High Wind Watch 5, NWS Los Angeles, CA

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
251 PM PDT Wed Apr 11 2018

.SYNOPSIS...11/250 PM.

Low pressure should arrive tonight, and another by early Monday
for cooler temperatures and possible precipitation, mainly north
of Santa Barbara and in the mountains. Gusty winds should occur
from this evening to Thursday evening. High pressure and offshore
flow will bring above normal temperatures over this weekend, and
for the middle of next week.

&&

.SHORT TERM (TDY-SAT)...11/246 PM.

Mostly sunny skies with a few hi clouds covered the forecast area
early this afternoon, with little change expected thru sunset,
except for some increasing clouds over SLO/SBA Counties. Onshore
gradients will increase thru the afternoon, with gusty W to NW
winds expected for the coast, some vlys, mtns and deserts. Temps
will be significantly cooler today with highs expected to reach
the mid 60s to low 70s along the coast and 70s to near 80 in the
vlys.

A flat upper level ridge over srn CA will weaken this afternoon. An
upper level trof over the E Pac today will sharpen a bit tonight and
move into the region along with a weakening cold front. The upper
trof is expected to move quickly E of the area on Thu. An upper
level ridge will then develop along and off the CA coast Thu night
thru Fri, then move inland over the area Fri night into Sat, with
500 mb heights increasing to around 581 to 583 dm on Sat.

The upper level trof will bring some cloudiness to the area tonight
along with a chance of showers to portions of SLO/SBA Counties and a
chance of rain and snow showers the N mtn slopes of VTU/L.A.
Counties. The chance of showers and snow showers should linger on
the N slopes Thu morning as well, but that should be it as far as
any pcpn goes, with generally less than 0.10 inch of rain expected
across the area thru the period, except locally up to 0.25 inch on
the N slopes. Snow levels will drop to just below 4000 ft by early
Thu morning, and an inch or two of snow will be possible on the N
slopes.

The larger story with this wx system will be an increase in NW to N
gradients and accompanying strong and gusty winds. There will be
plenty of cold air advection and upper level support for gusts up to
warning thresholds for the L.A./VTU County mtns, especially along
the I-5 Corridor, and over the Antelope Vly from this evening thru
Thu evening. The strongest winds during this period should be Thu
evening as the NAM was showing 850 mb winds peaking around 55 kt at
that time, with gusts up to 70 mph or more not out of the
question in the mtns.

Strong and gusty winds can be expected along the SBA S coast and
mtns as well, especially W of Goleta late tonight and early Thu,
then expanding to areas from Santa Barbara thru Montecito Thu into
Fri morning. It looks like the strongest winds for the SBA County S
coast and mtns will be Thu night and early Fri when the NAM
forecasts the SBA-BFL gradient to be around -5.7 mb by 12Z Fri.
Gusts to 60 mph will be possible at times around Montecito Hills Thu
morning, with gusts up to 65 mph not out of the question Thu night.

High Wind Warnings are already in effect for the L.A./VTU County
mtns and Antelope Vly. A wind advisory will be issued for the SBA
County S coast and mtns thru tonight, and a High Wind Warning will
be issued for these areas Thu thru Fri morning.

In the Santa Monica Mtns, strong and potentially damaging NW to N
winds will move into the area Thu night into Fri morning, and a High
Wind Watch will be issued for this area.

It looks like Wind Advisories will also be needed for the VTU County
Coastal Vlys, Santa Clarita Valley, San Fernando Vly, San Gabriel
Vly foothills, and the coastal areas of VTU/L.A. Counties. The
Wind Advisories for these areas will be needed for Thu thru Fri
morning. Of interest is the gusty NW winds which may impact LAX
mainly Thu afternoon and evening, where gusts up to 40 mph will be
possible. isolated gusts to 50 mph cannot be ruled out below the
passes and Canyons for some of these areas as well.

All the High Wind Warnings, Watches and Wind Advisories will be
issued with the afternoon zone package. Please see the latest Non-
Precipitation Weather Message (LAXNPWLOX) for further details.

Gusty NE winds will also be possible Fri night into Sat morning
across the region, and additional Wind Advisories may be needed for
the usual wind-prone areas of VTU/L.A. Counties at that time.

With all the offshore flow developing over swrn CA, any lingering
clouds over interior areas Thu will dissipate, and any marine layer
clouds near the coast will be pushed offshore, with mostly clear
skies expected in all areas Thu afternoon thru Sat.

