Winter Storm Warning 2, NWS Los Angeles, CA

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
1105 AM PST Tue Jan 9 2024

.SYNOPSIS...09/548 AM.

Windy, cool and mostly dry conditions are expected this week.
Temperatures will fall below freezing across many interior
locations tonight and potentially again the next couple of nights.
Winds will increase over the mountains and foothills today into
Wednesday, with even stronger, potentially damaging winds late
Wednesday through Thursday. Widely scattered light showers will
affect the region late Wednesday into early Thursday, with a
chance of light snow accumulations over the north slopes. High
surf and coastal flooding is possible starting on Wednesday on
west and northwest-facing beaches.

&&

.SHORT TERM (TDY-THU)...09/1010 AM.

***UPDATE***

The forecast has been updated to expire Freeze and Hard Freeze
Warnings as well as Frost Advisories from last night and earlier
this morning. In addition, the forecast has been updated for the
issuance of a Freeze Warning for Calabasas and Agoura Hills for
tonight and Wednesday morning. No other changes have been made to
the ongoing forecast.

***From Previous Discussion***

Clear skies across the region this morning. Some high clouds will
likely push into the forecast area today, mainly north of Pt.
Conception, but overall, today should be mostly sunny. Some gusty
north winds were occurring in the L.A. County mountains, thru the
I-5 Corridor, in the Santa Ynez Range, and across southwestern
coastal sections of SBA County, but so far winds were below
advisory levels. It was rather cold, with areas of frost or light
freezes likely in the valleys, portions of the Central Coast, and
in interior coastal sections of VTU County early this morning.

Thru mid morning, Hard Freeze Warnings are in effect for the
interior valleys of SLO County and the Cuyama Valley, while Freeze
Warnings remain in effect for the interior portions of the SLO
County coastal plain, the entire Central Coast of SBA County, the
Santa Ynez Valley, the Valleys of VTU County, the Santa Clarita
Valley, the western San Fernando Valley, and the Agoura Hills/
Calabasas area. Frost Advisories are in effect for interior
portions of the Ventura County Coastal plain, the San Gabriel
Valley and the eastern San Fernando Valley.

Fast W-NW flow aloft will continue across the region thru tonight.
The flow will increase and become more cyclonic Wed as a trough
drops southeastward thru the Pac NW, causing the upper height
gradient to tighten. North to south low level gradients will
sharpen today, then remain fairly steep thru Wed. W to NW winds
are expected to increase to Wind Advisory levels across the
mountains of SBA/VTU Counties, the southwestern coast of SBA
County, thru the I-5 Corridor and in the western foothills of the
Antelope Valley later this morning or early this afternoon, with
westerly winds reaching advisory levels in the Antelope Valley
later this afternoon. Winds will remain at advisory levels or
higher in all of these areas at times right thru Thu afternoon,
though there may be some breaks in the wind, especially Wed
morning into early Wed afternoon. Winds may also get close to
advisory levels in the western San Gabriel mountains as well.

Elsewhere, expect some locally gusty north winds at times late
today thru Wed morning in the valleys of VTU and northern and
western L.A. Counties, in the Santa Monica Mountains, and in the
Malibu area, but winds in these areas should remain mostly below
advisory levels---at least thru Wed morning.

Max temps today may be a couple of degrees higher than they were
Mon, but will still be below normal. It will be another cold night
tonight, but with more in the way of wind, some increase in high
clouds, and a slightly less cold and dry airmass, do not expect
frost or light freezes tonight/early Wed to be as widespread as
they will be this morning. Later shifts may have to change course
if it appears that skies will remain clear or there is less wind.
High clouds will increase across the region Wed, and max temps
will likely be down a few degrees in most areas.

A vigorous vort will drop down the western side of the trough
late Wed and Wed night, causing it to sharpen, with strongly
cyclonic flow extending into the region. A surface cold front
will move thru the area late Wed and Wed night. While it will be
rather moisture-starved, strong height falls and a period of
increasing lift may allow it to hold together to bring some light
rain to much of the region Wed night, possibly beginning as early
as late afternoon in far northwestern SLO County, With the
northwesterly flow pattern, the threat of rain will be higher
north of Pt. Conception and in the mtns (50-60% chance), and
across far eastern Los Angeles County (30-40% chance), with very
little chance (15-25% chance) of measurable rain on the south
coast of SBA County, and in coastal sections of VTU/L.A. Counties.
This will be a cold system, and snow levels will drop quickly to
between 3000 and 4000 ft late Wed night. There may be some
lingering snow showers across the northern slopes of the mountains
of Ventura and northwestern L.A. Counties Thu morning, otherwise
Thu will be dry, with decreasing clouds. Max temps on Thu will be
6 to 12 degrees below normal across the region.

