Winter Storm in California, December 24, 2016

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
1041 AM PST Sat Dec 24 2016

New Aviation Discussion

.SYNOPSIS...
Partly cloudy skies, cool and breezy conditions are expected
today. However, the north slopes, including the I-5 corridor near
the Grapevine, will continue to see mostly cloudy skies with snow
showers. Warmer conditions are expected by the middle of next week
with offshore winds. Showers are possible with an area of low
pressure late next week.

&&

.SHORT TERM...(TDY-MON)

The cold front is now well east of the area and most of the precip
has come to an end, other than some north slope snow showers. The
Winter Storm Warning remains in effect through late tonight, but
we will likely downgrade to a Winter Weather Advisory later
today. There have been reports of 12-16" of snow above 7000 ft in
the San Gabriels, with accumulating snow on the I-5 near the
Grapevine. The Tejon Pass was shut down earlier this morning and
just recently re-opened, with cars being escorted over the pass.

The upper-level trough is still overhead, so could see some
isolated showers for the coastal/valley areas today, mainly north
of Pt. Conception and in the foothills of the San Gabriels. Most
of the populated areas south of Pt. Conception will be mostly
sunny today. It will be cool and breezy though, and a Wind
Advisory has been added for the coastal areas of Ventura and LA
County.

Tonight will be clear and chilly, so we will have to look at
possibly putting out frost/freeze products for some coastal
and/or valley areas.

***FROM PREVIOUS DISCUSSION***

There will be advisory level NW winds in the mtns today as the
cold air rushes in behind the front. The advisory level mtn winds
are covered by the winter weather products. There will be advisory
level gusts in the Antelope Vly and a wind advisory is in effect
for the area today and this evening. Downright chilly hgts of
542DM will only allow max temps to climb into the mid and upper
50s today across the coasts and vlys or 8 to 12 degrees blo
normal.

Christmas day will be cool and dry as a little pop up ridge will
be over the area. Skies will be clear. Hgts only rise to 560 DM
and max temps will only rise 2 to 3 degrees.

On Monday...all mdls agree that an upper low will skirt to the
west of the area. The was some concern that this low would track
far enough east to bring rain to SLO and SBA counties but at
least for now this seems to be minimal worry. Skies will be mostly
sunny and Max temps will rise another 3 degrees. Max temps across
the coasts and vlys will mostly be in the mid 60s.

.LONG TERM...(TUE-FRI)

The upper low that sailed on past the area on Monday will then
take up residence several hundred miles to the SW of L.A.. The SFC
reflection of the upper low will set up offshore flow across the
area Tuesday through Thursday.

Dry NW flow with 576 hgts will set up over the area Tuesday and
continue into Wednesday. Temps will warm each day and will be a
few degrees above normal esp Wednesday.

The upper low will begin to move to the north and east on
Thursday. The GFS takes a faster and more northerly track and
hence brings cooler and cloudier conditions to the area while the
EC is slower and does not move the low too much to the north -
therefor its solution would result in sunnier skies with little or
no cooling from Wednesday.

The difference in the handling of the upper low are further
amplified on Friday as the GFS brings the upper low right over the
area along with widespread showers. The EC keeps the low and hence
the showers more to the south. This is very much like the scenario
that plagued the area last Wednesday and expect the upper low to
similarly misbehave through its forecast evolution.

&&

.AVIATION...24/1835Z

At 18z at KLAX there was no marine layer nor an inversion.

Good confidence overall in generally VFR TAFs. Light to
occasionally moderate LLWS is possible for KBUR mainly from 00Z
to 06Z. At KPRB, there is a 30 percent chance of LIFR cigs/vsbys
between 10Z and 16Z. Lower confidence in north winds at KSBA
mainly between 00Z and 00Z and KLAX KSMO between 10Z and 16Z with
a 20 percent chance of wind gusts to 15kt during this time.

KLAX...Good confidence the 12Z TAF. There is a 20 percent chance
of wind gusts to 15kt between 10Z and 16Z.

KBUR...Good confidence the 12Z TAF. Light to occasionally moderate
LLWS is possible, mainly from 00Z to 06Z. There is a 20 percent
chance of wind gusts to 25 kt through 06Z.

&&

.MARINE...24/830 AM

Good confidence in SCA winds and seas through tonight for
southern coastal waters to Sunday afternoon for the outer waters.
Local Gale force gusts are possible near the Channel Islands
through early this evening. There is also a slight chance of tstms
across the waters this morning. Any thunderstorm could produce
dangerous cloud to water lightning, gusty winds and small hail.
Winds and seas will likely remain below SCA levels Monday through
Wednesday.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory in effect until 3 PM PST Sunday for zones
      34-35. (See LAXCFWLOX).
     Beach Hazards Statement in effect through Sunday afternoon
      for zones 40-41. (See LAXCFWLOX).
     Wind Advisory in effect until 9 PM PST this evening for zones
      40-41-87. (See LAXNPWLOX).
     Winter Weather Advisory in effect until 4 AM PST Sunday for
      zone 52. (See LAXWSWLOX).
     Winter Storm Warning in effect until 4 AM PST Sunday for
      zones 53-54. (See LAXWSWLOX).
     Wind Advisory in effect until 10 PM PST this evening for zone
      59. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 9 AM PST Sunday for zone
      645. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PST Sunday for
      zones 650-655. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 PM PST Sunday for
      zones 670-673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK...(MON-FRI)
No significant hazards expected.

&&

PUBLIC...Sukup/Rorke
AVIATION...Munroe
MARINE...Kaplan
SYNOPSIS...Munroe

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