Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 161835
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
1035 AM PST Sat Dec 16 2017

...Aviation discussion updated...

.SYNOPSIS...

Cooler temperatures today along with locally strong northerly
winds. The wind direction will become northeast tonight and impact
Ventura and Los Angeles Counties into early next week.
Temperatures will remain slightly above normal through next week
with another jolt of gusty offshore winds starting on Thursday.

&&

.SHORT TERM...(TDY-MON)

The strong and gusty NW to NE winds quickly developed as expected
over the SBA County mtns and S coast this morning. Winds quickly
ramped up with gusts reaching 65 mph at Montecito Hills, 55 mph at
the Santa Barbara Botanic Gardens, and 53 mph at Tepusquet. The
gradients over this area as of 16Z were -4.4 mb for SBA-SMX and -6.1
mb for SBA-BFL. With winds stronger than expected, have upgraded the
Wind Advisory to a High Wind Warning for the SBA County mtns thru
this afternoon, altho the strongest winds should be this morning. A
Wind Advisory will also continue for the SBA County S coast thru
this afternoon. Needless to say, the strong N winds around Montecito
has caused a significant flareup of the Thomas Fire in the hills
above Montecito to near Santa Barbara, and will continue to affect
the fire thru the afternoon.

Skies over the forecast area this morning were sunny to partly
cloudy, except mostly cloudy in the Antelope Vly, and areas of
smokey skies from the S SBA County coast thru srn VTU County. Any
cloudiness over the region should give way to sunny skies this
afternoon. Gusty NW to N winds will also affect the L.A./VTU County
mtns and foothills today, with the strongest winds approaching
advisory levels along the I-5 corridor.

An upper level trof over the forecast area this morning will move
off to the SE as it deepens into an upper level low over nwrn Mexico
by this evening. The upper low will meander between nwrn Mexico into
srn AZ tonight thru Sun then into New Mexico on Mon. As the upper
level trof moves to SE and E of the area, upper level ridging will
gradually build in thru the period.

The passage of the upper level trof will help to build surface high
pressure into the Great Basin and offshore pressure gradients will
increase quickly thru tonight. The latest NAM was forecasting the
LAX-DAG gradient to lower to -6.1 mb by 12Z Sun. In addition, mid
and upper level support for gusty offshore winds will increase thru
tonight, along with good cold air advection. These ingredients will
support another round of gusty Santa Ana winds over swrn CA from
this evening through Sun afternoon. The gusty winds will turn to the
NE in the L.A./VTU mtns by early this evening then descend to the
lower elevations including coastal areas thru the evening hours then
continue into Sun afternoon. 850 mb winds up to 45 to 50 kt and 950
mb winds up to 45 kt are predicted by the latest NAM tonight into
Sun morning. Gusts up to 55 mph are expected in the mtns including
the Santa Monica Mtns, and gusts up to 40 to 50 mph are expected for
the wind-prone vlys and coastal areas, including the Santa Clara
River vly and other vlys and hills of sern VTU County, the Santa
Clarita Vly, San Fernando Vly, and the VTU County coast and coast of
L.A. County from Malibu to the Hollywood Hills. Wind advisories are
in effect for these areas tonight thru Sun afternoon. Please see the
latest Non-Precipitation Weather message (LAXNPWLOX) for further
details on the High Wind Warning and Wind Advisories.

For Sun night into Mon morning, there will continue to be gusty NE
winds in the wind-prone areas of VTU/L.A. Counties, and winds may be
close to advisory levels as times. However, upper-level support for
widespread advisory-level winds will diminish. At this time, do not
anticipate the Wind Advisories for L.A./VTU Counties to be extended
into Mon, altho there is still a small chance of that happening.

With all the dry offshore flow moving in again, skies will be mostly
clear across the forecast area tonight thru Mon. Temps will be mainly
near normal to slightly above normal over the region today thru Mon,
with the coolest day for interior areas on Sun.

***FROM PREVIOUS DISCUSSION***

.LONG TERM...(TUE-FRI)

The offshore gradients weaken considerably for Tuesday and
Wednesday with the persistent ridge remaining to our west keeping
us dry and temperatures just above normal. Winds will be lightly
offshore overall on Tuesday, then swing onshore on Wednesday and
could be breezy over the interior areas. At this point, both the
GFS and ECMWF are in generally good agreement with large scale
features advertising another inside slider dropping into Utah
Wednesday night then retrograding toward the southwest and into
northern Baja California by the end of the week. If this solution
holds, it looks like we are in store for another gusty northerly
wind event Wednesday night focused over Santa Barbara County and
the I-5 Corridor, with gusty northeasterly winds Thursday into the
weekend. More fire weather concerns therefore are unfortunately
in the cards. Rain chances look bleak through Christmas.

&&

.AVIATION...16/18z.

At 1730z at KLAX... the inversion was around 3000 feet deep. The
top of the inversion was around 3600 feet with a temperature of
about 11 degrees Celsius.

