Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000
FXUS66 KLOX 210613
AFDLOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
1113 PM PDT Thu Jul 20 2017

...Aviation discussion updated...

.SYNOPSIS...

The overnight coastal marine layer will spread into the local
valleys, at times, and persist into next week. The dominate high
will bring temperatures around normal this week, with a slight
cooling for next week. A moist monsoonal flow will bring possible
showers and thunderstorms in the afternoons and evenings for the
deserts and mountains on Monday and Tuesday.

&&

.SHORT TERM...(THU-SUN)

The marine inversion was near 900 ft deep at LAX and near 1500 ft
deep at VBG early this evening. Low clouds were noted along portions
of the SBA County Central Coast and also near the L.A. County coast.
The low clouds are expected to expand overnight and cover much of
the coast and some adjacent vlys later tonight, except along the SBA
County s coast due to northerly canyon winds blowing thru and below
the Santa Ynez Mtns. Otherwise, mostly clear skies will prevail
across the forecast area thru tonight. Locally gusty sub-advisory
level winds will prevail this evening across the SBA County mtns and
s coast mainly w of Goleta. Gusty sw winds in the Antelope Valley
this evening will diminish overnight.

Upper level ridging with 500 mb heights around 591-592 dm will
persist over srn CA thru Fri night, then the ridge will expand over
the area on Sat with 500 mb heights increasing to around 593 dm
before slightly weakening on Sun.

Little change in the overall weather pattern can be expected Fri
thru Sun. The marine inversion will remain shallow thru the period,
in the 800 to 1400 ft range or so, and an eddy is expected over the
SoCal bight each night and early morning. Varying amounts of night
and morning low clouds and fog will prevail along much of the coast
and into some of the adjacent vlys. Otherwise, mostly clear skies
can be expected across the region thru Sun.

Decent onshore flow will prevail each afternoon and evening, with
some gusty s to w winds expected for the foothills, mtns and
Antelope Valley. Locally gusty north canyon winds will also be
possible each evening thru Sat for the SBA County s coast and mtns,
especially w of Goleta.

Temps across the region will warm to several degrees above normal in
the warmest vlys Fri thru Sun, altho Sat will be the warmest day
during the period. Temps closer to the coast will be near normal for
the most part thru Sun.

***FROM PREVIOUS DISCUSSION***

.LONG TERM...(MON-THU)

Overall, 00Z models in good synoptic agreement through the period.
At upper levels, center of ridge will meander around the Four
Corners area. Near the surface, weak onshore flow will continue.

Forecast-wise, main concern for the extended will be the potential
for some monsoonal moisture. At this time, mid-level flow turns
southeast to south which will be favorable for some monsoonal
moisture to move into the area. At this time, the moisture still
looks to be rather high-based, so chances of any significant
thunderstorm activity is minimal. However, there will be a slight
chance (15-20%) of thunderstorms over the mountains and desert
areas in the afternoon/evening hours on Monday and Tuesday. If any
thunderstorms do develop, they will likely not produce a lot of
rain due to the forecast moisture profile. So, gusty outflow winds
and dry lightning would be the main potential threats. For
Wednesday and Thursday, the flow turns more southwesterly which
will shunt any moisture to the east, limiting any thunderstorm
chances.

Otherwise, the marine layer will continue to impact the coastal
plain through the period. As for temperatures, expect minor
fluctuations from day-to-day, but still at or slightly above
seasonal normals.

&&

.AVIATION...21/06z

At 0527z at KLAX... the inversion was around 800 feet. The top of
the inversion was around 3600 feet with a temperature of about
37 degrees Celsius.

Overall... Moderate confidence in the current coastal and coastal
adjacent TAFs and high confidence elsewhere. LIFR/IFR conditions
will move over coastal locations through 12z with the exception of
KSBA where there is only a twenty percent chance of CIGs or low
VSBY. Conditions will clear to VFR between 16z-18z with a thirty
percent chance of reduced conditions lingering until 19z along
Los Angeles County. Similar conditions and timing will return to
KLAX tomorrow morning. There is a twenty percent chance of MVFR
conditions at KBUR 11z-17z. Otherwise and elsewhere VFR conditions
will prevail.

KLAX... Moderate confidence in the current TAF. LIFR/IFR conditions
will impact the terminal 08z-18z with a thirty percent chance of
conditions lingering through 19z. Similar conditions will return
after 22/09z. Otherwise VFR conditions will prevail. East winds
greater than 7 knots are not expected.

KBUR... Moderate to high confidence in the current TAF. There is
a twenty percent chance of MVFR conditions 11z-17z. Otherwise VFR
conditions will prevail.

&&

.MARINE...20/800 PM.

High confidence that Small Craft Advisory winds will continue
through at least Saturday and possibly through Sunday across the
Outer Waters. There is a 30 percent chance of gale force winds
on Friday afternoon and evening, mainly northwest of the Channel
Islands.

For the nearshore waters north of Point Conception, Small Craft
Advisory level winds will likely continue through Friday evening.
There is a 40 percent chance that winds could drop below criteria
between 3 AM and 9 AM PDT Friday, but winds will increase by the
afternoon hours at the latest.

For the Inner Waters south of Point Conception, winds and seas
are expected to generally remain below advisory level through the
weekend.

&&

.BEACHES...20/205 PM.

The National Hurricane Center indicates an 80-90 percent chance
of tropical cyclone formation off the Mexican Coast by early next
week. A wind-driven swell from one or two tropical cyclones could
develop and bring the potential for strong rip currents and
elevated-to-high surf for Southern California beaches for mid-to-
late week next week.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement in effect from Friday afternoon
      through Sunday evening for zones 40-41-87. (See LAXCFWLOX).
PZ...Small Craft Advisory in effect until 9 PM PDT Friday for zone
      645. (See LAXMWWLOX).
     Small Craft Advisory in effect until 9 PM PDT Saturday for
      zones 670-676. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PDT Sunday for zone
      673. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK...(SUN-THU)
No significant hazards are expected during this period.

&&
$$

PUBLIC...Sirard/Thompson
AVIATION...Kj
MARINE...Gomberg/Hall
BEACHES...Hall
SYNOPSIS...STu

weather.gov/losangeles



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