High Wind in California, February 21 to 22, 2023

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
356 PM PST Tue Feb 21 2023

.SYNOPSIS...21/1251 PM.

A strong cold front will move over southwest California through
Wednesday morning with very windy conditions and rapidly falling
snow levels. Cold, showery weather will persist until an unusual
winter storm brings periods of heavy rain and heavy mountain snow
to the region Friday through Saturday night. Improving conditions
are anticipated by Sunday.

&&

.SHORT TERM (TDY-FRI)...21/143 PM.

A very complex storm event is on our doorstep with many
significant impacts expected in the next few days, some not
experienced in decades. Onshore pressure gradients had rapidly
increased to over 10mb from LAX-TPH today with gusty SW winds
across the mountains and the Antelope Valley. A very cold low
pressure trough and surface front are dropping southward down the
Central Coast this afternoon. Winds were gusting near 50 mph at
SFO Airport at midday! Heights will drop over 300m from today
through early Wednesday with our winds increasing this evening
with widespread gusts of 30-50 mph, except 55-75 mph in the
mountains and AV through Wednesday morning. There will be the
potential for tree damage and power outages just due to winds
alone through Wednesday, along with travel impacts at our major
airports. Snow levels drop rapidly from the current 6k feet range
to near 1k feet tomorrow. Precipitation will not be too organized
through Wednesday night, however, northwest upslope flow will
bring the risk of several inches of snow to the mountains with
impacts on I-5 near the Grapevine. Other foothill areas and
elevated valley floors may also see light snow at times on
Wednesday. Due to this risk, will issue a winter weather advisory
for the Cuyama and Antelope Valleys with amounts of 3-6 inches on
nearby foothills and less than 3 inches for valley floors. Some
uncommon areas of the LA foothill communities, Santa Clarita
Valley, and Santa Ynez foothill communities could experience a
dusting of snow at times through Wednesday night. Thursday will
remain very cool with snow levels remaining near 2500 ft, so
continued scattered rain and snow showers will occur. Temperatures
will be stuck in the 50s for highs in most valleys and coasts
through the next 2-3 days.

The next big impact will be a closed low pressure system that
evolves off the Oregon coast on Thursday, and then dives
southward along our coast to the Channel Islands late Saturday.
Deterministic model data have waffled on the over land vs over
water trajectory since last week, but have now matched the
ensembles with a slow moving system staying over the ocean and
increasing the south wind component for our local terrain.
Precipitation will ramp up due to strong orographic flow with
enhanced rain and snow amounts expected late Thursday night
through early Saturday. Snow levels will fluctuate quite a bit as
the southerly flow will raise levels to about 4500 ft briefly on
Friday afternoon. This could create a mixture of rain/snow at the
I-5 Grapevine area before precipitation turns back to all snow
Friday evening. Rainfall rates will range from 0.50-1.0" per hour
near the main frontal band on Friday bringing a threat of urban
flooding and issues near recent burn scars.

The precipitation totals for the majority of the south Santa
Barbara coast, Ventura, and Los Angeles coasts/valleys will be in
the 2-4 inch category. Low snow levels will mean that this could
be the largest amount of 24-48 hour snowfall seen in decades for
our Ventura and Los Angeles County mountains. Depending on the
snow-line, rainfall in the foothills will be from 4-6 inches, but
the mountains above 4000 ft could see upwards of 2-5 FEET of snow
with isolated amounts to 7 feet at higher elevations. Snowfall of
this rate and amount could lead to damage to structures and trees
with an immense threat of avalanches, especially in the eastern
San Gabriel Mountains by Saturday.

.LONG TERM (SAT-TUE)...21/136 PM.

Saturday will be the last day of precipitation in the forecast
period and could be quite interesting as the closed low moves
directly overhead. The cold, unstable air will be conducive to
development of heavy showers, lightning, and small hail or
graupel. Cyclonic spin would allow for waterspout activity over
the ocean with brief small tornadoes near the coast. Precipitation
coverage would not be as widespread, but most areas are likely to
see additional showers through the day Saturday and snow levels
will remain below 3000 ft.

Sunday could be about the only break in the wet conditions as
there is yet another storm system on the horizon possibly as soon
as Monday or Tuesday next week. ECMWF ensemble data supports a
significant trough along the West Coast near Tuesday-Wednesday
which also shows widespread precipitation amounts. Given the
minimal recovery of upper level heights, snow levels are likely to
be on the lower side once again when this system moves into the
region next week.

&&

.AVIATION...21/2354Z.

At 2147Z at KLAX, there was no marine inversion.

