Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 281143
AFDLOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
443 AM PDT Fri Jul 28 2017

.SYNOPSIS...
Night and morning low clouds and fog will affect coastal areas
through the middle of next week. Otherwise, upper level high
pressure will keep mostly clear skies over southwestern
California through Saturday, then monsoonal moisture will move in
for partly cloudy skies Sunday through next Thursday. There will
also be a slight chance of mountain and desert thunderstorms each
day during the period starting Sunday. Possibly affecting the coast
and valleys Tue and Wed nights Temperatures will be seasonably warm
through Saturday, then several degrees above normal Sunday through
next Thursday.

&&

.SHORT TERM...(TDY-SUN)

The marine layer this morning was around 1200 ft around LAX this
morning. Latest fog product imagery indicated widespread stratus
across the Central Coast with areas of low clouds reaching the
Santa Ynez Valley this morning. For coastal areas S of Point
Conception, expect low clouds to fill in across the Ventura Coast
and much of the SBA South Coast. The LA Coast is having a tough
time seeing low clouds filling in. Looks like there will be some
patchy low clouds filtering into the Ventura County Valleys and
possibly in the eastern San Gabriel Valley by sunrise. Skies
should clear out quickly in any valley locations this morning,
then clear to the beaches by mid to late morning. A weak upper
trough moving across the northern half of the state will help to
lower boundary layer temps and H5 Heights which will translate to
a few degrees of cooling in most areas today. Expect the Antelope
Valley to reach around 101 as well as Paso Robles this afternoon.
Valleys will remain mostly in the lower to mid 90s. Could be a
few flat cu build ups across the mountains this afternoon.

For tonight, a weak eddy will develop and should bring another
round of low clouds to coastal areas and possibly into a few
coastal valleys by Sat morning. The cooling trend is expected to
continue into Saturday with more flat cumulus likely to develop
across the LA/VTU County Mountains. Not expecting any showers as
most of the deeper moisture remains to the south and east of the
forecast area. High temps will continue to trend cooler a degree
or two with up to 5 degrees of cooling across the Salinas River
Valley yet still remain quite warm in the mid 90s. No significant
changes from Friday.

By Sunday, the upper level pattern will begin
to shift out of the southeasterly direction. The upper lvl ridge
set up closer to the Four Corners Region, which will allow mid
level moisture to advect into SE California. All models now show
the monsoonal front (850 mb DewPoint Temp) remaining east of LA
County on Sunday. The monsoonal flow will be delayed 24 hours due
to the dry air between 700-500 mb therefore have taken down slight
chance for thunderstorms Sunday afternoon for the LA County Mtns.
Not much change temperature wise for Sunday.

.LONG TERM...(MON-THU)

Both the GFS and ECMWF models remain to be in good synoptic
agreement with large scale features through the long term period.
The southeaster flow will continue into Tuesday with the
monsoonal front expands westward into Ventura County. Have added
slight chance for thunderstorms to the Ventura County Mtns Tuesday
afternoon as well as the LA County Mtns and Antelope Valley. PWAT
values are not too impressive at around 1.3". However, an
Easterly Wave develops across LA/VTU Counties by Tue evening.
There will be an increase in mid level moisture, therefore have
added a slight chance for thunderstorms for coast and valleys of
LA/VTU Counties through the overnight hours. Showers will be
elevated and with some cloud top cooling across the coastal waters
would expect a few cells to develop. Although the forecast calls
for slight chance thunderstorms, there is a good chance it could
just be showers.

Wednesday looks to be the best chance for showers and
thunderstorms across the LA/VTU County Mtns, Antelope Valley
during the afternoon hours, and once again spilling over into the
valleys and coastal areas Wednesday night. PWAT Values will reach
1.5" with easterly flow steering winds over 15 mph. There could be
the potential for local flooding, but if storms develop, they
should be moving fast enough not to cause any flash flooding. The
flow should turn more SE Thursday, therefore only expecting some
showers and thunderstorms across the LA/VTU County Mtns. As far as
temps go, the upper ridge will continue to strengthen and with
weaker offshore flow, expect the warmest valleys to reach the
lower 100s, while the Antelope Valley is expecting highs around
105. Of course, if a thick cloud shield sits over the region, then
high temps would likely be a few degrees cooler than what`s in
the forecast.

&&

.AVIATION...28/1135Z.

At 11Z, the marine layer depth at KLAX was around 1200 ft. The
top of the marine inversion was around 3000 ft with a temperature
of 25 degrees Celsius.

Widespread low clouds with LIFR to IFR conditions currently across
coastal sections from VTU County northward, in the Santa Ynez
Valley and locally in the VTU County valleys. Skies should become
mostly clear during the mid to late morning hours.

Clouds have pushed into south coastal sections of L.A. County,
with mostly low MVFR conds. Expect stratus to push across the
remainder of coastal L.A. County coastal areas by 13Z and should
clear by mid to late morning. Stratus with IFR conds will affect
the San Gabriel Valley for a few hours through mid morning.

Low clouds should be widespread in all coastal areas as well
as the Santa Ynez and San Gabriel Valleys and locally in the VTU
County valleys tonight/Sat morning. Conds will be mostly IFR to
LIFR, except low MVFR across coastal sections of L.A. County.

KLAX...Moderate confidence in the 12Z TAF. There is a 20-30%
chance that skies will remain clear and conds VFR this morning.
There is a 20-30% chance that cigs tonight will not arrive
until after 08Z.

KBUR...High confidence in the 12z TAF with VFR conditions
expected thru the period. There is a 10-20% chance of IFR conds
between 12Z and 16z tonight/Sat morning.

&&

.MARINE...28/300 AM.

For the Outer Waters, moderate to high confidence in current
forecast. Expect SCA level winds across the northern two thirds of
the outer waters this afternoon through late tonight, and there is
a 20% chance that winds will remain below SCA levels. Across the
southern outer waters, local SCA gusts are expected this afternoon
through late tonight, and there is a 30% percent chance that a
SCA will be needed there. After late tonight, SCA conds are not
expected through Mon, with a good chance of SCA levels winds Tue.

For the Inner Waters, high confidence in current forecast. For
all the waters, winds and seas are expected to remain below SCA
levels through Tue. However, there may be local small craft
advisory level gusts across the Inner Waters each afternoon and
evening through Sat...strongest in the Santa Barbara Channel.

A long-period southerly swell will spread into the coastal waters
tonight and Saturday, then a moderate swell with a rather long
period will affect the waters through Mon. The Santa Barbara
Channel will be mostly blocked from the swell energy due to the
Channel Islands...except for possible the far eastern portion.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement in effect from Saturday morning
      through Tuesday evening for zones 40-41-87. (See LAXCFWLOX).
PZ...Small Craft Advisory in effect from 3 PM this afternoon to 3
      AM PDT Saturday for zones 670-673. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK...(SUN-THU)
A high surf event should peak over the weekend as a long-period
southerly swell arrives at the Southern California beaches. High
surf and strong rip currents will occur through the weekend and
probably into late next week.

&&

$$

PUBLIC...Kaplan
AVIATION...DB
MARINE...DB
SYNOPSIS...Kaplan

weather.gov/losangeles



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