Freeze Watch 3, NWS Los Angeles, CA

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
222 PM PST Tue Nov 23 2021

.SYNOPSIS...23/220 PM.

Offshore flow will bring mostly clear skies to the area through
next Tuesday. Another surge of gusty north winds will develop
early Wednesday in predawn hours. The winds will then transition
to a Santa Ana wind event later Wednesday through Friday. High
temperatures will remain a few degrees above normal for the coast
and valleys through Thursday. An extended duration of very dry
and warm weather will return through the holiday weekend.

&&

.SHORT TERM (TDY-FRI)...23/221 PM.

Sunny skies covered the forecast area early this afternoon and
will continue thru the rest of the day. Onshore flow can be
expected this afternoon, especially for the coast and vlys of
VTU/L.A. Counties. For SLO/SBA Counties and interior VTU/L.A.
Counties the flow will become gusty W to NW this afternoon. Temps
this afternoon will be much cooler than the last couple of days
for the coast and vlys, with highs expected to be in the 70s. It
will be a few degrees warmer in the Antelope Vly with highs in the
low to mid 70s.

Weak upper level troffiness will move thru the region thru this
afternoon, with another weak upper level trof moving thru from
the N tonight. Upper level ridging will build along and off the CA
coast on Wed with a broad N flow aloft. The upper level ridging
will build further into CA Wed night and Thu, with H5 heights over
SW CA increasing to 585-586 dam by afternoon.

Surface hi pressure will build into the central Great Basin
tonight, with offshore pressure gradients to the E and N expected
to increase again. By 12Z Wed, the NAM fcst gradients from LAX-DAG
lower to -3.6 mb, while the LAX-BFL gradient drops to -3.7 mb.
These offshore gradients are forecast to increase even further
thru Wed morning, with offshore trends continuing thru the
afternoon. Gusty mainly sub-Advisory level N winds will affect
southern SBA County this evening. The flow will turn quickly NE
later tonight and continue Wed, with winds increasing thru Wed
morning, likely to Advisory levels, over with wind-prone areas of
VTU/L.A. Counties. Gusty sub-Advisory level NE winds will also
affect the Santa Lucia Range in SLO County later tonight into Wed
morning.

A strong 1043 mb surface high is expected to build along the
Utah/NV border late Wed night into early Thu according the the
latest NAM. Offshore gradients to the N and E are fcst to peak at
an impressive -9.4 mb LAX-DAG and -4.5 mb LAX-BFL at 12Z Thu.
There will also be good cold air advection and upper level support
for strong and gusty NE winds to affect much of VTU/L.A. Counties
Wed night and Thanksgiving Day. 950 mb winds are forecast by the
NAM to peak around 60 kt Thu morning, and to around 50 to 55 kt at
850 mb in the L.A. County mtns late Wed night into Thu morning.
Surface wind gusts of 30 to 50 mph will be widespread, with
damaging gusts up to 60 mph or more possible in the foothills and
mtns.

Wind Advisories will be issued with the afternoon zone package
for the L.A./VTU County mtns, Santa Clarita Vly, San Fernando Vly,
VTU County vlys, the VTU County coast and the L.A. County coast
from Malibu to the Hollywood Hills. These Advisories will begin
anywhere from late tonight to late Wed night. In addition, a High
Wind Watch will also be issued for the L.A./VTU County mtns and
Santa Clarita Vly for later Wed night into Thu afternoon. Needless
to say, critical fire weather conditions are expected with the
gusty winds and widespread single-digit humidities. Please see the
Fire Weather Discussion below for further details.

