Wind Advisory 23, NWS Los Angeles, CA

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
500 PM PST Mon Feb 20 2023

.SYNOPSIS...20/232 PM.

Mostly sunny skies today with max temps near normal. It will turn
windy and much cooler Tuesday and Wednesday with an increasing
chance of rain and very low elevation snow through Saturday.

&&

.SHORT TERM (TDY-THU)...20/1258 PM.

One last day of mild temperatures today before a deep trough dives
southward along the west coast and alters the weather course
dramatically for the remainder of the week. Pressure gradients are
trending onshore this morning, likely triggering more of a sea
breeze this afternoon with attendant cooling of high temperatures
in the coastal sections. Inland temperatures will remain similar
to yesterday.

For tonight, the onshore flow may result in some low cloud
formation on the central coast and in the LA coastal sections, but
confidence is somewhat low. Looking at the boundary level
moisture for tonight, moisture levels do look supportive of low
clouds in the aforementioned areas, so will keep a mention of
partly cloudy in the forecast for now.

On Tuesday, the expected deep trough will start to drop into
central California with a very strong jet stream of 130 knots
moving over the region Tuesday night. The onshore flow will
increase to 8 mb to the east. The very strong surface winds
associated with this advancing trough will be the primary focus of
the early phase of the storm's advance. A high wind watch is in
place for the Antelope valley, the southwestern coast of Santa
Barbara county and the western portion of the Santa Ynez mountains
as well as islands in the southern California bight. Wind
advisories will be needed in many other locations. Blowing dust is
likely for the Antelope Valley Tuesday afternoon through Wednesday
morning. Temperatures will also take a tumble on Tuesday.

Very strong and dangerous winds are more than likely for the LA
and VTA mtns but hazards from these winds (60 to 70 mph gusts with
a chc of 80+ mph gusts) are covered in a winter storm watch that
will also incorporate the hazards posed by snow and bitter wind
chills. Almost all other areas will be under wind advisories for
gusts between 45 and 55 mph which will feel quite strong to people
unaccustomed to these sorts of velocities. The strongest winds
will not last too long and should diminish to below warning levels
by dawn. Breezy conditions will continue Wednesday.

The other major issue with this area of low pressure will be much
colder temperatures due to the cold origins of the storm system,
coming down from western Canada. Amazingly, the snow levels look
to drop down to around 1500 feet Tuesday night into early
Wednesday. However, since the atmosphere will start out fairly dry
the chance of snow will not be too widespread with light snow
possible (30-40 percent chance) mainly near the hills and
mountains of the interior sections. Areas west of the mountains
will have an increasing chance of showers during the day Wednesday
mainly north of coastal LA County. The snow level does manage to
creep upward a bit to around 2000 feet Wed afternoon and Wednesday
night, except for isolated portions of the far interior where it
will hover near 1500 feet.

The threat of precipitation spreads to the entire region
Wednesday night. Temperatures will remain quite cold for this time
of year with highs in the 50s and lows in the 30s and 40s at low
elevations.

For Thursday, the large cold trough of low pressure remains in
place and scattered showers will be likely through the day over a
widespread area. Temperatures will remain 10 to 20 degrees below
normal for this time of year.

.LONG TERM (FRI-MON)...20/210 PM.

During the extended period, the cold trough is held in place by
reinforcing energy dropping down the back side of the trough and a
low drops down to a position west of Point Conception Saturday
morning. Without a question, Friday and Saturday will continue to
be wet and cold with the snow level rising to 3500 feet Friday and
lowering to 2500 to 3000 feet Saturday as the cold core of the
system gets closer to the region. Valley rains and mountain snows
will persist into Saturday with rainfall totals approaching 2
inches for the entire period, and highest snowfall amounts in the
mountains above 5000 feet could range between 1 and 3 feet with
higher amounts.

Some differences remain in timing as the GFS deterministic model
takes the low out of the area Saturday afternoon or evening, while
the EC deterministic model allows the low to linger into Sunday
morning before finally exiting to the east of the area.

A perusal of the GEFS and EC ensemble means show a bit better
agreement in the timing with the low finally exiting the area
sometime Saturday night.

Looking further into the future, models are hinting at another
cold trough poised to drop into southern California early next
week.

&&

.AVIATION...21/0059Z.

At 0032Z at KLAX, there was no marine layer. There was a sfc-
based inversion with a top at 1300 ft and a temperature of 17 C.

Moderate to high confidence in TAFs. High confidence in VFR
conditions most sites through the period. Only exceptions will be
a chance of IFR/LIFR conds at KSMX (40%) and KSBP (30%) after 08Z
and a 30% chance of IFR conds at KLAX and KLGB after 12Z.