Rainfall totals should be one quarter of an inch or less in most
areas, with local totals up to a third of an inch possible across
northern SLO County and in the mtns. Snow accumulations of 1 to 3
inches are possible above 3500 or 4000 ft, and snow and icy roads
could bring travel problems to portions of I-5 near the Grapevine.

The main impact from this system will be the widespread strong
to possibly damaging west to northwest winds beginning late Wed,
then becoming northwest to north and increasing in strength and
coverage Wed night. This will all be caused by increasingly strong
northwest to north winds thru the atmosphere, a very strong jet
nosing into the region, and widespread subsidence and cold air
advection behind the front.

High Wind Watches are in effect for the mtns of SBA County
including the Santa Ynez Range, the southwest coast of SBA County,
the mountains of VTU County, the I-5 Corridor, the western
foothills of the Antelope Valley, the Santa Monica mountains, the
Malibu Coast, and the islands including Catalina Island. The
strongest winds are expected in these areas Wed night and Thu
morning, when gusts to 60 to 70 mph are possible in the Watch
area. High Wind Watches may have to be expanded to the valleys of
northern/western L.A. County and the eastern valleys of VTU
County. Winds will likely be strong enough to require Wind
Advisories across most of the rest of the forecast area Wed night
and Thu. There is a chance (30%) that Winter Weather Advisories or
Winter Storm Warnings will be needed for the mtns of northern VTU
County and NW L.A. County late Wed night/Thu morning. Winds will
begin to diminish slowly late Thu.

.LONG TERM (FRI-MON)...09/533 AM.

The trough will move east late Thu/Thu night, and with decreasing
upper support, winds will diminish. It will be cold Thu night.
Where winds drop off sufficiently, frost or freeze conditions are
expected in some valley areas, and even portions of the coastal
plain from VTU County northward. Dry W to NW flow aloft will
continue across the area Fri thru early Sat. Max temps should rise
a few degrees, though will still be a bit below normal Fri. Expect
one more cold night Fri night, with frost or light freezes possible
in the colder valley areas and maybe coastal sections from VTU
County northward. There could be some locally gusty NE winds late
Fri night/Sat morning as gradients between KLAX and KDAG briefly
flip offshore, but winds should be well below advisory levels.

The upper flow will become westerly Sat as a trough or upper low
moves into the Pac NW (deterministic run of the EC shows a cold
upper low, while the GFS shows a broad trough). Both models show
the system once again taking an inside track to our northeast Sat
night, into the Great Basin and Rocky Mountains Sun. The EC shows
the jet and a band of moisture sagging far enough to the south to
bring a slight chance of rain, mainly to northern areas Sat
afternoon into Sat night. The GFS keeps all rain to our north,

Lowering heights shown by the EC would bring some cooling Sat,
while higher heights and weak offshore flow indicated by the GFS
would allow for some warming.

Heights will rise across the region Sun as an upper ridge
amplifies in the eastern Pacific. Skies should be mostly clear.
Expect some warming Sun, with max temps possibly rising to
slightly above normal levels in some areas.

The upper ridge in the Pacific will move eastward into the
forecast area Mon, with dry weather continuing. There will likely
be additional warming, with max temps above normal in most areas.

&&

.AVIATION...09/1859Z.

Around 1830Z, there was no marine layer at KLAX.

High confidence in the current forecast through 00Z Thu. There is
a 40% chance that MVFR cigs do not develop at northern terminals
this evening. Moderate low-level wind shear and turbulence is
possible at all terminals after 00Z Wednesday.

KLAX...VFR conditions are expected through the period. Any
easterly winds will be less than 7 knots.

KBUR...VFR conditions are expected through the period.

&&

.MARINE...09/841 AM.

Moderate-to-high confidence in the current forecast. Winds will
increase and seas will build to Small Craft Advisory (SCA) levels
through Wednesday across the coastal waters as a frontal system
moves into the region. Due to the large swell, west and
northwest-facing harbor entrances could have hazardous conditions
with large breaking waves, especially Wednesday night through
Thursday night.

