208
FXUS66 KLOX 060427
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
927 PM PDT Fri Jul 5 2024

.SYNOPSIS...05/857 PM.

A long-lasting and extreme heatwave will continue across the
region, and especially the interior, through much of next week.
There is a high risk for dangerous heat illness and fast-growing
fires. High temperatures will reach 95 to 105 degrees in many
areas away from the coast, and 105 to 115 across interior valleys
and mountains. All-time records will be threatened. Dense fog may
develop across some beaches during the night and morning hours.

&&

.SHORT TERM (TDY-MON)...05/927 PM.

***UPDATE***

There were some impressive high temperatures today from SLO County
to LA County, perhaps the most notable being Saugus at 118.
Official temperature records are kept there so it`s unknown if
that was an all-time record or not. In fact, the entire Santa
Clarita Valley was exceptionally hot today as the entire valley
was anywhere from 112-118. The expected northerly flow did develop
earlier today and that was certainly a contributing factor there.
Farther south in the San Fernando Valley temperatures were hot as
well but not close to the what the Santa Clarita Valley
experienced, likely because the northerly flow just didn`t reach
down that far in elevation, though in the Chatsworth area highs
did reach around 109, and 106 at Woodland Hills Pierce College.

Still monitoring the northerly flow this evening across the Santa
Ynez Range down into the south coast areas. It`s still quite hot
in the foothills with temperatures around 100 at 9pm at 1500 feet
elevation on San Marcos Pass and throughout all the coastal
foothills there. Could still see some of that heat filter down
towards the coast over the next few hours but it looks like for
the most part it will stay elevated.

00z models continue to indicate significant cooling at lower
elevations tomorrow and again Sunday with a strong onshore trend
in the afternoon. Most valley areas expected to cool by 3-6
degrees Saturday, which still keeps most of those areas high 90s
to around 105. With a reversal of the low level from north to
south Saturday, places like the Santa Clarita Valley should see
even more cooling, but should still top out in the 100-110 range.
So despite the cooling, it should be emphasized that these
temperatures are still extremely hazardous to those outdoors.

Additional cooling expected Sunday and based on the heat risk
calculations most of the coast and coastal valleys may be at a
much lower risk level by Sunday. Some consideration may have to
given to possibly ending the heat hazards on Saturday based on the
current forecast for Sunday. However, a warming trend is expected
again early next week as onshore flow weakens so there are still
some very hot days in the near future.

***From Previous Discussion***

The long lasting and extreme heat wave continues, peaking through
Saturday. This is a dangerous situation with all the ingredients
for a high risk of heat-illness and fast growing fires. PLEASE
avoid hiking in the mountains and the hills through this weekend,
make plans on how you will stay cool in the afternoon and evening
hours, and stay away from anything that could spark a fire.

A 595-98 decameter upper level high pressure system will dominant
the west coast through most of next week. The high is currently
centered over northwest California, which is in a position
favorable for causing the near neutral onshore pressure gradients
that we saw today, and the shift to northerly for the north-to-
south gradients. Any of those three ingredients alone would heat
things up, but when they all happen together we are in extreme
territory. Many valley and mountain areas are already near to or
exceeding 100 degrees, with the Santa Clarita Valley hovering
around 115 (no official records available for that location). The
extreme heat is also causing a deep mixing/boundary layer which
has allowed for some fair weather cumulus clouds over the
mountains but will not be a convection threat. Near the coast, a
shallow but persistent marine layer remains, and does not look to
be going anywhere. As a result, the immediate coastal areas will
be closer to mild than hot, but the temperatures will ramp up
quickly for every mile inland of the beach. With the shallow
marine layer, dense fog will remain a concern especially with the
lingering smoke particles in the air from all the firework
activity.

The high will gradually slide into southeast California through
Monday. As a result, the northerly shift in the flow from today
will transition to more onshore Saturday afternoon through Sunday
or Monday. On the COASTAL side of the mountain ranges, this shift
will bring a much earlier than usual daytime peak in temperatures
(closer to 10am than the afternoon) as a less hot air mass over
the ocean pushes in. While it will still be hot Saturday and
Sunday, will not be as hot as today and the trends should be going
down. The marine layer should also expand a little as well. As a
result, decided to pull the end time of the Heat Warnings and
Advisories back a day to Saturday or Sunday (depending on your
location)...and they back need to all be pulled back to Saturday.
Over the INTERIOR mountains and valleys/deserts, this shift will
do very little. In fact, with the shift of the core of the high
moving closer, Saturday very well could be the hottest day of the
event for the furthest interior areas, with Sunday still hot but
down a few degrees with the peak of the onshore flow. As such, did
not touch the Heat Warnings for those locations.

Many calendar day records are expected to be broken today. All-time
records (for any calendar day) could break on Saturday at
Palmdale, Lancaster and Paso Robles.

.LONG TERM (TUE-FRI)...05/213 PM.

The upper level high, centered over southeast California on
Monday, is poised to meander northwest into Nevada Tuesday through
at least Thursday. This will cause the strength of high pressure
over southwest California to drop a bit, resulting in a few
degrees drop in the temperatures over the mountains and interior
(still very hot). This will also cause the onshore flow to weaken
once again (similar to today but likely not to this magnitude). As
a result, coastal and valley areas will likely trend hotter again.
While there is a range in the ensemble projections, most push
temperatures inland of the beaches back up to about 5 degree below
today and tomorrows temperatures. On top of that, northwest winds
will increase, especially over southwest Santa Barbara County,
which will further warm it up. So the morale of the story is that
this heat wave may not be done with us just quite yet.

