765
FXUS66 KLOX 200348
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
848 PM PDT Tue Aug 19 2025

.SYNOPSIS...19/753 PM.

Gusty Sundowner winds and northerly winds through the Interstate 5
Corridor will continue nightly through Wednesday. A significant
multi-day heat event is expected Wednesday through Saturday with
many areas likely to see near record temperatures. There will be a
slight chance of thunderstorms over the Los Angeles and Ventura
County mountains, and portions of the Antelope Valley, during the
afternoon hours Friday through Monday.

&&

.SHORT TERM (TUE-FRI)...19/847 PM.

***UPDATE***

High pressure is building in rapidly over the region, with heights
rising from 587 to 589 DAM up to 593 to 594 DAM through the day.
Highs came in on the warm side, with high temperatures peaking in
the mid to upper 90s for the valleys and deserts. Coastal valleys
reached the 80s to around 90 degrees, and coastal areas warmed
well into the 70s and 80s. Marine layer clouds have become quite
sparse, with only some brief clouds affecting the LA Basin and
portions of coastal Ventura County this morning. This trend will
continue as high pressure further compresses the marine layer
Wednesday and Thursday. Dense fog is possible where ever clouds
manage to form. Clouds and fog were decreased over the region to
better represent this. Temperatures were also warmed along the
Central Coast to better represent the lack of clouds. Otherwise,
the current forecast looks on track with minimal changes needed.

***From Previous Discussion***

SoCal is on the precipice of the hottest stretch of days so far
this summer as the high pressure system over the desert southwest
expands westward while at the same time onshore flow weakens.
Temperatures will begin warming up Wednesday, but then really kick
into gear Thursday and Friday. A mix of heat advisories and
extreme heat warnings have been issued across the 4 county area,
with highs approaching 110 across the Antelope Valley and western
San Fernando Valley, mid to high 90s in Downtown LA, and 80s to
low 90s across interior parts of the coastal plain from the
Central Coast down to coastal LA County. It`s likely some daily
records will be tied or broken during this heat wave. It`s
strongly encouraged to complete any outdoor activities early in
the morning or hold off well into the evening as temperatures
start to cool off.

Overnight night lows will be warming up as well, especially as we
get into Thursday and Friday as monsoon moisture begins to enter
the area. Some valley areas will stay in the 70s, with even some
areas, such as the Antelope Valley, not dropping below 80.
with
potential for dense fog at times.
Despite the very hot temperatures, a shallow marine layer will
likely continue along some parts of the immediate coast and over
the coastal waters creating some dense fog at times. And there
will be some gusty north winds across southwest Santa Barbara
County the next couple evenings.

As the high moves west, the upper level flow will become more
favorable for monsoon moisture to move into the area. The first
day for this will be Friday as the EPS ensembles show PW`s
increasing to at least 1.25", with some solutions as high as
1.5". So far not seeing any well defined easterly waves moving in,
however the NAM shows CAPE values increasing to around 700j/kg
across the eastern San Gabriels Friday afternoon. This will likely
be very high based moisture but can`t rule out a shower or
thunderstorm there with brief heavy rain and gusty winds.

.LONG TERM (SAT-TUE)...19/158 PM.

Saturday will be another very hot day but likely not quite as hot
as Friday by 1-3 degrees. High pressure will begin to weaken, but
not really enough to make much difference. In addition, monsoon
moisture will continue to stream into SoCal over the weekend which
will likely increase the humidities, making it feel even more
uncomfortable. Thunderstorms are again possible across the
mountains as far west as Ventura County. Can`t completely rule out
a shower or storm over the lower elevations but without a defined
trigger and steering flow mostly from the south, storms should
stay confined to the mountains and possibly spilling into the AV.

The upper high will continue to weaken on Sunday and esp Monday.
There will be enough cooling Sunday to eliminate the threat of
warnings but a few advisories are still likely. The TSTM threat
will continue on Sunday over the eastern San Gabriels.

The forecast calls 3 to 6 locally 8 degrees of cooling on Monday
and this will bring most max temps to near normals. The monsoon
threat will end and the marine layer cloud deck will likely
increase and may make it into some of the vlys.

