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Southwest California area forecast discussion 
National Weather Service Los Angeles/Oxnard California
342 am PDT Tuesday Sep 16 2014

Synopsis...
high pressure aloft and weak onshore flow will result in very hot
weather today...especially for areas away from the immediate coast.
There will be some cooling on Wednesday...with more significant
cooling on Thursday as a trough approaches the West Coast. There is
a slight chance of afternoon and evening thunderstorms across the
eastern mountains and the Antelope Valley Wednesday and possibly
Thursday due to remnant moisture from Hurricane Odile. Temperatures
will return to near normal for Friday and Saturday...then slight
warming may begin by late in the weekend.

&&

Short term (today-thu)...clear skies across the region this
morning. West-east pressure gradients were weakly offshore from klax to
kdag. North-S gradients were moderately offshore...and gusty winds continued
through and below passes and canyons of southern sba County. Have
extended wind advisories through 9 am for the Santa Ynez range and
adjacent S coast of sba counties below passes and canyons. It was
very warm early this morning...especially in the valleys and in breezy
areas...where temperatures were still in the 80s as of 3 am PDT...and upper
80s in some cases. Expect today to be a very hot day just about
everywhere away from the immediate beaches. While heights/thicknesses
have dropped a bit...950 mb temperatures remained very high...with amdar
soundings showing temperatures at 950 mb of near 90f or 32c. With such a
warm start to the day...and weak offshore flow to begin...expect maximum
temperatures to be as high as they were on Monday in many areas...and would
not be surprised if a few locations were even a bit hotter.

While there will be some increase in middle level moisture and
increasing precipitable water values today...feel that the
strong upper ridge axis overhead will suppress any convection.
However...there could be a few buildups in the mountains

An upper trough will approach the West Coast tonight and Wednesday. Low
level north-S gradients should produce gusty sundowner winds through the
Santa Ynez range and across the South Coast of sba County this
evening...and winds could get close to advisory levels there
tonight. Some stratus could move into the central coast...but
otherwise...expect skies to remain mostly clear tonight. Maximum temperatures
on Wednesday should be down several degrees in most areas...but temperatures will
probably still reach or slightly exceed 100 degrees in the warmest
locations in the valleys...lower elevations in the mountains and in the
Antelope Valley. With a bit more in the way of middle level moisture
over eastern sections of the forecast area Wednesday and less subsidence aloft...
the slight chance of thunderstorms in the afternoon and evening in
the mountains of l.A. And vtu counties and in the Antelope Valley looks
reasonable.

The trough will evolve into an upper low Wednesday night and move into
the northern California coast by Thursday afternoon. At the surface...N-S gradients
actually increase a bit across sba County Wednesday evening...so expect
another round of gusty northwest-north winds...possibly to advisory levels
across southern sba County. The WRF indicates stratus becoming widespread
in coastal areas Wednesday night/Thursday morning...with the exception of the S
coast of sba counties...where north-S gradients should keep stratus at
Bay. Good height falls...cooling at 850 mb and 950 mb and
strengthening onshore flow should lead to significant widespread
cooling across the region Thursday...with maximum temperatures down 8 to 15 degrees
in many valley locations and across interior sections of the l.A.
County coastal plain. There may still be a slight chance of
convection over the mountains of l.A. And eastern vtu counties and the
Antelope Valley Thursday...but the latest models show the bulk of any
moisture associated with the remnants of Odile pushing well east
of the region as the upper flow turns southwesterly ahead of the trough.
Later shifts may be able to remove those slight chances from the
forecast.

Long term (fri-mon)...the upper low will drop southward through California
Thursday night and Friday...and be located near Point Conception Friday
afternoon. There should be a rather deep marine layer Thursday night/Friday
morning. A few showers are not out of the question north of pt
Conception with the weakening surface front Thursday night and early
Friday...and there could be some drizzle or light rain across the
foothills of l.A. County as some low level lift develops in the
increasingly cyclonic flow. The latest run of the GFS is a bit
farther west with the upper low...keeping it west of the region through
the day...so clearing may be slower and less complete than currently
forecast. Maximum temperatures will be down a few more degrees in most areas
Friday...down to near or below normal levels. The weakening upper low
will drift across the region Sat and then move eastward...so maximum temperatures
could begin to rise in many areas by Sunday and Monday.

&&

Aviation...

16/1145z

Overall...high confidence in 12z taf package. Locally gusty winds
through and below passes and canyons of southern sba County through late
tonight...and again Tuesday evening with local low level wind shear and MDT uddf near
ksba for the area through Tuesday.

Klax...high confidence in ceiling and visibility unlimited taf.

Kbur...very high confidence ceiling and visibility unlimited taf.

&&

Marine...

16/300 am

High confidence in current coastal forecast. The strongest winds
will occur around Point Conception from middle-afternoon through early
evening.

The western half of the Santa Barbara Channel will see local
northwest gusts to 25 to 30 knots during the next few late afternoons
and evenings.

&&

Beaches...

16/300 am

A long period (19-20+ second) southern hemisphere swell will move
through the waters through today. It will bring elevated surf
along south facing beaches and a significant amount of rip current
activity.

There is no longer a threat of swells from Hurricane Odile.

&&

Lox watches/warnings/advisories...
excessive heat warning (see laxnpwlox).
Red flag warning (see laxrfwlox).
Wind Advisory (see laxnpwlox).
Small Craft Advisory (see laxmwwlox).
High rip current risk (see laxsrflox).

&&

$$

Public...db
aviation/marine...asr
synopsis...db

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