000
FXUS66 KLOX 161515
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
815 AM PDT Sun May 16 2021

.SYNOPSIS...16/241 AM.

Night through morning low clouds will be common through much of
next week along with gusty winds across the Antelope Valley.
Drizzle or light rain will be possible at times this morning,
especially near the foothills. Temperatures will remain below
normal through the period, except inland early next week.

&&

.SHORT TERM (TDY-TUE)...16/814 AM.

***UPDATE***

Overall, a very gloomy morning across the area today. Latest
sounding data indicates a very deep marine inversion, ranging
between 4000 and 5000 feet deep. With the deep inversion, clouds
have pushed well into the foothills and mountain slopes.
Additionally, some light marine layer showers continue, especially
across the foothills with amounts ranging from a trace to about
0.15 inches.

Forecast-wise, main issue in the immediate short term will be the
deep marine layer. Given the surface gradients and inversion
depth, will anticipate a reverse clearing pattern today with skies
becoming partly cloudy/mostly sunny along the coast, but
remaining cloudy inland. The drizzle/light showers should end this
afternoon across the area. The combination of clouds and onshore
flow will keep temperatures on the cool side today. As for winds,
onshore gradients are weaker than yesterday, but are strong enough
to generate some gusty southwesterly winds across the mountains
and deserts. Any advisory-level gusts should remain localized
today, so do not anticipate any need for an advisory.

Current forecast looks to have a great handle on the immediate
short term. Will need to watch how the marine layer acts today,
but no significant updates are expected.

***From Previous Discussion***

Latest GOES-Water Vapor Imagery was showing the upper low centered
around Fresno Ca. and will continue to pivot across eastern Cal into
southern Nevada by this afternoon. By Monday afternoon, the upper
low will have pushed east to around the Four Corners region. Broad
cyclonic flow associated with the upper low will continue across
Southern California along with continued strong onshore flow. Onshore
gradients will trend slightly weaker today but continue to bring gusty
SW winds across the Antelope Valley and adjacent foothills including
the Hwy 14 corridor today through this evening. The LAX- DAG gradient
should be a couple millibars weaker to around +8.3 MB this afternoon.
This will translate into slightly weaker winds across the Antelope
Valley and adjacent foothills today through this evening. Except for
local gusts to around 45 mph around Lake Palmdale and adjacent foothills,
winds across the Antelope Valley should remain below wind advisory
thresholds. A few light showers were occurring across portions of
the Central Coast and should begin to develop across a more widespread
area west of the mountains this morning especially across L.A.
County.

The marine layer, or deep moist layer was around 5000 ft already this
morning, and could continue to increase slightly higher by mid morning.
The combination of the deep moist layer, relative strong onshore flow
and cyclonic flow aloft associated with a 90 knot jet core moving across
L.A. and Orange Counties causing some lift will help to squeeze out
some light rain for most areas west of the mountains this morning.
Current pops ranging between 10-30 percent seem reasonable, with best
chances of measurable light precipitation across LA county and the
Central Coast. Any areas that do receive measurable rainfall will likely
just see a few hundredths of an inch, however the foothills of the
eastern San Gabriels could see local amounts exceeding one tenth of
an inch. The deep moist layer and potential drizzle or light rain
this morning is expected to bring improving weather conditions to
the Palisades Fire in the Santa Monica mountains.

There is a good chance that another "reverse clearing" scenario will
occur where coastal areas will see partial clearing in the afternoon,
while valleys and mountains will continue stay mostly cloudy today.
The NAM-WRF was picking up on some marginal afternoon instability across
the Ventura County Mtns and eastern SBA County Mtns, but both deterministic
and mean ensembles as well as the HRRR were not picking up on any convection
across the mountains today, so will keep showers out of the forecast
for this afternoon but keep 10 percent POPs through this afternoon.

.LONG TERM (WED-SAT)...16/429 AM.

The upper ridge that sets up over Southern and Central California
will be short lived as another relatively strong upper low
pressure system across the PAC NW will start to dig south into
northern California with a deep trough across Southern California.
Both the GFS and EC models stay in good agreement with large scale
features through Thursday with the placement of the upper low over
Northern Cal and Nrn Nevada, but models become out of phase by
Friday as the GFS continues to keep a 549DM low in the same area
with a sharp base to the trough over SoCal, while the EC is more
progressive with the upper low across the Intermountain West with
a weaker trough across Southern Cal. The GFS pivots the upper low
to the north, while the EC advertises a short wave along the
western periphery of the low and then the main core of the low
retrogrades back over Central California on Saturday. Confidence
is low with the tracking of the closed low from Friday/Saturday,
but the EC seems to be the bigger anomaly for this time of year.
So have kept the same forecast hedging with the GFS.

Overall, high temps Wed-Thu will trend lower several degrees
across inland locations away from the coast with 5-10 degrees below
normal for this time of year. Some modest warming inland on Friday
with more widespread warming on Saturday if the GFS is the model
that remains on track. Night through morning low clouds will
continue for coast and coastal valleys through most of the week
with less coverage Friday and Saturday due to weaker onshore flow
and some northerly winds across inland locations.

&&

.AVIATION...16/1307Z.

At 12Z, there was a deep moist layer up to 6500 feet, with a
few different cloud layer within.

It was cloudy across the entire region except for the higher
mountain elevations and the Antelope Valley this morning.
Conditions were mostly MVFR to VFR, except IFR to VLIFR in the
mountains and foothills. Expect limited clearing today, though
cigs should rise into the VFR category in most coastal and valley
areas. There may be some light rain this morning, especially in
the foothills of L.A. County.

Expect similar conds tonight, with cloudy everywhere except for
the higher mountains and the Antelope Valley. Conds should be MVFR
to VFR in most areas, except IFR to VLIFR in the foothills and
mtns.

KLAX...Moderate confidence in the 12Z TAF. There is a 20-30%
chance that cigs will rise into the VFR category as early as
18Z. There is a 20% chance that skies will scatter out between
22Z and 01Z.

KBUR...Moderate confidence in the 12Z TAF. There is a 20-30%
chance that cigs will rise into the VFR category as early as
18Z. There is a 20% chance that skies will scatter out between
22Z and 01Z.

&&

.MARINE...16/803 AM.

Patchy fog and drizzle will continue across the coastal waters
into next week.

Across the outer waters... Winds will likely increase to Small
Craft Advisory (SCA) level Monday afternoon and continue at least
at that level through Thursday. The winds will likely increase to
gale force on Tuesday and may remain at that level through
Thursday. The strongest winds will occur during afternoon and
evening hours. Seas will be SCA level Tuesday through Thursday.
Otherwise, conditions will be below SCA level.

Across the nearshore waters of the Central Coast... There is a
forty percent chance that SCA level gusts will develop Monday
afternoon and evening, then winds will likely be SCA level Tuesday
through Thursday. The strongest winds will occur during afternoon
and evening hours. Seas will be SCA level Tuesday afternoon
through Thursday. Otherwise conditions will be below SCA level.

Across the inner waters south of Point Conception... SCA level
gusts will develop Monday afternoon and evening near Point
Conception and through the Santa Barbara Channel and will
continue through Thursday. The strongest winds will occur during
afternoon and evening hours. Otherwise and elsewhere, conditions
will be elevated but below SCA level.

&&

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

&&

.HAZARD POTENTIAL OUTLOOK (TUE-SAT).

No significant hazards expected.

&&

$$

PUBLIC...Kaplan/Thompson
AVIATION...DB
MARINE...Kj
SYNOPSIS...Kaplan

weather.gov/losangeles




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