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Southwest California area forecast discussion...updated 
National Weather Service Los Angeles/Oxnard California
1020 PM PDT Wednesday Apr 1 2015

Updated aviation section

Synopsis...

Gusty northwest winds will persist into Thursday morning...then turn
northerly on Thursday for a warmup. On Friday...a moderate Santa Ana
wind event will raise the temperatures to well above normal. A low
pressure system will move in late Saturday for a cooling trend
through midweek...with possible precipitation on Tuesday.

&&

Short term (tonight-sat)...strong and gusty winds continued to
affect portions of the forecast area early this evening...including
areas along the central coast...the sba County mountains especially in
the Santa Ynez range...sba County S coast...vtu/l.A. County mountains
especially along the I-5 corridor...and in the Antelope Valley. A High
Wind Warning is in effect until 9 am Thursday for the sba County mountains...
and from 9 PM this evening to 9 am Sat for the vtu/l.A. County mountains
a Wind Advisory is in effect for the sba S coast until 9 am Thursday...
the central coast until 9 PM this evening...and the Antelope Valley
until 10 PM this evening. Gradients at 02z this evening include -4.8
mb sba-smx and +5.3 mb lax-dag...which help to support the winds.
Please see the latest non-precipitation weather message (laxnpwlox)
for further details on the high wind warnings and wind advisories.
Skies across the area this evening were generally clear. Some hi
clouds should move in overnight with fair skies overall...although
there is a small chance some low clouds could affect parts of the
l.A. County coastal plain late tonight into Thursday morning.

An upper level trough will move into the forecast area overnight
then push off to the S and east on Thursday. A broad west to west-northwest flow aloft
will persist over the region Thursday night and Friday. The upper level flow
will turn more to the SW on Sat as a broad upper level trough
approaches from the east Pacific. The gusty winds are forecast to diminish
some on Thursday over the sba mountains and S coast...but could linger into
Thursday night mainly below advisory levels. Winds in the l.A./Vtu County
mountains will diminish on Thursday as well...then turn northeast and become
gusty again Thursday night into Friday morning...but should be generally
below or near advisory levels at times. Gusty northwest winds should affect
the central coast each afternoon and evening through Sat. For the
coast...valleys and foothills of vtu/l.A. Counties and the Santa Ynez
range...gusty north to NE winds can be expected later Thursday night into Friday
morning especially below and through the favored passes and canyons.
These winds should be mainly below advisory levels...with a few
advisory level gusts possible at times mainly over the hills. Skies
over the region will be mostly clear into Sat...although a few more hi
clouds should move in during the day on Sat. Temperatures across the region
are forecast to be a few degrees above normal on Thursday...warm to
significantly above normal levels Friday...with highs well into the 80s
in the warmest valleys...then cool back to a few degrees above normal
for Sat.

***From previous discussion***

Long term (sun-wed)...cooling trend continues Sunday with highs
mostly 60s to lower 70s and a relatively deep marine layer in place.
Would not be surprised to see minimal, or at least slow clearing for
coastal areas. Along the central coast a weak frontal boundary
associated with the trough over northern California will move through. It
doesn't look like it will be strong enough to produce rain this far
south but could keep things pretty cloudy through the afternoon.

Another trof, slightly stronger than over the weekend will arrive
Tuesday and move east by early Wednesday. Models have really had trouble
with this one and while today's agreement is fairly solid it
certainly hasn't been the case the last few days so my confidence in
any one set of model runs remains very low. It does seem to favor a
fairly cool pattern at least through Tuesday with a pretty strong
onshore flow and plenty of night/morning marine layer. By Tuesday
afternoon today's models do show a small amount of rain, mainly
north of pt Conception. Then dry Wednesday with some weak ridging
developing and slightly warmer temperatures.

&&

Aviation...02/0520z.

At 0420z...the marine layer depth at klax was 1100 feet deep. The
inversion top was at 2800 feet with a temperature of 16 degrees c.

Expect VFR conds through the period...except some MVFR ceilings possible
across southern coastal sections of l.A. County. There will be gusty northwest
to north winds through and below passes and canyons of southern sba County
and through the Interstate 5 corridor with low level wind shear and MDT uddf.

Klax...high confidence in the 06z taf with VFR conditions expected
through the period.

Kbur...high confidence in the 06z taf with VFR conditions expected
through the period.



&&

Marine...01/800 PM
high confidence in solid northwest gales across the outer waters
through late tonight. Local gusts to 35 knots may continue through
Thursday evening...with a 50% chance the Gale Warning will need to
be extended. The western portions of pzz645 and pzz650 will
experience some locally stronger gusts...but should not be
widespread enough to require a warning. All areas...including areas
that do not see the gusty winds...will experience large and steep
seas at short periods peaking during the overnight hours. Some
improvement is expected Thursday and especially Friday as offshore
flow and Santa Ana winds develop. Widespread gusty northwest winds to
return across the outer waters Saturday afternoon with inner waters
possibly affected by Sunday. Gales will be possible again over the
outer waters and the western portion of the nearshore waters.

&&

Beaches...01/800 PM
a large northwest swell of around 12 seconds will combine with short
period wind seas to produce combined northwest seas of 10 to 13 feet
over the nearshore waters north of Point Conception. High surf
resulting from the large seas will bring strong currents to the
beaches and large waves that may break over jetties and rocks along
the water's edge. The surf will begin to subside as winds diminish
slightly on Thursday...but the high surf advisory may need to be
extended through Thursday afternoon and evening.

&&

Fire weather...01/235 PM...

Gusty northwest to north winds will continue across the area tonight
and Thursday. The strongest winds (gusts 50-60 mph) are expected
across the mountains...specifically the Interstate 5 corridor and
the Santa Ynez Mountains. The South Coast of Santa Barbara County as
well as the valleys of Ventura/Los Angeles counties will experience
wind gusts 25-45 miles per hour. Drier air has moved into the area this
afternoon so humidity recovery tonight will be poorer away from the
coast with humidity dropping into the teens and single digits on
Thursday. So elevated fire danger will continue across the
area...with a couple hours of critical conditions
likely...especially across the Santa Ynez range.

On Thursday night and Friday...the flow will turn northeast with
winds generally impacting Ventura and Los Angeles counties. In the
wind prone areas...gusts between 35 and 50 miles per hour can be expected. The
northeast flow will bring well above-normal temperatures and
widespread single digit humidity to the area on Friday. Elevated
fire danger will continue across the entire area...with several
hours of critical fire weather conditions likely across inland areas
of Ventura and Los Angeles counties.

By Saturday...the flow will turn onshore...with the onshore flow
increasing into early next week. So...cooler temperatures and higher
relative humidity can be expected...along with gusty southwesterly
winds across the mountains and deserts.

&&

Lox watches/warnings/advisories...
High Wind Warning (see laxnpwlox).
Wind Advisory (see laxnpwlox).
Gale Warning (see laxmwwlox).
Small Craft Advisory (see laxmwwlox).
High surf advisory (see laxcfwlox).
High rip current risk (see laxsrflox).
Beach hazards statement (see laxcfwlox).

&&

$$

Public...sirard/mw
aviation...db
marine...Smith
fire...rat
synopsis...seto

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