Area Forecast Discussion
Issued by NWS Los Angeles, CA
FXUS66 KLOX 061217
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
417 AM PST Tue Dec 6 2016
A trough will drop into the Great Basin today and tonight bringing
cooling and gusty west to north winds will across portions of the
region. Gusty Santa Ana winds will affect Ventura and Los Angeles
Counties Wednesday and there will be some warming. Moist westerly
flow will develop across northern and central California Thursday
and continue into the weekend. There will be a slight chance of rain
north of Point Conception at times Thursday through Sunday, with
partly cloudy skies and seasonable temperatures elsewhere. Warmer
and dry weather is expected in all areas Monday.
Marine layer has deepened significantly south of Pt Conception this
morning, and was now up to 3500 feet. Low clouds were widespread
in all coastal and valley areas from the south coast of SBA County
through L.A. County. With the deep marine layer and some low level
lift, there could be some drizzle this morning, particularly in
the foothills. Expect rather slow clearing of the low clouds
today, and some clouds could linger at the beaches south of Pt
Conception through the afternoon. N of Pt Conception, low clouds
were patchy in nature, confined mainly to southern portions of the
Central Coast, and the Santa Ynez and Salinas Valleys. The marine
layer was more shallow there, and there was some local dense fog,
though not widespread enough to require advisories.
Heights and thicknesses will lower across the region today as a
trough drops from the Pac NW into the Great Basin. There will be
cooling at 850 mb and 950 mb, and onshore gradients will be quite
strong. This should induce a few more degrees of cooling in most
areas today. Expect winds to reach low end advisory levels across
the Antelope Valley late this morning through this evening, so a
Wind Advisory has been issued there.
Low level N-S gradients will sharpen tonight, and an area of
decent subsidence will overspread the region. This should support
some gusty NW-N winds across the Santa Ynez Mountains and through
the Interstate 5 corridor tonight, with gusty winds spreading
into the south coast of SBA County and possibly the Santa Clarita
Valley. Wind advisories may be needed for these areas for tonight.
Fairly good cooling should weaken the marine inversion tonight, so
expect the marine layer stratus to be largely disrupted. Still,
there may be some patchy low clouds across portions of the
forecast area tonight and early Wed. Surface high pressure will
build into Nevada on Wed, and low level flow will turn
northeasterly. This should bring gusty northeast winds to the mtns
of L.A. and VTU Counties including the Santa Monicas, to the
valleys and coastal sections of VTU County, the Santa Clarita
Valley, western portions of the San Fernando Valley, and the L.A.
County coast below passes and canyons from Malibu to the
Hollywood Hills. Winds could reach low end advisory levels in most
areas there areas on Wed. Any low clouds will clear quickly on
Wed. There should be some warming, especially west of the
A weak ridge will develop across the region Wed night and Thu. Low
level gradients will actually be more strongly offshore, but
support will be weaker. Still, there should be some gusty
northeast winds across portions of L.A. and VTU Counties Wed night
and early Thu. Skies will be partly cloudy south of Pt Conception
on Thu, and there will be a few degrees of warming in most areas.
North of Pt Conception, moisture will increase throughout the
atmosphere Wed night, and skies should become mostly cloudy as a
warm front develops across Central CA and extends southward. While
most of the rain will remain north of the forecast area, there is
a slight chance that light rain could make it as far south as SLO
County Thu, so slight chance pops are warranted.
General zonal flow pattern will set up persist across CA
Friday through Sunday. Across L.A. and VTU Counties, it should
remain dry through the period, and rather high heights will likely
keep temps near or slightly above normal. Abundant moisture and
plenty of rain is expected across northern and central CA during
this period. Northern sections of the forecast area will be close
to the souther extent of the moisture plume, and while most of the
time will likely be dry, there is at least a slight chance of rain
from time to time, mainly across SLO County. A slight ridge
building into the area Mon may force any rain farther north, and
bring a bit of warming to most areas.
At 1040Z at KLAX, the marine layer was around 2500 feet. The top
of the inversion was near 3200 feet with a temperature of 13
North of Point Conception...Good confidence in KSMX and KSBP TAFs.
Low confidence in forecast for KPRB thru 21Z where flight cat
changes could be off by as much as 2.5 hours.
South of Point Conception...Good confidence in high MVFR/low VFR cigs
but low confidence in the exact time of clearing. There is a 30
percent chc that clearing could be two hours later than forecast.
KLAX...Fair confidence in TAF. There is a 30 percent chc of MVFR
cigs lasting until 00Z. There is a 30 percent chc of no cigs
KBUR...good confidence in TAF. Clearing could occur any time from
18Z to 21Z.
Outer Waters...High confidence in northwest SCA winds lasting
through early Wednesday...and moderate confidence that the SCA
winds will persist through Wednesday afternoon. There will be
local Gale Force gusts this afternoon and evening between Point
Conception and San Nicolas Island. Hazardous seas consisting of a
long period northwest swell and short period wind waves will
continue through Tuesday night.
Inner Waters north of Point Sal...moderate to high confidence in
SCA winds developing this evening.
Inner waters south of Point Conception...moderate to high confidence
in SCA winds in the Western Santa Barbara Channel this evening.
CA...Wind Advisory in effect from 10 AM this morning to 9 PM PST
this evening for zone 59. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 3 PM PST Wednesday for
zones 670-673-676. (See LAXMWWLOX).
.HAZARD POTENTIAL OUTLOOK...(THU-MON)
No significant hazards expected.