263
FXUS66 KLOX 030634
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
1134 PM PDT Tue Jul 2 2024

.SYNOPSIS...02/126 PM.

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 (TUE-FRI)...02/827 PM.

***UPDATE***

Low clouds and some dense fog were along much of the immediate
coast early this evening. these low clouds will expand to all
coastal areas overnight, with some inland penetration to the lower
coastal vlys. There is a strong and low inversion over the area
this evening (around 900-1000 ft) which will help to develop at
least patchy dense fog where there is low clouds. There is a
chance the dense fog could have a larger aerial extent overnight
which would lead to the issuance of a Dense Fog Advisory.
Otherwise and elsewhere, mostly clear skies can be expected thru
the night.

Upper level ridging will continue nosing into southern CA from
the E Pac overnight where a strong 597-598 dam H5 high will be
parked about 700 miles NW of Point Conception. This upper level
ridging was helping to promote the strong and shallow marine
inversion. A large warm layer was noted in the VBG sounding and
the LAX ACARS soundings at around 2500-5000 feet or so with temps
in the upper 70s to low 80s.

As a result of the warm layer in the soundings, low temperatures
tonight should be quite warm for some of the inland vlys, as well
as the foothills and lower mtns. Temps are expected to fall only
into the 70s for much of this area, with near 80 possible in the
lower mtns and deserts.

***From Previous Discussion***

High pressure across the eastern Pacific continues to slowly creep
toward the West Coast. While onshore flow and night and morning
marine layer stratus is still keeping coast and valley areas on
the milder side, inland areas have started to heat up. Interior
areas are showing temperatures trends up 5-10 degrees today and
expecting that trends to continue through the week. Coastal
valleys will start noticing the warmup Wednesday as the high
starts to compress the marine layer and confine it to the coastal
areas at most. And by Thursday and Friday the warming trend will
include the coastal areas as well as onshore flow weakens in
response to increasing subsidence from the near 600dam high that
by then will be centered over northern California, but
encompassing the entire western third of the US. Highs across our
far interior areas like the Antelope Valley,interior SLO County,
and the lower mountain elevations will see highs between 108-116,
15-20 degrees above normal. Warmer coastal valleys expected to
reach as high as 107-109. Expecting many high temperature records
this weekend, though possibly more on Friday as Saturday`s records
are quite a bit warmer due to a heat wave in 2018 that saw
Woodland Hills reach 116 and Downtown LA reach 108.

The biggest adjustments to the forecast today include the addition
of Excessive heat warnings for the south coast of Santa Barbara
County and a Fire weather watch for portions of the interior
(addressed in the fire weather section). Models continue to
advertise an impressive amount of heat along with low grade
Sundowners Thu-Sat across southern Santa Barbara County, though
mostly Friday and Saturday. The NAM is showing temperatures as
high as 40c (104F) at 950mb in the Santa Ynez Range Friday night.
For the time being gradients thankfully are not excessive, but
enough to bring some wind over and down the coastal slopes of the
SY Range. Given these conditions chances are increasing that much
of southern SB County will see temperatures in the 90s Fri and
Sat, and possibly some lower 100s in the foothills. For this
reason an Excessive heat warning has been issued for that area.

Other coastal areas will be warming up as well later this week
with the possibility of lower 90s away from the immediate coast.

No other major changes to the forecast in the short term. Marine
layer stratus will decrease in depth and areal coverage through
the period. The lowering depth will result in increasing
visibility restrictions due to dense fog.

.LONG TERM (SAT-TUE)...02/223 PM.

Latest ensemble based guidance suggesting this heat wave may
continue, at least in some areas well into next week. The ensemble
mean 500mb height is still around 597dam as late as next Thursday,
though the high does start to shift a little to the east. In
addition, models have been indicating increasing onshore flow next
week, which would also increase the risk for larger fires. There
is certainly a chance that at least for inland areas the current
suite of heat warnings will need to be extended beyond Monday.
Coastal areas should start to cool off with the onshore flow
increase and the possibility of a weak eddy circulation
developing over the coastal waters that would also bring a return
of marine layer stratus, at least to coastal areas south of Pt
Conception.

&&

.AVIATION...03/0556Z.

At 0505Z at KLAX, the marine layer was 1000 feet deep. The top of
the inversion was at 2500 feet with a temperature of 26 Celsius.

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

Good confidence in TAFs for KBUR and KVNY 30 perent chance of
MVFR vsbys due to haze from 11Z-16Z.