There may be some low clouds developing on the L.A. County coast
tonight thanks to an eddy over the inner coastal waters. However,
any low clouds will quickly be pushed off the coast Wed morning.
Otherwise, mostly clear skies for the most part will prevail
across the region thru Thanksgiving Day. Even with the offshore
flow, temps will not warm up significantly for the coast and vlys
with highs in the upper 60s to mid 70s Wed, and 70s to around 80
on Thanksgiving Day. Inland vlys and deserts will be cool and
generally in the 60s on Wed, and in the lower 70s Thu except
remaining in the 60s for the Antelope Vly. Low temperatures will
turn quite cold Wed night, especially in wind-sheltered areas.
Frosts and freezes will also be possible for the interior vlys and
deserts, with even a hard freeze possible in the Antelope Vly. A
Frost Advisory will be issued with the afternoon zones for the
SLO Interior Vlys for later tonight into Wed morning, and a
Hard Freeze watch will be issued for the Antelope Vly from late
Wed evening into Thu morning.

The upper level ridging will persist over swrn CA Thu night and
Fri, altho H5 heights should lower to around 582 dam on Fri.
Pressure gradients will remain significantly offshore Thu night
into Fri morning (e.g. NAM fcst LAX-DAG -6.4 mb at 12Z Fri). This
will keep gusty offshore flow over the region during the period,
strongest Thu night into Fri morning over wind-prone areas of
VTU/L.A. Counties. Some areas may have Advisory level gusts as
well. Skies will remain mostly clear over the area thru Fri. It
will turn several degrees warmer Fri as well, with the warmest
coast and vlys expected to reach the upper 70s to mid 80s, while
temps in the Antelope Vly should remain in the mid to upper 60s.

A continued very dry airmass over the region will result in
another cold night for Thu night across wind-sheltered areas. Hard
freeze conditions are likely in the Antelope Vly, with widespread
frost and freezing conditions for the interior vlys possible.

.LONG TERM (SAT-TUE)...23/215 PM.

Both the Deterministic runs of the EC and the GFS along with
almost all of their respective ensemble members keep the upper
ridge over the southern half of the state for Sat thru Mon then
flattens the ridge with lowering heights for Tue. High pressure
over the Great Basin will remain in place as well although it will
weaken with time. There will be offshore flow both from the east
and north each morning. By early next week however there should be
a diurnally driven return to onshore flow in the afternoon (esp
to the east).

Skies will be mostly clear through the period as the offshore flow
should keep low clouds away largely away from the coast, except
patchy low clouds cannot be entirely ruled out by Mon night. Max
temps will be quite a bit above normal each day through the
period, altho Sat will be the warmest day and most above normal
overall.

&&

.AVIATION...23/1816Z.

At 1705Z at KLAX, the marine layer was 2000 feet deep. The top of
the inversion was around 2900 feet with a temperature of 17 C.

Moderate to high confidence in 18Z TAFs. There is a 40% chance of
KLAX and KLGB having IFR cigs.

KLAX...Moderate confidence in the 18Z TAF. There is a 40% chance
of lower cigs being BKN007-009 from 08-11Z. No significant
easterly wind component expected.

KBUR...High confidence in CAVU 18Z TAFs.

&&

.MARINE...23/1024 AM.

For the outer waters, good confidence in forecast. Small Craft
Advisory (SCA) level NW winds are expected to overspread the
waters from north to south this afternoon, then continue thru late
tonight across the southern zone (PZZ676), and thru mid morning
Wed across the rest of the outer waters. There is a 20% chance of
Gale Force winds across the outer waters north of Pt. Conception
this evening into late tonight. Winds are expected to be mostly
below SCA levels Wed afternoon thru Sat, though there is a 40%
chance of SCA level NE winds across eastern portions of the
southern zone late Wed night thru Thu.

For the inner waters north of Pt. Sal, moderate to high confidence
in the forecast. SCA level NW winds are expected this afternoon
through late tonight, though winds may drop below SCA levels
before midnight. Otherwise, winds and seas will remain below SCA
level thru the period.

For the inner waters south of Pt. Conception, moderate confidence
in the forecast. SCA level W to NW winds are likely across the
western SBA Channel late this afternoon thru late tonight, but
there is a 30% chance that winds will remain below SCA levels thru
tonight.

