Scientific Forecaster Discussion
fxus66 klox 130503
Area forecast discussion
National Weather Service Los Angeles/Oxnard California
903 PM PST Thu Dec 12 2019
Friday will be warm with partly cloudy skies, before a weak low
pressure system brings some cooler temperatures, clouds, and a
chance for light rain and snow for the mountain areas over the
weekend. Areas of gusty winds will persist through the weekend,
and Santa Ana winds are expected Monday.
Short term (thu-sun)...12/903 PM.
Overall, forecast is working pretty well in the immediate short
term. Latest satellite and surface observations indicate some
stratus/fog across the central coast as well as over parts of
Catalina Island. With marine inversion expected to remain very
shallow overnight (under 600 feet), stratus should not make much
inland headway across the central coast and should not impact
coastal areas south of Point Conception (except for Catalina
island). Given the shallow nature of the inversion, dense fog will
develop and a dense fog advisory has been issued for the central
coast. Other than the stratus, skies should generally remain
partly cloudy overnight as some scattered cirrus drift overhead.
Other phenomena of note this evening is northerly winds. Latest
surface observations indicate gusty northerly winds in the usual
spots (santa ynez range and the I-5 corridor). There are some
local gusts exceeding advisory thresholds, but widespread
advisory-level winds are not anticipated overnight. So, will not
issue any wind advisories at this time.
Overall, forecast has a good handle on the immediate short term.
Did issue an update earlier to account for stratus and fog.
However, no further updates are expected at this time.
***From previous discussion***
We managed to get at least one 80 degree high temperature today
from Woodland Hills (record is 86 there) while many other areas
south of pt Conception were well into the 70s for the first time
since before Thanksgiving. A little cooler up north but still a
few degrees above normal.
Another nice day on tap Friday but we'll probably cool a degree or
two across coast/valleys as we start trending onshore by mid day.
Still expecting some locally gusty northerly winds especially srn
sb County and i5 corridor areas but below advisory levels.
Temps will come crashing down below normal again over the weekend
as a cold front pushes through Saturday night and clouds
increase. The trough isn't taking a favorable path for precip in
most of our area as northwest flow will continue to dominate
through the period. However, that will favor the north facing
slopes from the Grapevine to the Cuyama Valley as well as
southeast slo County. Best precip chances will be from nrn
Ventura County through the Grapevine and pops there have been
increased to likely from late Saturday through early Sunday. Not a
whole lot of moisture to work with so we're probably only looking
at an inch or two of accumulation. But the cold air coming behind
it Saturday night will lower snow levels to around 3500' and some
light snow accumulations are possible at pass level over
Strong northwest winds will accompany the cold front Saturday into
early Sunday. Advisory level and possibly low end warning level
winds expected in and around the Grapevine while advisory levels
likely in the Antelope Valley. Gusty west winds expected at lower
elevations Saturday, especially near the coast, but probably just
below Wind Advisory levels.
Dry, breezy, and cool weather expected Sunday with gusty
northerly winds continuing, strongest in the mountains. Some of
the European model (ecmwf) ensembles showing advisory level winds even down into
the la/Ventura valleys.
Long term (mon-thu)...12/206 PM.
A modest upper level ridge keep the area dry Monday/Tuesday with
moderate offshore gradients in place. Minimal upper support for
Santa Ana winds so likely sub-advisory level northeast winds both
days, but strongest on Tuesday. Here again the ec ensembles are
stronger and do favor some advisory level winds across la/Ventura
counties. The air mass remains quite cool however so temperatures
will likely stay in the 60s across lower elevations despite the
Plenty of uncertainty for the middle of next week as models remain
at odds regarding the strength of the ridge across the west. The
ec, including most of the ensembles, is much stronger, thus
delaying and significantly weakening the approaching trough from
the west. Opted to keep pops on the low side for Wed but increase
them slightly Thu as roughly half of the ec ensembles bring rain
to about Ventura County by then. Either way a fairly light precip
event with minimal impacts.
