Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 161216
AFDLOX

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

.SYNOPSIS...
A low pressure system over the West Coast will displace a ridge of
high pressure this weekend. Some clouds and a cooling
trend will return to the area along with breezy northerly winds
Saturday. The wind direction will veer to northeast, become gusty
Saturday night, and impact the Ventura and Los Angeles Counties
into early next week. The temperatures will remain slightly above
normal through next week with gusty offshore winds starting on
Thursday.

&&

.SHORT TERM...(TDY-MON)

Synoptically...A positively tilted trough was digging south along
the Central Coast early this morning, and will continue to drop
south along the coast riding the eastern peripheral of the upper
ridge. The upper level trough will continue to dig down into Nrn
Baja and become cutoff by this afternoon. Clouds have developed as
expected across portions of the Central Coast and will fill in
across areas S of Point Conception through this morning due to the
height falls and cyclonic flow aloft. A strong NW surface
gradient was beginning to develop as a 1034 mb surface high was
located several hundred miles off the coast of Eureka Ca to a 1006
mb low over SoCal. With this NW gradient strengthening this
morning, Sundowner winds have already started to develop across
the western portion of the Santa Barbara South Coast. Winds across
Refugio were already gusting into the 40s this morning. As the
upper trough continues to push south, the surface gradients will
start to shift to the north later this morning into this
afternoon. A wind advisory will be issued with the morning package
for the SBA South Coast and adjacent mountains through early this
evening. The NW to N winds will eventually shift to the N-NE
which will put most of the wind focus on the hills above
Montecito later this morning into this afternoon. This could be
problematic for the firefighters in SBA County today. A Red Flag
Warning remains in effect for the same zones through 10 pm this
evening.

Winds are expected to diminish later this evening across the SBA
South Coast. As the trough continues to push towards the south,
cold air will settle into the Great Basin and cause the offshore
surface gradients to strengthen rapidly late this evening into
the overnight hours. The parameters are coming together for
another moderately strong Santa Ana do develop across the Los
Angeles and Ventura County wind prone areas late this evening and
continue into Sunday afternoon. The combinator of a decent
surface gradient between LAX-DAG, cold air advection from the
high desert, and good upper level support as the upper low remains
located over NRN Baja will bring the strongest gusts over the
area Sunday morning. Gusts 50 to 55 mph with local are expected
across the mountains with local gusts to 60 mph possible, while
valleys should see gusts between 40 and 50 mph. the Ventura and
L.A. County Coast between Leo Carrillo Beach, malibu and the
Hollywood Hills will see gusts to 40 mph. A wind advisory will be
issued for these areas beginning this evening through mid
afternoon Sunday. By Sunday night, the upper support will not be a
factor as the upper low over Baja will continue to push towards
the east. There will continue to be gusty offshore winds Sunday
night into Monday, but should remain sub wind advisory levels.
Some local gusts to 45 mph in the mountains is likely.

As far as temperatures, widespread cooling is expected today as
the trough moves through and ushers in cooler temps. Expect most
areas to be 6 to 12 degrees cooler with mountains over 20 degrees
cooler in some locations. Not expecting any freeze issues tonight
for coastal areas or around the Ojai area, but Sunday Night could
bring some possible freeze issues to a few Central Coast
locations and the Ojai Valley. There will be enough mixing of the
air in most areas with the winds to keep temps above freezing.
Just a reminder freeze and hard freeze warnings are no longer
issued for interior valleys, and the Antelope Valley as low temps
consistently lower into the 20s this time of year.

For Sunday expect warmer temps across the LA/VTU county coast and
coastal valleys, with cooler conditions across the interior
valleys, Antelope Valley and mountain locations. For Monday, the
offshore winds will be much weaker and this should allow for
widespread warming 3-6 degrees for most areas. Highs will remain
in the upper 60s to lower 70s across coastal areas, with cooler
conditions for the interior.

.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...16/1210Z.

