High Wind Watch 7, NWS Los Angeles, CA

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
152 PM PDT Sat Oct 13 2018

.SYNOPSIS...13/1150 AM.

Skies will continue clearing this afternoon as a low pressure
center exits the area. Offshore flow will increase resulting in
drier air. Gusty Santa Ana winds will persist for the next few
days.

&&

.SHORT TERM (TDY-TUE)...13/149 PM.

The upper level low that affected the area last night into this
morning was centered over extreme south-central CA early this
afternoon. This system will move E to the lower Colorado
River Vly by early this evening.  Wraparound showers continued
along and just E of the L.A./SBD county border from the mtns to
coast. Otherwise, partly to mostly cloudy skies covered much of
L.A./VTU Counties with mostly sunny skies elsewhere. Temperatures
today will be on the cool side for VTU/L.A. Counties with highs 5 to
10 deg below normal, while SLO/SBA Counties with a bit more sunshine
should have highs near to slightly  below normal overall. The
warmest vlys will be in the lower 70s this afternoon, with some
temps around 80 for the interior SLO County vlys.

The upper level low will move further E into AZ tonight. A rather
sharp E-W oriented upper level trof is forecast to develop over
the central Great Basin Sun then drop S into srn CA Sun night
before developing into an upper level low near the lower Colorado
River Vly by late Mon afternoon. The upper low will then become
nearly stationary near this area Mon night thru Tue, with a broad
N flow aloft over srn CA.

Marine layer clouds will expand along the coast and vlys tonight,
with mostly clear skies elsewhere. Some offshore flow will
develop later tonight and push the low clouds closer to the coast
by early Sun morning, but overall it looks like skies will be
mostly sunny during the day on Sun except for patchy low clouds
near the beaches thru the afternoon. Temps on Sun will be warmer
for L.A./VTU Counties with more sunshine, but overall temps across
the region will be near normal to a few degrees below normal.

Swrn CA is still on track to have it's first significant Santa Ana
wind event of the season Sun night and Mon, with possible damaging
winds at least in the L.A./VTU County mtns including the Santa
Monica range. The upper level trof moving into the area will help to
increase offshore surface pressure gradients, with the NAM
forecasting LAX-DAG down to -7.2 mb at 12Z Mon morning. These strong
offshore gradients will also be accompanied with cold air advection
and upper level support. 850 MB winds up to 50 kt and 950 mb winds
up to 60 kt are predicted by the NAM over portions of VTU/L.A.
Counties 12Z-15Z Mon morning. All-in-all it looks like there is the
potential for a high wind event at least for the L.A./VTU County
mtns with gusts over 60 mph, possibly as high as 70 mph or more over
isolated peaks. At lower elevations across the L.A./VTU County vlys
and coasts, a strong wind advisory event with gusts of 45 to 55 mph
is expected, altho winds could approach high wind criteria at times
especially in the hills where isolated gusts to 60 to 65 mph cannot
be ruled out.

Support for at least advisory-level northeast winds will continue
for Mon night and Tue for much of L.A./VTU Counties, with the
potential for some gusts to 60 mph in the mtns. There may also be
the need for Wind Advisories in the Antelope Vly as northeast wind
gusts up to 45 mph can be expected Mon and Mon night.

Due to the expected winds, will be issuing a High Wind Watch for
Sun night and Mon for the L.A./VTU County mtns with this
afternoon's zone package. Wind advisories will likely be issued for
much of the rest of L.A./VTU Counties either tonight or Sun.

Otherwise, except for a few coastal low clouds possible early Sun
evening, skies will be clear across the region Sun night thru Tue.
Temps on Mon and Tue should turn a few degrees above normal for the
coast and vlys, but cool to near normal to several degrees below
normal for the Antelope Vly.

.LONG TERM (WED-SAT)...13/150 PM.

The GFS and EC are in generally good agreement for the extended
period. The upper level low will meander over AZ to the Four Corners
region Wed thru Sat for the most part, while upper level ridging
persists along and off the CA coast and into the Pac NW.

Clear skies will prevail across the forecast area during the period
thanks to persistent offshore flow. Some gusty NE winds can be
expected again Tue night into Wed morning in the wind-prone areas,
but should be below advisory levels. Weaker offshore flow can then
be expected night and morning hours Wed night thru Sat, with weak
onshore flow each afternoon and evening.

Temps are forecast to have minor day-to-day differences and should
be a few degrees above normal overall across the region. Even so,
the warmest day during the extended period should be on Sat with
highs in the warmest vlys expected to reach the mid 80s to around
90.

&&

.AVIATION...13/1847Z.

At 18z at KLAX... There was no inversion.

