137
FXUS66 KLOX 291308
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
608 AM PDT Sat Jun 29 2024

.SYNOPSIS...29/450 AM.

A general warming trend will establish across the area through
next week as high pressure aloft strengthens over the region. Warm
temperatures over the area this weekend will likely turn
dangerously hot across the interior toward the middle of next
week. Near record heat is possible between Independence Day and
Saturday, especially across the mountains and desert. A hot air
mass could linger into next weekend.

&&

.SHORT TERM (TDY-MON)...29/458 AM.

Low clouds and fog are well-entrenched across the coast and lower
coastal valleys this morning as moderate onshore flow remains in
place. Stronger onshore pressure gradients brought some cooling
on Friday, which led to more cloud coverage across the area last
night and into this morning. While the coastal areas will see
temperatures closer to persistence today, a warming trend will
develop outside the marine influence as 500 mb heights climb
across the region through the weekend.

Earlier AMDAR soundings from KLAX indicated the marine layer
depth around 950 feet deep around midnight, which did agree well
NAM BUFR time height sections. If the NAM BUFR time heights
section played out as progged, the marine layer depth has likely
deepened to close to 2000 feet deep at KLAX. This is partially due
to the influence of weak troughing to the northwest of the area
and the eddy circulation still intact across the southern
California bight. Actually, several eddy vortices can be seen on
satellite early this morning, including one into the Santa Barbara
Channel.

Clouds could struggle to clear from the beaches today, but with
the high pressure building in, the marine layer depth will shrink
and thin rapidly throughout the late morning hours. Outside of the
marine intrusion, the air mass will heat up across the region.
EPS, GEFS, and CMC ensemble members solutions suggest a steady
warming trend taking shape through Sunday. Closer to the coast due
to the persistent marine layer depth, the warming trend will be a
bit more muted, with less warming likely taking place.

With the marine layer turning more shallow through tonight and
into Sunday morning, there is a moderate-to-high chance that any
low clouds and fog could form dense fog across the coastal areas.
High-resolution multi-model ensemble members suggest a 40-50
percent chance of dense fog developing along the Central Coast and
into the Los Angeles County beaches by daybreak Sunday.

By Monday, the upper-level ridge of high pressure over north Texas
this morning will push a bit to the east and allow for a weak
upper-level trough over the North Pacific to drop into the Pacific
Northwest. This trough should bring slight height falls and an
increase in onshore flow. As a result, low clouds and fog could
become more pronounced on Monday or Monday night, and the warming
trend should level off, or maybe see a degree or two of cooling
across the area.

.LONG TERM (TUE-FRI)...29/457 AM.

High pressure aloft will quickly lift the trough out of the region
and build into the region from the west. Strong ridging over the
North Central Pacific Ocean will build into the state through
Friday. While there is still quite a large spread in the model
solutions over how warm it will get and the strength of the high,
the forecast ensemble members favor a very warm to hot air mass on
Tuesday turning much hotter by Friday. Temperatures break away
from NBM values in the extended period to advertise near record
heat between Independence Day and Saturday. Record heat is
introduced for Friday in the latest forecast with forecast
temperatures of 111 degrees at Paso Robles and 114 degrees at
Palmdale and Lancaster, with daily record values at 110 and 113
degrees respectively. While the hottest temperatures and highest
likelihood of record high temperatures will be for the interior
portions of the area, it should be noted that Woodland Hills
Pierce College has a lower record high for July 5th. The record
high for Pierce College is 105 degrees on July 5th, bookended by
a 112 degree record high on July 4th and a 116 degree record high
on Saturday, July 6th. The forecast currently advertises a tie of
the record high for July 5th, but there is a moderate chance that
this record could be broken.

With the near record high temperatures expected and very warm
overnight low temperatures forecasted, an Excessive Heat Watch
remains in effect for the interior portions of the area as
dangerously hot weather could develop causing heat stress and a
higher likelihood of heat illness for anyone planning outdoor
activities.

The forecast keeps some semblance of a low clouds field near the
coast into late week, but there is a moderate chance that low
clouds and fog could be very patchy in nature given the high
pressure center location. If any monsoonal moisture sneaks in from
the southeast, the low cloud field could become non-existent as
the clouds aloft will play tricks on the marine inversion.

