Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000
FXUS66 KLOX 281235
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
535 AM PDT Thu Mar 28 2024

.SYNOPSIS...28/345 AM.

A cooling trend will continue through the weekend as a series of
storms drop into the region. A weak weather system, moving to the
north of the area, will bring some showers or light rain to the
northern areas through tonight, then an unseasonably cold and
vigorous storm system will affect the region between late Friday
and Monday night. Rain and mountain snow with a slight chance of
thunderstorms will develop through Friday and Saturday, turning to
showers on Sunday and Monday. A warming and drying trend will
develop for the remainder of next week.

&&

.SHORT TERM (TDY-SAT)...28/532 AM.

The latest infrared imagery shows a weakening and dying cold front
over the San Francisco Bay area this morning. The front,
associated with a broader trough circulation off the Pacific
Northwest coast, is falling apart currently. Enough moisture and
instability is present to produce light rain or showers for San
Luis Obispo and Santa Barbara Counties through tonight and along the
northern slopes of the mountains later today and into tonight.
Light rain is falling along the northwestern portion of San Luis
Obispo County this morning. PoPs have been nudged up over the
previous shift inline with high-resolution multi-model ensemble
members in advertising high PoPs but low QPF amounts. Amounts
should remain less than one quarter inch with this system.

To the south, stratus coverage is broken up with the best coverage
over Ventura County. Coverage is slowly expanding, and in general,
the coverage should come more inline with forecast as the morning
progresses. The marine layer is being rather stubborn with an
inversion struggling to develop this morning. The low-levels
should continue to moisten the remnants of the cold frontal
boundary to the north sag south. The latest high-resolution model
solutions suggest the pseudo-marine layer or moist layer deepens
to near 4000-5000 feet tonight and into Friday morning. With the
deep moisture in place, some dynamics scraping the area tonight
and into Friday morning could squeeze out some heavy drizzle or
light rain, especially along the coastal slopes of the mountains.

A cooling trend will continue through Saturday as a more
vigorous, stronger, and colder storm system moves into the region
between Friday and Saturday. A vorticity maximum rotating around
trough circulation to the north will swing around the back side
and dig the trough into the region to near Point Conception by
late Saturday night. The colder trough will tap into the
subtropics and bring a moist air mass into region along the cold
front on late Friday. PoPs trend even wetter over the previous
forecast with categorical rain being mentioned across the entire
area. All members of the EPS, GEFS, and CMC ensembles indicate
rain developing across the region between late Friday and Saturday
night. With a difluent flow pattern setting up aloft and a much
colder air mass aloft, a slight chance of thunderstorms remains in
the forecast between late Friday night into Sunday. Brief
heavy downpours with small hail could develop. There is also
enough wind shear to produce weak tornadoes or waterspouts over
the coastal waters.

EPS ensemble members have trended slightly higher with precipitable
water values with means ticking up slightly to between 1.0 and
1.1 inch. There is a low-to-moderate chance that a Flash Flood
Watch could be issued as precipitable water values are ticking up
closer. Convective parameters creating more instability could tip
the scales more in favor for a watch, but this will need to be
monitored closely.

Storm total rainfall amounts remain fairly consistent, near 1.50
to 3.00 inches across the coastal and valleys areas with up to 5
inches possible along favored south facing mountain slopes. Most
of the precipitation will arrive with along the cold front between
Friday and Saturday, but there is a secondary boundary that
develops on Sunday in the latest solutions, which could bring
additional rainfall and a higher potential for convective burst.

The latest deterministic solutions show 700 mb temperatures
cooling to between -7 degrees Celsius right behind the cold front,
then cooling to -9 degrees Celsius by Sunday. While the snow
levels were previously advertised to remain between 5000 and 6000
feet, 700 mb temperatures suggest snow levels falling to 4500 feet
quite rapidly with the cold front. This could bring some
accumulating snowfall to the Tejon Pass on the Interstate 5
freeway. There is an increasing concern for accumulations of snow
lower than previously surmised. Almost all of the EPS ensemble
members have accumulating snow for KSDB, with a range from a
dusting up to 3 inches. Most EPS members show a half inch or less
for KSDB. Highest confidence exists for significant snowfall
above 6000 feet. A foot or two of snow above 6000 feet, impacting
higher roadways such as Lockwood Valley Road in Ventura County and
Angeles Crest Highway and Highway 39 in Los Angeles County.
Winter weather headlines will likely be needed as we get closer to
the storm`s arrival and the details become clearer.

Gusty southerly winds will also develop ahead of the storm
system`s cold front. NAM 850 mb winds increase to between 40 and
50 knots over San Luis Obispo County on Friday and Friday night.
A High Wind Watch was added for the higher terrain in San Luis
Obispo County, and wind advisories were added for areas where
winds will likely start to increase as soon as Friday. Wind
advisories likely need to expanded, and possibly extended by
future shifts.