At 10Z, the marine layer was 1200 ft deep at KLAX. The top of the
marine inversion was around 2000 ft with a temperature of 16C.

Patchy low clouds and fog will affect the Central Coast, the Santa
Ynez Valley and coastal sections of Ventura County through mid
morning, with IFR to locally LIFR conds. Any low clouds should
clear by mid morning. VFR conds are then expected thru the period
in all areas, except for some local MVFR conditions in smoke
across portions of SBA and VTU Counties.

Gusty north winds will affect the Santa Ynez Range and the south
coast of SBA County thru this evening, with some LLWS and
moderate to strong UDDF. Areas of gusty NE winds will affect a
good portion of L.A. and VTU Counties tonight, with areas of LLWS
and moderate to strong UDDF.

KLAX...Moderate confidence in the 12Z TAF. There is a 30% chance
of IFR cigs between 12Z and 16Z. There is a 10-20% chance that
east winds will reach 8 to 10 kt between 13Z and 19Z this morning,
and that NE winds will reach 8 to 10 kt between 09Z and 16Z Sun.

KBUR...High confidence in the 12Z TAF for VFR conds thru the period,
with just a 20% chance of MVFR conditions in smoke through 18Z.
Lower confidence in the wind forecast for tonight. N winds could
gust to 20 kt after 09Z.

&&

.MARINE...16/315 AM.

Across the outer waters, good confidence in Gale force NW winds
through late tonight. SCAs will have to be issued once the Gale
Warning ends late tonight, since winds will remain at SCA levels
across most of the outer waters through Sunday morning, then seas
will remain above SCA thresholds through at least the afternoon.
Winds will likely reach SCA levels again Wed.

Across the inner waters north of Point Sal, high confidence in
SCA levels winds through late tonight. There is a 30% chance that
SCA conds due to hazardous seas will linger through Sunday
morning. Winds will likely reach SCA levels again Wed.

Across the inner Waters south of Point Conception, winds are
expected to 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 should create choppy seas and short period
wind waves which could affect Avalon and Two Harbors. SCA winds
are possible again Wed.

There will be areas of smoke from the Thomas fire over portions
of the coastal waters through Sun, 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.

&&

.FIRE WEATHER...16/400 AM.

Red Flag Warnings in effect until 10 pm this evening for the
Santa Barbara County Mountains and adjacent foothills of the South
Coast. A Red Flag Warning is in effect for the Los Angeles and
Ventura County Valleys and Mountains from 1 AM to 8 PM Sunday.
Red Flag Warnings have also been issued for the Los Angeles and
Ventura County Coasts from 6 AM to 8 PM Sunday.

After the passage of an upper level disturbance, there will be
increasing upper level wind support and cold air advection that
will bring strengthening north to northeast winds across the
mountains and adjacent coastal foothills of Santa Barbara county
(including the Thomas Fire) through this evening, with gusts of
30 to 40 mph being common. Due to the stronger winds in the upper
atmosphere, there is the potential for locally stronger gusts
across exposed ridgetops today. The combination of these gusty
winds with humidities generally ranging between 10 and 20 percent
will result in critical Red Flag conditions across the Santa
Barbara County mountains and adjacent coastal foothills, mainly
east of Santa Barbara. As a result, there will be an increased
threat of very rapid fire spread, long range spotting, and extreme
fire behavior across the warning area,including portions of the
Thomas Fire incident. In addition, there will be increasing
northerly winds on Saturday across the Ventura county mountains,
especially near the Highway 33 and Interstate 5 corridors.

For the remainder of Ventura and Los Angeles Counties, the flow
is expected to shift to the northeast by this evening, with a
threat of increased Santa Ana winds and low humidities late
tonight 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. An
additional Santa Ana wind event is possible next Thursday into
Friday.

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...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 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...Kaplan
AVIATION...DB
MARINE...DB
FIRE...Gomberg/DB
SYNOPSIS...STu/Hall

weather.gov/losangeles



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