Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 172348 AAA
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
348 PM PST Wed Jan 17 2018

...updated aviation discussion...

.SYNOPSIS...
Ridge of high pressure aloft will peak today before a trough of
low pressure with a weakening cold front pushes through the region
by Friday. This will bring some warming with fair skies today
with a cooling trend and increasing clouds through Friday. Light
rain and mountain snow showers possibly by Friday, lingering into
Saturday morning for the northern slopes. Conditions now look
pretty dry for next week.

&&

.SHORT TERM...(TDY-SAT)

Nice warm up today with the offshore flow and additional solar
radiation. However, we`re starting to see indicators that a
cooling trend is on the way. Offshore trends are weakening and
marine layer stratus is pushing back onto the Central Coast this
afternoon. So the Central Coast will definitely be cooler Thu and
coastal areas south of Pt Conception should also see a few degrees
knocked off today`s highs. Elsewhere, either little change or
slightly warmer.

The tightly wound upper low off the WA coast is moving northeast
into British Columbia but a weak cold front will move well out
ahead of it and into SLO/nrn SB Counties Thursday night and
through Ventura/LA Counties early Friday. It has zero southerly
low ahead of it and no dynamics aloft as the trough is still well
to the north and west so it won`t have much going for it in terms
of lift and precipitation, especially south of Pt Conception.
Northern areas could see some very light rain, mostly under a
tenth of an inch but southern areas, including areas near the
Thomas burn, at best just some sprinkles or very light showers.
Much cooler temperatures Friday with highs mostly in the 50s and
lower 60s.

Strong west/northwest winds expected to develop behind the front
Friday, generating near advisory level gusts across the coastal
areas. Also, as the trough arrives Friday afternoon and night even
colder air will move in lowering snow levels to around 3000`. With
strong northwest flow in place this will mostly impact the
extreme northern Ventura mountains near the Kern County line and
the Grapevine as well as the extreme eastern San Gabriels near
Wrightwood. Advisory and possibly near warning level northwest
winds expected over these areas Friday night into early Saturday
along with accumulating snow, including interstate 5 through the
Grapevine. Could see 3-6 inches of snow, the higher amounts over
the higher peaks and a few inches possible over Interstate 5 by
Saturday morning. Given the ongoing closures of Highways 101 and
33 forcing additional vehicle traffic through the Grapevine this
could have significant impacts to drivers trying to go north and
south.

A cool but mostly dry and breezy day on Saturday with highs again
in the 50s to low 60s at lower elevations and 30s and 40s in the
mountains. Advisory level northwest winds possible along the
Central Coast, srn SB County, and the I5 corridor.

Overnight lows will be quite cold, likely dropping to near or below
freezing in many wind protected locations away from the immediate
coast. Frost advisories and/or freeze warnings may be needed.

.LONG TERM...(SUN-WED)

Temps will continue to slowly rebound Sunday/Monday but still
remain cooler than what we`ve been used to this winter so far but
actually very close to seasonal norms. The tail end of a weak
system will brush northern SLO County Monday and there could be
some very light precip there, otherwise just some increasing mid
and high clouds. Dry conditions and slowly warming Tue/Wed as
weak offshore flow develops. Forecast highs were trimmed a few
degrees as there doesn`t appear to be enough offshore gradient and
ridging aloft to justify temps much warmer than the lower 70s.

Next chance of rain looks to be next Thursday, but again a
glancing blow at best and likely nothing south of Pt Conception.

&&

.AVIATION...17/2345Z...

At 2309Z, there was an inversion around 300 ft deep at KLAX. The top
of the inversion was near 1100 ft with a temperature of 23 deg C.

Generally hi confidence in the 00Z TAFs. Low clouds and LIFR
cigs/vsbys are likely for KSBP and KSMX starting early this evening
and persisting thru Thu morning, with MVFR cigs expected to continue
thru Thu afternoon. For KPRB, there is a 70 percent chance LIFR
cigs/vsbys will develop at the airfield by 12Z and persist thru
about 19Z Thu, altho the timing of the onset of the LIFR conditions
may be up to 2 hours too late. MVFR vsbys will prevail at KLAX and
KLGB at times later tonight into Thu as well. Otherwise, VFR
conditions can be expected at the airfields thru Thu afternoon.

