Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000
FXUS66 KLOX 291115
AFDLOX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
415 AM PDT FRI APR 29 2016

.SYNOPSIS...

A broad trough of low pressure over the Western United States will
linger through the weekend. A cool, breezy and unsettled air mass
will remain in place into early next week, then high pressure
building in from the Eastern Pacific Ocean will bring a warming
trend through midweek next week. Another trough of low pressure
will approach the West Coast for late next week.

&&

.SHORT TERM...(TDY-SUN)

A trough of low pressure is centered over the Rocky Mountain
region this morning, while a ridge of high pressure is located
about 1500 miles west of Los Angeles. At the surface, a low-level
northwest flow remains in place and will reinforce a developing
eddy circulation over the Southern California Bight. Patches of
stratus over the South Coast Basin will likely become more
widespread as the morning progresses. Winds are starting to
diminish across the Transverse Mountains and the Santa Barbara
South Coast this morning, but a northerly surface pressure
gradient will redevelop from this afternoon through Saturday as
an upstream shortwave trough drops into the region.

The shortwave trough currently located near 48N and 133W will
stream over a weak ridge over Northern California later today,
dampening the ridge and digging into Southern California on
Saturday. The trough will scrape the area through Saturday
evening. A cooler weather pattern will continue across the area
with a chance of showers for the Southland. A few cloud build-ups
and high level cloudiness will stream over the area today ahead of
the trough, but the best instability will move over the area on
Saturday afternoon and evening when the shortwave`s vorticity
maximum brushes the area. While showers and thunderstorms have
the best chance over Los Angeles County and maybe Ventura County,
gusty winds will likely be the main impact with this trough.
Motorists, especially those driving high-profile vehicle and
traveling through the Antelope Valley will want to use caution due
to developing gusty westerly winds this afternoon and evening. A
Wind Advisory has been added for the Antelope Valley for this
afternoon and evening. This advisory may need to be expanded into
the typical northerly winds areas, such as the Interstate 5
Corridor and Southern Santa Barbara County from tonight through
Saturday morning. There is a chance that future shifts could
expand this advisory later today.

Broad troughing over the Western States will linger through the
weekend and keep the a chance of showers in the forecast, but
mainly for Los Angeles County. Winds may continue into Sunday
morning, although not as strong as tonight through Saturday
evening.

.LONG TERM...(MON-THU)

A ridge of high pressure will build over the area from the west
between the the exiting broad trough over the West and a trough of
low pressure currently located near 40N and 170W over the North
Central Pacific. A warming trend will occur between Monday and
Tuesday, but as the trough of low pressure approaches the region,
increasing onshore flow and cloudiness will start a cooling trend
on Wednesday. Model solutions are in pretty good agreement for an
unseasonably cold storm system to move over the region late next
week. Despite model solutions indicating a lack of moisture with
this system, dynamical features and the positioning of the
trough will have a higher weight. PoPs have been increased
slightly after Thursday. Future shifts may need to add
thunderstorms to the forecast if the 500 mb cold pocket remains
colder than -24 degrees Celsius as the model runs progress. With
good agreement between ECMWF and GEFS solutions, confidence is
increasing for a cool, unsettled and showery weather pattern for
late next week.

&&

.AVIATION...29/1110Z...

At 1100Z, the marine inversion at KLAX was based at 2100 feet. The
top of the inversion was 4200 feet with a temperature of 10
degrees Celsius.

Overall, low to moderate confidence in 12Z TAF package. MVFR/IFR
conditions firmly established across Central Coast, but
stratus/fog still struggling to get organized over Ventura and Los
Angeles county. Any cigs this morning will dissipate by early
afternoon with VFR conditions all areas this afternoon. For
tonight, expect a better stratus coverage pattern across the area
with widespread stratus across the Central Coast and across the
coasts/valleys of Ventura and Los Angeles counties.

KLAX...moderate confidence in 12Z TAF. High confidence in MVFR
cigs through this morning, then dissipating around 17z (although
there is a 30% chance of cigs lingering until 19Z). For tonight,
high confidence in return of MVFR cigs, but low confidence in
timing.

KBUR...moderate confidence in 12Z TAF. Moderate confidence in
MVFR cigs this morning, then dissipating around 16Z. For tonight,
high confidence in return of MVFR cigs, but low confidence in
timing.
&&

.MARINE...29/200 AM...

For the Outer Waters, moderate confidence in current forecast.
Solid Small Craft Advisory level winds will continue through
today. By this evening, the northwest winds are expected to
increase with moderate confidence in Gale Warning level winds
tonight and Saturday morning. Winds will diminish a bit Saturday
afternoon/night, but still remain at Small Craft Advisory levels.
For Sunday through Tuesday, winds and seas are expected to remain
below Small Craft Advisory levels.

For the Inner Waters, moderate confidence in current forecast.
For the waters north of Point Sal, northwest winds will likely
increase to Small Craft Advisory levels this afternoon/evening and
again Saturday afternoon/evening then from Sunday through Tuesday
wind and seas should remain below Small Craft Advisory levels. For
the southern Inner Waters, wind and seas are expected to remain
below Small Craft Advisory levels through Tuesday although there
is a chance of some advisory level gusts across western portions
this afternoon and again Saturday afternoon.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory in effect from noon today to 10 PM PDT this
      evening For zone 59. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect from 3 PM this afternoon to 9
      PM PDT this evening For zone 645. (See LAXMWWLOX).
     Small Craft Advisory in effect until 9 PM PDT this evening
      For zones 670-673-676. (See LAXMWWLOX).
     Gale Warning in effect from 9 PM this evening to 9 AM PDT
      Saturday For zones 670-673-676. (See LAXMWWLOX).

&&

$$

PUBLIC...Hall
AVIATION...RAT
MARINE...RAT
SYNOPSIS...Hall

weather.gov/losangeles



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