High Wind in California, December 10 to 11, 2022

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
219 PM PST Sat Dec 10 2022

.SYNOPSIS...10/218 PM.

A strong storm system will affect the region through Monday and
bring rain and mountain snow, heavy at times, gusty winds, and
high surf. A colder air mass will spread into the region between
Sunday and Monday and bring the possibility of isolated
thunderstorms. Another storm system could drop into the region
sometime late next week.

&&

.SHORT TERM (TDY-TUE)...10/217 PM.

Skies were mostly cloudy overall across the forecast area early
this afternoon as a Pacific storm system slowly approaches the
area from the NW. Pre-frontal moisture has been continuously
moving into the Central Coast and southern SBA County today with
many areas receiving measurable rain. Rain was also spreading into
VTU County early this afternoon. The most rainfall has been over
NW SLO County. Rocky Butte has already received 3.71 inches of
rain in the last 18 hours, while other nearby areas have had about
0.75 to 2.00 inches. The moisture feed will continue into these
areas while slowly moving down the coast thru this afternoon, with
rain moving into western L.A. County by late afternoon.
Additional rainfall this afternoon could be significant over the
Central Coast with continuous rainfall ahead of the main frontal
band and good orographic enhancement into the coastal range.

In addition, increasingly strong southerly winds can be expected
thru this afternoon over SLO/SBA Counties and into the higher
terrain of VTU/L.A. Counties. Damaging winds are possible as well
over interior SLO County including the SLO County mtns and over
the interior SBA County mtns where High Wind Warnings are in
effect. There are also Wind Advisories in effect for the remainder
of SLO/SBA Counties.

A strong and cold upper level low off the Pac NW coast will drop
south southeastward to a position just off the coast of the
California/Oregon border late tonight. As it does so, a strong jet
will sag southward into the forecast area. A diffluent upper
pattern and improving jet dynamics will allow a surface cold front
to maintain its strength as it sweeps across the region tonight
and early Sunday. This front will move fairly quickly, and it
should bring a 4 to 6 hours period of moderate to heavy rain to
the entire forecast area.

The main frontal band should affect SLO County from very late
this afternoon through midnight or so, SBA County from this
evening through the middle of the night, VTU County from about
midnight through just after daybreak, and L.A. County from the
middle of the night through about noon. This will be a fairly
dynamic front, so will not be surprised if there are a couple of
thunderstorms with it as it rolls through the region. Strong south
to southwest winds up to 55 knots at 850 mb tonight and Sun
morning will cause significant enhancement of the rain on and
below southwest facing slopes ahead of and with the front.

High Wind Warnings will continue for the mountains of SLO and SBA
Counties and the elevated interior valleys of SLO County through
late tonight, and will be in effect for the Ventura and L.A.
County mountains and the Antelope Valley this evening through
Sunday morning. Damaging wind gusts of 60 to 70 mph are expected
in these areas. The strongest winds are likely in the LA county
mountains and foothills of the Antelope Valley, where isolated
gusts to 80 mph are possible.

With the front, rainfall rates of one quarter to one half inch
are expected in coastal and valley areas, with rates of one half
inch to one inch in the foothills and mountains due to orographic
enhancement. Rainfall at these rates will likely cause plenty of
urban and street flooding, as well as minor mud and debris flows
in and around recent burn scars. With the potential for rainfall
rates up to one inch per hour, more significant mud and debris
flows are possible, so a Flash Flood Watch is in effect for the
Lake and Fish burn scars in Los Angeles County late tonight
through Sunday afternoon.

Rain will turn to scattered showers by Sunday afternoon, but
showers will likely be quite numerous Sun night. Cooling aloft and
a favorable jet position will likely cause some of the showers to
be convective Sun afternoon, with heavy downpours and small hail
possible. Then it looks like the upper level low will move right
over the forecast area Sunday night and early Monday, bringing a
slight chance of thunderstorms to the forecast for SLO and SBA
Counties Sun night, and for VTU and L.A. Counties late Sun evening
through mid morning Monday. Since rainfall rates may still be
high, later shifts may have to extend the Flash Flood Watch for
the L.A. County burn areas through early Mon morning.

