Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 291145
AFDLOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
445 AM PDT Mon May 29 2017

...Aviation discussion updated...

.SYNOPSIS...

A weak upper level ridge will breakdown and give way to an upper
level trough across the region early this week and persisting
over much of California through most of the week. Expect more
widespread low clouds and fog with a few showers possible Monday
and Wednesday in the mountains with patchy drizzle for a few
valley and foothill areas by mid week.

&&

.SHORT TERM...(TDY-WED)

Synoptically, the weak upper ridge that was over much of
California and Nevada will begin to push east ahead of an
approaching deep upper trough associated with a 542 DM low that
will remain well north off the PAC NW coastal waters. There will
be a couple weak disturbances within the upper flow that will
bring a chance of showers to the SBA/VTU County mountains late
this afternoon and across the northern slopes of the SBA/VTU
county mountains on Wednesday with most the precip remaining well
to the north and east. Expect high temps to trend a bit lower for
most areas today and Tuesday. Then more significant cooling on
Wednesday when high temps will be a few degrees cooler than normal
for this time of year.

For this morning, low clouds have filled in nicely across the
Central Coast and Santa Ynez Valley. Low clouds have also started
to fill in across the LA and Ventura County Coastal areas and into
the San Gabriel Valley. Some high clouds were also moving through
the region as a very weak frontal boundary will bring some high
clouds through the forecast area this morning. With the marine
layer now rising to around 1400 ft, expect low clouds to make it
into the San Fernando Valley and Ventura valleys as well before
sunrise.  Latest AMDAR sounding indicated the marine layer around
1000 ft deep this morning around LAX. As a weak Catalina Eddy
gets going this morning, expect the marine layer to deepen to
around 1400 ft this morning. With a relatively strong inversion
in place, smokey conditions are likely to continue over the
Mandeville Fire region today. Smoke will have a tough time mixing
out until later this afternoon. People suffering from respiratory
conditions should stay indoors until the smoke diminishes and
mixes out late this afternoon. Low clouds could linger along a few
coastal areas into early this afternoon, thanks in part to the
stronger inversion.

The main issue for today will be the potential for a few elevated
thunderstorms developing across the Ventura/Santa Barbara County
Mtns later this afternoon. There is enough instability with
limited mid level moisture to justify a slight chance for showers
or thunderstorms. If storms do initiate, the main impact would be
dry lightning, as well as strong downdraft winds when storms
collapse. The San Gabriel Mountains should see some partly cloudy
skies as there is less in the way of instability.

Low clouds are expected to redevelop and push inland across coast
and valleys tonight into Tuesday morning. With little change
synoptically, expat for slightly stronger onshore flow, expect a
degree or two of cooling across coastal areas, with little change
inland. An upper disturbance will move through the upper trough on
Wednesday bringing a more significant deep marine layer. Some
patchy drizzle has been added for the San Gabriel foothills. There
will be just enough lift with this trough that some showers will
be possible across the northern slope of the SBA/VTU County
mountains. Took out the chance for thunderstorms as the soundings
looked quite anemic in respect to convection potential for
Wednesday. High temps will bottom out on Wednesday with warmest
valleys reaching the mid to upper 70s with a few locations
reaching 80 degrees. Otherwise most areas will be the mid 60s to
lower 80s across the Antelope Valley.

.LONG TERM...(THU-SUN)

Both the GFS and ECMWF models are in fairly good agreement with
large scale features through next weekend. After the trough axis
moves through the region on Wednesday, broad NW flow aloft will
occur on Thursday then by Friday a weak upper ridge will form over
southern California briefly. Expect a modest warming trend
Thu/Fri across the entire region as heights and thickness lvls
rise. Onshore flow will weak late this week, but there should
continue to be night through morning low clouds. A weak upper low
will build in from the SW over the weekend which will help to
increase low clouds and begin another modest cooling trend. Models
seem to have a tough time dealing with systems coming up from the
SW. Will continue to go with cooler solution for the weekend.

&&

.AVIATION...29/12z...

At 09z at KLAX... The inversion was based near 1100 feet. The top
of the inversion was near 4100 feet with a temperature of about
21 degrees Celsius.

Overall... Moderate confidence in the current TAFs. LIFR/IFR
conditions at most coastal locations will clear by 20z. There is
a forty percent chance of LIFR/IFR conditions at KBUR and KVNY
through 18z and a thirty percent chance at KPRB and KSBA through
17z. LIFR/IFR conditions will likely develop at coastal and
adjacent valley locations after 30/08z. Otherwise and elsewhere
VFR conditions will prevail.

KLAX... Moderate confidence in the current TAF. LIFR/IFR
conditions will clear by 20z then return again around 30/09z.
Otherwise VFR conditions will prevail. No east winds above 7 knots
are expected.

KBUR... Moderate confidence the current TAF. There is a forty
percent chance of LIFR/IFR conditions through 18z. Otherwise VFR
conditions will prevail.

&&

.MARINE...29/200 AM

Small Craft Advisory (SCA) conditions continue across the Outer
Waters and in the nearshore waters of the Central Coast into at
least Wednesday. There will be periods during overnight and early
morning hours when winds dip below SCA levels.

The stronger winds will spill into the western half of the Santa
Barbara Channel each evening but not far enough to warrant a SCA
for the entire channel.

The winds peak Monday and Tuesday and there is a thirty percent
chance that Gale conditions will form beyond 30 nm of the Central
Coast.

The elevated winds will create a short period chop over all
waters including the Santa Barbara Channel and Santa Monica Basin
in the Inner Waters.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory in effect until 9 AM PDT Wednesday for
      zones 645-670-673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK...(WED-SUN)
No significant hazards expected.

&&
$$

PUBLIC...Kaplan
AVIATION...Kj
MARINE...Kj
SYNOPSIS...Kaplan

weather.gov/losangeles



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