Overall... Moderate confidence in the current TAFs. Showers are
moving off to the southeast but low clouds are developing in the
immediate aftermath near coastal and adjacent valley terminals.
All of this will scatter out by mid afternoon. There is a slight
chance of isolated thunderstorms developing in primarily Los
Angeles County this evening. After 06z there is a fifty five
percent chance of MVFR conditions developing at coastal and
adjacent valley locations... LIFR/IFR at KSMX 10z-15z. These
chances will drop dramatically south of Point Conception if the
offshore winds begin sooner rather than later. Otherwise and
elsewhere VFR conditions will prevail.

KLAX... Moderate confidence in the current TAF. Showers are
moving off to the southeast but some low clouds are developing in
the immediate aftermath. All of this will scatter out by mid
afternoon. There is a less than ten percent chance of isolated
thunderstorms developing in the vicinity this evening. From 09z to
19z there is a fifty five percent chance of MVFR conditions
developing. This chance will drop dramatically if the offshore
winds begin sooner rather than later. Otherwise VFR conditions
will prevail. There will be no east winds greater than eight knots
during the forecast period... unless... thunderstorms move over
the terminal. Thunderstorm winds can be erratic and shift quickly.

KBUR... Moderate confidence in the current TAF. Showers are
moving off to the southeast but some low clouds are developing in
the immediate aftermath. All of this will scatter out by mid
afternoon. There is a less than ten percent chance of isolated
thunderstorms developing in the vicinity this evening. After 13z
there is a fifty five percent chance of MVFR conditions developing.
This chance will drop dramatically if the offshore winds begin
sooner rather than later. Otherwise VFR conditions will prevail.

&&

.MARINE...13/129 PM.

For the Outer Waters... There will be occasional northeasterly
wind gusts to 25 kts late Sunday night through Monday morning
across the southern outer waters... otherwise and elsewhere
conditions will remain below Small Craft Advisory (SCA) levels
through Wednesday.

For the Inner Waters... Northeasterly wind gusts to 25 kts and
locally to 35 kts are likely late Sunday night through Monday due
to offshore winds. Otherwise conditions will remain below SCA
levels through Wednesday. The strongest winds will be south of
Ventura and out to the Channel Islands and Santa Catalina Island.
Boaters should be aware of rough seas especially in and around
east facing harbors.

A moderate-period south to southwest swell from former Tropical
Cyclone Sergio will diminish through the weekend.

&&

.BEACHES...13/122 PM.

Elevated surf and strong rip currents will continue through the
weekend as a swell from former Tropical Cyclone Sergio slowly
diminishes.

&&

.FIRE WEATHER...13/124 PM.

Our first Santa Ana wind event of the season will bring gusty
northeast winds Sunday afternoon through Wednesday. These winds
will be strongest Sunday night through Monday when gusts in the
45 to 65 mph range are expected over the favored areas of Los
Angeles and Ventura Counties. The winds weaken some each day
through Wednesday, but remain gusty at times, especially Monday
night and Tuesday. Widespread minimum humidities of 5 to 10
percent are likely. While recent rains may delay some fuels from
becoming critically dry until later Monday, live and fine dead
fuels will be critical. As a result, Red Flag conditions are
possible as early as Sunday afternoon, and all but certain Sunday
night through Tuesday over most of Los Angeles and Ventura
Counties. The previous Fire Weather Watches will be converted to
Red Flag Warnings. There is a chance that that Red Flag conditions
will persist through Wednesday in the mountains and some valleys.
With weaker winds but very dry conditions, Santa Barbara and San
Luis Obispo Counties will experience elevated conditions but are
not expected to be Red Flag. Some improvement is expected by
Thursday, but light and dry offshore flow will persist into the
following week.

This is a dangerous situation. The public needs to use extreme
caution with any potential fire ignition sources. Large fires
have been started by things like discarded cigarettes, campfires,
welding equipment, metallic weed wackers, and dragging trailer
chains.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement in effect through Sunday evening for
      zones 40-41-87. (See LAXCFWLOX).
     High Wind Watch in effect from late Sunday night through
      Monday afternoon for zones 46-53-54. (See LAXNPWLOX).
     Red Flag Warning in effect from 3 AM Monday to 8 PM PDT
      Tuesday for zones 240-241-244-245-288-547-548.
      (See LAXRFWLOX).
     Red Flag Warning in effect from 10 PM Sunday to 8 PM PDT
      Tuesday for zones 246-253-254. (See LAXRFWLOX).
PZ...NONE.

&&

.HAZARD POTENTIAL OUTLOOK (TUE-SAT).

Gusty Santa Ana winds are expected Tuesday through Wednesday. The
Santa Ana winds will bring the possibility of an extended period
of critical fire weather conditions.

&&

PUBLIC...Sirard
AVIATION...Kj
MARINE...Kj
BEACHES...Kj
FIRE...Kittell
SYNOPSIS...TF

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