Small Craft Advisory 63, NWS Los Angeles, CA

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
1221 AM PDT Fri May 5 2017

.SYNOPSIS...

A low will arrive by Friday to deepen the overnight marine
layer for patchy coastal drizzle and cooling into Saturday
morning. The low will bring possible showers and thunderstorms
from late Saturday into Monday with near normal temperatures.
Another high will build in from the west on Wednesday and develop
the overnight marine layer into Friday.

&&

.SHORT TERM...(FRI-MON)

The marine inversion early this evening ranged from near 1100 ft
deep at VBG to near 1500 ft deep at LAX. Good onshore flow was
helping to push low clouds and fog along the coast inland some over
the coastal plain. Patchy dense fog was also noted along the
immediate coast. The low clouds will continue to push inland
overnight to the adjacent vlys, with low clouds also expected to
develop over the Salinas River Vly. Otherwise, mostly clear skies
can be expected across the forecast area overnight. Locally gusty s
to nw winds across the area will diminish by later this evening.

An upper level trof over the e Pac will approach the CA coast thru
Fri. The upper trof is forecast to move to the coast by Sat morning.
An upper level low will develop along the central CA coast Sat
morning then move quickly s to SLO/SBA Counties by late in the day
on Sat. It looks like the upper low will track slowly e on Sun to a
position close to the srn NV border Sun afternoon. However, there is
some uncertainty with the track of the upper low as the 12Z EC
positions the upper low along the SAN County coast by late Sun.

The marine layer pattern will persist Fri into Sat morning, with
night and morning low clouds and fog for the coast, vlys and lower
coastal slopes by early Sat. Skies should be mostly sunny for most
areas Fri afternoon, altho some coastal areas may have low clouds
all day.

With the approach of the upper trof, the marine layer will
transition into a deep moist layer Sat. Patchy drizzle can be
expected mainly over VTU/L.A. Counties from the coast to the coastal
slopes Sat morning followed by a chance of light rain for many of
these areas Sat afternoon along with plenty of cloud cover. Further
n, partly to mostly cloudy skies can be expected on Sat. There will
also be a slight chance of an afternoon and evening thunderstorm for
the SBA/VTU/L.A. County mtns and Antelope Vly thanks to an
increasingly unstable airmass with the approach of the upper
trof/upper low.

As the upper low moves thru the area Sat night and e of the area on
Sun, it will bring mostly cloudy skies with a chance of showers and
mountains snow showers to much of southwest CA. With cold air (-25
deg C at 500 MB) and cyclonic flow aloft, there will be enough
instability to warrant a slight chance of thunderstorms over much of
the region Sat night, shifting to L.A. County by Sun afternoon.

This will be a showery weather system with highly variable precip
amounts. In general, most areas should receive between 0.10 and 0.50
inches of rain through Sunday evening although locally higher
amounts will be possible with any thunderstorm development. Snow
levels will drop to around 5000 feet Saturday night/Sunday, so a
couple of inches of snow accumulation will be possible at higher
elevations.

Temps will turn quite a bit cooler for Fri to near normal to
slightly above normal for most areas, then turn sharply cooler Sat
and Sun, with highs several degrees below normal across the region.

.LONG TERM...(TUE-FRI)

Through the extended period, rather benign weather is anticipated.
For Sunday night and Monday, models wobble cutoff low over
northern Baja Mexico. Given this trajectory, precipitation chances
will gradually diminish from northwest to southeast through
Monday afternoon, although there will at least be a slight chance
for all areas by Monday afternoon. Temperatures should rebound a
few degrees Monday afternoon due to increasing thicknesses/H5
heights as low moves out of the area.

For Tuesday through Thursday, the upper low will continue to move
out of the weather picture as a weak upper level ridge noses over
the area. With this pattern, skies will be partly cloudy on
Tuesday and mostly clear on Wednesday/Thursday although some
stratus may return by Thursday morning to the coastal plain.
As for temperatures, a general warming trend will continue through
Thursday.

&&

.AVIATION...05/0700Z.

At 06Z, the marine layer depth at KLAX was around 1300 ft deep.
The top of the inversion was near 3200 ft with a temperature of
25 degrees Celsius.

LIFR to IFR conditions should gradually improve to IFR to MVFR
conditions through 15Z at coastal terminals while spreading into
valley terminals, then to MVFR to VFR conditions between 16Z and
19Z. Some coastal terminals may remain in MVFR conditions
throughout the day, especially coastal terminals south of Point
Conception. IFR to MVFR conditions will make an earlier arrival on
Friday evening.

KLAX...IFR conditions should improve to MVFR conditions through
08Z. There is a 60 percent chance of MVFR conditions lingering
throughout the day on Friday. At the latest, MVFR conditions will
redevelop by 04Z on Friday evening. Drizzle is possible on Friday
night.

KBUR...IFR conditions should arrive between 09Z and 13Z, then improve
to MVFR conditions between 13Z and 16Z. MVFR conditions could
linger as late as 18Z or 19Z.

&&

.MARINE...04/800 PM.

Areas of dense fog with visibility one nautical mile or less will
be possible through at least this evening.

Otherwise, gale force winds are likely by Friday evening across
the Outer Waters. Gales will likely linger into Saturday and
Sunday. A Gale Warning has been added for the Outer Coastal
Waters. There is a 50 percent chance that seas could be between 2
and 4 feet larger than forecast across the Outer Coastal Waters. A
period of steep short-period seas should develop between Friday
and Friday night and continue into Monday.

Across the Inner Waters, winds and seas are expected to increase
and build respectively by Friday for the Central Coast and across
all inner waters by Saturday and possibly continuing into Sunday.
A Gale Watch remains for the nearshore waters north of Point Sal.
A Gale Watch has been added for the inner waters south of Point
Conception for Saturday afternoon and evening. There is a 50
percent chance of Gale conditions across the Southern California
Bight sometime between Saturday afternoon Sunday night. An
interval of short- period steep seas is possible between Saturday
and Sunday.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement in effect through this afternoon for
      zone 41. (See LAXCFWLOX).
PZ...Gale Watch in effect from this afternoon through Saturday
      evening for zone 645. (See LAXMWWLOX).
     Gale Watch in effect from Saturday afternoon through Saturday
      evening for zones 650-655. (See LAXMWWLOX).
     Small Craft Advisory in effect until 9 AM PDT this morning
      for zone 670. (See LAXMWWLOX).
     Gale Warning in effect from 9 AM this morning to 3 AM PDT
      Monday for zone 670. (See LAXMWWLOX).
     Gale Warning in effect from 3 PM this afternoon to 3 AM PDT
      Monday for zones 673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK...(MON-FRI)
A late season cool storm will likely bring scattered showers and
accumulating snow as low as 5000 to 6000 feet late Saturday into
Sunday with a slight chance of thunderstorms by Sunday.

&&

PUBLIC...Sirard/Thompson
AVIATION...Hall
MARINE...Sweet/Sirard
SYNOPSIS...STu

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