Moderate confidence in remainder of the TAFs. There is a 25
percent chc 1/4SM FG conds at any site where it is not forecast.
There is 30 percent chc of no afternoon clearing at KOXR or KSBA.
There is a 30 percent chc of VFR conds arrive 1 hour later than
fcst at KLAX and KSMO.

KLAX...Moderate confidence in TAF. TAF VIS will reflect SFC VIS
and not VIS from tall tower. There is a 25 percent chc of 1/4SM FG
conds 10Z-15Z. There is a 30 percent chc that VFR conds will not
arrive until 20Z. Low clouds could arrive as early 00Z. No
significant easterly wind component is expected.

KBUR...Good confidence in TAF with only a 30 percent chc of 5SM HZ
conds 11Z-16Z.

&&

.MARINE...02/754 PM.

For the Outer Waters, Small Craft Advisory (SCA) conditions are
not expected through Thursday afternoon. For Thursday night
through Saturday, there is a 40% chance of SCA winds.

For the Inner Waters north of Point Sal, SCA conditions are
generally unlikely through the upcoming weekend, though there is
a 20% chance for SCA winds for Friday afternoon and evening.

For the Inner Waters south of Point Conception, SCA conditions
are not expected through the upcoming weekend.

Dense fog is expected over the coastal waters for the remainder
of this week during the overnight to morning hours, with a
gradual decrease in the coverage of fog as the week progresses.
Please reference the Marine Weather Statement for additional
information.

&&

.BEACHES...02/134 PM.

A southerly swell front will overspread the Southern California
coastal waters Thursday into Friday, followed by 15-17-second
southerly swell persisting from late this week into the weekend.
While surf is not expected to be particularly high, surf heights
upwards of around 5 feet are anticipated at beaches exposed to
southerly swell -- especially the LA and Ventura County beaches.
Moreover, 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 beaches of LA and Ventura
Counties. A Beach Hazards Statement has been issued from Thursday
mid-day through the weekend to address these concerns.

&&

.FIRE WEATHER...02/545 PM.

Wednesday will be the beginning of a long duration heat wave
across Southwestern California. Afternoon temperatures will be on
the increase, topping out in the 100-110 range across interior
sections on Wednesday with cooler temperatures closer to the
coast. With the developing heat, lower relative humidity can be
expected away from the coast. Typical diurnal winds can be
expected through Wednesday with gusty southwesterly winds across
interior sections in the afternoon and evening. Elevated fire
weather conditions can be anticipated across interior sections
through Wednesday.

For Thursday through the weekend, the heat will continue to build
with Friday likely the hottest day. Dangerous heat can be
expected for most areas through the weekend. Very low relative
humidity will accompany the hot temperatures with minimum relative
humidity dropping into the low teens and single digits with poor
overnight recovery. Additionally, there will be some gusty
northwesterly winds late Thursday through Friday night across the
Interstate 5 corridor as well as southern Santa Barbara county.
This combination will bring the chance of widespread critical fire
weather conditions and FIRE WEATHER WATCHES are in effect for the
Interstate 5 Corridor and southern Santa Barbara County Thursday
evening through Friday night. Elsewhere across the region, typical
diurnal winds can be expected through the weekend. So, elevated
fire weather conditions are expected through this weekend away
from the coast.

The hot and unstable conditions will also increase the threat of
large vertical plume growth for any fires that develop across the
interior. The very hot and dry conditions will also cause a
significant drop in both live and dead fuel moisture levels this
week. These drying fuels combined with the expected fire weather
conditions and increased outdoor activities associated with 4th of
July festivities this week will cause the large fire threat to
become high for areas away from the coast through at least Monday
and possibly into the middle of next week. This is a serious fire
weather event, and a hazardous heat event for human health.

&&

.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 remains in effect from 11 AM Thursday to 6 PM
      PDT Sunday for zones 341-347-355-368. (See LAXNPWLOX).
     Excessive Heat Warning in effect from 11 AM Thursday to 6 PM
      PDT Saturday for zones 349-350. (See LAXNPWLOX).
     Beach Hazards Statement in effect from Thursday morning
      through Sunday evening for zones 354-362-366. (See LAXCFWLOX).
     Heat Advisory remains in effect from 11 AM Wednesday to 6 PM
      PDT Sunday for zone 548. (See LAXNPWLOX).
     Fire Weather Watch in effect from Thursday evening through
      late Friday night for zones 349>353-376>378-381. (See LAXRFWLOX).
PZ...NONE.

&&

$$

PUBLIC...MW/Sirard
AVIATION...Rorke
MARINE...Cohen/Smith/Lewis
BEACHES...Cohen
FIRE...Thompson
SYNOPSIS...Cohen/Smith/MW

weather.gov/losangeles

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