Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 120631
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
1031 PM PST Mon Dec 11 2017

.SYNOPSIS...
Gusty offshore winds, warm afternoon temperatures, and dry
conditions will persist through the week. Smoke from the fires
will impact regional air quality through the week as well.

&&

.SHORT TERM...(MON-THU)

High pressure aloft with offshore flow closer to the surface
continues to cling to the area this evening. A trough of low
pressure over northern Mexico continues to undercut the ridge and
reinforce offshore flow. Offshore gradients will tighten Tuesday
morning as vorticity maximum moving east to west moves over the
area. Surface pressure gradients should turn more offshore behind
the vorticity maximum and reinforce the overall offshore flow.

Winds should remain below advisory levels into Tuesday as upper-
level wind and low-level thermal support looks marginal. Model
solutions do indicate some breezy to locally windy conditions
developing supporting the current Red Flag Warning, but remaining
just below advisory criteria.

Weaker offshore flow this evening is allowing for a cooler start
to the night and temperatures have been cooled for the forecast
for tonight. Patchy to areas of frost have been added to the
forecast for some of the interior valleys and wind-sheltered
locations. Temperature were dropped substantially along the
Central Coast and in the Cuyama and Ojai Valley. No frost
advisories were added as air mass may be too dry to support frost
or not enough coverage exists to support an issuance. In
addition, most other locations that will solid at or below
freezing have experienced two prior frost or freeze events
already.

*** FROM PREVIOUS DISCUSSION ***

Very similar weather conditions expected across the 4 county area
through mid week. Light offshore flow generating 15-25 mph Santa
Anas across Ventura and LA Counties (some isolated gusts to 35 mph
in the mountains) but no Sundowners expected in SB County which
is good news for people in the vicinity of the Thomas fire. There
have been some ridge winds along the Santa Ynez range generally in
the 10-15 mph range but that`s about it and even lighter down at
lower elevations. The pattern changes very little through mid week
so what you see today is what you`ll likely get through Thu.
Temperatures will remain 10-15 degrees above normal in most areas
except where thick smoke is obscuring the sun.

.LONG TERM...(FRI-MON)

An upper low will move into the Pac NW Friday and into the Rockies
Saturday. Onshore trends ahead of it will cool temps a few degrees
Fri/Sat but still well above normal. Models going back and forth
on how much offshore flow will develop behind it Sunday and Monday
but the 12z runs were pretty light with the gradients. So a slight
warm up expected Sun/Mon with the weak offshore push but at this
time it doesn`t look like we`ll see any significant Santa Anas or
Sundowners from it.

&&

.AVIATION...12/0630Z.

At 06Z, there was no marine inversion at KLAX.

VFR conditions are expected throughout the period, except for a
chance of MVFR conditions in smoke at coastal and valley
terminals across SBA, SLO and VTU counties. Periods of moderate
low-level wind shear and turbulence are possible Ventura County
terminals through 20z.

KLAX...VFR conditions are expected throughout the period. There is
a 30 percent chance of MVFR conditions in smoke through 010Z. Any
east winds should remain less than 7 knots.

KBUR...VFR conditions are expected throughout the period. No wind
issues are expected at this time.

&&

.MARINE...11/900 PM.

For the Inner Waters south of Point Conception, winds will remain
below SCA strength tonight through Wednesday.

The near shore waters north of Point Sal will remain below SCA
level through at least early Friday.

Elsewhere, winds and seas are expected to remain below Small
Craft Advisory levels through Thursday, and then rise to SCA level
from the northwest on Friday. There is a 30 percent chance of Gale
level winds for the Outer Waters North of Point Conception
sometime Friday or Saturday.

There will be areas of smoke from the Thomas fire over portions
of the Coastal Waters, mainly from the waters west of Ventura
County through the Santa Barbara Channel and over the outer
waters. Local visibilities could possibly drop to near one
nautical mile or lower at times.

&&

.FIRE WEATHER...11/100 PM.

The Red Flag Warnings have changed. It has been EXTENDED to 8
PM Wednesday for the Los Angeles and Ventura Interior Mountains.
It has been EXTENDED to 8 PM Tuesday for the Ventura Coasts,
Ventura Valleys, the Santa Clarita Valley, and the Santa Monica
Mountains. It is NO LONGER in effect for the Los Angeles Coasts,
the San Gabriel Valley, and the San Fernando Valley due to the
winds aloft being more easterly than before, which has weakened
the winds significantly in those areas.

Little change is expected through Thursday. The extended period
of offshore flow will continue, but will be half as strong as what
occurred last week. Expect daily peak gusts in the 20 to 40 mph
range...but some weakening is expected Wednesday into Thursday.
The humidities will remain incredibly dry with extremely poor
overnight recoveries nearly everywhere.

San Luis Obispo and Santa Barbara Counties will continue to see
periods of north to east winds (gusts of 15 to 25 mph) through
Thursday morning, including areas near the Thomas Fire. While
these winds are NOT Sundowner winds in terms of strength and
source, they will combine with the continued warm and very dry
conditions to result in elevated to near critical fire weather
conditions. In addition, the air mass is fairly unstable above
the Thomas Fire through Wednesday, resulting in a greater risk for
large fire plumes which will locally enhance winds near the fire.

Some improvement is expected for Friday into Saturday as the winds
shift to more westerly, but more offshore flow is possible
beginning Saturday night or Sunday.

If fire ignition occurs, very rapid spread and extreme fire
behavior is likely. Those near current wildfires need to stay
aware of and follow official evacuation orders. Everyone needs to
exercise extreme caution when handling any potential fire ignition
sources...such as campfires, cigarettes, welding and brush
clearing equipment.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Red Flag Warning in effect until 8 PM PST Tuesday for zones
      240-244>246-288. (See LAXRFWLOX).
     Red Flag Warning in effect until 8 PM PST Wednesday for zones
      253-254. (See LAXRFWLOX).
PZ...NONE.

&&

.HAZARD POTENTIAL OUTLOOK...(THU-MON)
Critical fire weather conditions possible Thursday with light
offshore winds and single digit humidities.

&&

$$

PUBLIC...Hall/MW
AVIATION...Kaplan
MARINE...Kaplan
FIRE...Kittell
SYNOPSIS...Kj

weather.gov/losangeles


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