Winter Storm Warning 3, NWS Los Angeles, CA

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
155 PM PDT Mon Mar 11 2019

.SYNOPSIS...11/137 PM.

Today will be warmer with decreasing clouds and lingering showers
in the mountains. Heavy snow will be likely in the San Gabriel
Mountains tonight with light rain elsewhere mainly for LA County.
It will be breezy and dry on Wednesday. Mostly clear skies and
above normal temperatures are expected for the end of the week and
the weekend.

&&

.SHORT TERM (TDY-THU)...11/137 PM.

The focus of the short term is on the impacts associated with the
cut off upper level low pressure system, currently about 550 DM
and 300 miles to our southwest. Mid and high level clouds
associated with the feature are producing mostly cloudy skies in
LA and Ventura counties. Still expecting the low will move east
and by this afternoon with a little PVA and moisture will wrap
around into LA county from the SE. This will produce a slight
chance of showers for most of LA County with less than a tenth of
an inch expected. The exception is the in the San Gabriel Valley,
the LA County mountains and the foothills of the Antelope valley
where higher elevations could get between a half and a third of an
inch.

The moisture and PVA strengthens rapidly tonight and will wrap
back into the slopes of the eastern San Gabriel Mountains with
heavy snow at times through daybreak. Gust northeast to north
winds will create near whiteout conditions above 5000 feet and
especially in the Big Pines and Wrightwood area. National Blend,
HRRR, and NAM support strong accent and qpf amounts over 1-1.5
inches, even 2.0 inches on the Blend. This easily equates to over
a foot of snow in this region through noon Tuesday. Winter Storm
Warning will be issued shortly. In addition, when precipitation
rates become intense late tonight the evaporative cooling is
likely to drive snow levels down another 1k feet.

Weak ridging and offshore flow set up on Tuesday. The LAX-DAG
gradient gets to about a +3. Skies will clear out. The CWA will
see heights up to 565 DM in the western portions dropping to 555
DM in the east. The clear skies, offshore flow, and areas of
higher heights will bring temperatures up a couple degrees in most
areas. Highs away from the mountains will mostly be in the mid to
upper 60s and only a few degrees under seasonal normal.

Things change by Tuesday afternoon when a minor trof moves
through the area. Advisory level north winds are expected by evening
and overnight in the wake of the trof over the SBA/VTA/LA
mountains. Advisory level winds are also possible for the SBA
south coast and the Antelope Valley.  The north flow will also
bring some upslope clouds and a chance of showers to the north
slopes along the Kern County line.

The precipitation should end for the week by Wednesday. NW flow
will be over the area and it will be breezy. Heights will be about
565 DM and afternoon high temperatures will probably drop a
degree or two.

A significant west coast ridge builds in on Thursday and it should
be enough to end the below-70 streak in downtown LA.  There will be
a little Santa Ana on Thursday with perhaps some localized advisory
level gusts. Max temps will be at or above normal for almost all
of the area.

.LONG TERM (FRI-MON)...11/1158 AM.

Deterministic models are in general agreement for the long term.
The ridge will drop 5DM or so with a weak trough on Friday, but it
will build back into the area Saturday and continue through
Monday.

It will be dry through the period and skies will be mostly clear.
Not expecting low clouds and stratus.

Warming over the weekend as ridging, offshore flow and plenty of
sunshine combine to produce above normal temps each day.

&&

.AVIATION...11/1715Z.

At 1800z at KLAX...there was no inversion.

N of Point Conception...High confidence with VFR conds thru the
period. Except 40% chance for VLIFR/LIFR conds at KPRB thru 18z.

S of Point Conception...High confidence with VFR conds thru the
period. Except 30% chance for MVFR cigs from 22z through 12z Tue.
There is a 20% chance of VCSH for L.A. County TAF sites from 22z
through 10z. Best chances further east.

KLAX... High confidence in the 18z TAF thru this afternoon, then
moderate confidence after that. There is a 50 percent chance of MVFR
conditions and VCSH 22z through 12z. There is a ten percent
chance of east winds greater than 8 kts thru 16z.

KBUR... High confidence in the 18z TAF through this afternoon, then
moderate confidence after that. There is a thirty percent chance
of MVFR conditions and VCSH 22z through 12z.

&&

.MARINE...11/928 AM.

For the Outer Waters... Winds will increase to above Small Craft
Advisory (SCA) thresholds by mid morning in the north and central
areas and in the afternoon in the south. There is a 60 percent
chance for Gale Warning level wind gusts by Tuesday morning
through Wednesday morning. Therefore a Gale Watch has been issued
for the outer waters valid from mid morning Tuesday through mid
morning Wednesday. Conditions drop below SCA thresholds on
Thursday.

For the Inner Waters North of Point Conception... Winds will
increase to above SCA thresholds this afternoon through this
evening. There is a 50% chance that a Gale Watch will have to be
issued for Tuesday afternoon through Tuesday evening. At the
least, SCA will be needed from Tuesday possibly through Wednesday.
Otherwise, conditions drop below SCA thresholds Wednesday night
into Thursday.

For the Inner Waters South of Point Conception... Winds will
increase to above SCA thresholds Tuesday morning. There is a
50 percent chance for Gale Warning level wind gusts across the
western portions from Tuesday afternoon through Tuesday evening.
Therefore a Gale Watch has been issued for this time period. Winds
should lower to below SCA thresholds by Wednesday. A Santa Wind
event will bring a 50 % chance for SCA level winds below the wind
prone areas between Ventura to Santa Monica and possibly across
the San Pedro Channel Thursday morning.

&&

.BEACHES...11/1112 AM.

A moderately large WNW swell will bring high surf between 9 and 13
feet across west to northwest facing beaches for the Central
Coast by this morning and persist through Thursday morning. There
will be some local sets to 15 feet between Tuesday and Wednesday.

There is a forty percent chance the swell could affect the Ventura
and Los Angeles County beaches at times tonight through Wednesday
and bring elevated surf to near 7 feet on exposed west facing
beaches. There is a possibility a Beach hazards Statement might
need to be issued for Tuesday/Wednesday period.

Along with the high surf will be an increased danger of high rip
currents, which can pull swimmers and surfers out to sea and cause
ocean drowning. Large breaking waves can cause injury... wash
people off beaches and rocks... and capsize small boats near shore.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory in effect until noon PDT Thursday for
      zones 34-35. (See LAXCFWLOX).
     Winter Storm Warning in effect until noon PDT Tuesday for
      zone 54. (See LAXWSWLOX).
PZ...Small Craft Advisory in effect until 9 PM PDT this evening
      for zone 645. (See LAXMWWLOX).
     Small Craft Advisory in effect from 9 AM to 3 PM PDT Tuesday
      for zones 650-655. (See LAXMWWLOX).
     Gale Warning in effect from 3 PM to 9 PM PDT Tuesday for
      zones 650-655. (See LAXMWWLOX).
     Small Craft Advisory in effect until 9 AM PDT Tuesday for
      zones 670-673-676. (See LAXMWWLOX).
     Gale Warning in effect from 9 AM Tuesday to 9 AM PDT
      Wednesday for zones 670-673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (THU-MON).

No significant hazards expected.

&&

PUBLIC...jld/EB
AVIATION...Kaplan/Sweet
MARINE...Kaplan/Sweet
BEACHES...Kaplan/Sweet
SYNOPSIS...Phillips

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