Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000
FXUS66 KLOX 230619
AFDLOX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
1119 PM PDT Thu Jun 22 2017

.SYNOPSIS...
High pressure aloft centered over Southern Arizona will continue
warm conditions away from the coast into next week. Skies should
be fair, except for night through morning low clouds and fog
closest to the coast. A cooling trend should develop Tuesday as a
low pressure system off the California Coast will weaken the
upper-level dome of high pressure and increase onshore flow.

&&

.SHORT TERM...(THU-SUN)

The latest satellite imagery shows a ridge of high pressure over
Southern Arizona this evening and a weak trough of low pressure
off the California coast. Fog product imagery indicates a well-
entrenched stratus deck along the coast this evening and more
"June Gloom" looks on tap for Friday along the beaches. A cooling
trend will take shape over the area as onshore flow strengthens
into Friday. Some tweaks have been made to the forecast, mainly to
add better coverage of low clouds and fog for the Santa Ynez and
San Gabriel valleys and to add patchy drizzle south of point
Conception. A weak vorticity maximum moving north over the area
could produce some patchy drizzle late tonight and Friday morning
as it interacts with the marine layer stratus, lifts it, and
squeezes out very light precipitation.

The main wrinkle is the plume of convective debris over the Baja
California this evening. Model solutions do not have a great
handle on this feature this evening. Cloudiness has been increased
some, but Friday could have a bit more clouds than what the
forecast indicates. The forecast trends the direction of more
clouds, but the next shift will need to watch this feature for
possible development. With the dry air mass in place, higher
confidence is placed in a few middle and high level clouds moving
over the area on Friday, but there is a chance a bit more
cloudiness could exists and maybe a cloud build-up over the
mountains on Friday afternoon and evening.

An update will be issued shortly.

*** FROM PREVIOUS DISCUSSION ***

By late Friday into Saturday the low lvl flow is expected to
reverse as surface high pressure strengthens to the north. This is
expected to lead to a noticeable warming trend in most areas
Saturday along with some increase in north winds through the Santa
Ynez range and i5 corridor. These trends will continue into
Sunday which should be the warmest day of the period. Marine lyr
is expected to shrink in depth and areal coverage with clouds
mostly confined to the beaches north of pt conception and coastal
LA county. It`s possible the current heat advisory may need to be
expanded to cover some additional valley areas Saturday and/or
Sunday.

The NAM continues to show an increase in instability aloft
Saturday as some high level moisture and energy moves in from the
south. There are some decent lapse rates at very high levels but
the moisture is confined to 600mb and above. Not real confident in
this as the other models are much less unstable and don`t really
show much in the way of short wave features coming in from the
south. So for now will just indicate some high clouds moving in
Saturday but no thunderstorms. The main concern would be for dry
lightning given the lack of low lvl moisture but right now the
threat appears to be too minimal to include in the forecast.

.LONG TERM...(MON-THU)

Still very warm Monday but an increase in onshore flow should lead
to at least a few degrees of cooling for inland areas. Onshore
flow expected to increase a little each day through Thursday as a
series of troughs moves into the Pac NW. Confidence on the extent
of cooling beyond Tuesday is pretty low as models still show a lot
of differences with regard to how fast the high pressure ridge
will weaken and shift east. The GFS remains the coolest and
trending towards that solution for now.

&&

.AVIATION...

23/0600Z

At 0455Z at KLAX, the marine layer depth was near 1400 feet. The
top of the inversion was around 3300 feet with a temperature near
26 degrees Celsius.

Moderate confidence in TAFs. Flight Cat change times could be off
by +/- 1 hour. For terminals that have LIFR conds fcst here is a
30 percent chc that conds will remain IFR. Terminals that are
forecast to have no clearing may see some sct conds 22Z-01Z.

KLAX...Moderate confidence in TAF. There is a 30 percent chc of no
afternoon clearing. Very high confidence that there will not be an
east wind component over 5kt.

KBUR...Moderate confidence in TAF. There is a 10 percent chc that
clouds will not reach the terminal. MVFR cigs could remain until
1930Z.

&&

.MARINE...

22/900 PM.

Winds will remain below Small Craft Advisory levels through
Friday, then gradually increase through Monday. There is a 60
percent chance of Small Craft Advisory level winds developing as
soon as Friday night across the Outer Coastal Waters but more
likely Saturday and through the weekend. Across the Inner Waters,
there is a 30 percent chance of Small Craft Advisory level winds
developing each afternoon and evening through Saturday night,
then there is a better chance of Small Craft Advisory level winds
on Sunday afternoon and evening.

A 2-3 foot south swell will last through Saturday and may pose a
risk for breaking waves nearshore. People boating or kayaking near
shore should use extra caution. A small short-period swell will
impact the Santa Barbara Channel and Santa Monica Basin over the
weekend.

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

&&

.FIRE WEATHER...

22/200 PM.

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. Onshore
winds will peak today and Friday, which will focus the concerns to
interior Los Angeles County including the Angeles National
Forest, Highway 14 corridor, and the foothills of the Antelope
Valley. 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 Friday night and
Saturday. While this should have little impact on humidities at the
surface, this has a 10 percent chance of producing high-based
thunderstorms. Confidence is incredibly low with this, but the
potential for dry lightning exists.

A Red Flag Warning is in effect through 9PM this evening for
the interior Los Angeles County Mountains and Foothills and will
not be extended. With rapidly drying fuels/vegetation however,
elevated fire weather concerns will persist through Monday,
primarily 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
      38-52-53. (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
      zones 54-59. (See LAXNPWLOX).
PZ...NONE.

&&

.HAZARD POTENTIAL OUTLOOK...(SUN-THU)
Hot temperatures with potential heat impacts will continue for
inland areas Sunday.

&&

$$

PUBLIC...Hall/MW
AVIATION...Rorke
MARINE...Hall
FIRE...Kittell
SYNOPSIS...Hall

weather.gov/losangeles



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