571
FXUS66 KLOX 181035
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
335 AM PDT Mon Aug 18 2025

.SYNOPSIS...18/222 AM.

There will be below normal temperatures some morning low clouds
today and Tuesday. Gusty Sundowner and I-5 winds will continue
each night, strongest Monday and Tuesday. A very significant warm
up will occur Wednesday through Saturday with many valley and
lower mountain areas near or above 100 degrees. There is a slight
chance of thunderstorms over the L.A. mountains Friday and
Saturday.

&&

.SHORT TERM (TDY-WED)...18/253 AM.

***A SEVERAL DAY HEAT EVENT is coming Wednesday through next
 weekend, with a HIGH RISK FOR HEAT ILLNESS AND FIRE DANGER. Now
 is the time to adjust any plans for strenuous outdoor activities
 in the valleys and mountains to the cooler morning hours or for
 another week. If you live in a high fire danger area in the
 mountains or foothills, review your evacuation plans and route
 and stay tuned to your local emergency officials.***

The west end of a large hot upper high is beginning to nose into
the state from the east. Hgts will climb to about 589 dam. At the
sfc there will be neutral to weak onshore flow in the morning and
moderate onshore flow to the east in the afternoon with weak
onshore flow to the north. This morning the low clouds are
struggling to form and the only vly that will see low clouds will
be the San Gabriel. The SLO county coast and SBA south coast will
likely remain cloud free as well. The rising hgts and weaker
onshore flow will bring 3 to 5 degrees of warming to most of the
area. Despite this warming max temps will end up 3 to 6 degrees
below normal.

There will be another Sundowner tonight with low end advisory
gusts 45 to 50 mph across the western portion of the SBA south
coast. The low cloud coverage will likely be similar to today`s
except the higher hgts will likely keep the San Gabriel Vly clear.

Hgts rise to 592 dam on Tuesday as the upper high migrates
westward. The gradients will be similar to today`s values. Most
areas will warm another 1 to 3 degrees with the exception of the
Central Coast which will cool a few degrees as a there will be a
slightly stronger sea breeze. Max temps will remain below normal.

2 to 3 mb of offshore flow will develop from the north Tuesday
night. This will likely generate advisory level gusts 45 to 55 mph
across the western SBA county south coast but the I-5 corridor as
well. The north winds will keep the low clouds away from the SBA
south coast and there is a chc that they could eliminate many of
the coastal low clouds currently fcst for the LA/VTA coasts.

Hgts climb to 594 dam on Wednesday. These hgts will squash the
marine layer down to 600 or 700 ft and place a very strong capping
inversion on top of it. This could create some dense fog in the
morning (most likely across the SBA western coast) as well as
delaying or preventing low cloud clearing at the beaches in the
afternoon. The afternoon gradients will be weaker than Tuesday and
combined with the actual offshore flow in the morning and the
rising hgts will bring 4 to 8 degrees of warming to most areas
(The LA/VTA southern SBA county csts will only warm 1-2 degrees.)
This warming will bring most areas up to 4 to 8 degrees over
normal. Triple digit heat is likely for western San Fernando Vly,
the Calabasas area, the Santa Clarita Vly, the Antelope Vly and
its foothills, and the Paso Robles area.

An EXTREME HEAT WATCH goes into effect at noon for all of the non
coastal areas. A watch means that there is the potential for
dangerous heat conditions to develop. But it is not a guarantee
that the conditions will be met. The watch is out to help people
prepare for dangerous heat conditions. These conditions will be
continuously monitored and updated over the next few days.

.LONG TERM (THU-SUN)...18/314 AM.

***A SEVERAL DAY HEAT EVENT continues into next weekend, with a
 HIGH RISK FOR HEAT ILLNESS AND FIRE DANGER. Now is the time to
 adjust any plans for strenuous outdoor activities in the valleys
 and mountains to the cooler morning hours or for another week. If
 you live in a high fire danger area in the mountains or
 foothills, review your evacuation plans and route and stay tuned
 to your local emergency officials.***

The upper high will set up over the 4 corners area and likely
remain there through Sunday. Hgts peak Thu and Fri and fall a
little over the weekend as the upper high weakens. Onshore flow
will remain weak and even offshore in the mornings from the north.

Thursday and Friday will be the warmest two days of the next 7.
Thursday will warm 3 to 6 degrees and Friday will have only a
slight dip in temps. Almost all areas away from the coast will
have triple digit temps with 106 to 109 degree temps possible in
the western San Fernando Vly and Antelope Vly. In addition to the
hot day time highs the overnight lows in areas above the strong
marine inversion (the vlys and foothills) will have well above
normal overnight lows (some lows may end up in the mid 80s). One
further consideration will be the potential for some monsoon
humidity as the upper high is in the classic 4 corners position
for monsoon flow. Max temps will end up around 10 degrees over
normal for the two days. The EXTREME HEAT WATCH covers both days
and the watch will be converted into many warnings and advisories.

Records are possible, but they are fairly high for this stretch
of time and may be just out of reach.

The temperature forecast for the coastal areas is the least
certain. The interplay between the heat and cooling seabreeze is a
tough nut. Since there is onshore flow there will be a sea breeze
but it will likely not reach too far inland and advisory level
heat is quite possible across the interior coastal sections.

