Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 221800 AAA
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
1000 AM PST Thu Feb 22 2018

...updated aviation discussion...

.SYNOPSIS...22/727 AM.

An upper trough tracking to the northeast of the region will
bring a slight chance of rain showers with low elevation snow
showers this afternoon through early Friday, along with cool and
breezy conditions. Dry and cool weather is expected over the
weekend. Another trough may bring more widespread rain to the
region late Monday through Tuesday night or early Wed, with a more
significant storm later in the week.

&&

.SHORT TERM (TDY-SAT)...22/924 AM.

A trough is dropping south taking a similar path as many of its
predecessors, ie mostly inland with minimal moisture content.
Rain chances today not looking good except possibly eastern LA
County where some upslope flow from a strengthening sea breeze
could aid in lift up against the foothills and mtns. Otherwise
probably just some developing stratocu and temps near yesterday`s
levels. Better rain chances up north tonight and places like the
I5 corridor with better lifting mechanisms in place but still over
all light amounts, a tenth or less is most areas, possibly as
much as a quarter inch. And maybe an inch or two of snow.

***From previous discussion***

Gusty southwest winds will likely reach advisory levels across
the L.A. County mountains and the Antelope Valley this afternoon.
Gusty northwest winds should reach advisory levels on the Central
Coast this afternoon, and in the mtns and adjacent south coast of
SBA County from late this afternoon through late tonight. Once the
flow turns northwest across the VTU County mountains the evening,
expect advisory level winds there. Elsewhere, gusty winds will
also affect coastal sections of L.A. and VTU Counties, but winds
should remain below advisory levels there.

It will be cool across the region today and tonight. Snow levels
will be between 3500 and 4000 feet today, then should lower to
between 2500 and 3000 feet tonight and Fri morning. Any showers
should end in most areas by late tonight except could linger
through Fri morning across the eastern mountains of L.A. County,
and on the northern slopes of the VTU County mtns in the moist NW
flow there. Local snow accumulations of 1 to 2 inches are possible
in the mtns, mainly tonight and early Fri. Snow could potentially
affect travel on Interstate 5 near the Grapevine tonight and Fri
morning. Local snow is possible in the Antelope Valley, though
any accumulation should be less than one inch and confined to the
foothills. Skies will be partly cloudy in most areas Fri, and max
temps will remain at least 6 to 10 degrees below normal in most
areas. Winds should drop below advisory levels in most areas by
Fri afternoon.

Clear skies are expected Fri night and Sat. It will be very
chilly, especially where the wind completely drops off. Freeze and
possible Hard Freeze Watches will have to be considered for some
valley locations, and possibly coastal sections of SLO and SBA
Counties. Max temps may edge upward a bit on Sat, but will still
be well below normal everywhere across the region.

.LONG TERM (SUN-WED)...22/422 AM.

A weak upper trough will zip through the eastern Great Basin
Sat night and Sun, while a broad NW flow pattern sets up across
the region. Heights and thicknesses across the region will rise.
Low level flow will be offshore on Sunday, likely all day. Expect
several degrees of warming in most areas on Sunday, with temps
possibly getting close to normal in coastal and valley areas.

Another trough will drop southward from the Pac NW Mon and Mon
night, but there are important difference with its track and
ultimately how much rain it could bring to the region. The EC is
farther west with its track, which allows the system to pick up
more in the way of moisture from the Pacific. It also shows it
evolving into an upper low near Point Conception and lingering
near the region into Wed. The GFS, is not only farther to the east
with the system, keeping it across CA, and while it briefly shows
the system closing off early Tue, it keeps it progressive.
Therefore, with the EC has the upper low near Catalina Island Wed
morning, the GFS shows it already in northern Texas. That is quite
a difference. The EC would be much wetter than the GFS. Given the
general tendency toward inside slider type systems this winter so
far, will lean toward the GFS, but will still bump up pops some in
most areas Mon night through Tue night. Max temps on Mon should
change little from those on Sunday, then some cooling is expected
Tue, with a possible rebound in temps Wed if the GFS is correct.
For the end of the week, model disagreements continue with the EC
again farther west and much wetter with another system poised to
affect the region.

&&

.AVIATION...22/1758Z.

At 1730Z, there was no inversion present at KLAX.

Generally hi confidence in the 18Z TAFs. VFR conditions are expected
at all the airfields through Fri morning, altho some VFR cigs should
affect several of the airfields at times this afternoon and tonight.
There may also be a few showers around the region mainly this
evening. There will be gusty W to NW winds at many airfields this
afternoon into the evening, with low level wind shear possible at
times this evening at KSBA due to gusty N canyon winds in the
vicinity.

KLAX...Generally hi confidence in the 18Z TAF. VFR conditions are
expected through Fri afternoon, altho there is a 30 percent chance
of VFR cigs at times this afternoon and tonight with isolated
showers in the vicinity. There will also be gusty W to NW winds this
afternoon through Friday.

KBUR...Generally hi confidence in the 18Z TAF. VFR conditions are
expected through Fri morning, altho there is a 30 percent chance of
VFR cigs at times this afternoon and tonight with isolated showers
in the vicinity.

&&

.MARINE...22/843 AM.

For the Outer Waters, moderate confidence in current forecast.
Northwest winds will increase today with 70% chance of widespread
Gale force winds this afternoon/tonight. So, a GALE WARNING has
been issued. From Friday through Monday, 70% chance of Small Craft
Advisory (SCA) level winds continuing with a 40% chance of Gale
force winds Saturday afternoon/night.

For the Inner Waters, moderate confidence in current forecast. For
the waters north of Point Sal, SCA level winds are likely (70%
chance) today through Monday, especially during the afternoon and
evening hours. There is a 30% chance of Gale force winds this
afternoon/evening and again on Saturday. For the waters south of
Point Conception, 60% chance of SCA level winds from this
afternoon through Saturday night, especially across western
portions. After a lull on Sunday, SCA level winds are likely again
on Monday.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory in effect from 2 PM this afternoon to 9 PM PST
      this evening for zones 34-35. (See LAXNPWLOX).
     Wind Advisory in effect from 2 PM this afternoon to 4 AM PST
      Friday for zones 39-52. (See LAXNPWLOX).
     Wind Advisory in effect from 10 PM this evening to 10 AM PST
      Friday for zone 53. (See LAXNPWLOX).
     Wind Advisory in effect until 10 AM PST Friday for zone 54.
      (See LAXNPWLOX).
     Wind Advisory in effect until 10 PM PST this evening for zone
      59. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect from 3 PM this afternoon to 3
      AM PST Friday for zones 645-650-655. (See LAXMWWLOX).
     Gale Warning in effect from 3 PM this afternoon to 3 AM PST
      Friday for zones 670-673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (SAT-WED).

Widespread freezing temperature and frost are possible early
Saturday. Gusty advisory level winds are possible through the
Santa Ynez Range and the I5 corridor early Saturday. Low elevation
snow possible Monday night into Tuesday creating hazardous
driving conditions in the mountains, especially the I5 corridor
area.

&&

$$

PUBLIC...MW/DB
AVIATION...Sirard
MARINE...RAT/Sirard
SYNOPSIS...JLL

weather.gov/losangeles



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