Scientific Forecaster Discussion

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Southwest California area forecast discussion 
National Weather Service Los Angeles/Oxnard California
1100 PM PDT Wednesday Apr 23 2014

New aviation discussion

Synopsis...

High pressure aloft will bring a brief warmup through
Thursday...then a cold low pressure system will arrive with
breezy winds...a drop in temperatures...and possible
precipitation from Friday into Saturday for the mountains and
Santa Barbara northward. Offshore flow and high pressure aloft
will take hold for early next weekf for a significant warming
trend.

&&

Update...

A tight northerly surface gradient remains across the area this
evening. Ksba-ksmx and ksba-kbfl surface pressure gradients
tightening fairly strongly this evening creating gusty sundowner
winds across the area. A Wind Advisory was added earlier for
southern Santa Barbara County. Wind gusts up to 45 miles per hour have been
recorded...but isolated gusts up to 55 miles per hour may occur in some
locations. A marginal Wind Advisory was also added through the
Interstate 5 corridor earlier...but the latest data suggests weaker
winds later tonight. The advisory for the Los Angeles and Ventura
County mountains may be cancelled.

The marine layer stratus coverage was scaled back slightly for
Los Angeles County coast and added to the central coast for later
tonight. Temperatures look agreeable...especially with the absent
strong offshore flow forcing. Coast areas should warm
slightly...with the best warming occurring in the foothills and
valleys.

&&

Previous discussion...

Short term...temperatures will warm slightly on Thursday as
skies remain mostly sunny and a slight ridge builds over the
region. By late on Thursday the cloud shield ahead of the next
weather system will begin to move overhead. Skies should remain
clear long enough to allow for patchy fog to form in most coastal
and adjacent valley areas on Friday morning but early fog
development may lift into low clouds as the cloud shield moves in
and overnight temperatures remain a bit warmer as a result.

The incoming low pressure center digs down to Southern California
along or slightly on shore and swings eastward over Ventura and Los
Angeles counties. The moisture appears to be limited in this system
in general but the trajectory should keep the best dynamics to the
south of our service area and therefore the best chance of
precipitation and for strong winds. Our four County area has a
chance of light rain or drizzle on Friday but potential
precipitation amounts are less than a tenth of an inch. If the low
center swings east a little farther north than currently projected
there is a chance of increased precipitation in the San Gabriel
Mountains. The system could also stall a bit as the low swings
through and this would keep the light and drizzly conditions in
Ventura and Los Angeles counties into Saturday before clearing by
late afternoon.

Long term...near normal temperatures and partly cloudy skies on
Sunday give way to a stronger ridge building over the region and
offshore winds. By Monday afternoon temperatures across the region
push to above normal readings and most valleys locations will have
readings in the middle 90s. The warmer temperatures and offshore
winds continue into at least Tuesday.

&&

Aviation...

24/0600z.

Good confidence in all tafs except ksmx...klax and klgb where there is
a 30 percent chance of IFR ceilings and visible from 11z-16z.

Klax...good confidence in taf with a 30 percent chance of IFR ceilings
and visible from 11z-16z. Less confidence in taf after 08z.

Kbur...high confidence in taf.

&&

Marine...23/905 PM PDT.

Gale force northwest winds continue over the outer waters through
early Thursday morning...with short-period steep seas near or in
excess of 10 feet occurring. Winds at Small Craft Advisory levels
will continue across much of the inner waters. The exception will
be local gusts to 35 knots over the far western portion of the
Santa Barbara Channel. With the stronger winds offshore...hazardous
seas could propagate across the entire coastal waters area later
tonight.

Winds will diminish slightly Thursday into early Friday. The models
continue to depict stronger winds developing across the waters
Friday night into Saturday...with gales possible across the
southern waters including the near-shore waters south of Point
Conception. The winds are likely to remain gusty through Saturday
night...with hazardous boating conditions expected to persist
through the weekend due to large short period seas.

In addition to steep northwest seas...a long period south swell
building to 3 to 4 feet will bring rising surf to most of the
southwest California surf zone.

&&

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

&&

$$

Public...Hall/kj
aviation...asr
marine...Hall/Smith
synopsis..seto/Hall

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