Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 202142
AFDLOX

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

.SYNOPSIS...
There will be a slight chance of thunderstorms today with rain...
heavy at times...into tonight and 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...20/1630Z...

At 1615Z, there was no marine inversion at KLAX.

Overall, low confidence in 18Z TAF package. With cold front
sweeping through tonight, CIGs and VSBYs will vary greatly from
one hour to the next through this evening (conditions will likely
range between MVFR and LIFR). For tonight, MVFR CIGs/VSBYs will
be likely, but moderate confidence in conditions improving to VFR
levels after 10Z.

Through this afternoon, there is the possibility of thunderstorms
across all sites. The best chances will be from Ventura county
southward. So, will include a VCTS remark through early this
evening for KOXR and sites south and east. Any TSTMs that develop
will be capable of producing gusty/erratic winds, reduced VSBY in
heavy rain and small hail.

KLAX...low confidence in 18Z TAF. CIGs and VSBYs will vary greatly
between MVFR and LIFR levels through about 02Z. Gusty south winds
will develop this afternoon and shift to the west this evening and
overnight. Through 02Z, there is a chance of TSTMs.

KBUR...low confidence in 18Z TAF. CIGs and VSBYs will vary greatly
between MVFR and LIFR levels through about 02Z. Gusty south winds
will develop this afternoon and shift to the southwest and west
this evening and overnight. Through 02Z, there is a chance of
TSTMs.

&&

.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...Coastal Flood Advisory in effect until 6 AM PST Sunday for
      zones 34-35. (See LAXCFWLOX).
     High Surf Advisory in effect until 4 PM PST this afternoon
      for zones 34-35. (See LAXCFWLOX).
     Wind Advisory in effect until 3 PM PST this afternoon for
      zones 34>38. (See LAXNPWLOX).
     High Surf Warning 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).
     High Wind Warning in effect until 6 PM PST this evening for
      zones 51-52. (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 54-88-548. (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...RAT
MARINE...RAT
BEACHES...RAT
SYNOPSIS...STU

weather.gov/losangeles


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