KLAX...Moderate to high confidence in TAF. High confidence in VFR
conditions through 13Z. 13Z-17Z, there is a 30% chance of
bkn008-10 conditions, then a 30% chance of cigs rising to
BKN025-BKN030 after 020Z. Otherwise, VFR conds are expected. No
significant easterly wind component is expected.

KBUR...High confidence in VFR TAF.

&&

.MARINE...20/250 PM.

For the Outer Waters, moderate to high confidence in current
forecast. Through tonight, high confidence in winds and seas
remaining below Small Craft Advisory (SCA) levels. For Tuesday
through Wednesday evening, widespread GALE FORCE winds will
develop with large SCA level seas. Therefore, a GALE WARNING is in
effect during this time. There is a 20% chance of STORM FORCE
winds (gusts 48+ knots) developing Tuesday night into Wednesday
morning. There is a 30% chance the winds drop below Gale force by
late morning on Wednesday. On Thursday, SCA level winds and seas
will continue. For Friday, there is a 30-40% chance of winds
shifting Southwesterly and continuing at SCA levels (especially
across PZZ676). There is also a 30% chance that SCA level seas
could linger into late friday night.

For the Inner Waters north of Point Sal, high confidence in
current forecast. Through Tuesday morning, winds and seas will
remain below SCA levels. For Tuesday afternoon through Wednesday,
widespread GALE FORCE winds will develop with SCA level seas.
Therefore, a GALE WARNING is in effect for that time. There is a
10-20% chance of STORM FORCE winds (gusts 48+ knots) Tuesday
night into Wednesday morning. There is a 30% chance the winds drop
below Gale force by late morning on Wednesday. For Thursday and
Friday, winds and seas will likely remain below SCA levels.

For the Inner Waters south of Point Conception, moderate to high
confidence in current forecast. Today through Tuesday morning,
winds and seas will remain below SCA levels. From late Tuesday
afternoon through Wednesday afternoon/evening, widespread GALE
FORCE winds will develop with SCA level seas. Therefore, a GALE
WARNING is in effect for that time. There is a 20-30% chance of
STORM FORCE winds (gusts 48+ knots) Tuesday night into Wednesday
morning. There is a 30% chance the winds drop below Gale force by
late morning on Wednesday. On Thursday and Friday, winds and seas
will remain below SCA levels.

Large and steep period seas of 13-18 feet are possible across all
Inner Waters by Wednesday, with 17-22 feet possible across the
Outer Waters. Waves this large and steep could be capable of
capsizing vessels or breaking vessels off of anchors or moorings.
Breaking waves may also be possible at Ventura and Morro Bay
Harbor entrances.

&&

.BEACHES...20/241 PM.

Strong winds and high seas developing Tuesday lasting until late
Thursday night are expected to increase the size of breakers to
above High Surf Advisory criteria with a 10-20 percent chance of
reach High Surf Warning criteria. High surf of 10 to 18 feet will
affect the Central Coast, 7 to 10 feet with sets to 14 feet along
Ventura and Los Angeles County beaches, and 4 to 7 feet for Santa
Barbara south coast Beaches. Surf will be highest along northwest
and west facing beaches.

Frequent steep and chaotic breaking waves along
with very strong winds will create life threatening conditions,
even for experienced ocean swimmers. High surf along with strong
rip currents may continue into Thursday or Friday.

Minor Coastal flooding is possible due to the combination of high
tides and large swells Tuesday night and Wednesday morning. High
tides will be 5.2-5.8 feet occuring around 1030-1130 PM Tuesday
and 1000-1100 AM on Wednesday. Please see the Coastal Flooding
Product (LAXCFWLOX) for more details.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Winter Storm Watch in effect from Tuesday evening through
      Saturday afternoon for zones 53-54. (See LAXWSWLOX).
     High Wind Watch in effect from Tuesday evening through late
      Tuesday night for zones 59-87-349-351-549-550. (See LAXNPWLOX).
     High Surf Advisory in effect from noon Tuesday to 3 AM PST
      Thursday for zones 340-346. (See LAXCFWLOX).
     High Surf Advisory in effect from 8 PM Tuesday to 3 AM PST
      Thursday for zones 349-350-354-362-364. (See LAXCFWLOX).
PZ...Gale Warning in effect from 1 PM Tuesday to 3 PM PST
      Wednesday for zone 645. (See LAXMWWLOX).
     Gale Warning in effect from 4 PM Tuesday to 3 PM PST
      Wednesday for zones 650-655. (See LAXMWWLOX).
     Gale Warning in effect from 9 AM Tuesday to 3 PM PST
      Wednesday for zones 670-673-676. (See LAXMWWLOX).

&&

PUBLIC...Sweet
AVIATION...Lund
MARINE...RAT/Lund
BEACHES...Munroe/Lund
SYNOPSIS...Sweet/Rorke

weather.gov/losangeles

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