.LONG TERM (SUN-WED)...28/532 AM.

To be issued shortly.

&&

.AVIATION...28/0208Z.

At 0101Z at KLAX, the marine layer was 700 ft deep with a weak
inversion up to 1600 ft and a maximum temperature of 13 C.

Low confidence in TAF package due to uncertainty with cigs and
vsby tonight. Expect mostly MVFR to IFR cigs, with 10-20% chance
of dense fog for all coasts and valleys from 06Z-17Z. Light
rainfall is expected starting around 06Z for SLO County portions
of SBA County by around 12Z.

KLAX...Low confidence in TAF. Cig arrival may be off by +/- 2
hours with a chance of BKN015 cigs to start before lowering to
BKN004. There is a 20% chance of dense fog from 06Z-17Z, and a
10% chance for an 8 kt easterly wind component wind between
12Z-16Z.

KBUR...Moderate confidence in TAF, there is a 30% chance of
BKN004-BKN015 cigs from 10Z-16Z.

&&

.MARINE...28/535 AM.

Fairly complex marine forecast, with rapidly changing conditions,
and moderate confidence thru the weekend

For today thru Fri morning...

Small Craft Advisory (SCA) level W-NW winds are expected to develop
this morning in the SBA Channel, then across the remainder of the
waters this afternoon. Winds will drop below SCA levels in most
areas late tonight, except early Fri in the SBA Channel and the
southern inner waters. However, seas will remain above SCA levels
in the outer waters and the inner waters N of Pt Sat thru Fri, so
a SCA will remain in effect for those areas into Fri afternoon.

From Fri afternoon into the weekend...

Winds will shift to S and increase ahead of a cold front Fri. In
the northern two outer waters zones (PZZ670/PZZ673) and in the
inner waters N of Pt Sal, winds may reach gale force Fri afternoon
thru Fri night, so a GALE WATCH is in effect. SCA level S-SW winds
are likely Sat/Sat night, with SCA level seas thru early Sun.

In the southern outer waters, high end SCA level S winds are
expected Fri afternoon thru Sat morning, with a 40% chance that
winds will remain at SCA levels thru Sat night. Seas will remain
at or above SCA level thru early Sun.

In the SBA Channel and in southern inner waters, SCA level SE-S
winds are likely (60% chance) Fri evening thru Sat morning, with
a 40% chance that winds will remain at SCA levels thru Sat night.

Conds are expected to be below SCA level across all waters Sun
afternoon thru Mon.

There is a 20-30% chance of thunderstorms late Fri night in
northern areas and across all of the waters Sat thru Sun.

&&

.BEACHES...27/1041 PM.

A return of high surf is expected between Thursday afternoon and
the weekend as a storm system will bring a large northwesterly
swell to the region. Surf as high as 8 and 12 feet with local sets
to 13 feet is expected at Central Coast beaches, and 4 to 7 feet
with local sets to 8 feet for Ventura County beaches. Los Angeles
and Santa Barbara South Coast will see surf 3 to 6 feet, with
local sets to 7 feet. Surf should peak on Saturday or Saturday
night. Strong and dangerous rip currents are expected during this
period.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory in effect from 9 AM this morning to 9 AM
      PDT Sunday for zones 340-346. (See LAXCFWLOX).
     Wind Advisory in effect from 3 PM Friday to 6 AM PDT Saturday
      for zones 340-341-343-344-346-347. (See LAXNPWLOX).
     High Wind Watch in effect from Friday afternoon through late
      Friday night for zones 342-345. (See LAXNPWLOX).
     High Surf Advisory in effect from 3 PM this afternoon to 3 PM
      PDT Friday for zone 354. (See LAXCFWLOX).
PZ...Small Craft Advisory in effect from 3 PM this afternoon to 3
      PM PDT Friday for zones 645-673. (See LAXMWWLOX).
     Gale Watch in effect from Friday afternoon through late
      Friday night for zones 645-670-673. (See LAXMWWLOX).
     Small Craft Advisory in effect from 9 AM this morning to 9 AM
      PDT Friday for zone 650. (See LAXMWWLOX).
     Small Craft Advisory in effect from 3 PM this afternoon to 9
      AM PDT Friday for zone 655. (See LAXMWWLOX).
     Small Craft Advisory in effect from 3 PM this afternoon to
      noon PDT Friday for zone 670. (See LAXMWWLOX).
     Small Craft Advisory in effect from 3 PM this afternoon to 9
      AM PDT Sunday for zone 676. (See LAXMWWLOX).

&&

$$

PUBLIC...Hall
AVIATION...Schoenfeld
MARINE...DB
BEACHES...MW/Schoenfeld
SYNOPSIS...Hall

weather.gov/losangeles

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


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