Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000
FXUS66 KLOX 200247
AFDLOX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
647 PM PST Thu Jan 19 2017

.SYNOPSIS...

Several storms will bring precipitation and gusty winds into early
next week. There may be a slight chance of thunderstorms on
Friday. The second storm will be from late Tonight into early
Saturday with heavy rain especially in the foothills...and lower
snow levels. The third storm will be from Sunday into Tuesday and
have the highest precipitation amounts on Sunday. Temperatures
will be below normal into next week.

&&

.SHORT TERM...(THU-SUN)

Currently in between storms with just a few lingering showers
around, mainly in the higher terrain. Action will pick up early
Friday though as storm #2 rolls in with a 160kt jet just offshore.
This jet will basically sit there most of the day while
additional moisture and pva arrive and generate periods of
moderate to heavy rain across the area. There is some CAPE with
the front and combined with the favorable jet dynamics could
spawn a few thunderstorms across the area. Overall this should be
a slightly stronger system than we saw last night and given the
potential for thunderstorms it seems prudent to go with another
flash flood watch for the most sensitive burn scars, those being
the Fish and Sand fires in LA County. Look for precip amounts to
generally be a quarter to half inch higher than we saw with last
nights system. Snow levels should hover around 6000 ft for most
of the day with another several inches of snow expected at higher
elevations.

Gusty west to southwest winds expected with and behind the front
Friday, especially for LA/Ventura coast and the Antelope Valley
and wind advisories have been posted.

Precip should wind down pretty quickly Friday evening, though not
stop entirely as there`s plenty of moisture and enough upper level
energy to keep at least some showers going through Friday night,
but especially north of Pt Conception and in the mountains. Snow
levels will be lowering to between 4500 and 5000 feet but probably
not cold enough yet for any issues over the Grapevine.

Saturday is expected to be dry in most areas with likely some
sunshine as well. Still a cool day and breezy but not quite as
windy as Friday.

The break in the precip should last through Saturday evening
before storm #3 arrives. Models still painting this one as the
biggest of the series as it`s tapping into a deeper more
subtropical source of moisture with pwats rising up to 1.2-1.4",
which is a good half inch higher than what we`ve seen with the
previous two. Additionally, the storm will be slower to move
through, extending the period of time that moderate to heavy rain
will linger over any one area. Rain should start up early Sunday
morning and continue for much of the day. Not seeing much of a
thunderstorm threat, but impressive 50-60kt south winds and a deep
moisture source as well as decent warm advection should make for
a very efficient rainfall producer. Some areas could see twice the
amount of rain with this system than with Friday`s storm. No snow
though due to snow levels rising up to around 9000`. Strong south
winds likely will require at least wind advisories for the
mountains and SLO interior, possibly low end warnings for higher
elevations.

Colder air will start filtering into the area Sunday night and
snow levels will be falling rapidly. Though moisture will be on
the decrease and so should precip areal coverage and rates. Will
likely need at least a winter weather advisory starting Sunday
night for the mountains.

.LONG TERM...(MON-THU)

With colder air arriving Monday and the trof axis moving through
expect plenty of shower activity, possibly a thunderstorm or two,
and very low snow levels down to as low as 3500 feet. This could
pose travel issues over the Grapevine on Interstate 5, though
accumulations should be on the light side as a lot of the moisture
will have already exited to the east. Should be an interesting day
with a mixture of showers, thunderstorms with some hail possible, and
likely some sunshine at times as well.

Another system quick on the heels of the Monday storm, though with
limited moisture, will move through Tuesday maintaining at least a
threat of showers, though best chances over the mountains.

We start drying out Tuesday night into Wednesday as the trof moves
east and a ridge slowly builds in from the west through the end of
the week and into next weekend.

&&

.AVIATION...20/0245Z.

Predominantly VFR conditions will deteriorate to MVFR conditions
from northwest to southeast between 05Z and 15Z as another trough
of low pressure approaches the area. IFR conditions along with
periods of moderate to strong turbulence will likely develop
around the timing of frontal passage. Conditions should improve
to MVFR between 17Z and 23Z after the frontal band passes. There
is a chance of LIFR conditions in heavy rain for a period south of
Point Conception between 18Z and 22Z.

KLAX AND KBUR...MVFR conditions will spread through 10Z. There is
a 80 percent chance of IFR conditions in rain along with periods
of moderate to strong turbulence between 18Z and 22Z. There is a
30 percent chance of LIFR conditions in heavy rain for a period
south of Point Conception between 20Z and 22Z. There is a 30
percent chance of southerly cross winds greater than 20 knots
between 18Z and 20Z. At KLAX, southeast winds greater than 7 knots
will develop between 13Z and 15Z, likely increasing further after
15Z.

&&

.MARINE...19/130 PM...

