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Southwest California area forecast discussion 
National Weather Service Los Angeles/Oxnard California
440 am PDT Monday Apr 27 2015

Aviation discussion updated

Synopsis...

Gusty north to to northeast winds will bring warm and dry conditions
to the area through Tuesday. For the second half of the week..a weak
low pressure system will approach the West Coast. This low will bring
cooler temperatures and a gradual increase in the night and morning
clouds and fog.

&&

Short term (today-wed)...
winds are in the process of transitioning form north to northeast as
the surface high slides into Nevada. The wind advisories for the sba
South Coast will expire at 300 am and the the advisories for the
northeast winds will start up at 600 am. It will be interesting to
see how strong the winds get as the surface gradients are not too
impressive but the NAM has been consistently forecasting strong 850
mb winds which should mix down and augment the surface grads. This will
be a quick hitter of a wind event and it will be done by early
afternoon. The la mountains should see the windiest conditions today with
some gusts to 55 miles per hour. The other big news for the day will be the
heat as 580 dm heights from an east Pacific Ridge will combine with the
offshore flow and sunny skies to drive maximum temperatures into the 80s and
lower 90s for most of the csts and valleys.

Much less windy on Tuesday morning with less offshore flow and
little or no upper support. Still it will be sunny and warm. Heights
will be few dm higher as the axis of the upper ridge moves over Southern
California. The valleys will almost all be in the upper 80s and lower 90s.
There might be a couple of degrees of cooling near the beaches as
the weaker offshore flow will allow for an earlier sea breeze.

No winds at all on Wednesday with only about one mb offshore flow in
the morning and onshore flow in the afternoon. Heights will fall some
as well as the ridge weakens. Cooling everywhere but most
significantly along the coastal areas where there will be good sea
breezes arriving with no delay.

Long term (thu-sun)...
rather dull pattern sets up for the extended period as a trough
develops off the West Coast. Weak offshore flow develops each
morning Thursday and Friday and this should prevent low cloud formation on
Thursday morning and limit it on Friday morning. Maximum temperatures will slowly
slide downward as heights fall.

The weekend looks cloudier and cooler as onshore flow develops this
along with the general trofing pattern should allow an extensive
low cloud deck to develop and overspread the coast into many of the
valleys. The afternoon onshore diurnal maximum does not seem too strong so
there should be good afternoon clearing each day. The much deeper
marine layer will accelerate the cooling trend over the weekend.

&&

Aviation...27/12z...

At 0840z at klax... the inversion was 2700 feet deep with the top at
3250 feet and a temperature at the top of seventeen degrees celsius.

Overall...high confidence in the 12z tafs. VFR conditions are
expected throughout the forecast period. Through midday in eastern
Ventura County and western Los Angeles County light to MDT
low level wind shear/turbulence is possible.

Klax...high confidence in the 12z taf. VFR conditions are expected
throughout the forecast period. Through midday light low level wind shear/turbulence
is possible.

Kbur...high confidence in the 12z taf. VFR conditions are expected
throughout the forecast period. Through midday light low level wind shear/turbulence
is possible.

&&

Marine...27/300 am

Outer waters...
strong and gusty winds have diminished across the outer waters such
that gale warnings have been expired and replaced with small craft
advisories. Strong advisory level winds will continue through at
least Wednesday and at that Point May increase again to gale force
levels... or they may remain at advisory level through the end of
the week. There may be periods during the week of winds diminishing
to less than advisory levels but seas will likely remain hazardous
throughout.

Inner waters...
strong and gusty winds have diminished across the inner waters
though remain at advisory levels in some areas... especially in the
the western portions of zones 650 and 655. Therefore small craft
advisories have been extended for thoses zones through middle morning.
Offshore winds will increase through the day and mariners along the
Ventura and Los Angeles County coastlines will experience the
strongest winds. It is expected that the winds will remain below
advisory levels other than near passes and canyons along the
immediate coastline from Point Mugu to Malibu. There is a forty
percent chance that winds will develop more strongly and a Small
Craft Advisory will be needed for zone 655.

&&

Fire weather...26/1015 am
northerly winds will be on the increase once again this evening for
the sba South Coast and Santa Ynez range...as well as the Interstate
5 corridor extending from the la County mountains southward into the
Santa Clarita valley. Humidity values will generally remain above 30
percent during the evening hours. Winds will shift to the northeast
and increase in speed overnight into Monday morning. The strongest
surge of winds in the la/Ventura County mountains is expected to
occur between 2 am and 10 am on Monday...when gusts between 50 and
60 miles per hour will likely occur. For the valleys and coastal areas...the
strongest winds will likely occur between 4 am and noon...when gusts
between 30 and 50 miles per hour are expected. Humidity values are expected to
lower into the teens by middle to late morning on Monday...with some
single digit reading by afternoon. Temperatures will climb into the
80s across much of the district...with warmest coastal/valley
locations around 90 degrees. The combination of gusty Santa Ana
winds...low humidities...and warm temperatures...and drying fuels
will bring elevated fire danger to Los Angeles and Ventura counties
on Monday. There will also likely be a brief period of critical fire
weather conditions from middle morning Monday through early
afternoon...but durations are not sufficiently long to warrant a red
flag warning.

&&

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

&&
$$

Public...rorke
aviation...kj
marine...kj
fire...g
synopsis...rat

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