Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000
FXUS66 KLOX 210025
AFDLOX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
425 PM PST Fri Jan 20 2017

.SYNOPSIS...

There will be a slight chance of thunderstorms and rain into tonight
with lower snow levels. A chance of showers will occur early on
Saturday. 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...(TDY-MON)

The main part of storm #2 has passed through the area and now
we`re dealing with post-frontal showers, with still a possibility
of a thunderstorm or two through the afternoon. The showers will
continue off and on through the night, but will be most prevalent
north of Pt Conception, in the mountains, and in eastern LA County
as the low lvl winds have shifted to the west northwest. Showers
will taper off later tonight and Saturday morning and most areas
except for possibly the Central Coast should remain dry Saturday.

Attention then turns to what looks to be the biggest storm of this
series and quite possibly the biggest in some time. The key
factors with this one are 40-60kt of south wind in the low lvls
(about 10-20 kt higher than with today`s storm), pwats 1.2-1.4"
(at least a quarter inch higher than today), and a much slower
movement through the forecast area. So while we don`t expect any
convection with this storm, the other factors could easily
generate hourly rain rates of at least 1 inch and locally higher
in upslope areas and for a longer period of time. This should
lead to rainfall amounts that are roughly double what we saw
today in most areas, so 2-4" coast/valleys (highest near the
foothills), 3-6" foothills/mtns looks reasonable. Will likely need
a larger scale flash flood watch for Sunday if models continue to
show the storm holding together.

This will be a much warmer storm than the one we`re dealing with
today so snow levels will rise dramatically, likely up to at least
8000`. Thus, snow won`t be much of a factor initially. However,
colder air will arrive Sunday night and Monday and this will drive
snow levels down rapidly to around 3500 ft. A lot of the moisture
will have left the area by then, but there`s enough to generate
showers and low elevation snow that could pose travel issues on
Interstate 5 over the Grapevine. Overall probably another quarter
to half inch of rain Monday most areas with the scattered showers.

.LONG TERM...(TUE-FRI)

One last little bit of energy aloft will come through Tuesday and
could spawn a shower or two across the area but moisture will be
limited. Still, can`t rule out some light showers and will leave
a slight chance in the forecast. Mainly just a continuation of
the cool temperatures.

A ridge will build in through next weekend for a warming trend and
no additional precip expected through the end of the month.

&&

.AVIATION...21/0025Z.

VFR conditions, with periods of MVFR conditions will continue
throughout the period, especially near any heavier showers.
Periods of moderate to strong low-level wind shear and turbulence
are possible at all terminals through 14Z. MVFR conditions are
likely across the valley terminals on Saturday afternoon.

KLAX...Ceilings at or below 5000 feet will continue through 10Z. There
is a 50 percent chance of MVFR conditions through 09Z, especially
near any heavier showers. Periods of moderate to strong low-level
wind shear and turbulence are possible through 14Z.

KBUR...Ceilings at or below 5000 feet will continue through 10Z. There
is a 50 percent chance of MVFR conditions through 09Z, especially
near any heavier showers. Periods of moderate to strong low-level
wind shear and turbulence are possible through 14Z. There is 60
percent chance of MVFR conditions after 20Z Saturday.

&&

.MARINE...20/130 PM.

For the Outer Waters, moderate confidence in current forecast.
Gale Force westerly winds will continue through tonight. On
Saturday, winds will abate, but still remain above Small Craft
Advisory (SCA) levels (at least through Saturday morning). On
Sunday, southerly winds will increase yet again with Gale Force
winds expected. The winds will shift to the west Sunday evening
with SCA level winds likely to continue through Monday.

For the Inner Waters, moderate confidence in current forecast. For
the waters north of Point Sal, Gale Force westerly winds will
continue through this evening. On Saturday, winds will abate, but
still remain above Small Craft Advisory (SCA) levels (at least
through Saturday morning). On Sunday, southerly winds will
increase yet again with Gale Force winds expected. The winds will
shift to the west Sunday evening with SCA level winds likely to
continue through Sunday night. For the waters south of Point
Conception, westerly winds will remain at Gale Force levels
through this evening, before diminishing to SCA levels tonight and
Saturday. On Sunday, southerly winds will increase again with SCA
level conditions likely (and a 30% chance of Gale Force gusts).
The SCA level winds will likely continue through Monday.

A large long period west swell will continue to build across the
coastal waters this afternoon, building to very large levels by
tonight and 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.

Through this evening, there will be the possibility of
thunderstorms across the coastal waters. Any thunderstorms that
develop will be capable of producing locally strong winds and
rough seas, heavy rainfall with reduced visibilities and isolated
waterspouts.

&&

.BEACHES...20/830 AM.

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 this
morning. From this 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 this afternoon. For tonight 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 of 4-7 feet today will build to
8-12 feet tonight 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 will be likely Saturday
and Saturday night.

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 Warning in effect until 6 AM PST Sunday for zones
      34-35. (See LAXCFWLOX).
     Coastal Flood Advisory in effect until 6 AM PST Sunday for
      zones 34-35. (See LAXCFWLOX).
     High Surf Advisory in effect until 6 AM PST Sunday for zone
      39. (See LAXCFWLOX).
     Wind Advisory in effect until 3 AM PST Saturday for zone 39.
      (See LAXNPWLOX).
     Coastal Flood Advisory in effect from 3 AM Saturday to 6 AM
      PST Sunday for zones 39>41-87. (See LAXCFWLOX).
     High Surf Advisory in effect until 10 PM PST this evening for
      zones 40-41-87. (See LAXCFWLOX).
     Wind Advisory in effect until 6 AM PST Saturday for zones
      40-41-46-59-87. (See LAXNPWLOX).
     High Surf Warning in effect from 10 PM this evening to 6 AM
      PST Sunday for zones 40-41-87. (See LAXCFWLOX).
     Wind Advisory in effect until 9 PM PST this evening for zones
      44-45-88-547. (See LAXNPWLOX).
     Winter Storm Warning in effect until 9 AM PST Saturday for
      zones 53-54. (See LAXWSWLOX).
     Flash Flood Watch in effect until 6 PM PST this evening for
      zones 54-88. (See LAXFFALOX).
PZ...Gale Warning in effect until 9 PM PST this evening for zones
      645-650-655. (See LAXMWWLOX).
     Gale Warning in effect until 3 AM PST Saturday for zones
      670-673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK...(MON-FRI)

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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