Area Forecast Discussion
Issued by NWS Los Angeles, CA

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS66 KLOX 200349
AFDLOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
849 PM PDT Thu Oct 19 2017

.SYNOPSIS...
An upper-level trough of low pressure will brush the area through
Friday. Showers could develop over the Central Coast tonight and
along the north mountain slopes late tonight and Friday. Winds
will increase through Friday evening as a weak cold front moves
over the region, then Santa Ana winds will likely affect the area
from later Friday night through Sunday. A significant warming
trend is expected Sunday into early next week, with record heat
possible Monday and Tuesday.

&&

.SHORT TERM...(TONIGHT-SUN)

Mostly clear skies covered much of the forecast area this evening.
However, patchy low clouds were forming along the Central Coast and
along the foothills of the San Gabriel Vly. Low clouds are expected
to expand over much of SLO/SBA Counties overnight as a surface cold
front moves into the area by late tonight. There could also be a few
showers over this area after midnight and toward morning. S of Point
Conception, low clouds are expected to expand over the coast and
vlys, and along the foothills as a deep moist layer develops with
good onshore low level flow. Patchy drizzle cannot be ruled out
in these areas later tonight as well. Otherwise clear to partly
cloudy skies can be expected overnight.

Gusty NW to N winds developed across the SBA County S coast and mtns
early this evening and will persist through later tonight. Gusts up
to 40 to 45 mph can be expected, and a Wind Advisory is in effect
for this area thru 3 AM PDT Friday. Strong and gusty W winds in the
Antelope Vly this afternoon have diminished some this evening, but
will remain gusty overnight. Gusty NW winds will also affect the
VTU/L.A. County mtns later tonight, especially along the I-5
corridor.

An upper level trof over the eastern Pac will move quickly E
overnight and into central and nrn CA late tonight and early Fri,
along with a dissipating cold front. The upper trof will move E into
the srn Great Basin on Fri, then upper ridging will form along the
CA coast thru Sat. The upper ridge will build further Sat night and
Sun, with 500 mb heights over swrn CA increasing to around 591 dm by
late Sun.

There will be lingering moisture associated with the dissipating
cold front on Fri, mainly on the N mtn slopes, where there will
be a slight chance to chance of showers thru the day. Otherwise,
skies will have a clearing trend thru the day across the forecast
area. Mostly clear skies will then prevail across the entire
region Fri night thru Sun as offshore flow increases.

Gusty NW winds can be expected on the Central Coast on Fri. Gusty W
to NW winds will also affect the mtns and deserts thru the day Fri
into Fri evening. Advisory-level winds will be possible at times in
these areas. For Fri evening and night, there is the potential for
even stronger N canyon winds for the SBA County S coast and mtns,
where a Wind Advisory will likely be needed. Winds will also
become northerly over the VTU/L.A. County mtns and some of the
vlys, and may approach advisory levels at times in the vlys,
especially in the adjacent hills. Offshore flow will persist
across much of the forecast area Sat thru Sun, with some wind
gusts near advisory levels at times over the favored valleys and
foothills of VTU/L.A. Counties.

Temps across the forecast area are expected to be a few degrees
below normal for most areas on Fri, except slightly above normal
along the SBA County S coast. Temps on Sat will warm up for areas S
and W of the mtns, where above normal temps can be expected,
especially from the SBA County S coast thru L.A. County. For the
interior vlys of SLO and SBA Counties, and the mtns and deserts,
temps will remain several degrees below normal. Even warmer temps
are expected Sun, with above normal highs in all areas, except much
above normal from the SBA County S coast thru the coast and vlys of
VTU/L.A. Counties. Highs on Sun afternoon should reach the mid 90s
in the warmest vlys.

***FROM PREVIOUS DISCUSSION***

.LONG TERM...(MON-THU)

Offshore gradients will continue to strengthen early next week,
peaking Tuesday morning in the 5-7mb range (LAX-DAG). At the same
time a strong ridge of high pressure will develop over the west
coast with 597dm center over northern California. There`s a little
better upper support than what we saw with the event earlier this
week so surface winds may be a touch stronger. This is also a
warmer air mass than what we saw before so with the downslope
winds we should easily see temps reaching 100 degrees across a
pretty wide area in LA and Ventura counties with the warmest day
being Tuesday. Expect plenty of high temperature records to fall
those two days. Though it`s a little ways out yet confidence in
this event is high enough to go with an Excessive Heat Watch for
the LA/Ventura coast/valleys and the southern Santa Barbara
County coast Mon/Tue.

