High Wind in California, November 21, 2021

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
1021 PM PST Sat Nov 20 2021

.SYNOPSIS...20/827 PM.

Offshore flow across the area will bring a warming and drying
trend through Monday, with gusty winds likely for most of Ventura
and Los Angeles Counties. Cooler conditions are expected on
Tuesday and Wednesday as a weak weather system moves over the
region. Another Santa Ana wind event is possible beginning as
early as Wednesday.

&&

.SHORT TERM (SAT-TUE)...20/828 PM.

***UPDATE***

High clouds streaming in from the southwest have kept partly to
mostly cloudy skies over most of Southwest California this
evening. Underneath, low clouds from the San Joaquin Valley are
banking up across the northern mountain slopes and should hang
out through the night. Current satellite imagery indicates clouds
dissipating over the eastern SLO County border. Based on this
trend, feel comfortable that low clouds will not spill into
interior SLO County, except for the Carrizo Plain. As a result,
have decided to remove mention of low clouds and fog from the
Salinas Valley tonight, but there is a chance that clouds could
develop overnight. No marine layer stratus is expected tonight
over the coastal areas as north to northeast flow should keep it
away. A forecast update will be issued in tandem to tweak the
cloud cover tonight through Sunday morning.

Winds will be the main forecast issue for tonight and through the
short term. There are breezy northeast winds across the Santa
Lucia range this evening. Winds have been gusting to 45 mph,
locally up to 50 mph, and are expected to continue through Sunday
morning. A Wind Advisory will remain in effect through 8am, but
would not be surprised if gusty winds continue through late
morning or into the afternoon.

The forecast remains on track for a moderate Santa Ana wind event
late tonight through early Monday afternoon, peaking on Sunday.
The LAX-DAG gradient is forecast to peak around -7 mb on Sunday
morning according to the NAM, but history has shown the gradient
may peak 1 or 2 mb weaker. There will also be moderate upper
support and cold advection with this event. The combination of
these three important factors brings good confidence in wind gusts
ranging between 35 and 55 mph across the Santa Ana wind-prone
regions of LA and Ventura Counties, particularly straddling the
county line. Some locally damaging winds up to 60 mph are possible
across the mountains. Winds will likely start picking up over the
higher elevations after midnight, then become more widespread
towards the coastal and valley areas by early morning. Temperatures
will be on the rise on Sunday in response to the offshore flow,
but not nearly as high as the last event. High temperatures will
range from the low to mid 80s across the valleys and inland
coastal sections. No record highs are expected this time. Pressure
gradients remain similar on Monday, but upper support and cold
advection will weaken, so winds will likely be a bit weaker for
Monday. Temperatures will remain warm but cool a bit from Sunday.

***From Previous Discussion***

Synoptically, there is an upper level trough extending to the
southwest from Montana through SoCal, with an extended area of
lower heights bulging to the SW that looks like it wants to become
a cutoff low. By Sunday the lower offshore pressure will anchor
the pressure gradient force winds that will be our first Santa
Ana event of the week. By Tuesday another upper level trough will
be moving through Oregon and extends to the SW over our area.
There is no moisture with this system as a big rain producer, but
enough ensemble members are suggesting that there is a
possibility of more than a hundredth of an inch beginning Monday
night and slight chance PoPs remain in the forecast. There is a
chance of another quick Santa Ana event beginning Wednesday as
this system moves off to the east. For the later part of the week,
a ridge of higher heights moves overhead from the southwest
driving heights to 586 dam by Thursday.

Local knowledge suggests that the forecast models struggle with
the synoptic conditions expected by late Monday, with essentially
a cutoff low to our southwest. While the ensemble means remain
dry, enough members are showing precipitation that there is about
a 10-20% chance for greater than a hundredth of an inch falling
beginning Monday evening - with the best chances over the Ventura
County mountains and eastern San Gabriels. This is a pretty low
confidence forecast and will bear watching.

.LONG TERM (WED-SAT)...20/228 PM.

A cooler air mass will be in place on Wednesday and the skies will
be mostly clear. By later in the day the EPS and GEFS members indicate
offshore flow developing again with gusts around Newhall Pass
approaching 40 mph. This should be both a weaker and shorted Santa
Ana event than the one this weekend.

Thanksgiving day through Saturday should be warmer than average as
a 590 dam ridge builds over the area from the SW with 586 dam over
our area. Temperatures should range from the mid 70s along the
coast to low 80s in the valleys.  The return of higher heights
will traditionally bring a return of overnight low clouds and fog along
the coast.

&&

.AVIATION...21/0614Z.

At 0518Z at KLAX, there is a surfaced based inversion with a top
around 1900 feet with a temperature of 20C.

