High Wind in California, October 9, 2017

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
443 AM PDT Mon Oct 9 2017

.SYNOPSIS...
A Catalina Eddy will continue to bring some clouds across the
southern portion of the forecast area early this morning. This
will be followed by the first significant Santa Ana event of the
season later this morning. Strong damaging winds will occur across
the mountains early today then winds will spread towards the
coast of Ventura and portions of the Los Angeles Coast later this
morning. Offshore winds will bring the warm and dry conditions to
locations west of the mountains in Ventura and Los Angeles
Counties through early Tuesday. Cooling will return midweek.

&&

.SHORT TERM...(TDY-WED)

A strong eddy circulation developed across the inner coastal
waters last evening, and help spread clouds into all coastal and
most valley areas south of Pt Conception by late evening, with
clouds even reaching the coastal slopes of the San Gabriel Mtns.
Pressure gradients were trending sharply offshore early this
morning, but the gradients were not quite as strongly offshore as
forecast by the models. It is possible that the westward expansion
of the strong surface high in Nevada was just a couple of hours
slower than expected, and the gradients may ultimately end up as
strong as predicted. In any event, winds have been slower to
develop in the mountains. but since about midnight, wind gusts to
nearly 60 mph have been observed at the Chilao RAWS sensor, with
a few other places gusting to at least 50 mph. Expect winds to
continue to increase in the mtns of L.A. and VTU Counties early
this morning, so high wind warnings look great there.

The deep marine layer was keeping all winds from surfacing in the
valleys and coastal areas, delaying the onset of the gusty winds
there. However, satellite imagery was beginning to show rapid
erosion of cloud cover in the valleys of L.A. and VTU Counties and
across the VTU County coast, which is a sign that the marine
inversion was beginning to get wiped out. Expect skies to clear
fairly quickly early this morning, with clear skies in most areas
by daybreak. Once the marine inversion is wiped out, gusty winds
will likely surface in coastal and valley areas of L.A. and VTU
Counties. There should be enough support aloft in the form of
strong winds at 850 mb, subsidence, and cold air advection to
allow winds to reach High Wind Warning levels in the Santa
Clarita Valley, the Santa Monica Mountains, and portions of the
VTU County valleys. In the remaining valleys of L.A. and VTU
Counties, across the VTU County coastal plain, and across the L.A.
County coast below passes and canyons from Malibu to the
Hollywood Hills, winds should reach advisory levels, and could get
close to warning levels in northern and western portions of the
San Fernando Valley and possibly coastal sections of VTU County.
Wind advisories are also in effect for the mtns and interior
valleys of SLO County and the Cuyama Valley, but winds should be
more marginal in those areas.

Winds will begin to diminish late this afternoon and this evening.
Where High Wind Warnings are in place, Wind Advisories may be
needed from late this afternoon through tonight or Tuesday
morning. But the models have been trending a bit weaker with the
winds for tonight and Tue. It is also possible that winds in
advisory areas may diminish below advisory levels earlier than
currently forecast. Max temps will be up several degrees in
coastal areas and probably the coastal valleys today, with highs
possibly close to 90 degrees in some locations. Max temps should
change little or will lower slightly in the interior valleys,
and will drop significantly across the mountains and deserts
as cool air spreads southwestward from the Great Basin.

The broad northwesterly flow pattern across the region tonight
will transition into a more zonal flow pattern on Tue, though
heights will rise slightly across the forecast area. Gradients
will still be offshore in the morning, then will turn onshore.
Expect several degrees of warming on Tue in the mtns and deserts,
with little change or possibly slight warming in the valleys, and
cooling across the coastal plain, especially near the beaches.

An upper low will move into the Pac NW Tue night and Wed, with a
trough extending southward into the forecast area. Heights
and thicknesses will fall across the region, and onshore flow
will increase. Some low clouds could return to coastal sections
and possibly the San Gabriel Valley Tue night/Wed morning. There
should be at least a few degrees of cooling to most areas Wed,
especially west of the mountains.

.LONG TERM...(THU-SUN)

The upper low in the Pac NW will move eastward Wed night and Thu,
and a positively tilted short wave trough will drop southward
down the West Coast. Expect widespread night through morning low
clouds and fog in most coastal and valley areas south of Point
Conception. Across SLO and SBA Counties, cooling aloft will weaken
the marine inversion and there could be some northerly low level
flow. This may keep skies clear there Wed night and Thu. Expect a
few more degrees of cooling in most areas Thu. The trough will
swing across the region Thu night and Fri. Once again, expect
widespread night through morning low clouds and fog in coastal and
valley areas south of Pt Conception, while north-south offshore
gradients will likely make for much less in the way of low clouds
across SLO and SBA Counties. Expect mostly minor changes in max
temps in most areas Fri.