Overall... Moderate confidence in the current TAF. Lingering
patchy low clouds across coastal sections of Ventura and Los
Angeles Counties through late morning. Gusty north winds will
affect the Santa Ynez Range and the south coast of SBA County
through this evening with some LLWS and moderate to strong UDDF.
Areas of gusty NE winds will affect a good portion of VTU and LA
Counties tonight with areas of LLWS and moderate to strong UDDF.
Local MVFR conditions due to smoke across portions of SBA and VTU
Counties. Otherwise and elsewhere VFR conditions will prevail.

KLAX... Moderate confidence in the current TAF. Lingering patchy
low clouds through late morning. Gusty NE winds tonight with LLWS
and moderate to strong UDDF. Otherwise VFR conditions will prevail.
East winds to 10 knots at times through 20z then a twenty percent
chance of NE-E winds to 10 kt 17/09z-16z.

KBUR... High confidence in the current TAF. Gusty NE winds
tonight with LLWS and moderate to strong UDDF possible. Otherwise
VFR conditions will prevail.

&&

.MARINE...16/800 AM.

Across the outer waters... Gale force NW winds will continue
through late tonight. Small Craft Advisories (SCA) will have to
be issued once the Gale Warning ends late tonight as winds will
remain elevated through Sunday morning and seas through at least
the afternoon. Winds will likely reach SCA levels again Wednesday.

Across the inner waters north of Point Sal... SCA level winds
will continue through late tonight. There is a 30% chance that
SCA conditions due to hazardous seas will linger through Sunday
morning. Winds will likely reach SCA levels again Wednesday.

Across the inner waters south of Point Conception... Winds will
reach SCA levels across the western portion of the Santa Barbara
Channel this morning and continue through this evening. SCA level
NE winds are expected from Ventura to Anacapa Island south to
Santa Monica and from San Pedro to Catalina Island. These winds
will create choppy seas and short period wind waves which could
affect Avalon and Two Harbors. SCA winds are possible again
Wednesday.

There will continue to 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
portions of the outer waters. Visibilities could locally drop to 2
NM or lower at times today in the inner waters.

&&

.FIRE WEATHER...16/1015 AM.

Red Flag Warnings in effect until 10 pm this evening for the
Santa Barbara County Mountains and South Coast. A Red Flag
Warning is in effect for much of Los Angeles and Ventura Counties
through from 1 AM to 8 PM Sunday.

Strong upper level winds behind the passage of an upper level disturbance
combined with strengthening north-south pressure gradients caused
a significant increase in winds across the Santa Barbara county
mountains and south coast this morning, causing major impacts
on the Thomas Fire. The SBA-Bakersfield gradient peaked at -6.2 mb
this morning. Wind gusts of 35 to 50 mph have been common this
morning across these areas, with isolated gusts up to 65 mph being
observed in the Montecito Hills. While humidities have modified
somewhat this morning, the strong north to northeast winds through
this evening will continue to maintain dangerous Red Flag
conditions for the Santa Barbara county mountains and south coast.
As a result of these strong winds, there will be very rapid fire
spread, long range spotting, and extreme fire behavior observed at
the Thomas Fire and any new fire ignitions. In addition, there
will be gusty north winds across the Ventura county mountains
today, especially near the Highway 33 and Interstate 5 corridors
which will impact the Ventura county portion of the Thomas Fire.

For the remainder of Ventura and Los Angeles Counties, the flow
is expected to shift to the northeast this evening, with increasing
Santa Ana winds overnight into Sunday when gusts between 35 and 55 mph will
be likely. A Red Flag Warning is in effect for late tonight
through Sunday evening for much of Los Angeles and Ventura
Counties. Another period of Santa Ana winds will be possible
from Thursday into next weekend.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory in effect until 9 AM PST Sunday for zones
      34-35. (See LAXCFWLOX).
     Wind Advisory in effect until 6 PM PST this evening for zone
      39. (See LAXNPWLOX).
     Wind Advisory in effect from 9 PM this evening to 3 PM PST
      Sunday for zones 40-41. (See LAXNPWLOX).
     Wind Advisory in effect from 6 PM this evening to 3 PM PST
      Sunday for zones 44>46-53-54-88-547. (See LAXNPWLOX).
     High Wind Warning in effect until 6 PM PST this evening for
      zone 52. (See LAXNPWLOX).
     Red Flag Warning in effect until 10 PM PST this evening for
      zones 239-252. (See LAXRFWLOX).
     Red Flag Warning in effect from 6 AM to 8 PM PST Sunday for
      zones 240-241. (See LAXRFWLOX).
     Red Flag Warning in effect from 1 AM to 8 PM PST Sunday for
      zones 244>246-253-254-288-547. (See LAXRFWLOX).
PZ...Small Craft Advisory in effect until 3 AM PST Sunday for zone
      645. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 PM PST Sunday for zone
      650. (See LAXMWWLOX).
     Small Craft Advisory in effect from 3 AM to 3 PM PST Sunday
      for zone 655. (See LAXMWWLOX).
     Gale Warning in effect until 3 AM PST Sunday for zones
      670-673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK...(MON-FRI)
Critical fire weather conditions are possible with gusty
Sundowner winds Wednesday night and gusty offshore winds
Thursday and Friday.

&&
$$

PUBLIC...Sirard/Kaplan
AVIATION...Kj
MARINE...DB/Kj
FIRE...Gomberg
SYNOPSIS...Kj

weather.gov/losangeles



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