393
FXUS66 KLOX 030046
AFDLOX

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

updated aviation and fire weather discussions

.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 (TDY-FRI)...02/213 PM.

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...03/0038Z.

At 00Z at KLAX, the marine layer was 900 feet deep. The top of
the inversion was at 4300 feet with a temperature of 25 Celsius.

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

For KBUR and KVNY there is generally hi confidence in the 00Z TAFs
except for a 50% chance of MVFR vsbys due to haze from about
11Z-16Z Wed.

Moderate confidence in remainder of the 00Z TAFs, with IFR-LIFR
conditions expected to return tonight and continue into Wednesday
morning with low clouds and fog near all coastal sites. Cig/vsby
restrictions should dissipate in the afternoon on Wednesday, with
onset and dissipation timing of cig/vsby restrictions varying by
+/- 3 hours of current forecasts.

KLAX...Moderate confidence in the 00Z TAF. High confidence in
LIFR conditions much of the night and into the morning, with a 70%
chance of dense fog. No significant easterly wind component is
expected.

KBUR...Generally hi confidence in the 00Z TAF except for a 50%
chance of MVFR vsbys due to haze from about 11Z-16Z Wed.

&&

.MARINE...02/134 PM.

For the Outer Waters, Small Craft Advisory (SCA) conditions are
not expected through Thursday. For Friday and 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 into Saturday.

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, 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
AVIATION...Lewis/Sirard
MARINE...Cohen
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