Area Forecast Discussion
Issued by NWS Los Angeles, CA

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365
FXUS66 KLOX 260406
AFDLOX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
906 PM PDT Sat Mar 25 2017

.SYNOPSIS...

The upper trough will exit today with some lingering mountain
showers. Sunday will warm a few degrees. Then a weak trough on
Monday may bring a few light showers over San Luis Obispo and
Santa Barbara counties. Gusty northerly winds will set up Monday
night and persist into Tuesday. Weak ridging aloft will bring
warm and dry conditions for the middle of next week.

&&

.SHORT TERM...(SAT-TUE)

A trough of low pressure, now located near the Four Corners continues
to exit the region this evening. Skies are clearing this evening,
except for clouds and isolated showers piled up along the northern
slopes. Shortwave ridging building into the West Coast this
evening will bring a warmer day for Sunday along with decreasing
showers chances later tonight.

Low confidence in the cloud cover forecast for this evening and
into Sunday morning. A moist air mass in the lower-levels of the
atmosphere will remain while ridging aloft start to build in. A
deep moist layer is in place on the latest KLAX AMDAR soundings.
The forecast leans toward mainly mostly cloudy skies by Sunday
morning as high pressure starts to clamp down on the near surface
moist layer, but with no clear marine inversion at this point,
the forecast is a little more difficult. As a result, a wide
range exists. Partly to mostly cloudy skies should prevail into
Sunday.

*** FROM PREVIOUS DISCUSSION ***

The upper trof will bring additional clouds and a slight chance
of showers over SLO/SBA Counties Sun night into Mon morning. As
the inside slider moves inland on Mon, a slight chance of rain and
snow showers can be expected mainly on the n mtn slopes to the
Cuyama Vly. Otherwise, partly cloudy skies overall should prevail
across much of the forecast area thru the day. A tightening
northerly pressure gradient and some cold air advection Mon
afternoon will help to bring strong and gusty nw winds to the mtns
and Antelope Vly, as well as gusty nw winds to the Central Coast.

Northerly gradients and cold air advection will increase further Mon
evening, with strong and gusty n winds expected to affect the
Antelope Vly, mtns and SBA County s coast. 850 mb winds up to 55 kt
was forecast by the 12Z NAM over these areas, with 950 mb winds up
to 30 kt. There is the potential for winds to approach or reach
warning thresholds in these areas Mon night, and high wind watches
may eventually be needed for this event. Gusty n winds to advisory
levels will also be possible for the Santa Monica Mtns, portions of
the VTU County vlys, the Santa Clarita Vly, San Fernando Vly, and
possibly even the L.A. County coast from Malibu to the Hollywood
Hills, with the potential for gusty n winds to affect areas from
Santa Monica to LAX. Wind advisories will likely be needed for these
areas from mid afternoon Mon thru Mon night.

Winds will decrease Tue morning and turn onshore Tue afternoon.
Except for a few clouds and showers lingering on the n mtn slopes
Mon night, skies will become mostly clear across the forecast area
Mon night thru Tue.

Temps Sun and Mon are forecast to be several degrees below normal
for many areas. Highs in the warmest vlys and inland coastal areas
should reach the upper 60s to low 70s both days, altho the Antelope
Vly will turn much cooler on Mon with highs 4 to 8 deg below normal.
With increased sunshine, a building ridge and offshore flow on Tue,
temps will warm significantly to several degrees above normal for
many areas. Highs in the warmest vlys and inland coastal areas on
Tue should reach the mid 70s to low 80s.

.LONG TERM...(WED-SAT)

The EC and GFS are in generally good agreement with the synoptic
scale features on Wed, then some significant differences show up Thu
thru Sat relating to the movement and an inside slider upper low.
Both models have an upper ridge over the area on Wed. For Thu, a
sharp upper trof moves into the Pac NW and pushes inland thru Oregon
as per the GFS, or dives s and deepens into an upper low over nrn CA
as per the EC. The GFS deepens the trof into an upper low over the
Great Basin on Fri then drifts the upper low into New Mexico for
Sat. The EC tracks the upper low into srn Nevada Fri and into
central AZ for Sat. At the same time, both models build an upper
level ridge along or off the CA coast.

The EC is the colder and wetter solution due to the proximity of the
upper low to srn CA , as the model brings showers to the forecast
area Thu and Thu night. The GFS more easterly solution to the track
of the upper low keeps the forecast area drier and warmer with
offshore flow for the most part. This forecast package has leaned
more toward the GFS solution, with mostly clear skies and generally
warm conditions over swrn CA Wed thru Sat, as the GFS has shown a
bit better run to run consistency over the last couple of days. The
offshore flow may also be gusty at times in the favored areas during
the period.

Temps are forecast to be about 4 to 12 deg above normal each day,
except near normal to a few degrees above normal on Fri. Highs in
the warmest vlys and inland coastal areas should reach the lower to
mid 80s Wed, mid 70s to low 80s Thu, mid 70s to around 80 Fri, and
80s on Sat.

&&

.AVIATION...26/0140Z.

At 00Z, there was a deep moist layer up to around 1900 feet at
KLAX.

Low confidence in the current forecast. MVFR conditions should
return to coastal terminals south of KSBA after 08Z tonight.
There is a chance of MVFR conditions spreading into valley
terminals after 13Z and lingering at coastal terminals throughout
the day on Sunday.

KLAX...There is a 70 percent chance of MVFR conditions returning
to KLAX as soon as 05Z or as late as 10Z. There is a 40 percent
chance of MVFR conditions lingering through 23Z Sunday.

KBUR...There is a 30 percent chance of MVFR conditions returning
to KLAX as soon as 10Z or as late as 13Z. Ceilings at or below
5000 feet could develop on Sunday afternoon.

&&

.MARINE...25/815 PM.

For the Outer Waters, moderate confidence in current forecast.
High confidence in Small Craft Advisory (SCA) level winds through
Monday morning. For Sunday afternoon/night, northwest winds are
expected to increase to strong SCA levels with gusts to 30 knots
and a few local gusts to 35 knots possible between San Nicolas and
Santa Rosa Islands. Stronger northwest winds are likely Monday by
late morning through Tuesday afternoon...and a Gale Watch is in
effect through that time.

For the Inner Waters, moderate confidence in current forecast. For
the waters north of Point Sal, there is a 30% chance of winds
reaching SCA levels Sunday evening. For the waters south of Point
Conception, moderate to high confidence that SCA level winds
across the western Santa Barbara Channel will continue to diminish
overnight. On Sunday, there is a chance (60%) of SCA level winds
across western portions. However for Monday through Thursday,
winds will increase and there is a good chance (50%) of SCA level
winds across the entire southern waters.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory in effect from 2 PM Sunday to 3 AM PDT
      Monday for zone 650. (See LAXMWWLOX).
     Small Craft Advisory in effect until 11 AM PDT Monday for
      zones 670-673-676. (See LAXMWWLOX).
     Gale Watch in effect from Monday morning through Tuesday
      afternoon for zones 670-673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK...(TUE-SAT)
Strong and gusty north winds will affect the area into early
Tuesday, with the potential for damaging wind gusts especially in
the mountains. Travel will be impacted by the winds over a large
area.

Another round of strong and gusty northwest to north winds will
be possible Thu night in the mountains and along the Santa Barbara
County south coast, with travel being affected by the winds.

&&

$$

PUBLIC...Hall/Sirard
AVIATION...Hall
MARINE...RAT/Smith
SYNOPSIS...B

weather.gov/losangeles



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