Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 150430

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
830 PM PST Sat Dec 14 2019

.SYNOPSIS...14/636 PM.

Strong northerly winds will persist in the mountains today in the
wake of an upper level trough passing over the area. Gusty
northeasterly winds are expected Monday and Tuesday evenings.
There is a slight chance of showers on Wednesday with the passage
of an upper level low to our north.


.SHORT TERM (SAT-TUE)...14/829 PM.

A fast moving upper level trough is moving through SW California
this evening. As the system moves east overnight into Sunday,
heights will gradually begin to increase over the area. This
system has minimal moisture associated with it, and will mainly be
a wind producer with an influx of colder temperatures. The
northwest flow will continue to pile up moisture across the
interior slopes where rain and snow showers will be likely at
times through Sunday. Snow levels are ranging between 5000 and
6000 feet this evening, but will fall to between 3500 and 4000
feet by late tonight into Sunday morning when there will be
potential impacts for Interstate 5 near the Grapevine. Winter
weather advisories are in effect for the LA/Ventura county
mountains through noon Sunday, with snow accumulations up to 2
inches across interior slopes along with wind gusts up to 50 mph.

This system is generating gusty northwest to north winds across
the region this evening, with the strongest winds currently
focused across the Santa Ynez mountains, SBA south coast, and
I-5 corridor in the LA county mountains. Wind gusts in these
areas will continue to increase tonight, with gusts in the 40 to
50 mph range. The northerly winds are also expected to strengthen
and expand into a larger portion of LA county overnight into
Sunday. In evening update, have expanded the Wind Advisory to
now include the San Fernando Valley, Santa Monica mountains,
and LA county coast, where wind gusts of 35 to 45 mph will be
common. For the LA county coast, the winds are expected to
increase after sunrise on Sunday, with the emphasis being
across the west side. These gusty winds could cause downed
trees and power outages.

*** From previous discussion ***

There will be some lingering clouds over the forecast area thru Sun
morning then skies will become mostly sunny for the most part Sun
afternoon. Offshore flow will increase Sun night and Mon with mostly
clear skies expected for the most part thru Mon. For Mon night and
Tue, plenty of hi clouds are expected to move into the area from the
W as the upper level ridge will be dirty with hi level moisture
being drawn into the area from the eastern Pac deep upper level trof.

Gradients will turn more NE and strengthen Sun night into Mon
morning. The NAM forecasts the 12Z LAX-DAG gradient Mon morning to
be -4.8 mb, a drop of 7.1 mb in 24 hours. There will be slight cold
air advection and not a whole lot of upper level support for strong
winds, but it still looks like wind prone areas of VTU/L.A. Counties
may reach low-grade Advisory levels at times late Sun night into Mon
morning. Offshore gradients are forecast to increase further Mon
night into Tue morning, with the NAM forecast LAX-DAG gradient
lowering to -8.2 mb at 12Z Tue. Advisory-level northeast winds
appear likely over much of the usual wind-prone areas of VTU/L.A.

Temps are forecast to turn cooler for Sun with highs 3-8 deg
below normal, then warm slightly for Mon and Tue but still remain
a few degrees below normal for many areas. The warmest temps
during the period are expected to be along the L.A./VTU County
coastal plain Mon and Tue where highs may approach 70 degrees.

.LONG TERM (WED-SAT)...14/213 PM.

The EC and GFS are not in complete agreement on the speed of the E
Pac upper trof and associated frontal system Tue night and Wed, with
the GFS slower than the EC. A model blend was used with a chance of
rain moving into central and western SLO/SBA Counties Tue night,
and a slight chance of rain and mountain snow spreading into
portions of VTU/L.A. Counties on Wed. This does not look like a
big rain producer mainly due to the system`s fast movement and
lack of organized upper level dynamics as it moves into CA.

Weak upper level ridging should move into srn CA on Thu into Fri
before it moves E for Sat as a large upper level trof approaches the
W coast from the E Pac. Dry weather is expected over swrn CA Thu
thru sat, with varying amounts of mid and hi level clouds moving
over the area thru much of the period for partly to mostly cloudy

Temps are forecast to be several degrees below normal on Wed, then
warm to generally near normal to slightly below normal overall Thu
thru Sat. The warmest day should be Fri with highs for the warmest
coast and vlys reaching the upper 60s to around 70.



