Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000
FXUS66 KLOX 252142
AFDLOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
242 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...(TDY-TUE)

Partly to mostly cloudy skies for the most part covered the forecast
area early this afternoon thanks to residual moisture behind a
departing upper level trof and increasingly strong spring sunshine.
Widely scattered showers developed over parts of SLO County and
moved into northern SBA County. These showers will likely persist
thru sunset. Additional showers are expected to develop on the n mtn
slopes of VTU/L.A. Counties as well thru the afternoon.

Weak upper ridging can be expected to move over srn CA tonight and
Sun. A fast-moving upper level trof will move thru the e Pac and
into CA Sun night, followed by an inside slider quickly moving thru
CA on Mon. This trof will deepen into an upper level low over AZ and
move off to the se Mon night thru Tue, while upper level ridging
builds along and off the CA Coast. This pattern will result in a
strong northerly flow aloft over srn CA for Mon into Tue.

The north mtn slopes should have persistent upslope clouds with a
few rain and snow showers tonight. Otherwise, partly to mostly
cloudy skies will prevail as low level moisture is expected to
persist. Lingering low level moisture combined with mid and hi level
moisture moving in from the w on Sun will keep partly to mostly
cloudy skies over the forecast area thru the day. 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...25/1730Z...

At 1715Z, there was a weak marine inversion at KLAX, based at
1500 feet. The top of the inversion was 2000 feet with a
temperature of 11 degrees Celsius.

Overall, low to moderate confidence in 18Z TAF package. Current
MVFR/IFR CIGs are expected to dissipate around 20-21Z with VFR
conditions anticipated through this evening. For tonight, low
confidence in coastal/valley TAF sites. Currently will indicate
some MVFR VSBYs developing after 10Z, but there is a 50% chance
that conditions could remain VFR or that MVFR CIGs could develop.
There is also a 10% chance that IFR/LIFR conditions could
develop.

KLAX...overall moderate confidence in 18Z TAF. High confidence in
MVFR CIGs dissipating after 20Z. For tonight, low confidence in
forecast as there is an equal chance of MVFR or VFR conditions
prevailing (and even a 10% chance of IFR/LIFR conditions
developing).

KBUR...overall moderate confidence in 18Z TAF. Moderate confidence
in MVFR CIGs 19z-21Z and VFR conditions 21Z-06Z. For tonight, low
confidence in forecast as there is an equal chance of MVFR or VFR
conditions prevailing (and even a 10% chance of IFR/LIFR
conditions developing).

&&

.MARINE...25/115 PM...

For the Outer Waters, moderate confidence in current forecast.
High confidence in Small Craft Advisory (SCA) level winds through
Sunday morning. For Sunday afternoon/night, northwest winds are
expected to increase, but only low to moderate confidence in winds
reaching Gale force levels. Strong northwest winds will continue
Monday through Thursday with SCA level conditions likely and a
chance of winds reaching Gale force levels.

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 this afternoon/evening and again Sunday
afternoon/evening. From Monday through Thursday, there is a high
likelihood of winds reaching SCA levels. For the waters south of
Point Conception, moderate confidence in SCA level winds across
the western Santa Barbara Channel this afternoon/evening. On
Sunday, there is a chance (30%) 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 until 9 PM PDT this evening
      for zone 650. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 PM PDT Sunday for
      zones 670-673-676. (See LAXMWWLOX).
     Gale Watch in effect from Sunday afternoon through late
      Sunday night for zones 673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK...(TUE-SAT)
Strong and gusty north winds will affect the area Monday night
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...Sirard
AVIATION...RAT
MARINE...RAT
SYNOPSIS...B

weather.gov/losangeles


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