Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 180346
AFDLOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
846 PM PDT Tue Oct 17 2017

.SYNOPSIS...
A weak upper level disturbance will bring a slight chance of
light showers or sprinkles this evening to San Luis Obispo and
Santa Barbara Counties. Otherwise, fair skies and cooler
temperatures will prevail through the rest of the week, with gusty
west to north winds mainly for the mountains and deserts at
times. High pressure will build into the area this weekend for
offshore flow and well above normal temperatures into early next
week.

&&

.SHORT TERM...(TONIGHT-FRI)

A weak upper level disturbance was moving thru SLO/SBA Counties
early this evening with plenty of mid and hi level clouds and a few
light showers and sprinkles. There was enough instability at mid
levels with this disturbance to support thunderstorm development off
the coast this afternoon, but this support has diminished this
evening and cloud tops have largely warmed as the system moved
inland. I updated the forecast shortly after 8 PM to remove mention
of showers and thunderstorms SLO/SBA Counties and the mtns of
VTU/L.A. Counties. For the rest of tonight, there will be a few
light showers or sprinkles over SLO County and northern SBA County
thru about midnight, otherwise partly to mostly cloudy skies will
prevail across the forecast area thru the night. For the SBA County
mtns and S coast, there was a strong northerly gradient (e.g., SBA-
SMX -4.5 mb at 03Z) which was helping to bring gusty N canyon winds
to the Santa Ynez range and S SBA Coast. Gusts over 50 mph have been
observed at Las Flores Canyon. The NAM was showing the winds
diminishing quickly later this evening, and a Wind Advisory is in
effect for this area until 10 PM PDT.

A flat upper ridge will be over the forecast area on Wed, followed
by gradually lowering 500 mb heights Thu thru Fri. An upper level
trof is forecast to move mainly over central and northern CA Thu
night into Fri morning, with a surface cold front expected to
dissipate just N of SLO County Fri morning.

It looks like varying amounts of mid and hi level clouds will drift
overhead from time to time thru Fri. There should also be a
redevelopment of marine layer clouds over the SoCal Bight and into
some coastal and vly areas night and morning hours for Wed night
into Fri morning. The dissipating cold front should bring some
clouds to the N mtn slopes by early Fri as well. Otherwise, fair
skies will prevail across the region during the period.

Some offshore flow night and morning hours can be expected over
SLO/SBA Counties and interior VTU/L.A. Counties thru Thu morning.
Gusty N canyon winds will continue each evening thru Fri, with gusty
NW winds expected in the L.A./VTU County mtns mainly along the I-5
corridor Wed night into Thu morning, and again Thu night and Fri.
Gusty W winds will also affect the Antelope Vly during the period.
Some gusts to near advisory levels will be possible in these areas
at times.

Temperatures will be considerably cooler on Wed but still a few
degrees above normal for most areas, then temps should fall to near
normal on Thu and to a few degrees below normal overall for Fri.

***FROM PREVIOUS DISCUSSION***

.LONG TERM...(SAT-TUE)

Northerly flow increases behind the trough passage Friday then
shifts to northeast Sunday through Tuesday. Earlier model
solutions had suggested a more southerly trajectory to the trough
but the last couple days the models have favored a more
progressive solution with less upper level support for the
offshore gradients. So this next offshore event is looking a lot
like the last one, but even warmer with a stronger ridge
developing. Temps will start warming Saturday and continue to warm
through early next week. By Tuesday, which could be the start of
the World Series in Los Angeles, highs downtown are expected to
reach or exceed 100 degrees while valleys are a few degrees warmer
than that. If the current forecast holds we`ll likely need heat
advisories or possibly warnings for much of LA/Ventura counties
Mon/Tue.

&&

.AVIATION...18/0020Z...

At 2309Z, the marine inversion at KLAX was 500 feet deep. The top
of the inversion was at 2100 feet with a temperature of 30 degrees
Celsius.

Generally hi confidence in the 00Z TAFs. VFR conditions with mid and
hi clouds will prevail during much of the period. There is a 20-30
percent chance MVFR vsbys due to mist or haze may affect some of the
airfields tonight and Wed morning as well. There will also be some
low level wind shear around KSBA this evening due to gusty N canyon
winds in the vicinity.

KLAX...Generally hi confidence in the 00Z TAF. VFR conditions can be
expected at the airfield thru Wed evening. However, there is a 20
percent chance MVFR vsbys due to mist or haze may affect the
airfield late tonight or Wed morning.

KBUR...Generally hi confidence in the 00Z TAF. VFR conditions can be
expected at the airfield thru Wed afternoon. However, there is a 20
percent chance MVFR vsbys due to mist or haze may affect the
airfield late tonight or Wed morning.

&&

.MARINE...17/300 PM.

High confidence in SCA level NW winds across the outer waters
through late tonight. SCA winds are likely over the nearshore
waters north of Point Sal, and the western SBA Channel later this
afternoon through late evening, diminishing after midnight. There
is a 30% chance winds will rise to SCA levels over western
portions of PZZ655 later today as well. Seas are expected to be
choppy throughout the waters. Winds should drop below SCA levels
by dawn Wednesday in most areas - but will likely increase again
by Wednesday afternoon to moderate to strong speeds through the
period. An upper disturbance will bring a slight chance of tstms
to portions of the waters from western PZZ650 and northwestward.

There will be a chance of gales across the outer waters late
Thursday through Saturday, with SCA conditions likely nearshore.

A large storm off western Canada will generate 40 foot seas in
that area. This will produce a large long-period NW swell, moving
into our waters by Friday. Seas up to 15 feet are likely, with 20
foot seas possible across the outer and northern waters. There
will likely be dangerous breaking waves on the Central Coast
through the weekend with dangerous conditions in/near harbors.

&&

.FIRE WEATHER...17/800 PM.

Elevated fire danger will continue across much of Southwest
California through this evening as weak offshore flow continues to
bring very warm and dry conditions...with widespread single digit
humidities today across inland areas.

Gusty sundowner winds are expected to impact southern Santa
Barbara county much of this week. This evening, wind gusts
between 35 and 45 mph with humidities falling into the teens will
bring elevated to brief critical fire weather conditions across
the Santa Ynez Range and Santa Barbara south coast. In the wake of
a passing upper level trough, there is the potential for stronger
sundowner winds Friday night into Saturday evening.

From Sunday through next Tuesday, there is the potential for a
prolonged duration of gusty Santa Ana winds with hot and very dry
conditions. While there is still some uncertainty with the
strength of this upcoming Santa Ana event (which will depend on
the upper level wind support), there will be the potential for at
least moderate Santa Ana winds, triple digit heat, and humidities
falling into the single digits and teens which could bring a
return of critical fire weather conditions to portions of
Southwest California.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement in effect from Friday morning through
      Friday evening for zones 34-35. (See LAXCFWLOX).
     Wind Advisory in effect until 10 PM PDT this evening for
      zones 39-52. (See LAXNPWLOX).
     Beach Hazards Statement in effect through Wednesday evening
      for zones 40-41. (See LAXCFWLOX).
PZ...NONE.

&&

.HAZARD POTENTIAL OUTLOOK...(FRI-TUE)
Hot temperatures and elevated fire weather conditions are
expected Sunday into early next week as another Santa Ana wind
event develops. Large surf is possible at Central Coast beaches
between Friday and Sunday. Strong rip currents are possible.

&&

$$

PUBLIC...Sirard/MW
AVIATION...Sirard
MARINE...Smith
FIRE...Gomberg/Sirard
SYNOPSIS...Sirard

weather.gov/losangeles



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