Gradients and the ridge weaken Wednesday which will finally bring
some relief but temperatures will still be well above normal.

&&

.AVIATION...20/0025Z...

At 2337Z, there was no marine inversion present at KLAX.

Moderate confidence overall in the 00Z TAFs. Low clouds and MVFR
cigs are forecast to develop tonight for most of the airfields then
persist into Fri morning before improving to VFR cigs late Fri
morning to early Fri afternoon then scattering out in the afternoon.
However, the low clouds may lower to IFR for a while at KSMX and
possibly KSBP late this evening and overnight. The timing of the
onset of the MVFR cigs and improvement to VFR may be off +/- an hour
or two.

For KSBA, KWJF and KPMD, generally hi confidence in VFR conditions
thru Fri afternoon. However, there is a 20-30 percent chance
IFR/MVFR vsbys due to blowing dusty and very strong W winds at KPMD
and KWJF on Fri. Otherwise, gusty winds will persist at these
airfields thru this evening before diminishing some overnight. For
KSBA, low level wind shear is expected at times this evening
due to gusty N canyon winds in the vicinity.

KLAX...Moderate confidence overall in the 00Z TAF. Low clouds and
MVFR cigs are forecast to develop around 05Z then improve to VFR
cigs around 20Z Fri. The timing of the onset of the MVFR cigs and
improvement to VFR may be off +/- an hour or two. VFR conditions
will then prevail thru Fri evening. Gusty W winds can be expected by
Fri afternoon.

KBUR...Moderate confidence overall in the 00Z TAF. Low clouds and
MVFR cigs are forecast to develop around 09Z then improve to VFR
cigs around 14Z Fri. The timing of the onset of the MVFR cigs and
improvement to VFR may be off +/- an hour or two. VFR conditions
will then prevail thru Fri afternoon.

&&

.MARINE...19/830 PM...

For the Outer Waters, high confidence in current forecast. Small
Craft Advisory (SCA) level winds or greater will continue through
Sunday and possibly into Monday. A Gale warning has been issued
for late Friday afternoon through late Friday night. There is a 30
percent chance winds remain below Gale criteria for the outer
waters north of Point Sal.

For the Inner Waters, moderate confidence in the current
forecast. For the waters north of Point Sal, a Gale warning has
been issued for late Friday afternoon through late Friday evening.
There is a 30 percent chance winds remain below Gale criteria.
For the waters south of Point Conception, SCA level winds are
likely from this afternoon through Friday night, strongest across
western sections of the southern Inner Waters. There is a 30
percent chance of gale force gusts in the western Santa Barbara
Channel.

A large long-period NW swell will move into our waters Friday and
persist through the weekend. Seas up to 15 feet are likely 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. South of Point
Conception...the westerly swell will contribute to continued
hazardous conditions at the beaches through this weekend.

&&

.BEACHES...19/1130 AM...

Central Coast...A significant storm system in the Gulf of Alaska
has caused large swells to develop. These large northwest swells
will approach the Central Coast by Friday morning. A High Surf
Advisory has been issued valid for the Central Coast Friday
morning through Sunday morning. Surf will quickly rise to around
10 to 12 feet initially Friday mid morning. By Friday evening
through early Saturday, surf should increase to between 14 and 20
feet. Surf will then begin to lower through Saturday afternoon
into Sunday morning, but remain above 10 feet. Some impacts from
these large and powerful waves and strong currents would be the
risk of ocean drowning. Also sneaker waves can suddenly overrun
previously dry beaches and jetties. With surf approaching 20 feet,
some low lying beach parking lots, harbor walkways and
campgrounds could see local coastal flooding during the peak of
the highest surf.