The latest EPS ensemble precipitable water value means continue
to trend higher in the latest runs with the potential for
monsoonal moisture. EPS PWAT means now exceed above 1.00 inch
between Wednesday and Thursday. There are handful solutions
offering a higher spread into the weekend and into early next
week. Any increase in cloud cover could put a damper of excessive
heat developing, especially if a thick cloud shield develops and
cuts into temperatures. Though unlikely at this time, very slight
chance PoPs remain in the forecast for each afternoon and evening
from Wednesday through Friday across the interior portions of the
area. As the forecast ensembles are at the mercy of convective
parameters working as advertised, it is a low confidence but high
impact type scenario. Stay tuned at this could become a wrinkle
in the forecast.

&&

.AVIATION...29/1306Z.

At 12Z at KLAX, the marine layer was 1700 feet deep. The top of
the inversion was at 4000 feet with a temperature of 22 C.

High confidence in VFR conditions for KPRB, KPMD, and KWJF, and
fairly high confidence in VFR conds at KBUR and KVNY.

Otherwise, low clouds were widespread in all coastal areas, with
clouds also in the lower valleys. Conds were mostly LIFR to VLIFR,
except IFR to locally very low MVFR on the L.A. County coast.
Skies should clear by mid morning in the valleys and late morning
on most of the coastal plain. Cigs could linger at some beaches
into the afternoon, but most likely will not.

Expect widespread low clouds and fog in most coastal areas
tonight with generally LIFR to VLIFR conds expected.

KLAX...Moderate confidence the 12Z TAF. There is a 30% chance that
IFR conds will not rise into the MVFR category this morning. There
is a 20% chance that cigs will not scatter out until 19Z-20Z.
There is a 20% chance that cigs will not arrive tonight until at
least 11Z.

KBUR...High confidence in the 12Z TAF with VFR conditions thru
the period. least 11Z. There is a 10% chance of IFR ceilings
from 14Z-16Z this morning.

&&

.MARINE...29/552 AM.

Areas of dense fog (with visibilities one nautical mile or less)
will likely affect a good portion of the coastal waters this
morning, possibly lingering into the afternoon. Dense fog is a
good possibilty again late tonight and Sunday morning.

In the outer waters, high confidence that Small Craft Advisory
(SCA) level NW winds will spread from north to south across the
area tonight, beginning into the northern zone (PZZ670) by mid
evening. SCA level winds and seas will continue thru at least late
Mon night in most of the outer waters. There is a 40% chance of
Gale Force winds in the northern two zones (PZZ670/673) Sun
afternoon thru late Sun night, and a 20% chance in the southern
zone (PZZ676). There is a 20% chance of gales in the northern two
zones Mon afternoon/eve. Mostly light winds are expected Tue thru
Wed night, though seas could be close to SCA levels Tue.

In the inner waters N of Pt. Sal, SCA conds are likely (70% chance)
during the afternoon/eve hours Sun/Mon. Seas may stay at or above
SCA levels Sun night/Mon morning when winds drop below SCA levels.
Winds are expected to be rather light Tue thru Wed night.

In the inner water S of Pt. Conception, there is a 60% chance of
SCA level winds across western portions of the Santa Barbara
Channel Sun evening, and a 30-40% chance late Mon afternoon/eve.
Otherwise, SCA conds are not expected thru Wed night.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Excessive Heat Watch in effect from Tuesday morning through
      late Friday night for zones
      38-88-343>345-353-376>379-381>383. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect from 9 PM this evening to 3 PM
      PDT Sunday for zone 670. (See LAXMWWLOX).
     Gale Watch in effect from Sunday afternoon through late
      Sunday night for zones 670-673. (See LAXMWWLOX).
     Small Craft Advisory in effect from 3 AM to 3 PM PDT Sunday
      for zone 673. (See LAXMWWLOX).
     Small Craft Advisory in effect from 3 AM Sunday to 3 AM PDT
      Tuesday for zone 676. (See LAXMWWLOX).

&&

$$

PUBLIC...Hall
AVIATION...DB
MARINE...DB
SYNOPSIS...Hall

weather.gov/losangeles

Experimental Graphical Hazardous Weather Outlook at:
https://www.weather.gov/erh/ghwo?wfo=lox