&&

.AVIATION...19/1810Z.

Around 1728Z, the marine layer depth was around 600 feet deep at
KLAX. The top of the marine inversion was around 2700 feet with a
temperature near 23 degrees Celsius.

High confidence in VFR TAFs for KPRB, KBUR, KVNY, KPMD, and KWJF.

Moderate confidence for VFR TAFs for KSBP and KSBA. There is a 30%
chance for LIFR cigs with potential for VLIFR cigs/vsbys between
10Z and 17Z.

High confidence in remaining TAFs through 06Z, then low
confidence thereafter. There is a 40% chance for LIFR to VLIFR
cigs/vsbys at KSMX between 08Z and 17Z. There is chance for LIFR
to VLIFR conds at KCMA (20%) and KOXR (30%) from 12Z to 17Z. There
is a chance for VFR conds to prevail at KSMO (40%), KLAX (30%),
and KLGB (20%). Otherwise, minimum cig height may be off by 300
ft and arrival time may be off +/- 2 hours.
KLAX...High confidence in TAF through at least 06Z, then low
confidence thereafter. There is a 30% chance for VFR conds to
prevail. There is a 30% chance for cigs 002-004 and vsbys 2SM+.
Any east wind component will remain less than 7 knots.

KBUR...High confidence in VFR TAF.

&&

.MARINE...19/801 PM.

Generally, high confidence in the current forecast. Slightly
higher confidence in the forecast for seas relative to winds.

For the outer waters and the nearshore waters along the Central
Coast, there is a likely-to-imminent (70-90 percent) chance of
Small Craft Advisory (SCA) conditions through early Thursday,
peaking during the afternoon and evening hours. Local Gale Force
gusts may occur each evening in the windier spots, highest across
the northern waters beyond 10 NM from the Central Coast and
south of Point Conception to San Nicolas Island tonight. Winds
and seas will see a likely chance of dropping below SCA levels for
the nearshore waters with 10 NM from the Central Coast, but there
is a moderate (30-40 percent) chance of SCA level winds Thursday
and Friday afternoons and evening. There is a high- to- likely
(50-60 percent) chance of SCA level winds returning to the outer
waters this coming weekend, especially for the southern zones
near and south of Point Conception.

Inside the southern California bight, SCA level winds have ended
across the western portion of the Santa Barbara Channel this
evening. There is a 40-60 percent chance of SCA level winds across
the western channel again Wednesday afternoon and evening, then
winds and seas should drop below SCA levels from Thursday through
the upcoming weekend.

&&

.FIRE WEATHER...19/1219 PM.

***RED FLAG WARNING IN EFFECT FROM 9 AM PDT WEDNESDAY TO 9 PM PDT
 SATURDAY FOR AN UNSEASONABLY HOT AND UNSTABLE AIR MASS CAPABLE OF
 PRODUCING EXTREME FIRE BEHAVIOR FROM VERTICAL PLUME GROWTH...LOW
 RELATIVE HUMIDITY...AND LOCALLY BREEZY WINDS FOR PORTIONS OF THE
 MOUNTAINS AND FOOTHILLS OF LOS ANGELES AND VENTURA COUNTIES***

***RED FLAG WARNING IN EFFECT FROM 9 AM PDT THURSDAY THROUGH 9 PM
 PDT SATURDAY FOR AN UNSEASONABLY HOT AND UNSTABLE AIR MASS
 CAPABLE OF PRODUCING EXTREME FIRE BEHAVIOR FROM VERTICAL PLUME
 GROWTH...LOW RELATIVE HUMIDITY...AND LOCALLY BREEZY WINDS FOR
 PORTIONS OF THE MOUNTAINS AND FOOTHILLS OF SANTA BARBARA AND SAN
 LUIS OBISPO COUNTIES***

The most significant heatwave of the summer season, so far, is
on the way for middle to latter parts of this week and into the
upcoming weekend, from Wednesday through Saturday. Expect
temperatures to soar into the 95-105 degree range over interior
areas, locally reaching near 110 degrees over some mountain valley
and desert locations. The intense surface heating will bring
strong vertical mixing to depths extending over 15-17 thousand
feet -- highest Thursday and Friday. Resultant unseasonably strong
instability will create a fire environment capable of producing
extreme fire behavior through significant vertical plume growth,
as minimum relative humidity ranges from 8 to 20 percent in the
dry air mass. Overnight relative humidity recovery will be poor to
moderate, while the shallow marine layer generally remains
displaced closer to the beaches.

