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Southwest California area forecast discussion 
National Weather Service Los Angeles/Oxnard California
330 PM PST Thursday Dec 18 2014

..updated aviation discussion...

Synopsis...

A weak storm system will bring another chance of light rain late
Friday into Friday night to areas mainly north of Point Conception.
Starting over the weekend...high pressure will build...bringing dry
weather and a warming trend through the middle of next week.

&&

Short term (today-sun)...a few light showers were occurring over
the eastern San Gabriel mountain range this afternoon...otherwise
skies remained partly to mostly cloudy. High temperatures will be fairly
similar to yesterday in most areas. The main trough axis has moved
east into ariz. A brief shortwave ridge will build in as another
weak upper trough approaches the forecast area within broad northwest flow
aloft. A weak cold front associated with this trough that will bring
light showers to areas north of Point Conception...mostly less than a
tenth of an inch...except for the northwest portion of slo County where
locally higher amounts can occur. The cold front weakens further as
it moves into Ventura and Los Angeles counties Friday
evening/overnight hours. With 850 mb winds (5,000 ft) expected to be
out of the northwest...this will not be conducive for any showers to hold
together as it approaches the Ventura and los angels County coast
and valleys. However...with all the low level moisture already in
place...have put in slight chance probability of precipitation for la/vtu counties Friday
evening through the overnight hours. As the front pushes
east...clouds will begin to bank up against the northern slopes of
the sba/vtu and northwest portion of la County mountains Friday night into
Saturday morning. A few light showers will be possible or a few snow
flurries above 6,000 feet. There may be an inch of total snow
accumulation above 6,500 feet.

For Saturday...there will continue to be some lingering low level
moisture in the morning...especially around the foothills...so will
go with partly cloudy skies...except mostly cloudy for the
mountains. High temperatures will be a few degrees warmer with most areas
in the middle to upper 60s west of the mountains.

As the trough moves to the east...a northerly surface pressure
gradient will develop Saturday afternoon bringing gusty northwest to
north winds to the Santa Barbara County mountains and adjacent sba
South Coast as well as the I-5 corridor. A low end Wind Advisory
might be needed for this area. Northerly winds will also strengthen
through Santa Clarita...San Fernando Valley and possibly into west
la Saturday night but remain below advisory thresholds. With better
clearing expected on Saturday night...there will be a better chance
for some patchy dense fog to develop across the Salinas
valley...wind protected areas across the central coast and a few low
lying la/vtu/sba valley locations.

Synoptically...a relatively strong upper high will build in over the
eastern Pacific on Sunday nudging heights and thickness levels higher
over the forecast area. Expect mostly sunny skies with high temperatures
expected to reach the lower to middle 70s for the la/vtu/sba County
valleys and inland coastal areas. Hi temperatures across the central coast
could be a few degrees warmer due to some offshore flow
coming off the san Lucia mountains

Long term (mon-thu)...
both the GFS and European model (ecmwf) are in pretty good agreement keeping the
upper high sitting over the eastern Pacific with heights peaking at
588dm over our forecast area. Skies will remain mostly clear through
the period with continued gusty northerly winds on Monday. A 1030 mb
surface high is prognosticated to set up by Monday night into Tuesday. This
will cause offshore winds to develop. There will be some marginal
upper level support allowing for a moderate Santa Ana wind event.
High temperatures will peak on Tuesday with some coast and coastal valleys
locations reaching the lower 80s...including the central coast. By
Wednesday/Thursday...another upper trough will be digging down
across Oregon/northern Nevada causing heights and thickness levels to
drop rapidly. High temperatures are expected to lower 4 to 6 degrees for
coast and valleys...with more significant cooling expected on
Thursday. Models cool things off an additional 5 to 8 degrees to the
middle 60s in most areas. I am not that confident that we will see high
temperatures only in the middle 60s as there will continue to be an offshore
component for the area. However...if colder air does filter into the
interior region as the GFS suggests...we could see another burst of
gusty Santa Ana winds on Thursday...but temperatures will be much cooler
than the prior Tuesday.

&&

Aviation...18/2320z.

Marine layer at klax at 2320z is none.

Considerable low level moisture across the region will continue to
maintain MVFR/VFR ceilings across many of the airfields tonight. There is
a good chance of some IFR/LIFR ceilings/visibilities at kprb and ksbp late
tonight. Another weak front will bring a 30 percent chance of rain
to kprb and ksbp on Friday afternoon...with a 15-20 percent chance
later in the day for the remainder of the airfields.

Klax...sct-bkn030-050 conditions through much of the period. As weak
cold front approaches area on Friday...increased chance of MVFR ceilings
at klax in the afternoon.

Kbur...sct-bkn030-050 conditions through much of the period. As weak
cold front approaches area on Friday...increased chance of MVFR ceilings
at kbur in the afternoon.

&&

Marine...18/200 PM.

Hazardous seas will likely return Friday night as seas generated
from a distant storm on Tuesday from 290-300 degrees relative to Los
Angeles County coast build. The conditions will likely persist
through Sunday. There is a chance small craft conditions for north
wind will exist in the vicinity of The Channel islands Saturday
night and persist through Sunday.

&&

Lox watches/warnings/advisories...
beach hazards statement (see laxcfwlox).

&&

$$

Public...Kaplan
aviation/marine...gomberg/30
synopsis...Sweet

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