Scientific Forecaster Discussion
fxus66 klox 141314
Area forecast discussion
National Weather Service Los Angeles/Oxnard California
514 am PST Sat Dec 14 2019
Low pressure will bring a chance of rain and snow showers to the
mountains through early Sunday, areas of gusty winds, and much
cooler weather to the region this weekend. Some warming is
expected Monday and Tuesday with dry weather and some gusty Santa
Ana winds. A storm system may bring some rain to the region
Wednesday into early Thu, followed by dry and cool weather for the
end of the week.
Short term (tdy-mon)...14/420 am.
Weakening frontal system was pushing across Monterey County
early this morning, bringing some scattered shower activity
with it. This front may hold together enough to bring a few
showers to slo County and northern sba County this morning.
Elsewhere, a deep marine layer has developed across l.A. And vtu
counties, with clouds widespread in all coastal and valley areas
except for the Santa Clarita valley. Clouds may push into the
Santa Clarita valley and into the coastal slopes by daybreak.
There could be some drizzle as well, especially in the foothills.
Gusty northwest to north winds continued across southern sba
County, and that has kept the South Coast of sba County clear so
far, but if the winds drop off, clouds should sneak northward from
vtu County around or shortly after daybreak.
Kind of a complicated forecast for today. Northwesterly to north
flow will increase across the region later today behind the
weakening frontal system. Expect advisory level northwest winds on the
central coast this afternoon, and west to northwest winds across the
Antelope Valley late this morning through tonight. Northwest winds will
likely also reach advisory levels thru and below passes and
canyons of the Santa Ynez range and the adjacent South Coast of
sba County, late this afternoon or evening through late tonight,
and through the Interstate 5 corridor and the Santa Clarita
valley this evening through Sun morning. Wind advisories have been
issued for these areas. Advisories may have to be expanded to
include the San Fernando Valley, the Santa Monica Mountains, and
the l.A. County coast below passes and canyons from Malibu to the
Hollywood Hills, but at this time, it appears that winds will
remain just below advisory levels in those areas.
Skies should become partly cloudy this afternoon, except remain
mostly cloudy in the mountains, and possibly across much of l.A.
County. Moist cyclonic westerly flow could bring a few showers to
the eastern San Gabriel Mountains and possibly even the San
Gabriel valley this afternoon and evening. Today will be
significantly cooler than it was on Fri in all areas, with temps
down to below normal levels in most areas.
Moist northerly flow will bring a chance of showers to
interior sections of sern slo and nern sba County, and to the
northern mountains of vtu County and northwestern l.A. County this
afternoon into tonight, lingering across the northern slopes of
vtu County through Sunday morning.
While precipitation totals in the mountains are not expected to
be excessive, snow could cause some travel problems on portions of
Interstate 5 late tonight/Sun morning. A Winter Weather Advisory
may have to be considered for the mountains due to potential
impacts for Interstate 5.
Skies will become mostly sunny across the region on Sunday, but it
should actually even be a few degrees cooler than today in most
areas. Expect northwest-north to remain mostly below advisory levels Sunday
evening. However, winds will shift to a more northeasterly
directions late Sun night and Monday morning. Offshore gradients
and upper support look to be sufficient for at least low end Wind
Advisory level northeast winds across the mtns and valleys of l.A.
And vtu counties, and the vtu County coastal plain Monday
morning. Monday should be several degrees warmer, especially west
of the mountains, but it will not be a particularly warm Santa Ana
wind event, with warmest locations likely topping out in the
lower 70s on Mon.
Long term (tue-fri)...14/506 am.
Models show stronger offshore gradients Tue morning, but they will
be trending onshore during the day, unlike on Mon. In addition,
upper level support should be weaker. Still, there should be some
gusty NE winds across l.A./Vtu counties in the morning, maybe even
close to advisory levels. The upper level ridge axis will move to
the east of the region on Tue, and high clouds will increase and
thicken during the day, especially across northern sections. One
more day of Santa anas/offshore flow Tuesday. Expect Max temps on
Tue to be about the same as those on Mon.
The models continue to exhibit significant differences with the
upper low moving into the region during mid week. The GFS is quite
a bit faster with it, showing it move into central California Tue night,
then into the Great Basin on Wed, bringing a shot of rain to most
of the region late Tue night into Wed. The ec is about 12 hours or
so slower, moving the upper center into Monterey County early Wed
afternoon and into the Great Basin Wed night. The GFS is also
wetter with the system. Will continue with the increasing chance
of rain Tue night, mainly across northern sections, then across
all areas on Wed, with a chance of showers lingering into Wed
night. Dry weather is expected Thu and Fri with a warming trend
as a ridge builds into the area.
