NWS Los Angeles, CA wrote its last area forecast discussion before the first event at Feb 27, 9:59 PM PST, 3 hours 1 minute earlier.
Area forecast discussion, Feb 27, 9:59 PM PST, 3 hours 1 minute before
Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
959 PM PST Sat Feb 27 2021
.SYNOPSIS...27/841 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 (SAT-TUE)...27/842 PM.
Cold upper level trough across the Great Basin this evening
expected to track southward and form a closed low in western
Arizona by early Sunday morning. Northerly winds on the increase
this evening, as evident by the 8 pm readings showing Montecito
Hills and Carpinteria Hills gusting at 58 mph, and Malibu Hills
gusting at 52 mph. The LAX-Bakersfield northerly offshore pressure
gradient has increased sharply during the past hour, currently at
-6.4 mb at 8 pm. Winds are still expected to abruptly shift to
northeast later this evening, with the focus of strongest Santa Ana
winds favoring wind prone areas of LA/Ventura counties. Already
seeing LAX-Daggett offshore pressure gradient increasing
rapidly from -2 mb at 7 pm to -4.1 mb at 8 pm. In addition, upper
level wind support from the northeast is expected to rapidly
increase after 10 pm this evening per latest NAM model.
Based on these trends, current upgrades to High Wind Warnings look
on track for 10 pm this evening for the LA/Ventura county mountains,
Santa Clarita Valley, and northern San Fernando Valley (especially
the foothills above the 118 and 210 corridors). These areas could
see damaging wind gusts as high as 70 mph in the mountains, and 55
to 65 mph in the foothills and valleys. Remaining coastal/valley
areas in LA/Ventura counties are under a wind advisory with gusts
generally in the 40 to 55 mph range. The peak of the Santa Ana
winds are expected later tonight through Sunday morning when there
will be increasing upper level wind support, cold air advection, and
steepening offshore pressure gradient (LAX-Daggett expected to
reach -7.0 mb). The moderate to strong Santa Ana winds combined
with lowering humidities will result in elevated to brief critical
fire weather conditions for LA/Ventura counties through Sunday.
Warmest temperatures on Sunday expected to be near the coast
due to compressional warming and drying effects.
*** From previous discussion ***
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.
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.
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...28/0558Z.
At 0430Z at KLAX, there was no marine layer and only a weak sfc
based inversion.
High confidence in CAVU conds for the next 30 hours.
Gusty north winds will affect the mtns and the valleys of L.A.
County this evening, then strong northeast winds will affect much
of L.A. and VTA Counties late tonight through early Sunday
afternoon. There will be areas of LLWS and mdt to stg UDDF
associated with the winds...esp near higher trrn.
KLAX...Very high confidence in CAVU conds for the next 30 hours.
Less confidence in wind fcst with a 20 percent chc of ocnl 25kt
xwnd gusts through 09Z. Then a 30 percent chc of an 8 kt east wind
component 11Z-17Z.
KBUR...Very high confidence in CAVU conds for the next 24 hours.
Less confidence in wind forecast which could vary from 300 to 080
06Z-17Z. Switch to south winds may be delayed til 23Z.
&&
.MARINE...27/814 PM.
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, except continuing in zone 676 through
3 pm Sunday. Seas will remain above SCA levels tonight and
possibly early Sun. 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
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 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 continue this 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 until 3 PM PST Sunday for zones
40-41-44-45. (See LAXNPWLOX).
High Wind Warning in effect until noon PST Sunday for zones
46-547. (See LAXNPWLOX).
High Wind Warning in effect until 3 PM PST Sunday for zones
53-54-88. (See LAXNPWLOX).
Wind Advisory in effect until noon PST Sunday for zone 87. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 3 AM PST Sunday for
zones 645-655-670-673. (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).
Small Craft Advisory in effect until 3 PM PST Sunday for zone
676. (See LAXMWWLOX).
&&
.HAZARD POTENTIAL OUTLOOK (TUE-SAT).
There is a possibility of widespread rain Tuesday night and
Wednesday.
&&
PUBLIC...Gomberg/Sirard
AVIATION...Rorke
MARINE...Gomberg
BEACHES...Sweet/DB
SYNOPSIS...Sirard
weather.gov/losangeles