155
FXUS66 KLOX 300621
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
1121 PM PDT Sat Jun 29 2024

.SYNOPSIS...29/855 PM.

A significant heatwave will impact a large part of the area for
the upcoming week. Temperatures will become dangerously hot
across interior areas, where daily highs up to 100 to 105 degrees
will be possible, with highs upwards of 105 to 115 possible over
interior valleys and foothills including the Antelope Valley. Late
in the upcoming week, temperatures could reach records at some
locations, and very warm to hot conditions could extend closer to
the coast. Also, areas of night and morning dense fog will be
possible near the coast this weekend and into early parts of the
upcoming week.

&&

.SHORT TERM (SAT-TUE)...29/853 PM.

Slight warming trend occurred today across the interior with many
locations climbing well into the 90s. Midlevel heights will
continue to rise on Sunday and continue through the upcoming
week, as an upper- level ridge builds westward from the south-
central states. This will continue supporting a warming trend into
the upcoming week. On Sunday, high temperatures are expected to
have warmed to the 90s in most inland areas, 100-105 over the
Antelope Valley, and the 70s near the coast. More significant
warming is expected early in the upcoming week, with Tuesday high
temperatures warming to 95-105 degrees in most inland areas,
105-110 over the Antelope Valley, and the middle 70s to the middle
80s near the coast. The Excessive Heat Watch for interior areas
for the significant and long duration heatwave begins on Tuesday.
This long duration heat wave will also bring an extended period
of elevated to brief critical fire weather conditions across
interior areas through much of next week (please see Fire Weather
Planning Forecast discussion for more details on this upcoming
fire weather threat).

Local surface pressure gradients will remain moderately onshore.
This overall pattern will maintain night and morning low clouds
and fog across mostly coastal areas, scattering out and clearing
in most areas during the afternoon. With the continued rising
heights over the region, there will be a tendency for the marine
layer to become increasingly shallow and favorable for dense fog
development. Coastal areas and some coastal valleys will have the
potential to experience dense fog tonight into Sunday morning, and
again during subsequent overnight and morning hours. As of 830 pm
this evening, already seeing a few coastal locations have
visibilities lower to around 1 mile.

Otherwise, dry conditions are expected into the upcoming week.
Gusty southwest to northwest winds are expected each afternoon
over interior areas, and strongest -- upwards of 35-45 mph -- over
the Interstate-5 corridor as well as the Antelope Valley and
nearby foothills. However, the issuance of Wind Advisories is
currently unlikely.

.LONG TERM (WED-SAT)...29/152 PM.

Dangerously hot conditions are expected to continue over the
region through the upcoming week, as an upper-level anticyclone
builds offshore and expands eastward over California. Medium-range
model guidance continues to suggest 500-mb heights rising to
around 596-600 dam to the north of the area by late in the
upcoming week. This should correspond to daily high temperatures
up to 100 to 105 possible in many areas away from the coast, with
highs upwards of 105 to 115 possible over interior valleys and
foothills including the Antelope Valley. Warm overnight low
temperatures will worsen the effects of extreme heat, with lows
not falling below 80 degrees at some locations over interior
valleys and nearby foothills. The Excessive Heat Watch continues
for a large portion of the region away from the coast through
late in the upcoming week, when temperatures could reach records
at some locations.

In addition, very warm to hot conditions will have the potential
to bring significant heat impacts toward the coast, starting on
Wednesday and continuing through the remainder of the upcoming
week. This would occur as the marine layer becomes increasingly
shallow and retreats toward the coast provided the rising heights
aloft, which could also eventually limit the chances for night
and morning dense fog. Heat headlines may need to be expanded to
include a larger portion of Southern California in later
forecasts.

Present indications are that precipitation will be unlikely
(below 20% chance) through late in the upcoming week. However,
given how hot and strongly mixed the boundary layer will be over
interior sections during latter parts of the week, any low-
predictability monsoonal moisture influx south of the midlevel
ridge axis could introduce chances for showers or thunderstorms
over higher terrain. Chances are too low for mention in the
forecast at this time, though this scenario will continue to be
monitored.

&&

.AVIATION...30/0620Z.

At 06Z at KLAX, the marine layer was 800 feet deep. The top of
the inversion was at 2200 feet with a temperature of 26 Celsius.

High confidence in VFR conditions through the TAF period at KPRB
KBUR KVNY KWJF KPMD. High confidence in lower ceilings and
visibility with less low cloud coverage tonight compared to last
night with inland coastal TAFs (i.e. KSMX & KCMA) has already
showed signs of at least intermittent return to VFR cigs through
15Z. Low confidence in return to VFR which may be off by 3 hours.
There is a 10-20 percent chance of brief to no return to VFR at
west facing coastal TAFs of KLAX, KSMO, and KOXR with 40-50
percent chance of return to IFR or lower cigs vsbys between
02-06Z, should they at least briefly clear.

KLAX...Low confidence in TAF. There is a 10 percent chance of a
few hours of VLIFR dense fog. The return to VFR is likely (80
percent chance) in the 16-20Z range with a 10-20 percent chance
of only a brief to no return to VFR. High confidence in any east
wind component remaining under 6 kt.

KBUR...High confidence in VFR conditions through the TAF period.

&&

.MARINE...29/735 PM.

Dense fog (with visibilities one nautical mile or less) will
threaten all waters through at least Sunday. There is a 40 percent
chance that the fog will clear later tonight over Santa Barbara
and San Luis Obispo Counties as the northwest winds increase.
Any fog that forms for the remainder of the week will likely be
dense, but expecting the coverage to shrink a little each day.

High confidence in northwest winds increasing quickly tonight
into Sunday and lasting through Monday Night. For the offshore
waters from the Central Coast to Point Conception, There is a 80%
chance of Gales by Sunday afternoon and night, and a 30% chance on
Monday. Otherwise, high confidence in at least Small Craft
Advisory winds from the Central Coast to San Nicolas Island. There
is a 20% chance of these winds pushing deep enough into the Santa
Barbara Channel to need a Small Craft Advisory, but the more
likely outcome is for those winds to stay confined to the far
western portion. As a result of these winds, expect building
choppy seas over most waters, even those areas that are not very
windy.

Moderate confidence for abnormally light winds Tuesday through
Wednesday. Winds will likely increase steadily starting Thursday
afternoon through Saturday, but the chance for any Gales during
that period is very small.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Excessive Heat Watch remains 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 2 PM Sunday to 6 AM PDT
      Monday for zone 645. (See LAXMWWLOX).
     Small Craft Advisory in effect until 2 PM PDT Sunday for
      zones 670-673. (See LAXMWWLOX).
     Gale Warning in effect from 2 PM Sunday to 6 AM PDT Monday
      for zones 670-673. (See LAXMWWLOX).
     Small Craft Advisory in effect from 2 PM Sunday to 3 AM PDT
      Tuesday for zone 676. (See LAXMWWLOX).

&&

$$

PUBLIC...Cohen/Gomberg
AVIATION...Munroe
MARINE...Kittell/Sirard
SYNOPSIS...Cohen

weather.gov/losangeles

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