Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 290553
AFDLOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
1053 PM PDT Sun May 28 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...(SUN-WED)

Latest fog product imagery indicated stratus filling in across the
Central Coast this evening, while much of the So Cal Bight
remained clear. However, low clouds should fill in this evening
and move in across the coastal areas of Los Angeles and then
across the Ventura County Coast overnight. Latest AMDAR sounding
around LAX was around 900 ft deep. Low clouds should move into the
San Gabriel Valley late tonight into Monday morning. Not as
confident for the San Fernando Valley and Ventura County Valleys.
Some stratus should filter into the Cahuenga Pass possibly
affecting the SE part of the SFV including Burbank. The marine
layer depth should increase a bit overnight while the inversion
strengthens some. The strong inversion will not be great news for
people living in and around the Mandeville Fire area as smoke will
not be able to mix out due to the inversion and should remain
fairly stagnant over the area overnight into early Monday
morning. People suffering from respiratory conditions should stay
indoors until the smoke diminishes.

For Monday, the upper ridge will be nudged further east while an
upper trough moves in across the region. Heights and thickness
lvls will trend down a bit while the surface onshore flow
increases. High temps will be a little cooler than earlier
forecasts were showing. Highs will range from the upper 70s to
lower 80s in the valleys, while coastal areas will range from the
mid 60s to the mid 70s inland. A couple of changes to the forecast
this evening...Have added a slight chance of showers or
thunderstorms in the Ventura and Santa Barbara County Mtns for
late Monday afternoon. There will be plenty of instability over
the areas mentioned plus a pool of 700-650 mb moisture that
should at least initiate some showers. If storms do initiate, they
will be elevated and have little trouble growing vertically. The
main concern would be dry lightning and chaotic downdraft winds
when storms collapse. This looks to be limited only to the
Ventura/SBA County Mtns for tomorrow. There will be some flat
cumulus build ups across the LA County Mtns, but lack of moisture
and instability should make for just partly cloudy conditions
over the LA County mtns.

The trough axis will persist over the region through Wednesday.
Expect more widespread night through morning low clouds both Tue
and Wed. The marine layer depth should increase to the coastal
slopes Tue night into Wed morning. Patchy drizzle is possible
across the San Gabriel Valley foothills Wed morning. Also, looking
at the current models, thunderstorms that were in the forecast for
Wed over the local mountains will be pulled down to just showers.
There will be enough PVA with the cyclonic flow to justify
showers, but the convective parameters look nil at this point.
Expect high temps to lower more significantly on Wed to below
normal for this time of year.

.LONG TERM...(THU-SUN)

A trough of low pressure will likely linger along the West Coast
into Thursday. Increased onshore flow and a deeper marine layer
will likely continue cooling into Thursday. Patchy night through
morning drizzle or light showers cannot be ruled out between late
Tuesday night through Thursday morning, especially in the
foothills and mountains. A mention of a slight chance of showers
and thunderstorms has been left in place for the mountains on
Wednesday afternoon and evening, but the possibility of night
through morning drizzle will likely need to be addressed.

A brief warm-up should develop for Friday, but model solutions are
handling a developing trough of low pressure to the southwest of
the area poorly for next weekend. The forecast takes a cooler
stance for now as higher confidence exists in a continued strong
onshore flow pattern.

&&

.AVIATION...29/06z...

At 03z at KLAX... The inversion was based near 1150 feet. The top
of the inversion was near 4150 feet with a temperature of about
22 degrees Celsius.

Overall... Moderate confidence in the current TAFs. LIFR/IFR
conditions will develop at most coastal locations by 11z then
will clear by 20z. There is a forty percent chance of LIFR/IFR
conditions at KBUR and KVNY in the 12z-18z period and a thirty
percent chance at KPRB and KSBA in the 10z-18z period. 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 develop around 08z and 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 in the 12z-18z period.
Otherwise VFR conditions will prevail.

&&

.MARINE...28/800 PM...

For the Outer Waters, high confidence in current forecast. Small
Craft Advisory (SCA) level winds will continue through Friday.
There is a 20% chance of Gale force conditions developing in the
afternoon/evening hours Tuesday and Wednesday.

For the Inner Waters, moderate confidence in current forecast. For
the waters north of Point Sal, SCA level winds are likely each
afternoon/evening today through Friday. For the waters south of
Point Conception, winds and seas are expected to remain below SCA
levels through Friday.

&&

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

&&

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

&&
$$

PUBLIC...Kaplan/Hall
AVIATION...Kj
MARINE...Gomberg/Thompson
SYNOPSIS...Kaplan

weather.gov/losangeles



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