At 00Z, the marine layer inversion was weakening at KLAX.

Moderate confidence in the current forecast. Mostly MVFR to VFR
cigs below 5000 feet across portions of the forecast area
this evening, mainly south of Point Conception. Exception
will be IFR to LIFR conditions across north facing mountain
slopes tonight. Conditions will continue to improve overnight
into Sunday for most areas except north facing mountain
slopes. Gusty NW to N winds with potential turbulence will impact
most TAF sites through period.

KLAX...Residual low level moisture will bring a 20 percent
chance of MVFR/VFR cigs through this evening. Otherwise VFR
conditions through forecast period. There is a chance of moderate
wind shear and turbulence after 06z continuing through Sunday.
North winds around 10 knots are likely after 06Z, with
further strengthening on Sunday morning. There is the potential
for northerly winds to gust between 25 and 30 knots on Sunday

KBUR...SCT-BKN025-035 conditions will continue through early
evening, then improving sky conditions through forecast period.
There is a chance of moderate wind shear and turbulence after
04Z. There is the potential for northerly winds to gust between
25 and 30 knots on Sunday.


.MARINE...14/148 PM.

For the northern and outer Waters, moderate to high confidence in
the current forecast. A GALE WARNING remains in effect through at
least late tonight south of Point Sal. Local gale warning level
gusts are possible north of Point Sal. With the gusty winds,
short-period, hazardous seas will be likely. High seas over 10
feet will continue through late Sunday night, therefore a SMALL
CRAFT ADVISORY (SCA) is not only in effect for winds, but for
hazardous seas. On Tuesday and Wednesday, there is a 30-50
percent chance of SCA level east to southeast winds.

For the Inner Waters south of Point Conception, moderate to high
confidence in the current forecast. A GALE WARNING remains in
effect through late tonight. The strongest winds are expected
across western sections. From Sunday night through Wednesday, the
winds will shift to the northeast with SCA level winds likely
Sunday night through Tuesday.

A large and long period west to northwest swell will impact the
coastal waters through at least late Sunday night, resulting in
hazardous sea conditions and large breaking waves near shore,
especially with a large short period wind swell on top of that.
Breaking waves at the Morro Bay and Ventura Harbor entrances will
be possible.


.BEACHES...14/217 PM.

A large long-period west to northwest swell across the coastal
waters of southwest California today will slowly subside over the
remainder of the weekend. A HIGH SURF ADVISORY remains in effect
for the Central Coast through Monday morning and through noon
Sunday for the beaches south of Point Conception. The highest
surf will occur across exposed west facing beaches. Strong rip
currents and dangerous breaking waves are expected.

With high tides between 6 and 6.5 feet Sunday morning, minor
coastal flooding is possible during the late morning high tide.
Any coastal flooding impacts should be confined to the beaches,
with flooding possible in the most vulnerable parking lots, bike
paths, and walkways.


CA...High Surf Advisory in effect until noon PST Monday for zones
      34-35. (See LAXCFWLOX).
     High Surf Advisory in effect until 4 AM PST Sunday for zone
      39. (See LAXCFWLOX).
     Wind Advisory in effect until 6 PM PST Sunday for zones
      39-52-88. (See LAXNPWLOX).
     High Surf Advisory in effect until noon PST Sunday for zones
      40-41-87. (See LAXCFWLOX).
     Wind Advisory in effect from 6 AM to 6 PM PST Sunday for
      zones 41-46. (See LAXNPWLOX).
     Wind Advisory in effect until 10 PM PST this evening for
      zones 53-54. (See LAXNPWLOX).
     Winter Weather Advisory in effect until noon PST Sunday for
      zones 53-54. (See LAXWSWLOX).
     Wind Advisory in effect until 3 AM PST Sunday for zone 59. (See LAXNPWLOX).
     Wind Advisory in effect from midnight tonight to 6 PM PST
      Sunday for zone 547. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 3 AM PST Monday for
      zones 645-670. (See LAXMWWLOX).
     Gale Warning in effect until 3 AM PST Sunday for zones
      650-655-673-676. (See LAXMWWLOX).



Gusty northeast winds possible across parts of LA/Ventura
Counties Tuesday.



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