Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 272214
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
214 PM PST Sat Feb 27 2021

.SYNOPSIS...27/212 PM.

Northerly winds across the region will be gusty through this
evening, then shift offshore late this evening and strengthen
into a moderate to strong Santa Ana event through Sunday. Dry
weather can be expected into Tuesday, then low pressure should
bring a chance of rain to the region Tuesday night and Wednesday.

&&

.SHORT TERM (TDY-TUE)...27/210 PM.

Sunny skies prevailed across the forecast area early this
afternoon with little change expected thru sunset. Temps this
afternoon are forecast to top out a few degrees above normal over
most of VTU/L.A. Counties, and near normal to slightly below
normal for the Antelope Vly and most of SLO/SBA Counties. The
warmest vlys and inland coastal will reach into the upper 60s and
70s.

Northerly pressure gradients were rather strong early this
afternoon, with LAX-BFL at -5.6 mb and SBA-BFL at -5.0 mb at 22Z.
These strong gradients combined with some upper level support has
resulted in gusty NW-N winds over much of the foothills and mtns
as well as parts of the SBA County S coast, NW San Fernando Vly,
Santa Clarita Vly and the L.A County coast around Santa Monica.
The strongest gusts early this afternoon have been up to 53 mph at
the Camp 9 RAWS, 52 mph at the Montecito RAWS, and 51 mph at
Whiteman Airport in Pacoima. Most of the higher gusts early this
afternoon have been in the 30 to 40 mph range. These winds are
expected to persist thru this evening, and even increase and
expand to the VTU County vlys, Santa Monica Mtns and along the
Central coast thru late this afternoon, especially the hills and
Santa Lucia Mtns. Wind Advisories are in effect for many of these
areas and will continue thru the evening.

A large upper level trof over the Great Basin this afternoon is
forecast to sharpen over srn NV into AZ later tonight and
strengthen into an upper level low over AZ on Sun, with a strong
NW to N flow aloft over swrn CA. A weak upper level ridge will
move into the area Sun night into early Mon. By Mon afternoon, an
upper level low is forecast to develop about 450 miles off the
central CA coast, with a broad SW flow aloft moving into the
forecast area. The upper level low will then track SE Mon night
into Tue to a position about 300 miles SW of Point Conception by
late Tue. The NAM and GFS were in pretty good agreement on the
track of the upper level low into Tue, while the EC kept the
system about 150 miles further to the SW.

Easterly offshore pressure gradients should strengthen
significantly tonight into Sun morning (NAM fcst LAX-DAG -7.0 mb
at 12Z Sun), while northerly gradients decrease a little but
remain offshore into Sun morning. These gradients combined with
decent upper level support and good cold air advection will cause
the northerly flow to quickly transition into a moderate to strong
NE Santa Ana wind event starting late this evening over the mtns
and spreading into the lower elevations toward the coast later
tonight into Sun. Damaging Warning-level wind gusts of 60 to 65
mph are expected for the L.A./VTU County mtns including the Santa
Monica Mtns as well as the Santa Clarita Vly from late this
evening into Sun afternoon. High Wind Warnings are in effect for
these areas starting at 10 PM this evening. There is a chance for
damaging wind gusts in the northwest part of the San Fernando Vly
into the adjacent hills, where a High Wind Warning is also in
effect. For much of the rest of VTU/L.A. Counties, Advisory-level
wind gusts in the 40-50 mph range can be expected, including the
coast and San Gabriel Vly foothill areas. Local gusts to 60 mph
cannot be ruled out in the foothills adjacent to the vlys later
tonight into Sun morning. For these areas, Wind Advisories are in
effect and will extend into Sun afternoon. Please see the latest
Non-Precipitation Weather Message (LAXNPWLOX) for further details
on the widespread Wind Advisories and High Wind Warnings.

Gusty NE winds should also affect the Santa Lucia Mtns and hills
along the Central Coast tonight and Sun, possibly to Advisory-
levels at times. There will be leftover gusty NE winds across the
wind-prone areas thru Sun night but should diminish below
Advisory-levels in all areas by early Mon.

Mostly clear skies will prevail across the forecast area tonight
thru Mon evening. For later Mon night and Tue, the approaching
upper level low and associated surface frontal system will spread
some cloudiness into the area, especially SLO/SBA Counties. There
will also be a slight chance of rain developing for the Central
Coast by Tue afternoon.

Temps will turn cooler in all areas Sun, but the cooling should
be most pronounced in the mtns, deserts and Santa Clarita Vly
thanks to cold air advection. Highs in the warmest coast and vlys
will generally be in the upper 60s to lower 70s on Sun. Temps
should then warm about 3-6 deg most areas on Mon before cooling
back a few degrees on Tue. The warmest vlys and inland coastal
areas are expected to reach the low to mid 70s on Mon, and in the
60s to around 70 on Tue.

.LONG TERM (WED-SAT)...27/210 PM.

The GFS and EC remain at odds with the movement of the mid-week
upper level low. The GFS tracks the low into the swrn CA coast
late Tue night then quickly inland to nrn AZ Wed afternoon. The
GFS mean ensembles are a tad slower with the system. The EC moves
the upper level low to a position just off the nrn Baja coast by
late Tue night then moves it E Wed morning and inland over nrn
Baja Wed afternoon. The EC mean ensembles track the system a
little closer to the coast and pushes it inland over San County by
18Z Wed.