The trough will wash out across the region Fri night, and heights
will begin to rise Sat. N-S offshore gradients may bring gusty
sundowner winds to southern SBA County Fri night, and gusty winds
may also affect the I-5 corridor. Expect a few degrees of warming
in most areas Sat. Heights will continue to rise on Sunday as an
upper high in Mexico expands into the region. This should bring a
few more degrees of warming in most areas, with temps possibly up
to 90 degrees in the warmer valley locations.

&&

.AVIATION...09/11Z.

At 10Z at KLAX...The marine layer was 2400 ft deep with a an
inversion top of 3400 ft at 19 degrees Celsius. Marine layer
should scour out as strong offshore flow takes over later this
morning into this afternoon.

Moderate confidence on stratus clearing across Ventura County by
13z this morning. Should take a bit longer possibly to 17z for
low clouds to scour out over LA County. Strong NE winds will
develop over the region this morning. Initially across the
interior areas, then to the coast by mid morning. Expect
widespread gusty winds with LLWS and UDDF concerns through early
this evening for many TAF sites in Los Angeles and Ventura
Counties. There will continue to be offshore winds, but should
much weaker this evening through Tue morning. Still 40% chance for
LLWS around KCMA, KOXR, KVNY and to a lesser extent KBUR.
KLAX...Moderate confidence that MVFR cigs will give way to clear
skies between 14-17z this morning. Strong NE winds will form over
the airport on Monday, likely not surfacing but producing strong
LLWS.
KBUR...Moderate confidence that MFVR cigs will give way to clear
skies between 13-15z this morning. Mainly VFR will be most
common. Strong NE flow will form over the area later this morning.
High confidence in LLWS issues, but low confidence on if the
winds will surface and if so how strong they will be.

&&

.MARINE...09/330 AM.

Moderate confidence in SCA for hazardous seas across the outer
waters through mid afternoon. Zone PZZ676 will Seas 8 to 11 ft
will .NW winds and/or seas over the outer waters through Monday
morning, although PZZ676 will likely maintain SCA conditions as
winds shift to offshore and strengthen over the waters south of
Point Conception.

Winds of 20 to 30 knots are expected over the waters from near
Ventura down to Santa Monica and westward out to Santa Rosa
Island...including the nearshore waters this morning through mid
afternoon. NE winds are also expected over the San Pedro Channel,
with a 40% chance of winds up to 20 knots reaching Avalon Harbor.
The timing of this possibility will be between 9 AM this morning
through at least the middle of this afternoon. Choppy short
period seas are expected throughout the waters during this
time...reaching heights of 5 to 7 feet in the area of strongest
offshore winds, and 2 to 4 feet across the San Pedro Channel.

A long period south swell will slowly decay through
today, and an increasing longer period northwest swell will begin
to move into the waters today.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory in effect until 6 PM PDT this evening for
      zones 34-35. (See LAXCFWLOX).
     Wind Advisory in effect until 8 PM PDT this evening for zones
      37-38-40-41-44-51-59-547. (See LAXNPWLOX).
     High Wind Warning in effect until 4 PM PDT this afternoon for
      zones 45-46-53-54-88. (See LAXNPWLOX).
     Red Flag Warning in effect until 10 PM PDT this evening for
      zones 237-238-251. (See LAXRFWLOX).
     Red Flag Warning in effect until 10 AM PDT Tuesday for zones
      240-241-244>246-253-254-288-547-548. (See LAXRFWLOX).
PZ...Small Craft Advisory in effect until 3 PM PDT this afternoon
      for zones 650-655. (See LAXMWWLOX).
     Small Craft Advisory for hazardous seas in effect until 3 PM
      PDT this afternoon for zones 670-673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK...(WED-SUN)
Gusty northerly winds could develop late next week bringing
Sundowner winds to Southern Santa Barbara County and Gales to the
adjacent coastal waters.

&&

PUBLIC...DB
AVIATION...Kaplan
MARINE...Kaplan
SYNOPSIS...Kaplan

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