Moderate confidence in the 06Z TAFs. There is a 30% chance of
of MVFR conditions forming at KPRB. There is a 20% chance of
VFR conditions returning before 08Z at KSMO, KLAX, KLGB. Gusty NE
winds will affect the mtns and valleys of L.A. and VTU Counties
with mdt turbulence and some LLWS.

KLAX...Moderate confidence in the 06Z TAF. There is a 20% chance
of VFR conditions returning before 10Z. There is a 20% chance
that there will be an easterly wind component up to 10 kt through
early Sunday morning.

KBUR...Moderate confidence in the 06Z TAF. Mdt turbulence and
some LLWS possible.

&&

.MARINE...20/1018 PM.

For the outer waters, fairly high confidence in the forecast.
There is a 30% chance of Small Craft Advisory (SCA) level NE
winds across portions south of San Miguel Island and north of San
Nicolas Island on Sun. Otherwise, SCA conds are not expected Sun
thru Mon. SCA level NW winds are likely Tue thru Wed, with a 20%
chance of seas reaching SCA levels Tue night through early Wed
morning.

For the inner waters north of Pt. Sal, moderate confidence in the
forecast. There is a 20-30% chance of SCA level NE winds near
shore late tonight Sun morning. SCA level NW winds are expected
Tue, then there is a 40% chance of SCA level NW winds Wed.

For the inner waters south of Pt. Conception, moderate to high
confidence in the forecast. Late tonight and Sun, and again late
Sun night/Mon morning, SCA level NE winds are likely from the
eastern Santa Barbara Channel south to Santa Monica. There is a
20-30% chance of SCA level NE winds affecting Avalon Harbor. There
is a 40% chance of SCA level W-NW winds across western SBA
Channel Tue afternoon and evening. Otherwise, winds and seas will
remain below SCA levels Mon afternoon thru Wed.

&&

.FIRE WEATHER...20/350 PM.

A Red Flag Warning remains in effect for Sunday/Monday time
period across much of LA/Ventura counties due to high confidence of
Red Flag conditions for these areas. The Fire Weather Watch was
canceled for Sunday across the mountains of Santa Barbara and San
Luis Obispo counties as Red Flag conditions are not expected to
meet duration thresholds for Red Flag. However, there will be
elevated to brief critical fire weather conditions across San Luis
Obispo and Santa Barbara counties Sunday into early Monday.

Northeast to east Santa Ana winds are still on track to increase late
tonight into Sunday, with the peak winds expected Sunday morning
and afternoon. During this peak, offshore wind gusts of 35 to 55 mph
are expected across Los Angeles and Ventura Counties, except isolated
gusts up to 60 mph in favored mountains and foothills. In addition,
wind gusts of 20 to 40 mph are expected across San Luis Obispo and
Santa Barbara counties. Gusty Santa Ana winds are expected to continue
into Monday morning, however wind gust speeds are expected to be 10
to 15 mph less than Sunday. Humidities are expected to fall to around
15 to 20 percent by mid morning Sunday, potentially lowering to
between 7 and 15 percent by Sunday afternoon and evening, and again
on Monday. Very poor humidity recoveries expected across most windy
locations on Sunday night, generally remaining in the 10 to 20
percent range. Temperatures generally look to peak between 75 and
85 degrees on Sunday and Monday. The potential for Red Flag conditions
is above 80 percent for Los Angeles and Ventura Counties, resulting
in the Red Flag Warning for those areas. There will be an increased
risk of wildfire ignitions on Sunday and Monday across the region.
Areas in a Red Flag Warning will have an increased risk for fires
with rapid spread, long range spotting, and extreme fire behavior,
especially considering the dry fuels in place across the region.

Conditions are expected to improve Monday night into Tuesday. There
is the potential for another round of weak to moderate offshore
winds and low humidities Wednesday through Friday. The focus of
this event will once again be Los Angeles and Ventura counties,
with a chance of Red Flag conditions.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory in effect until 8 AM PST Sunday for zone 34. (See LAXNPWLOX).
     Wind Advisory in effect from 3 AM Sunday to noon PST Monday
      for zones 40-41. (See LAXNPWLOX).
     Wind Advisory in effect until 3 PM PST Monday for zones
      44>46-53-54-88-547. (See LAXNPWLOX).
     Red Flag Warning in effect from 9 AM Sunday to 3 PM PST
      Monday for zones 240-241-244>246-253-254-288-547-548. (See LAXRFWLOX).
PZ...Small Craft Advisory in effect from 3 AM Sunday to noon PST
      Monday for zones 650-655. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (TUE-SAT).

Critical fire weather conditions and gusty Santa Ana winds are
likely into Monday. Another Santa Ana wind event is possible
beginning on Wednesday.

&&

PUBLIC...Stewart/jld
AVIATION...Lund/Sirard
MARINE...Lund/Sirard
FIRE...Gomberg
SYNOPSIS...jld

weather.gov/losangeles