&&

.AVIATION...06/0023Z.

At 00Z at KLAX, the marine layer was 900 feet deep. The top of
the inversion was at 3200 feet with a temperature of 37 deg C.

High confidence in 00Z CAVU TAFs for KPRB, KBUR, KVNY, KPMD, and
KWJF.

Moderate confidence in the rest of the coastal 00Z TAFs. There is
a 30% chance that KSBP reaches IFR conditions due to uncertainty
of cig/vsby arrival. There is a 20% KSMX remains MVFR throughout the
forecast period. All other coastal sites should reach IFR/LIFR
conditions tonight, clearing around midday. Arrival and
dissipation of cigs/vsbys may be off +/- 2 hours.

KLAX...Moderate confidence in the 00Z TAF. There is a 30% chance
that cigs may arrive as early as 04Z. There is a 20% that VLIFR
conditions may occur in the period after 10Z through 14Z. Cigs/vsbys
are expected to improve to at least MVFR conditions around 15Z.
No significant easterly component of the wind expected in the
forecast period. Arrival and disspation of cigs/vsbys may be off
+/- 2 hours.

KBUR...High confidence in the 00Z TAF. VFR conditions should
prevail for most of the forecast period. However, there is a 10-20%
chance of MVFR conditions due to decreased vsbys in the morning.

&&

.MARINE...05/803 PM.

In the Outer Waters, Small Craft Advisory (SCA) level winds will
continue in the southern zones (PZZ673/PZZ676) thru Sat morning.
In the northern zone (PZZ670), SCA conds are likely (70% chance)
this afternoon thru Sat morning. For the most part, expect winds
to remain below SCA levels Sat afternoon thru Wed night except for
a 50% chance of SCA level wind gusts at times Sunday night. There
is also a 30% chance of SCA level NW winds in the far outer
waters and from near Pt. Conception to NW of San Nicolas Island,
especially during the late afternoon thru late evening hours.

For the Inner Waters N of Pt. Sal, conditions have subsided below
SCA levels. There is a 30% chance of SCA level winds Sat
afternoon/eve, otherwise SCA conds are not expected Sat night thru
Wed night.

For the inner waters south of Pt Conception, SCA conditions are
not expected through Monday. SCA winds will be possible Tuesday
evening in western portions of the Santa Barbara Channel, mainly
from Santa Cruz Island to the SBA County south coast from Pt.
Conception to Gaviota to Refugio State Beach. Otherwise, conds
will be below SCA levels for the southern inner waters thru Wed
night.

Areas of dense fog will affect portions of the coastal waters
tonight into Sat morning. Please reference the Marine Weather
Statement for additional information.

&&

.BEACHES...05/115 PM.

A moderate southerly swell will affect the Southern California
coastal waters through Sunday, with a 15-17-second period this
weekend. While surf is not expected to be particularly high, surf
heights of up to 4 to 6 feet are anticipated at beaches exposed
to southerly swell, especially the LA and Ventura County beaches.

The significant wave energy with the long-period swell will
combine with the elevated surf to create dangerous conditions at
area beaches, with powerful and dangerous rip currents expected.
This is especially the case for the south-facing beaches of LA
and Ventura Counties. A Beach Hazards Statement is in effect
through the weekend to address these concerns.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Excessive Heat Warning now in effect until 9 PM PDT Wednesday
      for zones 38-343>345-353-376>379-381>383. (See LAXNPWLOX).
     Excessive Heat Warning now in effect until 9 PM PDT Sunday
      for zones 88-342-348-351-352-356>358-369>375-380. (See LAXNPWLOX).
     Heat Advisory now in effect until 9 PM PDT Saturday for zones
      341-347-355-367-368. (See LAXNPWLOX).
     Excessive Heat Warning now in effect until 9 PM PDT Saturday
      for zones 349-350. (See LAXNPWLOX).
     Wind Advisory remains in effect until 3 AM PDT Saturday for
      zones 349-351. (See LAXNPWLOX).
     Beach Hazards Statement in effect through Sunday evening for
      zones 354-362-366. (See LAXCFWLOX).
     Heat Advisory now in effect until 9 PM PDT Sunday for zone
      548. (See LAXNPWLOX).
     Red Flag Warning in effect until 6 AM PDT Saturday for zones
      342>345-349-351>353-376-377. (See LAXRFWLOX).
     Red Flag Warning in effect until 6 AM PDT Monday for zones
      378-381. (See LAXRFWLOX).
PZ...Small Craft Advisory in effect until 3 AM PDT Saturday for
      zones 645-670. (See LAXMWWLOX).
     Small Craft Advisory in effect until 9 AM PDT Saturday for
      zones 673-676. (See LAXMWWLOX).

&&

$$

PUBLIC...MW/Kittell
AVIATION...Lewis
MARINE...Sirard/Lewis/Smith
BEACHES...Sirard
SYNOPSIS...MW

weather.gov/losangeles

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