020
FXUS66 KLOX 031238
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
538 AM PDT Wed Jul 3 2024

.SYNOPSIS...03/235 AM.

A significant heatwave will affect the region this week and will
continue through much of next week, with dangerously hot
temperatures across much of the area. High temperatures will 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 affect the coasts this morning and
Thursday morning.

&&

.SHORT TERM (TDY-FRI)...03/316 AM.

The marine layer has shrunk down to about a 1000 ft. There is no
eddy this morning and weaker onshore flow as a result there is
much less inland penetration and low clouds are confined to the
coastal areas. There are also some patches of dense fog. Most of
the areas should clear by noon but its possible some beaches
(esp Carpinteria to Oxnard) may see limited or no clearing.

The heat wave will begin in earnest today with offshore trends at
the sfc and hgt rises from an encroaching upper high. Hgts will
reach 595 or 596 dam later this afternoon. Max temps will jump 2
to 4 degrees today and max temps will end up 12 to 18 degrees
above normal away from the coasts. Excessive Heat Warnings remain
in effect for the all non coastal areas today except for the San
Gabriel Vly which will be under a Heat Advisory which goes into
effect at 1100 am this morning.

The marine layer will be similar tonight to this morning will only
the near shore areas affected. The very strong marine layer
capping inversion will extend from around 1000 to 3000 ft with
temps as high as 82 degrees. Overnight lows in areas within these
elevations will experience very warm overnight lows in the mid to
upper 70s with some lower 80s possible.

Max temps will be a little warmer on Thursday. Heat advisories
will go into effect across the interior portions of the coastal
sections as the marine layer retreats closer to the shore. The
biggest concern on Thursday will be across the SBA south coast
where a northerly offshore push across the county will bring
sundowner winds to the area. Any downsloping winds will
adiabatically warm the already hot air further and temps of 100
degrees will be possible. Due to this likely scenario an excessive
heat warning is in effect for the SBA south coast both Thu and
Fri.

There will be only a bare minimum of marine layer clouds Thursday
night. Again the areas between 1000 and 3000 ft will experience
much warmer than normal overnight lows.

Friday will be the warmest day. As 596 dam hgts combine, with
warming subsidence from the upper high parked over nrn CA and
only weak onshore flow. Look for 3 to 6 degrees of warming for
most areas but some coastal areas may see 10 degrees of warming
and if the north flow hits just right the SBA south coast could
warm 20+ degrees. Highs across the far interior 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 are expected to reach 107-109. It is likely that
there will be many High temperature records on Friday.

Please see the product LAXNPWLOX for all the details on the heat
warnings and advisories.

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.

.LONG TERM (SAT-TUE)...03/331 AM.

Not much change in the forecast during the xtnd period.
Deterministic and ensemble means both indicate the upper high
remaining over the state through at least Tuesday. Hgts remain
steady between 596 and 597 dam. The only change is a noticeable
increase in the onshore flow which will help bring the marine
layer back and allow for some cooling across the coasts and lower
vlys. It is likely that the heat warnings for the mtn and inland
areas will have to be xtnd.

The downside of the increase in onshore flow will be increased
afternoon and early evening winds across the interior. This winds
will, for sure, increase the fire danger.

&&

.AVIATION...03/1237Z.

At 1211Z at KLAX, the marine layer was 1000 feet deep. The top of
the inversion was at 4700 feet with a temperature of 28 Celsius.

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

Good confidence in TAFs for KBUR and KVNY 20 percent chance of
MVFR vsbys due to haze from thru 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
through 16Z. 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 overnight will reflect
SFC VIS and not VIS from tall tower. There is a 25 percent chc of
1/4SM FG conds thru 15Z Wed. 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 thru 16Z Wed.

&&

.MARINE...03/311 AM.

For the Outer Waters, Small Craft Advisory (SCA) conditions are
not expected through Thursday afternoon. For Thursday night
through the weekend, there is a 40-50% chance of SCA winds. There
is a 10-15% chance of local Gale Force wind gusts on Friday
afternoon and evening.

For the Inner Waters north of Point Sal, SCA conditions are
generally unlikely through the upcoming weekend, though there is
a 30% chance for SCA winds for Friday afternoon and evening.

For the Inner Waters south of Point Conception, SCA conditions
are generally not expected through the upcoming weekend. However,
there is a 20-30% chance of local SCA level wind gusts across the
western portion of the waters Thursday afternoon and evening.

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...03/304 AM.

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 is in effect 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 this
      morning 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 this morning 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...Rorke
AVIATION...Lund
MARINE...Lund/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