South of Point Conception...A fairly significant long period
south swell will continue to move across coastal waters through
this afternoon and evening, bringing elevated surf between 3 and 6
feet for south facing beaches. However, gusty west winds are
forecast to develop across the Ventura Coast and the short period
wind waves could pile up to the surf zone causing local sets to 7
feet this afternoon and evening. There is high confidence of
strong rip currents during this period. A Beach Hazards Statement
remains in effect through this evening.

The large northwest swell forecast to bring very large surf to the
Central Coast should filter some of the energy into the Southern
California Bight allowing for higher surf potential by this
weekend. Confidence is high at least another Beach hazards
Statement will be needed or possibly a High Surf Advisory if surf
is expected to be higher. Will continue to monitor the situation.

&&

.FIRE WEATHER...19/315 PM.

A weakening cold front will move through the region bringing a
slight chance of rain showers or drizzle to many areas overnight
into Friday morning. The main impact will be increasing northwest
winds with and behind the front which will bring elevated fire
danger to many areas Friday into Friday night. The strongest winds
tonight through Friday night will be focused across the
mountains, Antelope Valley, Central Coast, and Santa Barbara
County south coast where gusts between 40 and 50 mph will be
common. Humidites are not expected to be sufficiently low during
this time to warrant any Red Flag Warnings.

Northerly flow on Saturday and Saturday night is expected to
bring a warming and drying trend along with elevated fire danger
to the region. The strongest winds during this period will remain
focused across the mountains, especially the Interstate 5 corridor
and Santa Ynez mountains where gusts between 40 and 50 mph can be
expected. A Fire Weather Watch has been issued accordingly for
the mountains beginning Saturday.

From Sunday through Tuesday, there is the potential for a
prolonged duration of gusty Santa Ana winds hot and very dry
conditions. The strongest Santa Ana winds during this period is
expected to be Monday through Tuesday when gusts between 35 and 50
mph will be possible across wind prone passes and canyons of Los
Angeles and Ventura counties. Record breaking triple digit heat
and humidities lowering into the single digits and lower teens
will be possible during this time. In addition, very warm and dry
conditions during the overnight hours in the mountains, foothills,
and wind prone areas will add to this fire weather threat during
this long duration of dangerous fire weather conditions. A Fire
Weather Watch is in effect for the mountains and valleys of Los
Angeles and Ventura counties Sunday through Tuesday, and may need
to be expanded into coastal areas as we draw closer to the event.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory in effect from 6 AM Friday to noon PDT
      Sunday for zones 34-35. (See LAXCFWLOX).
     Wind Advisory in effect until 3 AM PDT Friday for zones
      39-52. (See LAXNPWLOX).
     Excessive Heat Watch in effect from Monday morning through
      Tuesday evening for zones 39>41-44>46-88-547. (See LAXNPWLOX).
     Beach Hazards Statement in effect through Sunday afternoon
      for zones 40-41. (See LAXCFWLOX).
     Fire Weather Watch in effect from Sunday morning through
      Tuesday afternoon for zones 244>246-288-547-548. (See LAXRFWLOX).
     Fire Weather Watch in effect from Saturday morning through
      Sunday morning for zone 252. (See LAXRFWLOX).
     Fire Weather Watch in effect from Saturday morning through
      Tuesday afternoon for zones 253-254. (See LAXRFWLOX).
PZ...Gale Warning in effect from 3 PM to 9 PM PDT Friday for zone
      645. (See LAXMWWLOX).
     Small Craft Advisory in effect until 9 PM PDT Friday for
      zones 650-655. (See LAXMWWLOX).
     Small Craft Advisory in effect from 3 AM to 3 PM PDT Friday
      for zone 670. (See LAXMWWLOX).
     Gale Warning in effect from 3 PM Friday to 3 AM PDT Saturday
      for zones 670-673-676. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 PM PDT Friday for
      zones 673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK...(SUN-THU)
Hot temperatures and elevated fire weather conditions are
expected Sunday into early next week as another Santa Ana wind
event develops. Record heat is possible for Monday and Tuesday.
High surf and strong rip currents will linger along Central Coast
beaches Sunday.

&&

$$

PUBLIC...Sirard/MW
AVIATION...Sirard
MARINE...RM/RAT/Smith
BEACHES...RM/RAT
FIRE...Gomberg
SYNOPSIS...Hall/Sirard

weather.gov/losangeles


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.