369
FXUS66 KLOX 301605
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
905 AM PDT Sun Jun 30 2024

.SYNOPSIS...30/217 AM.

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 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 today and early next week.

&&

.SHORT TERM (TDY-TUE)...30/905 AM.

***UPDATE***

Surface observations indicate that fog is dissipating across the
region. Therefore, the Dense Fog Advisory has expired. However,
patchy fog will continue through the late morning near the coast.
The forecast has been updated to reflect the expiration of the
Dense Fog Advisory. Otherwise, no changes have been made to the
ongoing forecast.

***From Previous Discussion***

AMDAR soundings out of KLAX show the marine layer at 900 ft deep.
There is only light onshore flow and no eddy so there is not that
much inland penetration and the vlys will remain clear. The marine
layer is shallow enough that there will be pockets of dense fog.
The capping inversion in rather strong (rising 10 degrees C in 600
ft) and this along with a strong 8 mb onshore push to the east
this afternoon will likely keep some beaches cloudy all day. The
marine layer has shrunk 600 ft since ydy and this means no cool
air for the vlys. This and 2 dam of hgt rises will bring 3 to 6
degrees of warming to most areas except, perhaps, the beaches.
This will bring most max temps away from the coast to 4 to 8
degrees above normal.

A weak trof will move over the state on Monday. The slight lift
from this trof will deepen the marine layer and allow for some of
the low clouds to reach the vlys. The deeper marine layer will
also eliminate the threat of dense fog. Sightly lower hgts and
the deeper marine layer will combine to 2 to 5 degrees of cooling
to most of the area.

A dangerous and long duration heat wave will begin on Tuesday as very
warm east Pac upper high noses into the state. Hgts will rise to
592 dam. There will still be onshore flow at the sfc but it will
be weaker than on Monday. The marine layer will again be squashed
down to under a 1000 ft keeping it out of the vlys. Most areas
away from the beaches will see 2 to 5 degrees of warming. An
exception being western SBA county where much weaker onshore flow
will allow for about 6 degrees of warming. All of the vlys will
record highs in the 90s while the far interior, lower mtn
elevations and the Antelope Vly will all see triple digit heat
(The AV the warmest with max temps 104 to 107 degrees)

An Excessive Heat Watch for interior areas for the significant
and long duration heatwave begins on Tuesday Please see the
product LAXNPWLOX for details.

Hot temperatures and low humidities will combine to bring
increased fire danger to the interior (please see Fire Weather
Planning Forecast discussion for more details).

In addition, gusty west to northwest winds are expected each
afternoon over most of the interior areas. The strongest gusts (35-45
mph) will occur over the I-5 corridor and the western Antelope
Valley/foothills. These gusts will come in just under wind
advisories criteria.

.LONG TERM (WED-SAT)...30/414 AM.

Both the GFS and the EC along with their respective ensembles are
in very good agreement and there is high confidence that
dangerous heat wave will grow and peak during the extended period.

The very warm east Pac high will push further into the state and
hgts will peak at 597 dam which is in the 97th percentile of hgts
for July. While the anticyclonic flow around the upper high will
bring some offshore winds at higher levels moderate to strong
onshore flow will continue at the sfc. This will spare the coasts
from the most serious of the heat. The marine layer will likely be
squashed to under 600 ft by the hgts and this will allow the
coastal sections furthest from the beaches to warm significantly.

Look for 3 to 6 degrees of warming Wed, 2 to 4 degrees Thu and
then another 3 to 6 degrees on Friday which will be the peak of
the heat before 2 to 4 degrees of cooling occurs Sat.

On Friday Look for many readings from 100 to 106 degrees in the
vlys. The lower elevations of the mtns and the far interior will
see max temps from 110 to 115 degrees. These max temps are 12 to
18 degrees above normal.

Very warm overnight low temperatures (esp in the warm sector of
the inversion 800 to 1200 ft elevation) will worsen the effects
of extreme heat. Some locations in this heat bad will not see
temps fall below 80 degrees. The Excessive Heat Watch continues
for a large portion of the region away from the coast through late
Friday and may need to be extended into the weekend.

Even though they are not included in the watch the interior
coastal sections may well need Heat Advisories issued on Thursday
and Friday as the marine layer shrinks until it is too shallow to
provide much relief to the portion of the coast not in the near
shore area.

Night through morning low clouds will continue through the period
driven ashore by moderate to strong onshore flow. The marine
layer will be so shallow and capped by such a strong inversion
that some beaches may stay cloudy through the period or at least
the bulk of it.

Afternoon convection looks unlikely but there is a non zero but
less than 10 percent chc that some monsoon moisture could creep in
and trigger a round of showers/tstms.

&&

.AVIATION...30/1113Z.

At 07Z at KLAX, the marine layer was 900 feet deep. The top of
the inversion was at 2600 feet with a temperature of 26 Celsius.

High confidence in VFR conditions through the TAF period at KPRB
KBUR KVNY KWJF KPMD.

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. There is a 20-40
percent chance that coastal TAFs (except 10-20 percent KSMX) have
prevailing VFR cigs and MVFR/VFR vsbys after 03Z. One plausible
(30-40 percent chance) scenario for KLAX KLGB KSMO is for an
early return (03Z-06Z) of low LIFR/IFR cigs/vsbys and subsequent
early (12-15Z) clearing.

KLAX...Low confidence in TAF. 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. There is a 30 percent chance
that VFR cigs/vsbys prevail after 03Z. There is also a 30 percent
chance of an early return (02Z-05Z) and clearing (12Z-15Z) of low
cigs/vsbys. High confidence in any east wind component remaining
below 6 kt.

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

&&

.MARINE...30/737 AM.

For the Outer Waters, moderate to high confidence in current
forecast. Today through Monday night, high confidence in Small
Craft Advisory (SCA) level winds from San Nicolas Island
northward. For the waters north of Point Conception (PZZ670/673),
there is a 60-70% chance of Gale force winds this afternoon and
tonight and a GALE WARNING remains in effect. For Tuesday through
Thursday, high confidence in winds and seas remaining below SCA
levels.

For the Inner Waters north of Point Sal, moderate to high
confidence in current forecast. Today through Monday, there is a
50-70% chance of SCA level winds in the afternoon and evening
hours. For Tuesday through Thursday, high confidence in winds and
seas remaining below SCA levels.

For the Inner Waters south of Point Conception, moderate to high
confidence in current forecast. For the western half of the Santa
Barbara Channel, there is a 40-50% chance of SCA level winds this
afternoon/evening and a 20-30% chance of SCA level winds Monday
afternoon/evening. Otherwise, high confidence in winds and seas
remaining below SCA levels through Thursday across the Inner
Waters south of Point Conception.

Dense fog (with visibilities one nautical mile or less) will
threaten all waters through at least tonight. 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 as associated low cloud coverage gradually diminishes.

&&

.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 this afternoon to 6
      AM PDT Monday for zone 645. (See LAXMWWLOX).
     Gale Warning in effect from 2 PM this afternoon to 6 AM PDT
      Monday for zones 670-673. (See LAXMWWLOX).
     Small Craft Advisory in effect from 2 PM this afternoon to 3
      AM PDT Tuesday for zone 676. (See LAXMWWLOX).

&&

$$

PUBLIC...Rorke/Cohen
AVIATION...Munroe
MARINE...RAT
SYNOPSIS...Cohen

weather.gov/losangeles

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