For the Outer Waters, moderate confidence in current forecast.
Small Craft Advisory (SCA) level winds will continue through
this evening. For late tonight and Friday, southerly winds will
increase ahead of a cold front, likely reaching Gale Force levels.
The winds will show a bit of a lull on Saturday, but will likely
increase to Gale Force levels again on Sunday (as a third front
moves across the waters). SCA level winds can be anticipated on
Monday and Tuesday.

For the Inner Waters, moderate confidence in current forecast.
For the waters north of Point Sal, winds will remain below SCA
today, but SCA level seas will continue. For tonight and Friday,
southerly winds are expected to increase to Gale Force levels
ahead of the cold front. After a lull down to SCA level winds on
Saturday, winds will likely increase to Gale Force levels again on
Sunday. For the waters south of Point Conception, winds are
expected to increase to SCA levels today then to Gale Force levels
on Friday. Winds will diminish to SCA levels on Saturday, but will
likely again increase to Gale Force levels on Sunday.

A large long period west swell will build across the coastal
waters today, then continue to build to very large levels by
Friday night into Saturday. The swell will likely reach heights
of more than 20 feet over the northern and outer waters late
Saturday, and to 13 to 18 feet across the inner waters. West
to northwest facing bays and harbors may be affected by the swell
over the next coming days, including by not limited to Morro Bay
and Ventura Harbors.

&&

.BEACHES...19/130 PM...

A very large long-period westerly swell will bring very large surf
conditions to local beaches through early next week. For the
Central Coast, surf of 10-15 feet will continue through Friday
morning. From Friday afternoon through Saturday, the swell will
peak and produce damaging surf of 20-30 feet. For Sunday through
Tuesday, the swell will gradually diminish, but remain above high
surf advisory levels.

For the beaches south of Point Conception, surf of 4-8 feet will
continue through Friday afternoon. For Friday night and Saturday,
surf will increase to damaging levels of 10-16 feet across the
beaches of Ventura and Los Angeles counties. For the beaches of
southern Santa Barbara county, surf heights will build to 8-12
feet Friday night and Saturday. For Sunday through Tuesday, the
surf along all beaches will slowly subside, but remain above high
surf advisory levels.

High Surf Warnings have been issued for Friday and Saturday across
the beaches of the Central Coast as well as Ventura and Los
Angeles counties.

During this time...expect strong rip currents in all areas and
dangerous, rough surf due to period of strong south wind waves
and large westerly swell. Moderate to possibly severe beach
erosion is expected at times late Friday through Sunday. Dangerous
sneaker waves are likely. Minor coastal flooding is quite possible
at times Fri through Sunday.

Beach goers should use the highest level of caution during this
time. Much larger waves could wash over rocks, jetties and beach
areas near the water`s edge, potentially sweeping you into the
water. West facing harbor entrances will be dangerous with large
breaking waves. Breaking waves may also occur in shallow water
near the outer edge of the surf zone.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory in effect until 4 PM PST Friday for zones
      34-35. (See LAXCFWLOX).
     High Surf Warning in effect from 4 PM Friday to 2 AM PST
      Sunday for zones 34-35. (See LAXCFWLOX).
     High Surf Advisory in effect until 2 AM PST Sunday for zone
      39. (See LAXCFWLOX).
     High Surf Advisory in effect until 10 PM PST Friday for zones
      40-41-87. (See LAXCFWLOX).
     Wind Advisory in effect from 10 AM Friday to 6 AM PST
      Saturday for zones 40-41-46-87. (See LAXNPWLOX).
     High Surf Warning in effect from 10 PM Friday to 2 AM PST
      Sunday for zones 40-41-87. (See LAXCFWLOX).
     Winter Storm Warning in effect until 9 AM PST Saturday for
      zones 53-54. (See LAXWSWLOX).
     Flash Flood Watch in effect from 6 AM PST Friday through
      Friday afternoon for zones 54-88. (See LAXFFALOX).
     Wind Advisory in effect from 10 AM Friday to 8 PM PST
      Saturday for zone 59. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 3 AM PST Friday for
      zones 645-670-673-676. (See LAXMWWLOX).
     Gale Warning in effect from 3 AM to 9 PM PST Friday for zone
      645. (See LAXMWWLOX).
     Small Craft Advisory in effect until 10 AM PST Friday for
      zones 650-655. (See LAXMWWLOX).
     Gale Warning in effect from 10 AM to 9 PM PST Friday for
      zones 650-655. (See LAXMWWLOX).
     Gale Warning in effect from 3 AM Friday to 3 AM PST Saturday
      for zones 670-673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK...(SUN-THU)

Moderate to heavy rain is expected Sunday with strong southerly
winds. Rain rates could be high enough to generate mud and debris
flows in the burn areas. Lower snow levels Monday could bring
snow down to the Grapevine.

&&

$$

PUBLIC...MW
AVIATION...Hall
MARINE...RAT
BEACHES...RAT
SYNOPSIS...STU

weather.gov/losangeles



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