Area Forecast Discussion
Issued by NWS Los Angeles, CA
FXUS66 KLOX 291745
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
1045 AM PDT FRI APR 29 2016
Temperatures will remain below normal through Sunday as broad low
pressure remains over the Southwest...with marine layer clouds
and locally breezy conditions. Showers and thunderstorms are
possible for interior areas over the weekend as the low gets
close. Monday through Wednesday will bring warming to around
normal as high pressure nosing in from the south. A low pressure
system could bring light rain and cooler conditions toward the end
of next week.
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
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.
Mid/upper level ridge of high pressure upstream and trough of low
pressure downstream will persist. Upper level strong north-northwest
winds will prevail while mid level moderate northwest winds
become moderate northeast after 30/15z over the area. Moderate
onshore pressure gradient through 30/06z then mixed weak onshore
and weak northerly gradient between 30/06-30/20z then moderate
onshore gradiant and weak northerly gradient after 30/20z. A weak
low level capping marine inversion base ranged from 2.8kft along
the central coast to 3.5kft over the L.A. basin and cloud field
was overcast north and west of the Channel Islands and scattered
to broken over the bight and L.A. basin. The inversion base will
differ by minus 1.2kft along the central coast and the cloud
field will become scattered to broken. The inversion will differ
by little over the bight and cloud field will become overcast
Marine layer at LAX at 1500Z is 3527 feet deep and the inversion
top is at 4348 feet with a temp of 11.5 degrees C.
KLAX...Chance cigs 030-035 through 29/20z. chance cigs 015-020
between 30/04-30/13z and chance cigs 025-030 between 30/13-30/21z.
KBUR...Chance cigs 015 after 30/08z.
virtually certain - 95-100%
very likely - 80-95%
likely - 60-80%
chance - 30-60%
very unlikely - 20% OR LESS
Northwest winds and seas 10 feet or greater will create small
craft advisory conditions from Piedras Blancas to San Clemente
Island today with gale gusts tonight. Seas over 10 feet and small
craft advisory for hazadous sea conditions from Piedras Blancas to
San Clemente Island will exist through Saturday night as gales
north of the area persist. otherwise sca conditions are not
expected Sunday through Thursday. But a south swell will likely
arrive Saturday and extra currents and surging as well as
hazardous surf are likely along exposed south facing shores.
CA...Wind Advisory in effect until 10 PM PDT this evening For zone
59. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 11 PM PDT Saturday 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).