At 2245z, the marine layer was around 2200 feet deep. The top of
the inversion was 2700 feet with a temperature of 18 degrees
S of Point Conception...moderate confidence with coastal tafs with
MVFR to VFR conds today. Skies should remain mostly cloudy through
the day. Low confidence with valley tafs including kbur,kvny with
LIFR/IFR conds through 18z. Then higher confidence with MVFR/VFR
ceilings through much of the day. There is a 30% chance that cigs will
scour out by 19-20z.
North of Point Conception...low confidence with 12z tafs as flight
categories will jump from vlifr to MVFR to VFR through 20z. Timing
is difficult with ceiling categories. Best chance for MVFR/VFR will be
Klax...overall, moderate confidence in 12z taf. Cigs should vary
from MVFR to IFR, but less confidence in respect to timing with
VFR conds.Timing of dissipation of MVFR cigs could be +/- 2 hours
of current 22z forecast. No significant easterly wind component
over 6 knots is expected.
Kbur...overall with 12z taf, low confidence through 18z. 40%
chance for LIFR cigs could rise to IFR by 15z-17z. Moderate
confidence after that with timing of MVFR cigs within +/- 2 hours.
Timing of dissipation of MVFR cigs could be +/- 2 hours of
current 22z forecast.
For the outer waters, moderate to high confidence in current
forecast. Small Craft Advisory (sca) level winds and/or seas will
continue through at least late Sun night. The Gale Warning is in
effect for this afternoon and tonight night for pzz676 and now
pzz673. Mainly near Point Conception and areas south. With the
gusty winds, short-period, choppy seas will be likely. High seas
over 10 feet will continue through late Sun night, therefore a
Small Craft Advisory is not only in effect for winds, but for
hazardous seas. On Tuesday and Wednesday, there is a 50% chance
of Small Craft Advisory level east to southeast winds.
For the inner waters north of Point Sal, moderate to high
confidence in current forecast. Small Craft Advisory level winds are expected
today and tonight with short-period, choppy seas. Additionally,
Small Craft Advisory level seas will continue through tonight. On Tuesday, there
is a 50% chance of Small Craft Advisory level southeast winds.
For the inner waters south of Point Conception, moderate to high
confidence in current forecast. For this morning, Small Craft Advisory level west
to northwest winds are expected. A Gale Warning becomes valid this
afternoon through tonight (with the strongest winds across
western sections). From Sunday night through Wednesday, the winds
will shift to the northeast with Small Craft Advisory level winds likely Sunday
night through Tuesday.
A large and long period west to northwest swell will impact the
coastal waters through at least late Sunday night, resulting in
hazardous sea conditions and large breaking waves near shore,
especially with a large short period wind swell on top of that.
Breaking waves at the Morro Bay and Ventura Harbor entrances will
A large long-period west to northwest swell will continue across
the coastal waters of southwest California, peaking through
this morning, then slowly diminish over the remainder of the
Surf will likely peak between 12 and 16 feet for the central
coast. A high surf advisory is in effect for the central coast
through Monday morning.
A high surf advisory is also in effect through noon Sunday for
the beaches south of Point Conception with surf between 6 and 10
feet. Highest surf will occur across exposed west facing beaches.
Strong rip currents and dangerous breaking waves are expected.
With high tides around 6.5 feet this morning, minor coastal
flooding is possible during the late morning high tide. Any
coastal flooding impacts should be confined to the beaches, with
flooding possible in the most vulnerable parking lots, bike paths,
California...high surf advisory in effect until noon PST Monday for zones
34-35. (See laxcfwlox).
Wind Advisory in effect from noon today to 7 PM PST this
evening for zones 34-35. (See laxnpwlox).
High surf advisory in effect until 4 am PST Sunday for zone
39. (See laxcfwlox).
Wind Advisory in effect until 3 am PST Sunday for zones
39-52. (See laxnpwlox).
High surf advisory in effect until noon PST Sunday for zones
40-41-87. (See laxcfwlox).
Wind Advisory in effect from 4 PM this afternoon to noon PST
Sunday for zones 53-54. (See laxnpwlox).
Wind Advisory in effect from 10 am this morning to 3 am PST
Sunday for zone 59. (See laxnpwlox).
Wind Advisory in effect from 7 PM this evening to noon PST
Sunday for zone 88. (See laxnpwlox).
Pz...Small Craft Advisory in effect until 3 am PST Sunday for zone
645. (See laxmwwlox).
Small Craft Advisory in effect until noon PST today for zones
650-655-673-676. (See laxmwwlox).
Gale Warning in effect from noon today to 3 am PST Sunday for
zones 650-655-673-676. (See laxmwwlox).
Small Craft Advisory in effect until 3 am PST Monday for zone
670. (See laxmwwlox).
Hazard potential outlook (mon-fri).
Gusty northeast winds possible across parts of la/Ventura
counties Monday and Tuesday.