Overall low confidence in the 00Z TAFs. Rain showers will be
mostly confined to areas from KSBA northward, but there is a
10-20 percent chance of -shra over the Ventura County sites
Wednesday. Gusty moderate to strong westerly winds are expected
for all areas, increasing between 01Z-05Z this evening, and
continuing through the period. Moderate to high confidence that
strong winds will occur, but lower confidence in wind speeds and
timing of wind shifts from west to northwest. Wind gusts could be
off by 10 knots. LLWS and UDDFS are likely over the higher
terrain after 06Z.

KLAX...Low to moderate confidence in the 00Z TAF. MVFR cigs should
lift to VFR by 03Z but timing could be off by +/- 2 hrs. Arrival
of strong winds (sustained 35 knots) could be off by as much as 3
hours, and the wind gust speed could be 10 knots higher than
forecast.

KBUR...Low to moderate confidence in the 00Z TAF. MVFR cigs
should lift to VFR by 03Z but timing could be off by +/- 2 hrs.
Arrival of stronger winds (gusts to 35 knots) could be off by as
much as 3 hours, and the wind gust speed could be 10-15 knots
higher than forecast. LLWS and moderate turbulence on descent and
climb possible after 04Z.

&&

.MARINE...21/139 PM.

Gale force winds have already pushed into the northern portions
of the coastal waters. Storm force winds are still expected by
late afternoon or early evening. The marine forecast will remain
unchanged for now.

Overall, moderate confidence in the current forecast. High
confidence in widespread GALE FORCE winds and very large seas
across the entire coastal waters through Wednesday afternoon.
Moderate confidence exists in STORM FORCE (gusts 48+ knots) winds
from late this afternoon through late tonight. Winds will
increase rapidly through this afternoon. There is a 80-100 percent
chance of GALE FORCE winds moving from north to south between 9
am this morning and 6 am Wednesday morning. The highest chances
for GALES will across the entire coastal waters between 10 pm and
4 am tonight. There is a 40-70 percent chance of STORM FORCE
winds, highest for the waters from near Point Sal to the south and
into the southern California. It is likely that the nearshore
waters inside the southern California bight will see STORM FORCE
wind gusts.

There is a moderate (30-50 percent) chance of winds dropping below
GALE FORCE by late Wednesday morning, then there is a moderate-
to-high (30-60 percent) chance Small Craft Advisory (SCA)
conditions (winds and/or seas) between Wednesday night and early
Friday across the entire coastal waters. Winds and seas will
likely diminish and subside respectively below SCA levels on
Saturday.

Dangerous sea conditions are expected through Wednesday as very
large and steep seas build across the entire coastal waters,
peaking near 18 to 22 feet in the very nearshore coastal 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...21/127 PM.

Strong winds and large seas developing through this afternoon
will bring a high-to-very likely (50-90 percent) chance of high
surf at west and northwest facing shores by late this evening.
Then, increasing to a likely-to-imminent (70-100 percent) chance
by daybreak Wednesday. There is low-to-moderate (30-50 percent)
chance of a HIGH SURF WARNING being needed between late tonight
and Wednesday, highest at Central Coast 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 tonight and Wednesday morning. High tides
will be 5.2-5.8 feet occuring between 1000 and 1100 PM tonight
and between 1000 and 1100 AM Wednesday morning.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory in effect until 6 PM PST this evening for zones
      53-54-59. (See LAXNPWLOX).
     Winter Storm Warning in effect from 7 PM this evening to 4 PM
      PST Saturday for zones 53-54. (See LAXWSWLOX).
     High Wind Warning in effect until 6 AM PST Wednesday for
      zones 59-87-349-351-549-550. (See LAXNPWLOX).
     Winter Weather Advisory in effect from 4 AM Wednesday to 4 AM
      PST Friday for zone 59. (See LAXWSWLOX).
     Wind Advisory in effect until 10 AM PST Wednesday for zones
      88-350-352-354>359-362>364-547. (See LAXNPWLOX).
     High Surf Advisory in effect until 3 AM PST Friday for zones
      340-346. (See LAXCFWLOX).
     Wind Advisory in effect until 6 AM PST Wednesday for zones
      340>348-353. (See LAXNPWLOX).
     Winter Storm Warning in effect from 4 AM Wednesday to 4 PM
      PST Saturday for zones 345-353. (See LAXWSWLOX).
     High Surf Advisory in effect from 8 PM this evening to 3 AM
      PST Thursday for zones 349-350-354-362-364. (See LAXCFWLOX).
PZ...Gale Warning in effect until 3 PM PST Wednesday for zone 645. (See LAXMWWLOX).
     Gale Warning in effect until 8 PM PST this evening for zones
      650-655. (See LAXMWWLOX).
     Gale Warning in effect until 11 AM PST Wednesday for zone
      670. (See LAXMWWLOX).

&&

PUBLIC...EB
AVIATION...Smith
MARINE...Sweet/Hall
BEACHES...Sweet/Hall
SYNOPSIS...EB

weather.gov/losangeles

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