On Friday the monsoonal flow will raise PWATs to between 1.25 and
1.50 inches and this is enough to bring a slight chc of TSTMs to
the mtns of VTA and LA counties as well as the Antelope Vly.

This heat wave will bring fire weather dangers as well. Please
see the Fire Weather Watch and the Fire Weather discussion
section below for additional information.

There will be slight cooling Sat and Sun as the high weakens and
onshore flow increases. Still max temps will be well above normal
and the monsoon flow will continue to bring higher than normal
humidities which will increase the heat risk. The slight chc of
afternoon mtn/AV TSTMs will continue as well.

&&

.AVIATION...18/1032Z.

Around 07Z, the marine layer depth was 1200 feet deep at KLAX.
The top of the inversion was at 2200 feet with a temperature near
23 degrees Celsius.

High confidence in the current forecast for desert and interior
valley terminals. Otherwise, moderate confidence in the current
forecast for all other terminals. There is a high to likely chance
of IFR to MVFR conditions for coast terminals from KOXR south and
LIFR to IFR conditions for Central Coast terminals through 16Z,
and again after 06Z Tuesday. There is a low to moderate chance of
LIFR to IFR conditions for Los Angeles County valley terminals
through 16Z.

KLAX...There is a 30 percent chance of VFR conditions continuing
through the period. IFR to MVFR conditions could spread in as
as soon as 11Z or as late as 14Z. VFR condition should develop
between 16Z and 17Z. A return of IFR to MVFR conditions should be
expected after 07Z. Any easterly winds should remain less than 7
knots.

KBUR...VFR conditions are expected through the period, except for
a 30 percent chance of LIFR to IFR between 13Z and 16Z. No wind
impacts are expected at this time.

&&

.MARINE...18/332 AM.

High confidence in the current forecast.

For the waters southwest through northwest of the Channel Islands
and the nearshore waters along the Central Coast, a high to
likely (40-60 percent) chance of Small Craft Advisory (SCA) level
winds this morning will increase to a imminent (80-100 percent)
chance this afternoon. Chances for SCA level winds will likely
fall again overnight tonight, then increase again to the likely
to imminent (70-90 percent) chance again on Tuesday afternoon and
evening, and again Wednesday afternoon and evening. Local Gale
Force gusts to 35 knots may occur in the late afternoon and evening
hours through late Tuesday night. Winds and seas will likely drop
below SCA levels between Thursday and Friday afternoon, but there
is a moderate to high chance of SCA level winds returning from
Friday afternoon through the upcoming weekend.

Inside the southern California bight, there is a moderate to
likely (40-60 percent) chance of SCA level winds each afternoon
and evening through midweek, highest across the western portion
of the Santa Barbara Channel. The highest chances for more
widespread winds to spill into the bight will be on Tuesday
evening, but there is a chance for local SCA level wind gusts near
Anacapa Island, near Point Dume, and into the San Pedro Channel.

&&

.FIRE WEATHER...17/226 PM.

***FIRE WEATHER WATCH IN EFFECT FROM WEDNESDAY MORNING THROUGH
 SATURDAY EVENING FOR AN UNSEASONABLY HOT AND UNSTABLE AIR MASS
 CAPABLE OF PRODUCING EXPLOSIVE 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***

The most significant heatwave of the summer season, so far, is
on the way middle to latter parts of this week and into next
weekend, especially Wednesday through Saturday. Expect
temperatures to soar well over 100 degrees 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
explosive 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 Fire Weather Watch area covers portions of the mountains and
foothills of Los Angeles and Ventura Counties, which have been a
climatologically notorious area for large plume-dominated fires in
similar weather patterns to what is coming later this week. 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 -- southwest at 10-20 mph
gusting to 25-30 mph. 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 Saturday 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 explosive fire
behavior. And 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 Fire
Weather Watch 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, the
Bobcat Fire, and the Bridge Fire that burned significant portions
of the Angeles National Forest in 2009, 2020, and 2024,
respectively. 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 explosive fire
behavior and the growth of large fires. Interests in the Fire
Weather Watch area 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.

Fire-weather headlines may eventually need to be extended into
Sunday and into portions of interior Santa Barbara and San Luis
Obispo Counties.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Extreme Heat Watch in effect from Wednesday afternoon through
      Saturday evening for zones
      38-88-342>345-348-353-356>358-371>383-548. (See LAXNPWLOX).
     Wind Advisory remains in effect until 6 AM PDT early this
      morning for zones 349-351. (See LAXNPWLOX).
     Wind Advisory in effect from 6 PM this evening to 5 AM PDT
      Tuesday for zones 349-351. (See LAXNPWLOX).
     Fire Weather Watch in effect from Wednesday morning through
      Saturday evening for zones 288-375>382. (See LAXRFWLOX).
PZ...Small Craft Advisory in effect from noon today to 3 AM PDT
      Tuesday for zone 645. (See LAXMWWLOX).
     Small Craft Advisory in effect from 3 PM this afternoon to 9
      PM PDT this evening for zone 650. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PDT Wednesday for
      zones 670-673-676. (See LAXMWWLOX).

&&

$$

PUBLIC...Rorke
AVIATION...Hall
MARINE...Hall
FIRE...Cohen/Gomberg
SYNOPSIS...30

weather.gov/losangeles

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