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Southwest California area forecast discussion 
National Weather Service Los Angeles/Oxnard California
440 am PDT Tuesday Apr 28 2015

Aviation discussion updated

Synopsis...

A very gradual cooling trend is expected through Thursday as high
pressure aloft weakens and the sea breeze strengthens. For Friday
through the weekend...more significant cooling is expected along
with widespread low clouds and fog as weak low pressure impacts the
area.

&&

Short term (today-thu)...
overall...00z models in good synoptic agreement through the period.
At upper levels...ridge entrenched over the area will weaken a bit
today then will be shunted southeastward Wednesday/Thursday as a trough
develops along the West Coast. Near the surface...weak offshore flow
this morning will give way to weak onshore flow this afternoon...then
a typical diurnal gradient trend is expected Wed/Thu.

Forecast-wise...rather benign weather is anticipated through the
period. Main focus will be the battle of man versus marine layer
as onshore flow reestablishes.

Early this morning...stratus/fog has worked its way down the central
coast...with some patchy dense fog reported. Expect this stratus to
dissipate by this afternoon although some central coast beaches
could remain on the cloudy side through the afternoon. Elsewhere
skies are anticipated to be clear today...although will have to
watch some stratus working its way down the Salinas valley. With
weaker offshore gradients and limited upper support...will only some
very localized offshore winds this morning. As for temperatures will
anticipate some cooling along the coast...especially north of Point
Conception...and some warming across most inland areas.

For tonight/Wednesday...expect a near repeat of the marine layer
with stratus likely only impacting the central coast...and clear
skies elsewhere. However it would not be surprising to see some
stratus develop south of Point Conception. As for temperatures
coastal temperatures will a few more degrees...while inland areas will
generally hover around persistence.

For Wednesday night/Thursday...high res models...which are handling
the stratus pattern pretty well this morning...indicate little...if
any stratus for the area. So...will go with a clear forecast...with
a moderate confidence level. As for temperatures...highs north of
Point Conception look to be a bit warmer with an uptick in offshore
flow in the morning. South of Point Conception...expect some slight
cooling although the temperature change will likely not be
noticeable.

Long term (fri-mon)...
for the extended...models continue to be in good synoptic agreement.
At upper levels...trough will gradually develop...with a weak low
developing by Sunday and moving inland across northern Baja California. Near
the surface...moderate onshore flow will prevail.

Forecast-wise...the excitement level will remain very low. Main
challenge will continue to be the marine layer. With the upper
trough developing and strengthening onshore flow...stratus should
make an noticeable turn...pushing well inland Saturday through
Monday. With the more substantial marine layer influence...temperatures
will drop noticeably with coastal/valley areas generally in the middle
60s to middle 70s by Sunday/Monday.

As for winds...the increasing onshore flow will result in some gusty
southwest winds in the afternoon/evening hours across the mountains
and deserts.

&&

Aviation...28/12z...

At 1110z at klax... the inversion was surface based with a depth of
2000 feet and a temperature at the top of twenty three degrees
celsius.

Overall...moderate to high confidence in the 12z tafs. Through 18z
along the central coast... areas of vlifr and widerspread areas of
IFR to MVFR conditions. These conditions will redevelop again
tonight and likely will include locations as far south as in Los
Angeles County. Otherwise and elsewhere VFR conditions will prevail.

Klax...moderate to high confidence in the 12z taf. For 10z-16z there
is a twenty percent chance of IFR to MVFR conditions developing and
a ten percent chance of vlifr to LIFR conditions. Otherwise VFR
conditions will prevail.

Kbur...high confidence in the 12z taf. VFR conditions are expected
to prevail throughout the forecast period.

&&

Marine...28/300 am.

Small Craft Advisory conditions will continue across much of the
outer waters through this afternoon then winds will strengthen to
Gale Warning levels. These stronger winds will continue at least
through early Wednesday and possibly into Wednesday afternoon then
will diminish back to advisory levels. The winds will be generally
stronger to the north and zone 676 is expected to remain just below
advisory criteria though with periodic advisory level winds in the
northwest portion.

The inner waters will be generally onshore flow during the overnight
period and offshore during the day and evening. Locations along the
immediate coastline from Point Mugu to Malibu and near the outflow
from passes and canyons will have strong and gusty winds at times
during the day and evening hours.

&&

Lox watches/warnings/advisories...
Gale Warning (see laxmwwlox).
Small Craft Advisory (see laxmwwlox).

&&
$$

Public...rat
aviation...kj
marine...kj
synopsis...rat

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