Temps will turn sharply cooler on Thu, with highs in the warmest
vlys and inland coastal areas only reaching the mid 60s to low 70s.
Temps will warm up again on Fri to slightly above normal levels
overall, then warm further to several degrees above normal in all
areas on Sat. Highs across the warmest vlys and inland coastal areas
on Fri should reach the mid 70s to lower 80s, with highs Sat
reaching the 80s.

.LONG TERM (SUN-WED)...11/248 PM.

The EC and GFS are in generally good agreement with the synoptic
scale features across the eastern Pac and western U.S. during the
extended period. The upper ridge over srn CA on Sat will move E on
Sun as a large upper level trof approaches the W coast from the
eastern Pac. The upper trof will move into CA later Sun night and on
Mon along with a weakening cold front. The upper trof will move E
for Tue with weak and flat upper ridging expected over srn CA.
That upper ridging will move E Tue night with yet another upper
level trof expected to approach the CA coast from the E Pac on
Wed.

Dry and cooler conditions can be expected on Sun. The next wx system
should bring a slight chance to chance of rain to SLO/SBA Counties
and a slight chance of rain and snow to the the N mtn slopes late
Sun night and Mon, with light amounts of pcpn expected. Gusty W to
NW winds will move in behind this system later Mon into Mon night,
along with cooler-than-normal temperatures. Dry and gradually warmer
weather with breezy conditions at times can then be expected Tue
thru Wed.

&&

.AVIATION...11/1911Z.

At 18Z at KLAX, there was a 900 foot deep marine layer. The top
of the inversion was near 3100 ft and a temperature of 17 degrees
C.

High confidence in the vly and inland TAFs. Moderate confidence
for coastal TAFs. VFR conditions for all sites through 04Z.
Central Coast TAFs will experience occasional MVFR cigs with VCSH
from 05-12Z, then return to VFR in post cold frontal passage.
South of Pt Conception will remain mainly VFR with main impact
gusty west-northwest winds overnight shifting to north after 14Z.
Crosswinds and LLWS are likely during this wind shift.

KLAX...High confidence in TAF through 15Z. A few low clouds off
the coast have a 10 percent chance of moving onshore this
afternoon, otherwise VFR conditions expected. Gusty west winds
notably shift to north-northwest after 14Z with crosswinds and
LLWS possible.

KBUR...High confidence in TAF. Possible LLWS after 14Z.

&&

.MARINE...11/159 PM.

For the Outer and Inner Waters, moderate confidence in the
forecast. SCA winds have begun across the outer waters and near
the Channel Islands and will spread eastward across the inner
waters through the afternoon and evening. W to NW winds will
persist across all waters tonight with Gale Force gusts
developing across the outer waters, the northern inner waters, and
at least western portions of the SBA Channel and southern inner
waters. Winds will be strongest overnight then decrease a bit Thu
morning, but will pulse up again Thu afternoon. The bulk of the
gale force winds will remain off the southern coast across the
mid-channel and westward. Seas are expected to become rather
large and steep at times due to the gusty winds. Across the inner
waters, winds will create choppy seas and dangerous harbor
entrances especially late tonight and Thu. Gales are likely to
subside late Thu night, but SCA conds will likely continue in most
areas through at least Fri night.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory in effect until 6 AM PDT Thursday for zones
      39-52. (See LAXNPWLOX).
     High Wind Warning in effect from 6 AM Thursday to 3 AM PDT
      Friday for zones 39-52. (See LAXNPWLOX).
     Wind Advisory in effect from 10 AM to 10 PM PDT Thursday for
      zone 40. (See LAXNPWLOX).
     Wind Advisory in effect from 10 AM Thursday to noon PDT
      Friday for zones 41-45-547. (See LAXNPWLOX).
     Wind Advisory in effect from noon to 8 PM PDT Thursday for
      zone 46. (See LAXNPWLOX).
     High Wind Watch in effect from Thursday evening through
      Friday morning for zone 46. (See LAXNPWLOX).
     High Wind Warning in effect from 8 PM this evening to 10 PM
      PDT Thursday for zones 53-54-59. (See LAXNPWLOX).
     Wind Advisory in effect from 8 AM Thursday to 10 AM PDT
      Friday for zone 88. (See LAXNPWLOX).
PZ...Gale Warning in effect until 11 PM PDT Thursday for zones
      645-650-655. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 PM PDT this afternoon
      for zones 670-673-676. (See LAXMWWLOX).
     Gale Warning in effect until 5 AM PDT Friday for zones
      670-673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (SAT-WED).

Gusty northwest winds will be possible Monday into Monday night.

&&

PUBLIC...Sirard
AVIATION...Boldt
MARINE...Boldt
SYNOPSIS...STu/Sirard

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