Both models now show rain associated with the upper level low
moving into swrn CA, with the earlier onset with the GFS (late
Tue) and much later with the EC (Wed afternoon). Decided to
continue leaning toward the GFS solution for this fcst. It looks
like there will be rain chances over the region Tue night thru
Wed afternoon, with most of the rain falling over SBA/VTU/L.A.
Counties. Continued to go with slight chance to chance POPs for
much of this area altho POPs may eventually need to be boosted to
likely pending additional model runs. Snow levels should lower to
3500-4000 ft by early Wed morning as well, with light amounts of
snow possible in the mtns especially on the higher S slopes. Pcpn
amounts are forecast to be light, generally 0.20 inch or less, but
these numbers could go up with additional model runs and added
confidence.

Upper level ridging should move into the area later Wed night and
Thu. An approaching upper level trof over the E Pac will give the
area a broad SW flow aloft for Fri. Dry weather with a few clouds
at times can be expected Thu and Fri.

There are significant differences showing up for Sat with the EC
forecasting a sharp upper level trof with a surface front and rain
over much of the area, while the GFS has weak ridging and dry.
Decided to go with the NBM for Sat and introduce a slight chance
of rain to SLO/SBA/nwrn VTU Counties, altho there is low
confidence with this fcst.

Temps are expected to be generally a few degrees below normal on
Wed, then warm several degrees to slightly above normal for many
areas Thu and Fri before cooling slightly for Sat.

&&

.AVIATION...27/1847Z.

At 1802Z, there was no marine layer at KLAX.

Except for sct low clouds near KLGB, skies were clear across the
region. Any low clouds should clear by mid to late morning, then
VFR conds are expected through the period. Wind conditions have
been very complex this morning, with KSMO receiving gusty north
winds, yet KLAX getting east winds due to an eddy centered over
the Long Beach Harbor. Gusty north winds become a possibility
again later today, especially this evening across western LA
county, including KLAX, KSMO and KLGB.

Gusty north winds will affect the mtns and the valleys of L.A.
County today, then strong northeast winds will affect much of L.A.
and VTU Counties tonight and Sun morning. There will be areas of
LLWS and mdt to stg UDDF associated with the winds.

KLAX...Moderate confidence in the 18Z TAF. There is a 20-30%
chance of N to NE wind gusts to 20-25 knots between 06Z and 15Z
Sun.

KBUR...Moderate to high confidence in the 18Z TAF. There is a
20-30% chance of N to NE winds gusts to 25 knots after 09Z Sun.

&&

.MARINE...27/1013 AM.

Other than some minor changes to the digital database, the marine
forecast looks to be in excellent shape so no changes this
morning.

Across the outer waters, Gale force NW winds will continue thru
this evening, then Small Craft Advisory (SCA) winds and seas are
expected thru late tonight. Seas will remain above SCA levels
Sun, while NE winds also remain above SCA levels across the
southern zone (PZZ676) Sun morning. SCA conds are not expected Sun
night thru Tue. There is a 30% chance of SCA conds Wed.

Across the inner waters north of Pt. Sal, SCA level seas will
continue through late tonight, with SCA level NW winds this
afternoon through late this evening. Then, SCA conds are not
expected Sun through Tue. There is a 30% of SCA conds Wed.

Across the SBA Channel, SCA level W-NW winds are expected across
western portions this morning, and late this afternoon/evening,
SCA level NE winds will affect eastern sections late tonight/Sun
morning. Otherwise, SCA conds are not expected thru Wed.

Across the southern inner waters, SCA level N winds are expected
to develop late this afternoon or evening from Pt. Mugu to Santa
Monica. Winds will become NE and increase to Gale Force in that
area late tonight and also become strong in areas S of Palos
Verdes to Catalina Island. Gale force winds are expected from
Point Mugu to Santa Monica and S of Palos Verdes to Catalina Sun
morning. Then, winds will diminish, and SCA conds are not
expected thru Wed.

Gusty NE winds will cause steep short period NE wind waves across
the inner waters late tonight and Sunday morning. These waves
will create particularly hazardous conditions in the vicinity of
NE facing harbors such as Avalon and Two Harbors.

&&

.BEACHES...27/1043 AM.

No changes to the expected surf on the central coast.

A large northwest swell will peak across the waters today, then
slowly subside through Sunday. This will bring high surf
conditions to west and northwest facing beaches of the Central
Coast through Sunday morning. Large breaking waves of 8 to 12
feet with local sets to 16 feet are expected. In addition, there
will be dangerous rip currents.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory in effect until 10 AM PST Sunday for zones
      34-35. (See LAXCFWLOX).
     Wind Advisory in effect until 10 PM PST this evening for
      zones 34-35-46-53-54-88-547. (See LAXNPWLOX).
     Wind Advisory in effect until 3 AM PST Sunday for zones
      39-52. (See LAXNPWLOX).
     Wind Advisory in effect from 10 PM this evening to 3 PM PST
      Sunday for zone 40. (See LAXNPWLOX).
     Wind Advisory in effect until 3 PM PST Sunday for zones
      41-44-45. (See LAXNPWLOX).
     High Wind Warning in effect from 10 PM this evening to noon
      PST Sunday for zones 46-547. (See LAXNPWLOX).
     High Wind Warning in effect from 10 PM this evening to 3 PM
      PST Sunday for zones 53-54-88. (See LAXNPWLOX).
     Wind Advisory in effect from 10 PM this evening to noon PST
      Sunday for zone 87. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 3 AM PST Sunday for
      zones 645-655. (See LAXMWWLOX).
     Small Craft Advisory in effect until noon PST Sunday for zone
      650. (See LAXMWWLOX).
     Gale Warning in effect from 3 AM to noon PST Sunday for zone
      655. (See LAXMWWLOX).
     Gale Warning in effect until 9 PM PST this evening for zones
      670-673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (TUE-SAT).

There is a possibility of widespread rain Tuesday night and
Wednesday.

&&

$$

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

weather.gov/losangeles


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