For the waters northwest of San Nicolas Island, the chances for
SCA conditions will increase from 40-70 percent early this morning
to 70-100 percent by this evening. The highest chances are for
the waters from Point Sal south to San Nicolas Island where there
is also a 40 percent chance of low end gale conditions as early
as this afternoon and evening. Widespread Gales will develop by
late Wednesday afternoon. Hazardous seas in excess of 10 feet are
likely between Wednesday and Thursday. The highest chance is for
late Wednesday night and Thursday morning.

For the waters inside the southern California bight, the chances
for SCA conditions will increase from 30-50 percent early this
morning to 40-60 percent by this evening. The highest chances are
for the western portion of the Santa Barbara Channel and the
lowest chance are for the Santa Monica Bay. There is a 70-100
percent chance of widespread SCA conditions by Wednesday night and
a 50-80 percent chance of Gales. Hazardous seas in excess of 10
feet are likely during this time. West facing harbors could have
large breaking waves at harbor entrances. The highest chance is
for Thursday and Thursday night.

&&

.BEACHES...09/830 AM.

Another large northwesterly swell will arrive on the beaches
tonight through Thursday night. High surf will develop again on
all west and northwest facing shores. The latest swell guidance
suggest that sets to 10-15 feet are likely on the Central Coast by
Wednesday afternoon and peaking on Thursday morning at 12-17 feet.

Across LA/Ventura County beaches, surf heights up to 5-8 are
likely by Wednesday, and peaking Thursday with waves 6-9 feet.

With higher astronomical high tides from 6.9 feet to 7.3 feet
each morning, minor coastal flooding is likely around the times
of the morning high tide. The large swell combined with a locally
generated short-period swell produced by possible gales over the
coastal waters should result flooding of normally dry areas, such
as parking lots and walkways around the morning high tides.

Beachgoers are advised to remain off rock jetties and never EVER
turn their back to the ocean. Every set of waves has a much higher
wave embedded within that has a potential to sweep people off
jetties and shorelines.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory in effect from 3 PM Wednesday to 3 PM PST
      Thursday for zones 87-362-366. (See LAXCFWLOX).
     High Wind Watch in effect from Wednesday afternoon through
      Thursday afternoon for zones
      87-349-351>353-362-369-376>378-381-549-550. (See LAXNPWLOX).
     Coastal Flood Advisory in effect from 4 AM to noon PST
      Thursday for zones 87-354-362-366. (See LAXCFWLOX).
     High Surf Advisory in effect from 9 PM this evening to 9 AM
      PST Friday for zones 340-346. (See LAXCFWLOX).
     Coastal Flood Advisory in effect from 3 AM Wednesday to noon
      PST Thursday for zones 340-346. (See LAXCFWLOX).
     Wind Advisory in effect until 4 PM PST Wednesday for zones
      349-351>353-376>378-381-549-550. (See LAXNPWLOX).
     High Surf Advisory in effect from 9 AM Wednesday to 3 AM PST
      Friday for zone 354. (See LAXCFWLOX).
     Freeze Warning in effect from midnight tonight to 10 AM PST
      Wednesday for zone 371. (See LAXNPWLOX).
     Wind Advisory in effect from 3 PM this afternoon to 4 PM PST
      Thursday for zone 383. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect from 3 PM this afternoon to 2
      AM PST Wednesday for zone 645. (See LAXMWWLOX).
     Gale Watch in effect from Wednesday afternoon through late
      Wednesday night for zone 645. (See LAXMWWLOX).
     Small Craft Advisory in effect from 3 PM this afternoon to
      noon PST Wednesday for zone 650. (See LAXMWWLOX).
     Gale Watch in effect from Wednesday afternoon through
      Thursday morning for zones 650-655-670. (See LAXMWWLOX).
     Small Craft Advisory in effect from 3 PM this afternoon to 3
      PM PST Wednesday for zone 670. (See LAXMWWLOX).
     Small Craft Advisory in effect until 9 AM PST Wednesday for
      zone 673. (See LAXMWWLOX).
     Gale Watch in effect from Wednesday morning through Thursday
      afternoon for zone 673. (See LAXMWWLOX).
     Small Craft Advisory in effect until 4 PM PST this afternoon
      for zone 676. (See LAXMWWLOX).
     Gale Warning in effect from 4 PM this afternoon to 4 PM PST
      Thursday for zone 676. (See LAXMWWLOX).

&&

PUBLIC...DB/Cohen
AVIATION...MW
MARINE...MW/Hall
BEACHES...MW/Hall
SYNOPSIS...Cohen/Smith/DB

weather.gov/losangeles

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