At 0430z, the marine inversion at klax was based at 600 feet.
The top of the inversion was 2000 feet with a temperature of
20 degrees celsius.
For taf sites south of Point Conception, high confidence in
06z tafs as VFR conditions are anticipated. There is a 20% chance
of MVFR visibilities 06z-16z.
For taf sites north of Point Conception, moderate confidence
in 06z tafs. LIFR/vlifr conditions will continue through Friday
morning. However, confidence in timing of flight category changes
Klax...high confidence in 06z taf as VFR conditions are
anticipated through the period. No significant easterly wind
component is anticipated.
Kbur...high confidence in 06z taf as VFR conditions are
anticipated through the taf period.
For the outer waters, high confidence in current forecast. Small
Craft Advisory (sca) level winds and/or seas will continue through
at least late Sun night. There is also a 50% chance of gale force
winds Sat afternoon and Sat night for pzz676. With the gusty
winds, short-period, choppy seas will be likely. High seas over 10
feet will continue this evening through late Sun night, therefore
a Small Craft Advisory is not only in effect for winds, but for
For the inner waters north of Point Sal, moderate to high
confidence in current forecast. There is a 60%-70% chance of Small Craft Advisory
level winds Sat thru Sun night. With the gusty winds, short-
period, choppy seas will be likely. High seas over 10 feet will
develop this evening causing a Small Craft Advisory to go into
effect for hazardous seas which, along with the gusty winds, will
remain in effect through late Sun night.
For the inner waters south of Point Conception, moderate to high
confidence in current forecast. There is a 60% chance of Small Craft Advisory level
winds across the western half of the Santa Barbara Channel
through this evening, and 80% chance from Fri evening through sun,
(especially across western sections) and a 50% chance of gale
force gusts late Sat afternoon thru Sat night. The winds will
shift to the north on Mon then to the east on Tue, with a 30%-40%
chance of Small Craft Advisory level winds at times.
A large and long period west to northwest swell will impact the
coastal waters this evening through at least late Sun 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 be possible.
A large long-period west to northwest swell will fill into the
coastal waters of southwest California this evening, peak on
Friday into Saturday morning, then slowly diminish over the
remainder of the weekend.
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 Sunday morning.
A high surf advisory is also in effect through noon Monday for
the beaches south of Point Conception with surf between 6 and 10
feet possible. Highest surf will occur across exposed west facing
beaches. Strong rip currents and dangerous breaking waves are
With high tides around 6.5 feet Friday and Saturday, minor
coastal flooding is possible during the late morning high tides.
Any coastal flooding impacts should be confined to the beaches,
with flooding possible in the most vulnerable parking lots, bike
paths, and walkways. A coastal flood advisory may be issued
tomorrow. There is a chance of more impactful flooding over
vulnerable roads in the Ventura area.
California...dense fog advisory in effect until 9 am PST Friday for zones
34-35. (See laxnpwlox).
High surf advisory in effect until noon PST Monday for zones
34-35. (See laxcfwlox).
High surf advisory in effect until 4 am PST Sunday for zone
39. (See laxcfwlox).
High surf advisory in effect until noon PST Sunday for zones
40-41-87. (See laxcfwlox).
Pz...Small Craft Advisory in effect until 3 am PST Monday for
zones 645-670-673. (See laxmwwlox).
Gale watch in effect from Saturday afternoon through late
Saturday night for zones 650-655-676. (See laxmwwlox).
Small Craft Advisory in effect until 3 PM PST Saturday for
zone 676. (See laxmwwlox).
Hazard potential outlook (sun-thu).
Light snow may create driving hazards over the mountains Saturday
night into Sunday, including Interstate 5 over the Grapevine.
High surf is likely Sunday at area beaches and minor coastal
flooding is possible. Gusty northerly winds expected Sunday in
many areas but strongest in the mountains. Gusty northeast winds
possible across parts of la/Ventura counties Monday and Tuesday.