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Southwest California area forecast discussion 
National Weather Service Los Angeles/Oxnard California
905 PM PDT Thursday Sep 3 2015

Synopsis...

Fair skies through next week except during the overnight hours where
clouds and patchy fog will persist along the coast and some valleys.
Afternoon temperatures through Saturday will be below normal...then
warm to around normal for most of next week as high pressure moves
in.

&&

Short term (tonight-sun)...the marine inversion at klax this
evening was around 2900 feet deep...and should deepen some overnight
thanks to an eddy developing over the socal bight. Patchy low clouds
were noted from Catalina Island to near Palos verdes...and along
parts of the central coast this evening. The low clouds will expand
over the socal bight and along the coast through tonight and move
inland to the adjacent valleys and lower coastal slopes later tonight.
Low clouds should also develop in the Salinas River Valley late
tonight. Otherwise...mostly clear skies can be expected across the
forecast area through the night. Lingering gusty S to west winds in the
foothills...mountains and deserts this evening will diminish overnight.
There were also gusty North Canyon winds along the sba S coast and mountains
this evening...generally below advisory levels...which will diminish
overnight.

A broad upper level trough will persist over Southern California through Friday night
then gradually weaken on Sat. Much weaker upper level troffiness
should then linger over the area Sat night and sun.

Dry and generally cooler than normal weather will prevail across the
region Friday through Sat...with dry but warmer conditions expected on sun
as gradients trend offshore. A relatively deep marine layer will
keep varying amounts of night and morning low clouds and fog over
the area through Sat. There should be a shallower marine inversion by
Sat night...with low clouds expected mainly along the l.A. County
coast and San Gabriel valley Sat night and Sun morning. Otherwise...
mostly clear skies will prevail across the region through sun. Breezy
afternoon and evening onshore winds will affect portions of the
central coast...and foothills...mountains and Antelope Valley through
Friday...with somewhat weaker winds for Sat. Offshore flow is expected
over slo/sba counties and interior vtu/l.A. Counties Sat night into
Sun morning...with weaker onshore flow Sun afternoon.

Temperatures will be several degrees below normal in most areas Friday through
Sat...except near normal for the most part along the coastal plain.
The offshore flow will promote warmer temperatures for sun...with highs
closer to normal or slightly above normal for many areas...except
several degrees above normal for the central coast.

***From previous discussion***

Long term (mon-thu)...overall...12z models continue to be in decent
agreement through the period. At upper levels...weak trough will
linger over the area Monday/Tuesday...then a ridge will try to move
in from the southeast Wednesday/Thursday. Near the surface...it
looks like weak diurnal flow will prevail...weakly offshore at night
and onshore during the day.

Forecast-wise...the excitement levels will continue to be minimal.
Monday/Tuesday should see a gradual return of the marine layer
stratus and a gradual cooling trend. For Wednesday/Thursday...the
marine inversion will likely shrink a bit and remain confined
generally to the coastal plain. With the less marine influence...the
temperatures on Wednesday/Thursday should exhibit a warming trend.

&&

Aviation...04/0005z.

At 2309z...the marine inversion at klax was around 2500 feet deep. The
top of the inversion was around 4800 feet with a temperature of 17
degrees celsius.

Generally hi confidence in the 00z tafs with regard to low cloud and
mostly IFR/MVFR development tonight at all coastal and valley airfields
which will persist into late Friday morning to early Friday afternoon.
There is moderate confidence in the timing of the onset of the low
clouds which could be off plus/minus an hour or two. For kwjf and
kpmd...hi confidence in the 00z tafs with VFR conditions expected
through Friday. Gusty west to SW winds at these airfields this evening will
diminish tonight and increase again Friday afternoon. Gusty northwest winds
are also expected at ksbp and ksmx early this evening and again
Friday afternoon.

Klax...generally hi confidence in the 00z taf. Low clouds and MVFR
ceilings are forecast to develop by 06z and persist through 20z Friday with
VFR conditions through 03z before MVFR ceilings develop again Friday evening.
The timing of the onset of the low clouds tonight could be off
plus/minus an hour or so.

Kbur...generally hi confidence in the 00z taf. Low clouds and MVFR
ceilings are forecast to develop by 06z and persist through 19z Friday with
VFR conditions the rest of the day. The timing of the onset of the
low clouds tonight could be off plus/minus an hour or two.

&&

Marine...03/900 PM.

High confidence in forecast of Small Craft Advisory conds for northwest winds over
the outer waters tonight through Saturday night. A brief lull may
occur during the morning hours Friday...but otherwise gusts 25 to 30
knots are expected during this time. Combined seas will build to 6
to 9 feet offshore. Local gusts to 25 knots will affect the near-
shore waters north of Point Sal...50% chance that a Small Craft Advisory will be
needed.

Storm force winds in the southern ocean generated a swell that will
affect the coastal waters of southwest California over the weekend.
Swell heights will be 2 to 4 feet with intervals near 20 seconds.
Mariners should be prepared for long period swells that will likely
have extra surging and currents. Shoaling is likely in shallower
water and in some Harbor entrances.

Beaches...a long period south swell will likely bring elevated surf
to south and southwest facing beaches this weekend through next
Tuesday. An increasing risk of rip currents is expected starting
Friday afternoon as the first long period swell arrives...and it is
expected that a high rip current risk will be issued Sunday through
Tuesday.

&&

Lox watches/warnings/advisories...
beach hazard statement (see laxcfwlox).
Small Craft Advisory (see laxmwwlox).

&&
$$

Public...sirard/rat
aviation..sirard
marine/beaches...Smith
synopsis...seto

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