Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 162217
AFDLOX

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

.SYNOPSIS...
Winds will increase and shift overnight to the northeast over Los
Angeles and Ventura counties. Temperatures will remain slightly
above normal early next week. Below normal temperatures and
another round of strong offshore flow will begin by Wednesday.

&&

.SHORT TERM...(TDY-TUE)

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. With
winds stronger than expected, had upgraded the Wind Advisory to a
High Wind Warning for the SBA County mtns, but winds have already
peaked and were below warning thresholds early this afternoon, so
downgraded the warning to a Wind Advisory thru 6 PM for the zone
update. A Wind Advisory will also continue for the SBA County S
coast thru 6 PM. 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. The Montecito Hills RAWS station
was affected by the fire and was reported to have burned. The last
report we received from the Montecito Hills RAWS was at 1647Z when
winds were gusting to 62 mph.

Skies over the forecast area this morning were mostly sunny except
for areas of smoky skies from the S SBA County coast thru swrn VTU
County. Gusty NW to N winds continued to affect the L.A./VTU County
mtns and foothills this afternoon, with the strongest winds
approaching advisory levels along the I-5 corridor.

An upper level trof just E of the forecast area this afternoon 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. Upper level ridging
will then persist over srn CA Mon night and Tue.

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.
Winds will remain weakly offshore Mon night into Tue morning, then
turn onshore by Tue afternoon.

With all the dry offshore flow moving in again, skies will be mostly
clear across the forecast area tonight thru Mon. Mostly clear skies
should then continue into Tue, altho it cannot be completely ruled
out that a few marine layer clouds may push to the Central Coast or
the L.A. County coast by early Tue morning.

Temps will be mainly near normal to slightly above normal over the
region Sun thru Mon, with the coolest day for interior areas on Sun.
Temps are expected to warm to several degrees above normal for all
areas on Tue.

.LONG TERM...(WED-SAT)

There are some differences in medium range between the EC and GFS,
especially Fri and Sat. There will be an upper level trof
approaching srn CA from the N on Wed. This inside slider upper trof
will pass mostly NE and E of the forecast area on Wed, altho the srn
fringe of the trof will brush by. The EC is a bit more progressive
with the upper trof, moving it well to the E for Thu. The GFS drops
additional energy on the back side of the trof and develops and
upper low over AZ on Thu and Thu night, then into nrn Baja on Fri
before moving it E on Sat. Both the EC and GFS keep an upper ridge
off the W coast Thu and Fri. The EC weakens this ridge on Sat as a
broad upper trof moves into the Great Basin, while the GFS hangs
onto the upper ridge along the W coast.

Went with a general blend of the two models. Dry conditions will
persist over swrn CA thru the period. The upper trof passing by late
Wed and Thu will impart another Santa Ana wind event which could be
quite strong from late Wed night thru Thu night. Gusty N winds will
affect the SBA County mtns and S coast Wed evening then transition
to NE and gusty over the the wind-prone areas of VTU/L.A. Counties.
Winds are projected to be at least advisory levels, with a chance
some areas could have warning-level winds. The offshore flow will
weaken some but continue Fri into Sat as well, especially over
VTU/L.A. Counties. Skies will be mostly clear thru the period with
temps generally a few degrees above normal except mostly near normal
on Thu.

&&

.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...16/200 PM.

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 have a lull in the afternoon then elevate again and continue
through late tonight. No lull is expected in the hazardous seas
and there is a thirty percent 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 through this evening. The strongest winds will be near
shore.  SCA level NE winds are expected from Ventura to Anacapa
Island south to Santa Monica and from San Pedro to Catalina
Island tonight through Sunday. 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...16/200 PM.

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 9 PM tonight 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 were common this morning across these areas, with isolated
gusts up to 65 mph observed in the Montecito Hills. While
humidities have modified somewhat today, 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 Santa
Ana winds are expected to begin this evening, then peak overnight
into Sunday morning when gusts between 35 and 55 mph will be
likely. A Red Flag Warning is in effect for tonight through Sunday
evening for much of Los Angeles and Ventura Counties. There is the
potential for another round of gusty Sundowner winds Wednesday
into early Thursday, Another period of Sundowner winds will be
possible for Santa Barbara county from Wednesday into Wednesday
night, followed by a potential extended period of Santa Ana winds
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 zones
      39-52. (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).
     Red Flag Warning in effect until 10 PM PST this evening for
      zones 239-252. (See LAXRFWLOX).
     Red Flag Warning in effect from 1 AM to 8 PM PST Sunday for
      zones 240-241. (See LAXRFWLOX).
     Red Flag Warning in effect from 9 PM this evening to 8 PM PST
      Sunday for zones 244>246-253-254-288-547-548. (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...(TUE-SAT)
Critical fire weather conditions are possible with gusty
Sundowner winds Wednesday night and gusty offshore winds
Thursday and Friday.

&&

$$

PUBLIC...Sirard
AVIATION...Kj
MARINE...Kj
FIRE...Gomberg
SYNOPSIS...TF

weather.gov/losangeles



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