Area Forecast Discussion
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FXUS66 KLOX 271619
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
919 AM PDT FRI MAY 27 2016
Weak low pressure will linger over the area keeping temperatures
a little below normal through Sunday. There is a slight chance of
mountain showers or thunderstorms Saturday afternoon and early
evening. Next week, high pressure will build in causing a gradual
warming trend in inland areas while the coastal temperatures will
There was a more well-defined marine inversion this morning at
around 1700 ft deep at KVBG and around 2000 ft deep at KLAX. At mid
morning, low clouds covered the Central Coast, Santa Ynez Vly, and
L.A. County coastal area, with patchy low clouds into the San
Gabriel Vly. The eddy over the SoCal bight was pushing low clouds
into the VTU County coast as well. The low clouds are forecast to
dissipate as the morning progresses, altho may linger into early
afternoon at some of the beaches. Otherwise, mostly sunny skies
should prevail thru the afternoon, except pop-up cu is likely over
the mtns for partly cloudy skies there. Good onshore flow can be
expected this afternoon into early evening, with gusty sw to nw
winds from the Central Coast to the foothills, mtns and deserts.
Temps this afternoon will remain several degrees cooler-than-normal
for the coast/vlys, but warm to near to slightly above normal for
interior areas and deserts.
A broad mainly nw flow aloft will prevail over swrn CA thru today as
upper level ridging lingers off the coast. A weak, baggy upper level
trof will develop over srn CA tonight and linger over the area Sat
while developing into a weak upper level low. The weak upper low
will then drift se across the forecast area Sat night and into sern
CA for Sun.
The marine inversion will remain in place over the next few of days.
This will help more extensive night and morning low clouds and fog
to affect the coast and adjacent vlys tonight thru Sun morning, with
an eddy enhancing the marine layer clouds s of Pt Conception. There
will be the possibility of afternoon cu buildups in the mtns Sat and
Sun, altho the 12Z NAM was indicating there should be enough
moisture and instability for the formation of isolated showers or
thunderstorms Sat afternoon in the VTU/interior SBA County mtns.
LI`s down to -5, CAPE values over 1100 J/kg, and the presence of the
weak upper troffiness would support this possibility as well. Have
decided to put back into the fcst a slight chance of thunderstorms
for these areas, and also into the L.A. County mtns along the I-5
corridor, for Sat afternoon into the evening. In addition, there is
slim, non-zero chance of a shower or thunderstorm over the San
Gabriel Mtns Sun afternoon as the upper low slides off to the se,
but POPS in this area will be below 15 percent so there is no
mention in the zones. Otherwise, mostly clear skies are expected
over the forecast area tonight thru Sun. Weaker onshore flow is
expected each afternoon and evening, with locally gusty sw to nw
winds from the Central Coast to the foothills, mtns and deserts.
Temps are forecast to change little for Sat thru Sun. Highs will be
generally 3 to 6 deg below normal for the cst and adjacent vlys,
while inland vlys, mtns and deserts will be near normal to slightly
above seasonal norms.
***FROM PREVIOUS DISCUSSION***
Both the ECMWF and GFS are in pretty good agreement during the
extended period. The upper low will will shift east as an upper
ridge will build in from the eastern Pacific and persist through
at least next Wed before weakening as a broad upper level trof
over the e Pac approaches. The models start to diverge on
Wednesday as the ECMWF holds onto the upper ridging more so than
the GFS by Thu. Overall, it looks like a typical June gloom marine
layer pattern will prevail during the extended period with night
and morning low clouds and fog for the coast and coastal vlys.
The marine layer could be disturbed a bit across the central coast
Monday night/Tue Morning, and again the following night and
morning due to some weak offshore winds, but expect some patchy
low clouds to develop. Sundowner winds should also keep the SBA
south coast mostly clear with little chance of low clouds during
the same time period mentioned.
Temps are forecast to become increasingly warm and several degrees
above normal over interior areas, while the coast and adjacent vlys
will be near normal to a few degrees below normal thru the week. The
warmest day next week is expected to be on Wed with highs from the
upper 60s and 70s at the coast to upper 70s and 80s for the vlys and
foothills, except warming into the lower to mid 90s in the Antelope
At 11Z at KLAX...The marine layer was 2000 feet deep. The top of
inversion was 4500 ft with a temperature of 15 degrees Celsius.
N of Pt Conception, low clouds were widespread on the Central Coast
and in the Santa Ynez Valley, and were spilling into the Salinas
Valley. S of Pt Conception, clouds were beginning to push into
south coastal sections of L.A. County, and will become widespread
across coastal sections by daybreak. Clouds will likely push into
the San Gabriel Valley. Conditions were mostly low MVFR S of Pt
Conception, and IFR north. Expect skies to clear in most areas by
mid to late morning, except maybe early afternoon near the beaches.
More widespread low clouds are expected tonight/Sat morning, with
clouds expected in all coastal and most valley areas. Conds
should be mainly low MVFR or high IFR tonight.
KLAX...Moderate confidence in the 12z TAF. There is a 30 percent
chance that cigs will scatter out as early as 17z. There is
a 30 percent chance that cigs tonight will not arrive until
06z or later.
KBUR...Moderate confidence in the 12z TAF. There is a 30 percent
chance of MVFR cigs between 13z and 17z this morning. There is a
20 to 30 percent chance that cigs will arrive as early as 07z
tonight, and could be at IFR levels.
Northwest winds from Piedras Blancas to San Nicolas Island will
prevail through late tonight and small craft advisory conditions
will prevail. Otherwise a Catalina eddy is expected to develop
each night over the bight through Tuesday and northwest winds
are expected elsewhere and fill in the bight each afternoon. A
complex storm system over the Southern Ocean last Monday with a
fetch oriented 190-210 degrees from Ventura generated swells that
will arrive Monday and build through Tuesday. The swells will
remain below small craft advisory for hazardous sea conditions but
there will be extra surging and currents along exposed south
facing shores. In the meantime a small south swell will continue
and a locally generated swell from 310-330 degrees will subside
PZ...Small Craft Advisory in effect until 3 AM PDT Saturday For
zones 670-673-676. (See LAXMWWLOX).