Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000
FXUS66 KLOX 210555
AFDLOX

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

.SYNOPSIS...
There is a chance of showers and mountain snow showers through
Saturday morning. Another storm system is forecast to move into
southwestern California late Saturday night into Monday. The peak
of this storm will be on Sunday, with rain, heavy at times, a
slight chance of thunderstorms, and strong gusty southerly winds.
There will be lingering showers and mountain snow showers over the
region into Monday, and a slight chance of showers on Tuesday.
High pressure will then bring dry and milder conditions to the
area Wednesday through Friday.

&&

.SHORT TERM...(FRI-MON)

Mainly scattered showers continue across the region as a trough of
low pressure slowly exits the region as it moves east into the
Great Basin and Arizona. Shortwave ridging over the Eastern
Pacific Ocean with the axis near 145W will build into the area
through Saturday morning. There is still plenty of moisture
upstream, so Saturday should be a partly to mostly cloudy day.
With residual moisture left behind the system, clouds could linger
over the mountains during the day on Saturday. Ridging aloft will
give way to a stronger storm system to impact the region late
Saturday through Tuesday. An update will be issued to trim PoPs
slightly and drop snow levels slightly.

*** FROM PREVIOUS DISCUSSION ***

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...

21/0600Z

At 0508Z at KLAX there was no marine layer nor an inversion.

There is a 30 percent chc of a shower at all sites through 12Z.
There is a 30 percent chc of MVFR cigs at all sites through 16Z.

Fairly good confidence in TAFs. There is a 30 percent chc that
there will be no BKN conds 20Z-06Z.

KLAX...Fairly good confidence in 06Z TAF. There is a 30 percent
chc of a shower through 12Z. There is a 30 percent chc of MVFR
cigs through 16Z. There is a 30 percent chc that there will be no
BKN conds 20Z-06Z. Strong East winds will likely last until noon
on Sunday.

KBUR...Fairly good confidence in 06Z TAF. There is a 30 percent
chc of a shower through 12Z. There is a 30 percent chc of MVFR
cigs through 16Z. There is a 20 percent chc that there will be no
BKN conds 20Z-06Z.

&&

.MARINE...

20/800 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, Winds will be just below Small
Craft Advisory levels tonight and Saturday morning. Seas well
above 10 feet will result in a Small Craft Advisory for hazardous
seas through late Sat night. 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 at SCA levels can be expected tonight
into 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 tonight, building to very large levels by late
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.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Warning in effect until 6 AM PST Sunday for zones
      34-35-40-41-87. (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).
     Winter Storm Warning in effect until 9 AM PST Saturday for
      zones 53-54. (See LAXWSWLOX).
PZ...Small Craft Advisory for hazardous seas in effect until 3 AM
      PST Sunday for zone 645. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PST Saturday for
      zone 650. (See LAXMWWLOX).
     Small Craft Advisory in effect until noon PST Saturday for
      zone 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...Hall/MW
AVIATION...Rorke
MARINE...RAT/Sirard
SYNOPSIS...Sirard

weather.gov/losangeles


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