Showers will decrease across the region on Monday as the upper
low pulls east of the region, but could still be fairly numerous
in the morning in eastern sections and on northern slopes.

Rainfall totals through Monday should average 1 to 2 inches in
coastal and valley areas and 2 to 6 inches in the foothills and
mountains with isolated amounts up to 8 inches or more not out of
the question.

Snow levels will be rather high (generally above 7000-7500 feet)
through tonight, but then will fall quickly later on Sunday as
colder air pushes into the region behind the front, likely to as
low as 3000 to 4000 feet by late Sunday night into Monday.
Significant snow is expected at high elevations beginning Sunday,
with accumulating snow (up to an inch) on portions of I-5 near the
Grapevine late Sun night and early Monday. This could cause major
travel disruptions. As a result of the snow, some gusty winds and
hazardous wintry driving conditions, the current Winter Storm
Watch will be upgraded to a Winter Storm Warning for the higher
mtns of SBA/VTU/ L.A. Counties from Sunday afternoon through
Monday afternoon.

It will be very chilly across the region on Monday. Skies should
clear Mon night as the storm system moves well to the east, making
for a very cold night. Freezes are possible in the Ojai Valley
and other colder Ventura County valleys Monday night into Tuesday
morning, with frosts on the Central Coast. This will lead to
mostly sunny and cool conditions on Tuesday with highs several
degrees below normal despite the sunshine.

.LONG TERM (WED-SAT)...10/210 PM.

Forecast confidence remains relatively low for the extended
period. Wednesday will remain dry and cool across the region with
increasing clouds altho a weak disturbance may bring a slight
chance of showers to NW SLO County. A broad upper level low is
forecast to be over the E Pac off the nrn CA coast Thu and Fri
then drift closer to the central CA coast on Sat (deterministic
models) while the mean ensembles open up the low into a broad trof
late in the week. Moisture is forecast to be drawn northward into
the fcst area late in the week, with a chance of showers expected
for nwrn SLO County thru Thu then spread to all areas Fri and
Sat. Went with the NBM pops which were were a bit wetter than the
deterministic models but is more in line with the mean ensembles.
Temps will remain cooler than normal thru the period.

&&

.AVIATION...10/1826Z.

At 1753Z, there was a deep moist layer up to around 5500 feet.

Low-to-moderate confidence in current forecast. Timing of lower
flight categories could be 2 hour earlier than forecast or an
hour later than forecast. MVFR conditions will become predominant
around 19Z. There is a moderate (30-50 percent) chance of IFR
conditions through 19Z at terminals north of Point Conception,
then IFR conditions will spread north to south after 19Z.

There is a moderate (30-50 percent) chance of period of moderate
to strong low- level wind shear and turbulence as the storm's
frontal boundary moves south.

KLAX...MVFR conditions will become predominant around 19Z. There
is a 30 percent chance of IFR conditions at 07Z Sunday increasing
to 70 percent by 16Z Sunday. Southerly cross winds greater than 20
knots are likely after 08Z Sunday. There is a 30 percent chance
of a period of moderate to strong low-level wind shear and
turbulence after 14Z Sunday. There is a 30 percent chance of
easterly wind component greater than 10 kt Sunday morning.

KBUR...MVFR conditions will become predominant around 19Z. There
is a 30 percent chance of IFR conditions at 08Z Sunday increasing
to 70 percent by 17Z Sunday. There is a 40 percent chance of
period of moderate to strong low-level wind shear and turbulence
after 12Z Sunday.

&&

.MARINE...10/139 PM.

A storm system will affect the waters through Monday. South winds,
at least at Small Craft Advisory (SCA) levels with short-period
hazardous seas, will develop by this evening through Sunday
evening. There is a 70-100 percent chance of Gale Force winds for
the waters southwest through northwest of the Channel Islands and
along the Central Coast, highest for the northern portions. The
latest guidance for winds in the inner waters suggests a strong
SCA for tonight into Sunday morning, so the GALE WATCH has been
dropped and changed to a Small Craft Advisory.

