209
FXUS66 KLOX 021631
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
931 AM PDT Tue Jul 2 2024

.SYNOPSIS...02/913 AM.

A significant heatwave will impact the region this week through
early next week, with dangerously hot temperatures across much of
the area. High temperatures by mid to late week are expected to
reach 95 to 105 degrees in many areas away from the coast, with
highs upwards of 105 to 115 over interior valleys and foothills,
including the Antelope Valley. Very warm to hot conditions could
extend closer to the coast by late this week. Patchy night to
morning dense fog will be possible near the coast tonight as well
as Wednesday and Thursday mornings.

&&

.SHORT TERM (TDY-THU)...02/931 AM.

***UPDATE***

No changes this morning and likely minimal changes with the
afternoon update as well. Forecast remains in tact with a
significant heat wave developing across our interior areas today
and spreading into the valleys and to a lesser degree for the inland
portions of the coastal areas Wednesday and Thursday. Models still
indicating a very strong upper high over the eastern Pacific
drifting slowly towards northern California and encompassing the
entire state by around Thursday and peaking in strength Friday
through the weekend. Of particular interest and concern is the
bubble of very hot air coupled with increasing northerly flow
across the Santa Ynez Range Friday evening. The 12z NAM shows
950mb temps of 40c at that time and coupled with adiabatic
processes could be even warmer at the surface. This is one area
where additional heat hazards, either a heat advisory or warning
may be needed.

***From Previous Discussion***

The eddy picked up a little more than expected and low clouds have
penetrated a little deeper into the vlys than was expected. The
increase in marine layer depth has eliminated the threat of dense
fog. Other than the more robust low cloud coverage the forecast is
on track with slight warming today followed by more aggressive
warming Wed and Thu.

This heatwave will be generated by a large and warm upper high
that will nose into the state from the west. Hgts over KLAX will
rise from 590 dam this morning to a near record 597 dam (since
1948 the highest 500 mb hgt over KLAX was 598 dam). At the same
time the offshore flow will weaken. The impressive hgts will
smoosh the marine layer down until it will only affect the near
shore area.

Look for 2 to 4 degrees of warming away from the coast today with
the coastal areas not showing much change. On Wednesday there will
be 3 to 6 degrees of warming everywhere followed 4 to 8 degrees of
warming for the csts and vlys Thursday as the marine layer
retreats to the beaches. On Thursday the inland coastal areas will
be 4 to 8 locally 10 degrees above normal while the vlys and
interior will be 10 to 15 degrees over normal.

In addition to the highs overnight lows will be uncomfortably warm
in the warm inversion zone (elevations ~800 to 1600 ft) where lows
will only reach the lowers 80s or upper 70s.

Heat warnings already cover the interior and most of the vlys
(and last until Monday) Heat advisories were added for the San
Gabriel Vly for Wed to Sun and the interior coastal sections for
Thu to Sun. Please see the product LAXNPWLOX for all the details
and precautions.

Winds through the short term should be typical onshore winds each
afternoon to evening period, affecting the interior passes and
canyons, and the Antelope Valley.

.LONG TERM (FRI-MON)...02/303 AM.

Friday will be the warmest day as onshore flow reaches a minimum
and hgts remain near 597 dam. Look for another 2 to 4 degrees of
warming with max temps 110-115 across the interior, 100 to 105 in
the vlys, 90s across the interior coastal sections and 80s at the
beaches. These max temps are 6 to 12 degrees above normal for the
csts and 12 to 18 degrees over normals for the vlys and interior.

The very warm overnight lows will continue as well.

Sundowner winds are possible across the SBA south coast Thu and
Fri evenings and overnight and if these do occur very warm
conditions will rapidly develop in that area with unusual daily
highs occurs during the evening.

Only minimal cooling is forecast over the weekend and all of the
heat warnings and advisories will continue through the period. A
steady increase in onshore flow will bring cooling first to the
csts and then into the vlys. The interior will not see much relief
at all as hgts remain very high.

Long range guidance does not show the upper high breaking down
much at all next week and this extended heat wave may push deep
into next week (esp inland)

The combination of these very hot temperatures, areas of low
humidities and possible sundowner winds will lead to fire weather
risks. Please see the fire weather discussion below for all the
details.

&&

.AVIATION...02/1624Z.

At 16Z at KLAX, the marine layer was 1700 feet deep. The top of
the inversion was at 3400 feet with a temperature of 24 Celsius.

High confidence in CAVU TAFs for KPRB, KPMD and KWJF.

Lower confidence in remainder of TAFs. Where low cigs continue
this morning, VFR transition could be 2-3 hours off, especially
KSBA, KOXR, KSMO and KLAX and there is a 10-20% chance of brief to
no clearing today. There will be a return to MVFR/IFR cigs/vsbys
near the coast again tonight into Wednesday morning, with onset
timing +/- 3 hours of current forecasts.

KLAX...Moderate confidence in TAF. There is a 10-20 percent chance
of no clearing today. No significant easterly wind component is
expected.

KBUR...Moderate to high confidence in TAF.

&&

.MARINE...02/311 AM.

For the Outer Waters, through Thursday, high confidence in winds
and seas remaining below SCA levels. For Friday and Saturday,
there is a 20-30% chance of SCA level winds.

For the Inner Waters north of Point Sal, through Saturday, high
confidence in winds and seas remaining below SCA levels.

For the Inner Waters south of Point Conception, high confidence in
current forecast. Through Saturday, winds and seas will remain
below SCA levels.

Patchy dense fog (with visibilities one nautical mile or less)
will continue to impact the coastal waters through the week. The
areal coverage of the dense fog will likely decrease each day,
especially after Wednesday or Thursday.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Excessive Heat Warning remains in effect until 6 PM PDT
      Monday for zones 38-343>345-353-376>379-381>383. (See LAXNPWLOX).
     Excessive Heat Warning remains in effect from 11 AM Wednesday
      to 6 PM PDT Monday for zones
      88-342-348-351-352-356>358-369>375-380. (See LAXNPWLOX).
     Heat Advisory in effect from 11 AM Thursday to 6 PM PDT
      Sunday for zones 341-347-355-368. (See LAXNPWLOX).
     Heat Advisory in effect from 11 AM Wednesday to 6 PM PDT
      Sunday for zone 548. (See LAXNPWLOX).
PZ...NONE.

&&

$$

PUBLIC...MW/Rorke
AVIATION...Cohen/Munroe
MARINE...Munroe/Phillips/RAT
SYNOPSIS...Cohen/Smith/MW

weather.gov/losangeles

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