Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000
FXUS66 KLOX 240135
AFDLOX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
635 PM PDT Fri Jun 23 2017

.SYNOPSIS...

An upper-level ridge of high pressure centered over Southern
Arizona will continue to bring very warm conditions away from the
coast into next week. Subtropical moisture could bring a few
elevated showers and thunderstorms through Saturday, otherwise
night through morning low clouds and fog will continue into next
week. High pressure aloft will weaken Tuesday and a cooling trend
should develop as onshore flow increases.

&&

.SHORT TERM...(FRI-MON)

Marine lyr again hugging the coast and in some cases inland by
several miles. Gradients still showing decent northerly trends
which bodes well for less inland push tonight and earlier and more
complete clearing Saturday. This goes along with the 2-4 degree
(C) increase in 950mb temps which should translate into 4-8
degrees (F) of warming on average for the coastal valleys and less
warming in other areas. Temps should not require expansion of the
current heat advisory/warning product, though there will be small
portions of zones, particularly southeast SLO county where heat
risks will be higher due to the combination of hot daytime temps
and minimal overnight relief. For now though will leave the heat
advisory/warning alone and let it ride for the same areas through
Sunday.

Keeping a close eye on some moisture and energy coming up from the
southeast. Lightning had been detected earlier this morning but
nothing since then. Still, it`s a sign that there is some decent
instability with this feature even though most of it and the
moisture is above 600 mb. Since there is some energy with it it
won`t necessarily need afternoon heating to kick storms off.
However it`s so dry below 600 mb that the chances for anything
measurable reaching the ground are really low. So for now given
its history of lightning and the trajectory of the moisture have
added in a slight chance of dry lightning to the forecast for our
western zones (mainly extreme western Ventura County and all of
SB/SLO Counties) tonight into early Saturday. Air mass stabilizes
through the day Saturday so the dry lightning potential has been
confined to the night and early morning hours.

This feature is gone by Sunday leaving behind a warmer air mass
and continued northerly flow at the surface. So temps expected to
warm a couple more degrees Sunday which should be the highest of
the next several days.

Sundowner winds expected to start developing as early as this
evening in the srn SB area but stronger Saturday and Sunday
evenings. May be borderline advisory level there. Some winds also
through the I-5 corridor but below advisory levels.

A slight cooling trend is expected Monday as a weak trough moves
into or and Nrn CA. This will knock the ridge down and cool most
areas by at least a few degrees.

.LONG TERM...(TUE-FRI)

Both the GFS and EC in pretty good agreement through about
Thursday showing a trough developing along the west coast next
week. While the patterns are similar the ECMWF now has trended
slightly cooler than the GFS. So while the magnitude of cooling
may not be entirely certain, confidence is high that a cooling
trend will begin Monday and continue through Thursday. At that
point models both show the ridge returning through next weekend,
though somewhat stronger/warmer on the GFS. Expecting highs to
return to normal levels by Tue or Wed, then slightly below normal
Thu before warming again Friday. Marine lyr will become more
expansive especially by around mid week and again clear to near
the beaches.

&&

.AVIATION...24/0130Z.

At 00Z, the marine layer depth was around 1200 feet deep at KLAX.
The top of the inversion was around 4500 feet with a temperature
near 29 degrees Celsius.

Low to moderate confidence in the current forecast due to
increasing middle level cloudiness tonight. IFR to MVFR
conditions will spread into coastal terminals through 07Z and
valley terminals through 13Z, then lower to predominantly LIFR to
IFR conditions. Highest confidence in LIFR conditions exists for
terminals north of Point Conception, but there is a chance of LIFR
conditions for terminals south of the Point mainly between 05Z
and 16Z. There is a slight chance of thunderstorms, mainly after
06Z.

KLAX...Predominantly LIFR conditions will continue through at
least 16Z. There is a 20 percent chance of LIFR conditions
between 05Z and 16Z. There is a 10 percent chance of
thunderstorms after 06Z. Current forecast is optimistic for
scattering out on Saturday afternoon. There is a 40 percent chance
that KLAX could remain MVFR throughout the day.

KBUR...IFR conditions should spread into KBUR between 07Z and 13Z,
then linger until around 15Z before improving one category. VFR
conditions should develop between 16Z and 17Z. There is a 10
percent chance of thunderstorms after 06Z.

&&

.MARINE...23/900 AM.

Winds will remain below Small Craft Advisory levels through
Friday night across the outer waters, then gradually increase
through Monday. There is a 50 percent chance of Small Craft
Advisory level winds developing Saturday morning with a better
chance by the afternoon across the Outer Coastal Waters. Across
the Inner Waters, confidence is high there will not be any SCA
through the weekend. However there will be a 50-60% chance for
local gusts to 25 kt across the W portion of the SBA channel.

A 2-3 foot south swell at 16-17 second period will last through
Saturday and may pose a risk for breaking waves nearshore. People
boating or kayaking near shore should use extra caution.

Although the coverage of dense fog is easing a bit, there is still
a 40% chance of patchy dense fog during the night and mornings
through the weekend.

&&

.FIRE WEATHER...23/900 AM.

Hot and dry conditions will continue through Monday of next week.
The hot conditions will also bring the potential for plume
dominated fires which can create their own intense winds. Gusty
onshore winds will continue today focusing the concerns to
interior Los Angeles County. Weaker but locally breezy northwest
winds should follow Saturday through Monday...shifting the area of
concern to Santa Barbara County and the Tejon Pass.

Tropical moisture aloft will move through the area tonight and
Saturday. While this should have little impact on humidities at
the surface, this moisture is producing a small area of high-
based thunderstorms. If this feature persists, dry lightning will
be a major concern as an ignition source with little to no rain.

With such conditions, elevated fire weather concerns will persist
through Monday, especially over all interior sections away from
the influence of the marine layer. If fire ignition occurs,
dangerous fire behavior should be expected. As such, the public
should be extreme careful when handling potential ignition sources
such as cigarettes, campfires, hand torches and metallic weed
trimmers.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory in effect until 9 PM PDT Sunday for zones
      38-52>54. (See LAXNPWLOX).
     Beach Hazards Statement in effect through Saturday evening
      for zones 40-41-87. (See LAXCFWLOX).
     Excessive Heat Warning in effect until 9 PM PDT Sunday for
      zone 59. (See LAXNPWLOX).
PZ...NONE.

&&

.HAZARD POTENTIAL OUTLOOK...(MON-FRI)
No significant hazards expected.

&&

$$

PUBLIC...MW
AVIATION...Hall
MARINE...Sweet
FIRE WEATHER...Kittell
SYNOPSIS...STu

weather.gov/losangeles



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