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Southwest California area forecast discussion 
National Weather Service Los Angeles/Oxnard California
919 PM PDT Tuesday Jun 2 2015

Synopsis...

An approaching low pressure system will bring increasing onshore
flow and a deeper marine layer into the weekend...with patchy
drizzle for the coast and valleys overnight Wednesday and Thursday.
There will be a slight chance of thunderstorms and showers for
Ventura and Los Angeles counties in the afternoon and evening hours
on Friday and Saturday as the trough moves over the region.
Temperatures will be near normal into the weekend with a slight
warmup next week as the low weakens.

&&

Update...

Southwest flow aloft will increase into Wednesday as a weak ridge of
high pressure centered near Hawaiian islands weakens and the axis
rotates east of the area. A weak shortwave trough of low pressure
near 35n and 130w will move over the area through Wednesday. Strong
onshore gradients will tighten additionally on Wednesday and
continue a cooling trend with a deeper and more developed marine
layer. Immediate coastal and beach localities may be difficult to
clear from the typical marine layer stratus on Wednesday.

A Wind Advisory may be needed for the interior portions of the area
on Wednesday and Wednesday night...including the San Luis Obispo
County interior valleys and the Antelope Valley on Wednesday. Model
solutions handled and initialized surface pressure gradients poorly
for the evening. NAM-WRF solutions initialized surface gradients
about one to one and one half millibars too weakly onshore. Strong
upper-level support should arrive on Wednesday and allow for a
stronger onshore wind for the interior portions of the area. The
next shift has been briefed about a possible Wind Advisory.

An upper-level low pressure continues to develop in the Gulf of
Alaska near 45n and 145w...possibly bringing a cool and cloudy
weather pattern with a slight chance of showers for Thursday and
Friday.

&&

Previous discussion...

Short term..the upper low will slide down the coast and then over
Southern California late on Thursday and on Friday. With it will
come a chance for drizzle from the marine clouds both offshore and
onshore and a slight chance of brief periods of light rain. This
possibility of precipitation is slight enough in any particular
location not to put it into the forecast but a better chance that a
few drops will fall somewhere... especially along the central coast.

Skies will be cloudier on Friday due to the traversing low and any
marine intrusion will linger longer due to the reduced solar
heating. The moisture from the Andres remnants continue to appear
to be well to the south and east of the area and are not expected to
have an impact on weather in the service area.

Long term...cloudy skies will continue into Saturday. As the upper
low swings through Southern California there will be a brief period
of instability and wind flow such that cloud build ups will form
over the San Gabriel Mountains. No showers are expected at this
time for the area but as the low shifts southward during the next
few days it may shift an increased amount of moisture over the area
such that some showers may form Saturday night. Timing is the issue
for this to occur.

Skies will clear and temperatures will warm a bit each day by late
Saturday and into the next work week. A weak trophiness will linger
over the region though so temperatures will warm to near normal but
not become hot. The marine intrusion will continue and the
conditions next Tuesday could be similar to the conditions today.

&&

Aviation...03/0050z.

At 0000z...the marine inversion at klax was based around 1200 feet.
The top of the inversion was around 2500 feet with a temperature of
19 degrees celsius.

Moderate to high confidence in the current forecast. IFR to MVFR
conditions should spread into coastal and valley terminals through
13z. There is a chance of LIFR conditions at terminals north of
Point Conception between 06z and 15z. MVFR conditions could linger
into the afternoon hours at coastal terminals.

Klax...MVFR conditions will likely spread into klax between 05z and
08z. There is a 20 percent of IFR conditions between 05z and 06z.
VFR conditions could develop as soon as 18z or as late as 20z.

Kbur...MVFR conditions will likely spread into klax between 08z and
11z. There is a 40 percent of IFR conditions between 08z and 11z.
VFR conditions could develop as soon as 16z or as late as 18z.

&&

Marine...02/900 PM.

For the outer coastal waters and waters north of Point Conception...
moderate to high confidence in northwest winds increasing to small
craft levels through Thursday night. On Friday and Saturday...the
winds will weaken and switch to the south to southwest.

For the inner waters south of Point Conception...high confidence in
winds remaining below Small Craft Advisory levels through Saturday.
There is a 20 percent chance of gusts reaching Small Craft Advisory
levels across western sections each afternoon and evening through
Thursday.

There is very low confidence in remnant moisture from Hurricane
Andres bringing thunderstorms to the coastal waters south of Malibu
Friday and Saturday.

&&

Lox watches/warnings/advisories...
Small Craft Advisory (see laxmwwlox).
High rip current risk (see laxsrflox).

&&
$$

Public...Hall/kj
aviation...Hall
marine...Hall
synopsis...Hall

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