High Wind Watch 4, NWS Los Angeles, CA

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
1200 AM PDT Wed Apr 11 2018

.SYNOPSIS...

10/300 PM

Temperatures will cool significantly through Thursday then warm
into the weekend... then cool again into early next week. There is
a slight chance of rain north of Point Conception and in the
mountains Wednesday night and Thursday and then again on Monday.
Otherwise conditions will be breezy but dry into next week.

&&

.SHORT TERM (WED-SAT)...

10/828 PM

Another very warm day across inland areas with highs in the low
to mid 90s across some of the valleys. Much cooler at the beaches
with highs down 10-20 degrees on average. We'll see this cooling
reach inland areas Wednesday and Thursday as a couple of weak
troughs move through. In the short term, seeing some gusty
northwest winds develop this evening across SBA county mountains
and south coast with gusts in the 30 to 40 mph range. Current SBA-
SMX gradient as of 8 pm has climbed to -4.4 mb. In evening update,
have bumped up winds across these areas.

A weak cold front will bring a chance of light rain to areas north
of Point Conception and the north facing mountain slopes tomorrow
night into early Thursday. Significant cold air advection at lower
levels on Thursday morning could bring snow levels down to
3000-3500 feet. As a result, there is the possibility of brief
snow showers Thursday morning across Interstate 5 near the
Grapevine. But the main story will be strong and fairly widespread
northwest to north winds behind this front Wednesday night into
Thursday night. This wind event has tight surface pressure
gradients, strong upper level wind support, and cold air
advection. High wind watches already posted for the LA/Ventura
county mountains (especially through I-5 corridor) as well as the
Antelope Valley where peak gusts in the 60-70 mph range will be
possible Wednesday night into Thursday evening. Fairly strong
northerly winds also expected for the SBA county mountains and
south coast Wednesday night into Thursday night, with gusts up to
50 mph likely (with the potential for isolated gusts up to 60 mph
near Montecito Hills on Thursday night). The gusty winds will also
impact many coastal and valley areas due to the upper level wind
support and cold air advection. The main impacts from the strong
winds include the potential for downed trees and power lines.

*** From previous discussion ***

Winds will shift to northeast Friday as gradients turn offshore.
While winds will decrease in many areas with the shift to
northeast advisory level winds still look likely across the
LA/Ventura mountains and valleys. Possibly the coast as well as
there is some decent upper support. Temps will bounce back up
into the lower 80s for the warmer valleys and mid to high 70s for
the coast with the Santa Ana winds.

.LONG TERM (SUN-WED)...

10/149 PM

Offshore gradients and upper support weaken Saturday but the ridge
aloft continues to build so Saturday should be the warmest of the
next 7 (not including today). Winds should drop below advisory
levels but could still be locally gusty in the morning across
inland areas.

A cooling trend will begin Sunday as we shift to onshore flow
ahead of the next approaching trough. We continue to be on the
southern extent of any rain chances for Monday though it does have
decent dynamics and cold air aloft. Small rain chances are still
justified north of Pt Conception but with both the GFS and ECMWF
drying out the system as it moves south will keep most of
LA/Ventura county rain-free for the time being. As spring systems
tend to be the main impacts from this look to be wind related,
mainly Monday into Monday night, along with cooler temps.

Tuesday we transition back to a light offshore flow scenario with
slightly warmer temps.

&&

.AVIATION...

11/0659Z

At 06Z at KLAX, there was a 500 foot deep marine layer. The top of
the inversion was near 1400 ft and a temperature of 24 degrees C.

High confidence in the vly and inland TAFs. Lower confidence for
coastal TAFs. Central Coast TAFs will experience frequent changes
in cigs and esp vis. KSBA, KOXR and KCMA have a 30 percent chc of
IFR cigs 12Z-18Z. The LA county cstl sites have a 30 percent chc of
IFR cigs and there is a arrival window of the cigs any time
between 10Z and 15Z.

KLAX...High confidence in TAF through 10Z. Lower confidence with
exact arrival time with low clouds arriving during a 10Z-15Z
window. There is a 30 percent chc the cigs will be at 008. There
is a 30 percent chc of 18Z clearing.

KBUR...High confidence in TAF.

&&

.MARINE...

10/751 PM

For the Outer and Inner Waters, moderate confidence in the
forecast. SCA winds will become widespread across the outer
coastal waters tonight. On Wednesday afternoon SCA winds will
likely expand into the inner waters, with a large area of gales
likely late Wednesday afternoon/evening through Thursday night
focused near the Channel Islands and from PZZ673 southward.
Building seas are also expected with rather steep waves across
inner waters compared to longer periods moving across outer waters
and near the central coast. Gales are likely to subside by Friday
morning, but there could be redevelopment of SCA conditions
across inner waters south of Pt Conception as winds turn more
northerly near the coast.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...High Wind Watch in effect from this afternoon through
      Thursday evening for zones 53-54-59. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 3 AM PDT early this
      morning for zone 645. (See LAXMWWLOX).
     Gale Warning in effect from 6 PM this evening to 11 PM PDT
      Thursday for zones 650-655. (See LAXMWWLOX).
     Small Craft Advisory in effect until 5 AM PDT Friday for zone
      670. (See LAXMWWLOX).
     Small Craft Advisory in effect until 5 PM PDT this afternoon
      for zones 673-676. (See LAXMWWLOX).
     Gale Warning in effect from 4 PM this afternoon to 5 AM PDT
      Friday for zones 673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (SAT-WED).

There is the potential for gusty northeast winds Friday across
LA/Ventura counties. And gusty northwest winds Monday into Monday
night.

&&

PUBLIC...Gomberg/MW
AVIATION...Rorke
MARINE...Gomberg/Boldt
SYNOPSIS...Kj

weather.gov/losangeles