed by weakening of onshore pressure gradients. These
factors will allow the marine layer to lose depth and weaken to
some extent by late in the week, with the extent of fog gradually
lessening. Thereafter, further cooling aloft, decreasing onshore
flow, and weakening of the marine layer will occur with the
glancing influence of a deep midlevel trough amplifying over the
Great Basin late Friday into the weekend. However, despite the
weakening marine layer, cooling aloft will maintain high
temperatures in the 60s in many areas through Friday. Thereafter,
temperatures are expected to warm a few degrees next weekend,
especially as midlevel heights increase behind the deeper trough.

Regarding precipitation potential, abundant dry air aloft will
limit chances for precipitation with the passage of the upper low
on Thursday, though a couple of light showers could develop over
the higher terrain beneath the midlevel cold core. There will be
a slight chance for light showers Thursday night through Friday
night in conjunction with the second disturbance glancing the
area.

&&

.AVIATION...22/0020Z.

At 00Z at KLAX, the marine layer was 1200 ft deep. The top of the
inversion was at 3800 ft with a temperature of 22 degrees C.

High confidence in VFR conds through the period for KPRB, KWJF,
and KPMD.

Moderate confidence in cig timing for coastal terminals KSBA and
south including KLAX. Lower confidence in flight category which
may be off by one.

KBUR/KVNY: Low confidence in cig timing and flight category with a
30 percent chance that VFR conditions prevail. Cig timing may be
off by three hours.

KSMX/KSBP: Low confidence in TAF with cig timing possibly off by 3
hours.

KLAX...Moderate confidence in 00Z TAF. Flight category may be off
by one at times. There is a 30 percent chance of at least brief
VFR conditions after 20Z. No significant easterly wind component
is expected.

KBUR...Low confidence in TAF after 05Z. There is a 30% chance of
VFR conds through the period. Flight cat changes could be off by
3 hours.

&&

.MARINE...21/854 PM.

Forecast tracking well this evening. Updates focused on hazards,
including ending the northern Inner Waters SCA early and adding an
Marine Weather Statement for dense fog across the Santa Barbara
Channel.

For the Outer Waters, moderate to high confidence in current
forecast. Today through tonight, high confidence in Small Craft
Advisory (SCA) level northwest winds. For Monday and Tuesday, high
confidence in winds and seas remaining below SCA levels. On
Wednesday, there is a 40-60% chance of SCA level winds. Thursday
through next weekend, there is a 60-80% chance of SCA level winds
and seas, and a 20% chance of GALE Force wind gusts at times over
the weekend.

For the Inner Waters north of Point Sal, For Monday through
Wednesday, high confidence in winds and seas remaining below SCA
levels. On Thursday, there is a 40-50% chance of SCA level winds.
There is a 20-30% chance of SCA winds Friday afternoon through the
weekend.

For the Inner Waters south of Point Conception, moderate to high
confidence in current forecast. Today through Tuesday, high
confidence in winds and seas remaining below SCA levels. However,
there is a 20% chance of SCA wind gusts across the extreme western
portion of the Santa Barbara Channel this afternoon into early
evening. For Tuesday night through Thursday, there is a 40-50%
chance of SCA level winds across the western half of the Santa
Barbara Channel, but high confidence in winds and seas remaining
below SCA levels elsewhere. Over the weekend, there is a 20-30%
chance of SCA winds across the waters.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory in effect until 3 AM PDT Monday for
      zones 670-673. (See LAXMWWLOX).

&&

$$

PUBLIC...MW/Cohen
AVIATION...Munroe
MARINE...Munroe/RAT/Lund
SYNOPSIS...MW/Cohen

weather.gov/losangeles

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