KLAX...Generally hi confidence in the 00Z TAF. MVFR vsbys can be
expected late tonight into Thu morning, and a 60 percent chance MVFR
cigs will move into the airfield starting around 04Z Thu evening.
Otherwise, VFR conditions will prevail at the airfield during
the period.

KBUR...Generally hi confidence in the 00Z TAF with VFR conditions
expected through Thu afternoon.

&&

.MARINE...17/100 PM...

For the Outer Waters, moderate to high confidence in current
forecast. High confidence in Small Craft Advisory (SCA) level
conditions due to hazardous seas. Large westerly swell will
gradually diminish this evening into Thursday morning, but an
even larger westerly swell will move into the waters Thursday
afternoon, peaking Thursday night/Friday morning (with swell
heights 13-19 feet). SCA level seas will continue through Monday.
As for winds, northwest winds are expected to increase to SCA
levels on Thursday and remain at SCA levels through Monday. There
is a 50% chance of Gale force winds developing Friday afternoon
through Saturday evening across the southern two zones (PZZ673 and
PZZ676).

For the Inner Waters, moderate to high confidence in current
forecast. For the waters north of Point Sal, high confidence in
Small Craft Advisory (SCA) level conditions due to hazardous seas.
Large westerly swell will gradually diminish this evening into
Thursday morning, but an even larger westerly swell will move into
the waters Thursday afternoon, peaking Thursday night/Friday
morning (with swell heights 14-17 feet). SCA level seas will
continue through Monday. As for winds, northwest winds are
expected to increase to SCA levels Friday and Saturday. For the
Inner Waters south of Point Conception, winds are expected to
increase to SCA levels Friday and Saturday with a 50% chance of
Gale force winds developing.

&&

.BEACHES...17/100 PM..,

An extended period of large surf is expected along west and
northwest-facing beaches through Saturday as westerly swells move
through the coastal waters. The first pulse of large westerly
swell will slowly diminish this evening and Thursday morning.
However, a second, much larger westerly swell will develop
Thursday afternoon and continue through Saturday.

For west and northwest-facing beaches along the Central Coast,
surf heights of 10-16 feet with local sets to 18 feet will
continue through Thursday morning and a HIGH SURF ADVISORY will
remain in effect. By Thursday afternoon, the surf will increase to
15-20 feet with local sets to 25 feet through Saturday afternoon.
Therefore, a HIGH SURF WARNING remains in effect from Thursday
afternoon through 800 PM Saturday evening.

For the west and northwest-facing beaches south of Point
Conception, surf heights of 7-10 feet with local sets to 12 feet
will slowly diminish late tonight and Thursday morning. However,
surf heights are expected to increase to 8-12 feet with local sets
to 15 feet by Thursday evening and continue into Saturday evening.
A HIGH SURF ADVISORY remains in effect through 800 PM Saturday.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory in effect until noon PST Thursday for
      zones 34-35. (See LAXCFWLOX).
     High Surf Warning in effect from noon Thursday to 8 PM PST
      Saturday for zones 34-35. (See LAXCFWLOX).
     High Surf Advisory in effect until 8 PM PST Saturday for
      zones 40-41-87. (See LAXCFWLOX).
PZ...Small Craft Advisory for hazardous seas in effect until 3 PM
      PST Thursday for zones 645-670. (See LAXMWWLOX).
     Gale Watch in effect from Friday afternoon through Saturday
      evening for zones 650-655-673-676. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 PM PST Thursday for
      zones 673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK...(SAT-WED)
Gusty winds, cold temperatures and accumulating snow to low
elevations, likely including Interstate 5 over the Grapevine late
Friday into early Saturday. Frost advisories and/or freeze
warnings possible for parts of the area over the weekend due to
near or below freezing overnight temperatures.

&&

$$

PUBLIC...MW
AVIATION...Sirard
MARINE...RAT
BEACHES...RAT
SYNOPSIS...Sweet

weather.gov/losangeles



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