Winds will turn west to northwest Sunday through Tuesday. Widespread
SCA conditions are expected through Monday evening with gusty west
to northwest winds and hazardous seas. There is a 50 percent
chance of Gale Force winds on Monday beyond 30 miles from shore
between the Central Coast and San Nicolas Island. Scattered
showers and a 40 percent chance of thunderstorms are expected
Sunday through Monday. Seas will peak between Sunday and Monday
with heights of 12 to 18 feet, except 5 to 8 feet nearshore south
from Santa Barbara to Orange County. Moderate confidence that seas
and winds will subside Tuesday and Wednesday.

&&

.BEACHES...10/140 PM.

No changes to the High Surf Advisory this afternoon...

A storm system will usher in a large northwest swell for Sunday
and Monday. There will be enough westerly component to affect not
only the central coast but also west facing beaches south of Point
Conception.

A High Surf Advisory is in effect for the central coast and the
west facing beaches of LA and Ventura counties. Breakers of 10 to
14 feet with max sets to 16 feet are expected on west and
northwest facing beaches of the central coast. South of Point
Conception, west facing beaches of LA and Ventura counties will
have breakers of 5 to 9 feet. Finally, a Beach Hazards Statement
is now in effect for the south coast of Santa Barbara county for
elevated breakers of 3 to 6 feet.

Due to minor concerns over a relatively high tide occurring Sunday
morning, the west and northwest facing beaches of San Luis Obispo
county may also see some minor tidal overflow around the time of
high tide Sunday morning.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...High Wind Warning in effect from 7 PM this evening to noon
      PST Sunday for zones 53-54-59. (See LAXNPWLOX).
     Winter Storm Warning in effect from 4 PM Sunday to 6 PM PST
      Monday for zones 53-54-353. (See LAXWSWLOX).
     Flash Flood Watch in effect from late tonight through Sunday
      afternoon for zones 54-59-548. (See LAXFFALOX).
     High Surf Advisory in effect from 9 AM Sunday to 8 PM PST
      Monday for zones 87-340-346-354-364. (See LAXCFWLOX).
     Wind Advisory in effect from 10 PM this evening to noon PST
      Sunday for zones 88-362>365-547-548. (See LAXNPWLOX).
     Wind Advisory in effect until 6 AM PST Sunday for zones
      340>343-346>352. (See LAXNPWLOX).
     High Wind Warning in effect until 6 AM PST Sunday for zones
      344-345-353. (See LAXNPWLOX).
     Beach Hazards Statement in effect from Sunday morning through
      Monday evening for zones 349-350. (See LAXCFWLOX).
     Wind Advisory in effect from 7 PM this evening to noon PST
      Sunday for zones 354>359. (See LAXNPWLOX).
PZ...Gale Warning in effect until 3 AM PST Sunday for zones
      645-670-673. (See LAXMWWLOX).
     Small Craft Advisory in effect until 9 PM PST this evening
      for zone 650. (See LAXMWWLOX).
     Gale Watch in effect from 9 PM PST this evening through late
      tonight for zone 650. (See LAXMWWLOX).
     Small Craft Advisory in effect from 9 PM this evening to 3 AM
      PST Sunday for zone 655. (See LAXMWWLOX).
     Gale Watch in effect from late tonight through Sunday morning
      for zone 655. (See LAXMWWLOX).
     Small Craft Advisory in effect until 6 PM PST this evening
      for zone 676. (See LAXMWWLOX).
     Gale Warning in effect from 6 PM this evening to 3 AM PST
      Sunday for zone 676. (See LAXMWWLOX).

&&

PUBLIC...DB/Sirard
AVIATION...Sweet/Hall
MARINE...Sweet/Hall
BEACHES...Sweet
SYNOPSIS...Hall/Sirard

weather.gov/losangeles

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