Scientific Forecaster Discussion
fxus66 klox 140407
Area forecast discussion
National Weather Service Los Angeles/Oxnard California
807 PM PST Fri Dec 13 2019
Morning low clouds and fog will spread into the valleys this
morning. There is a slight chance of very light showers today
through Sunday morning. Elevated surf will persist this weekend. A
moderate Santa Ana is expected Monday and Tuesday, followed by
rain on Wednesday.
Short term (fri-mon)...13/806 PM.
For the immediate short-term, everything looks on track. Latest
satellite and surface observations indicate partly to mostly
cloudy skies across the area. Current soundings indicate marine
inversion around 1000 feet deep early this evening and some
stratus is impacting the coastal plain. Overnight, expect the
inversion to deepen as cold front approaches. So, low clouds
should push into the coastal slopes late tonight with the
possibility of some light drizzle.
With regard to the cold front, its still forecast to move across
the area tonight. There will continue to be a threat of light
showers across the central coast tonight and over the interior and
northern mountain slopes late tonight through Saturday afternoon.
Other issue of note this evening is gusty northerly winds. Latest
surface observations indicate northerly winds around 40 mph across
southern Santa Barbara County. So, will keep Wind Advisory in
effect for these areas through tonight. Otherwise, winds are
relatively light this evening, but west to northwest winds should
start to increase overnight as the cold front sweeps through.
Overall, current forecast has good handle on the situation. So, no
significant updates are planned.
***From previous discussion***
Interesting day along the coast today where a shallow marine
layer pushed onshore and lingered for much of the day near Lompoc,
the Oxnard coastal plain, and parts of the la coast. Even parts
of the southern Salinas valley stayed cloudy. The strong onshore
trends were a big reason for this and temperatures definitely
trended cooler for coastal areas and some of the valleys too.
A weak cold front is approaching from the north and this will
further increase onshore flow and cause the marine layer to
rapidly deepen later tonight into Saturday, mainly across
la/Ventura counties. In fact, there's a good chance we'll see some
drizzle or even light showers, especially along the foothills of
the eastern san Gabriels. Increasing west to northwest flow will
help clear skies out along the central coast south through Ventura
County by afternoon but clouds will likely linger in la County
much of the day. Several degrees of cooling all areas Saturday as
a result with highs just in the low to mid 60s for coast/valleys.
Slightly warmer across srn sb County due to downslope flow there.
It will be a breezy afternoon in many areas with marginal advisory
level winds. Even stronger winds expected Sat night into Sunday
morning, especially srn sb County with sundowners and in the i5
corridor and Antelope Valley. Some of those winds will filter down
into the coast and valleys of la/Ventura counties as well but
probably below advisory levels.
Moist, upslope flow near the Grapevine late Saturday into Sunday
morning will likely generate some showers there with the snow
level lowering to 3500-4000'. Good chance we'll see some light
snow at pass level and possibly even an inch or two of
accumulation. May need to consider a Winter Weather Advisory due
to snow and gusty winds and the impacts to major highways like
Breezy north winds expected to continue in many areas Sunday but
strongest in the mountains. Otherwise mostly sunny in most areas
with temps still a few degrees below normal.
By Monday we shift to a moderate Santa Ana wind event. The NAM
checked in with a lax-dag gradient close to -6mb with better upper
support than would be expected given the upper level pattern. The
European model (ecmwf) has been pretty consistent showing near advisory level
northeast winds across the usual favored parts of la/Ventura
counties Monday and the NAM would certainly agree. With the ridge
building in from the west we can expect at least a few degrees of
warming Monday with the warmest temps along the la/Ventura coast.
Long term (tue-fri)...13/206 PM.
One more day of Santa anas/offshore flow Tuesday. The ec has been
consistent showing the strongest gradients Tuesday morning but
would have to think that upper support would be weaker with the
ridge right overhead. Ec ensembles have been favoring Tuesday as
the strongest day for Santa Ana winds but would not be surprised
if that's reversed or at the very least similar. Either way
probably a second day of low end advisory level winds in
la/Ventura counties with similar or slightly warmer temps.
Forecast confidence drops quite a bit for mid week as models have
not been in good agreement on the pattern evolution and timing of
the next trough. GFS and ec are in better agreement today on the
pattern but the GFS is finding a much deeper source of moisture
than the ec is. So still a chance of rain Wed into Thu with best
odds across slo/sb counties. Rainfall amounts probably under a
half inch either way, and possibly much less.
Good confidence in dry and slightly warmer weather the last part
of Thursday and Friday with an upper ridge returning.
At 2245z, the marine inversion at klax was based at 1400 feet.
The top of the inversion was 3600 feet with a temperature of
18 degrees celsius.
Overall, moderate confidence in 00z taf package. High confidence
in ceiling/visibility restrictions at all coastal/valley sites, but low
confidence in flight categories and timing of flight category
changes. Most sites will have cigs start out at IFR/LIFR levels,
but will increase to MVFR levels overnight and into Saturday
Klax...overall, moderate confidence in 00z taf. Timing of change
from IFR to MVFR conditions could be +/- 3 hours of current 09z
forecast. Timing of dissipation of MVFR cigs could be +/- 2 hours
of current 22z forecast. No significant easterly wind component
Kbur...overall, moderate confidence in 00z taf. Timing of arrival
of MVFR cigs could be +/- 3 hours of current 10z forecast with a
30% chance of cigs starting at IFR levels. 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 Saturday afternoon and Saturday night for pzz676. 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. There is a 30% chance that gale force winds could
occur across the southern portion of zone pzz673 for areas S of
Point Conception during the same time as the Gale Warning in the
southern zone. 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
Saturday and Saturday night with short-period, choppy seas.
Additionally, Small Craft Advisory level seas will continue through Saturday night.
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 tonight through Sunday, Small Craft Advisory
level west to northwest winds are expected with a 70% chance of
gale force winds Saturday and Saturday night (with the strongest
winds across western sections). A Gale Warning will remain in
effect for Saturday and Saturday night. 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
Saturday 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 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 Saturday, 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, and
California...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).
Wind Advisory in effect until 3 am PST Saturday for zones
39-52. (See laxnpwlox).
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 Sunday for zone
645. (See laxmwwlox).
Small Craft Advisory in effect until noon PST Saturday for
zones 650-676. (See laxmwwlox).
Gale Warning in effect from noon Saturday to 3 am PST Sunday
for zones 650-655-676. (See laxmwwlox).
Small Craft Advisory in effect from midnight tonight to noon
PST Saturday for zone 655. (See laxmwwlox).
Small Craft Advisory in effect until 3 am PST Monday for
zones 670-673. (See laxmwwlox).
Hazard potential outlook (mon-fri).
Gusty northeast winds possible across parts of la/Ventura
counties Monday and Tuesday.