SCA level NE winds are likely across the eastern SBA Channel and
from Point Mugu to Santa Monica, and into the San Pedro Channel
Wed, and again late Wed night into Thu morning. These winds will
likely spread out to Santa Cruz and Anacapa Islands. The strong NE
winds may also affect Catalina Island, especially Wed night and
Thu morning, possibly generating 3 to 4 foot breakers across
northeast facing harbors including Avalon Harbor. Small Craft
Advisories for NE winds across the inner water for Wed into Thu
will likely by issued this afternoon or tonight.

&&

.FIRE WEATHER...23/154 PM.

The next Santa Ana wind event remains on target. Northeast winds
will begin to increase early Wednesday morning then peak late
Wednesday afternoon and early evening and continuing through
Thursday morning. Winds will weaken slightly through Friday
morning before weakening further Friday afternoon. Peak wind
gusts between 35 and 55 mph are expected, with isolated gusts to
between 60 and 70 mph possible in favored mountain and foothill
locations. Humidities will drop to between 10 and 15 percent on
Wednesday afternoon, then lower into the 2 to 8 percent range by
Thursday and Friday along with very poor overnight recoveries.
High temperatures will generally be in the 70s on Wednesday, and
warm to the mid 70s to lower 80s on Thursday and Friday. As such,
Red Flag Warnings are in effect for the extended period of strong
winds, very low humidity, and dry fuels for most of Los Angeles
and Ventura Counties Wednesday and Thanksgiving, then continuing
into Friday afternoon. This is the strongest Santa Ana thus far
this season, with strong offshore pressure gradients and with the
support of northeast winds in the low and mid levels. Elsewhere,
elevated to brief critical conditions will continue over Santa
Barbara and San Luis Obispo Counties, but at this time red flag
warnings are not needed for those areas.

This is a critical period with multiple days of Red Flag
conditions. The public needs to be extra cautious with anything
that could start a fire. Those living near fire prone undeveloped
areas, like the national forests, should make or review the
family plan including what to take and evacuation routes in the
event of an evacuation order is issued or a nearby wildfire
threatens. This is especially important with unaware visitors
during the holiday week.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Frost Advisory in effect from 2 AM to 9 AM PST Wednesday for
      zone 37. (See LAXNPWLOX).
     Wind Advisory in effect from 3 AM to 6 PM PST Thursday for
      zone 40. (See LAXNPWLOX).
     Wind Advisory in effect from 3 AM to 3 PM PST Thursday for
      zone 41. (See LAXNPWLOX).
     Wind Advisory in effect from 6 AM Wednesday to 6 PM PST
      Thursday for zones 44-45-547. (See LAXNPWLOX).
     Wind Advisory in effect from 6 AM Wednesday to 3 AM PST
      Thursday for zones 46-53-54-88. (See LAXNPWLOX).
     High Wind Watch in effect from late Wednesday night through
      Thursday afternoon for zones 46-53-54-88. (See LAXNPWLOX).
     Hard Freeze Watch in effect from Wednesday evening through
      Thursday morning for zone 59. (See LAXNPWLOX).
     Red Flag Warning in effect from 10 AM Wednesday to 6 PM PST
      Friday for zones 240-241-244>246-253-254-288-547-548.
      (See LAXRFWLOX).
PZ...Small Craft Advisory in effect until 3 AM PST Wednesday for
      zones 645-650-676. (See LAXMWWLOX).
     Small Craft Advisory in effect until 9 AM PST Wednesday for
      zones 670-673. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (FRI-TUE).

For Friday, very dry Santa Ana winds will likely create critical
fire weather conditions across Ventura and Los Angeles Counties.
Cold overnight temperatures in the interior valleys and deserts
could produce a frost or a freeze Thursday and Friday nights.

&&

PUBLIC...Sirard
AVIATION...Lund
MARINE...DB/Lund
FIRE...Jackson
SYNOPSIS...Sirard

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