The Red Flag Warning areas cover portions of the mountains and
foothills of Los Angeles, Ventura, Santa Barbara, and San Luis
Obispo Counties, which have been a climatologically notorious area
for large plume-dominated fires in similar weather patterns to
what is coming this week into the weekend. While background
surface winds are not expected to be strong, or even close to
reaching nominal Red Flag Warning criteria, they will be locally
breezy in the afternoon and evening over the western Antelope
Valley Foothills and vicinity and in other wind-favored areas such
as through passes and canyons -- sustained winds 10-20 mph
gusting to 25-30 mph following diurnal- wind patterns. These winds
will exacerbate the spread of any plume-dominated fires, and add
to the potentially dangerous fire- weather environment.

Moreover, the western edge of a southwest-states monsoonal
moisture influx will overlie Los Angeles and Ventura Counties,
which will contribute to the development of atmospheric buoyancy
by Friday and this weekend without significantly moistening the
air mass -- i.e., displaced away from the core of the moisture
source. While lightning-induced fire ignitions are a distinctive
possibility on the peripheries of rain cores, the increase in
buoyancy will further aid in vertical plume growth accompanied by
potential pyrocumulus development and related extreme fire
behavior. Combined with significant fuel loading of exceptionally
dry fuels, the fire environment in the mountains and foothills of
Los Angeles and Ventura Counties will become especially volatile
for Wednesday through Saturday, warranting the issuance of a Red
Flag Warning upon collaboration with local area National Weather
Service Core Partners.

Analogs to the forthcoming, highly volatile fire-weather
environment in Los Angeles County include the Station Fire in
2009, the Bobcat Fire in 2020, the Lake Fire in 2024, and the
Bridge Fire in 2024, which burned significant portions of
forested areas. In each case, winds were generally below Red Flag
Warning criteria, yet the extreme heat combined with buoyancy
greatly offset the sub-marginal wind to create extreme fire
behavior and the growth of large fires. Interests in the Red Flag
Warning areas should be prepared for similar activity if fires
were to start. Also, be aware of passing outflow boundaries that
could bring sudden wind-shifts and increased fire-spread rates,
even from distant thunderstorms.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Extreme Heat Warning in effect from 11 AM Thursday to 9 PM
      PDT Saturday for zones
      38-88-342>345-348-353-369-371>383-548. (See LAXNPWLOX).
     Heat Advisory remains in effect from 11 AM Thursday to 9 PM
      PDT Friday for zones 341-347-356>358-367. (See LAXNPWLOX).
     Wind Advisory remains in effect until 5 AM PDT Wednesday for
      zones 349-351. (See LAXNPWLOX).
     Extreme Heat Warning in effect from 11 AM Thursday to 9 PM
      PDT Friday for zones 351-352-368-370. (See LAXNPWLOX).
     Red Flag Warning in effect from 9 AM Wednesday to 9 PM PDT
      Saturday for zones 288-375>382. (See LAXRFWLOX).
     Red Flag Warning in effect from 9 AM Thursday to 9 PM PDT
      Saturday for zones 345-351>353. (See LAXRFWLOX).
PZ...Small Craft Advisory in effect until 3 AM PDT Wednesday for
      zone 645. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PDT Thursday for
      zones 670-673-676. (See LAXMWWLOX).

&&

$$

PUBLIC...Phillips/MW
AVIATION...Lewis
MARINE...Hall/Lewis/Ciliberti
FIRE...Cohen/Gomberg/Lund
SYNOPSIS...MW/Ciliberti

weather.gov/losangeles

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