121
FXUS66 KLOX 190420
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
920 PM PDT Tue Aug 18 2026

.SYNOPSIS...18/919 PM.

Night through morning marine layer clouds will be confined to the
coastal areas, mostly north of Pt Conception, through much of
this week. Warmer and drier conditions are expected away from the
immediate coast, with the heat peaking Wednesday and Thursday,
when moderate heat risk is expected in warmest locations.

&&

.SHORT TERM (TUE-FRI)...18/916 PM.

***UPDATE***

The marine layer is shrinking as high pressure builds over the
region, with clouds limited to the coastal areas north of Point
Conception this morning. Still, high temperatures on the Central
Coast were cool (widespread 60s to low 70s). Elsewhere, highs rose
to the 90s to low 100s for the interior and upper 70s to 80s
closer to the coast. Heights are forecast to rise up to 595-596
dam into Thursday, leading to the warming trend and further
limiting marine layer clouds. However, decent onshore flow will
continue to limit warming near the coasts. Gusty sundowner winds
have developed tonight, and a wind advisory was issued with gusts
of 45-50 mph expected. Sundowner winds will reoccur each night,
possibly reaching advisory levels Wednesday night as well.
Otherwise, the current forecast looks on track, with a slight
(5-10% chance for showers and thunderstorms over the Ventura
and LA County interior mountains Friday and Saturday.

***From Previous Discussion***

Very little change in the forecast today. The large and very warm
upper level high continues to sit over the area, stretching all
the way to Texas. 500 mb heights will remain around 595/594 dam
into Friday (higher than normal for this time of year), with
minimal changes in the surface pressure gradients with weak to
moderate onshore trends during the afternoons.

Night through morning marine layer clouds will continue to spread
into the Central Coast each night, but south of Point Conception,
marine layer clouds will struggle to form through at least
Thursday due to a combination of the warm sea surface
temperatures, lack of an eddy to bring clouds in from the south,
and weak onshore flow. If clouds do form south of Point
Conception, they will remain confined to the coastal areas due to
the shallow marine layer. Periods of high level clouds will stream
over the area, but skies will mainly be partly cloudy at most
during the afternoons.

Higher than normal heights, weaker than normal onshore flow, and
the sunny skies will all combine to bring 2 to 4 degrees of
warming today, 1 to 3 degrees on Wednesday and another 1 to 2
degrees on Thursday for areas south of Pt Conception (The Central
Coast will cool some as the sea breeze increases). Max temps in
the valleys, lower mountain elevations, and far interior will
range from 95 to 105 degrees, which is 4 to 8 degrees over normal.
The strong inversion, much warmer than normal sea surface temps
and the warm atmosphere will also bring above normal overnight low
temps to much of the area. Most coast/valley locations will only
have lows in the upper 60s to lower 70s.

The combination of warmer than normal high and low temps will
bring Moderate HeatRisk to many areas through at least Thursday.
Heat advisories are in effect through Thursday for the San
Fernando, San Gabriel, and Santa Clarita Valleys as well as the
lower mountain elevations. There is a small chance that advisories
need to be extended into the Santa Monica Mountains and Ventura
County Valleys starting Wednesday. Additionally, there is a 10-20
percent chance that heat advisories will need to be extended into
Friday for portions of the area, but it depends on the balance of
the humidities and cooling temperatures on Friday (See long term
discussion for more details about Friday). Please see the product
LAXNPWLOX for all of the details.

Gusty north winds will affect southwest Santa Barbara County and
the I-5 corridor near the Grapevine each evening and overnight.
The gusts should almost all be below advisory levels with only a
chance of isolated advisory level (45 mph) gusts in the Gaviota
area tonight.

.LONG TERM (SAT-TUE)...18/236 PM.

All medium range models agree that the upper high will shift to
the four corners area by Friday, which will set up SE monsoon flow
over Southern CA. This SE flow will allow Precipitable Water
values to approach 1.5" across southern L.A. County starting
Friday afternoon. This influx of moisture will allow for a 5-10
percent chance of showers or thunderstorms to to develop over the
LA County mountains and Antelope Valley Friday afternoon through
the weekend.

The upper high will shift slowly eastward Saturday through Monday
and hgts will fall to 592 dam on Saturday and about 590 dam by
345-351-353-371>373-375-376-379-380-548. (See LAXNPWLOX).
     Wind Advisory in effect until 2 AM PDT Wednesday for zones
      349-351. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 3 AM PDT Wednesday for
      zone 650. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PDT Thursday for
      zones 670-673-676. (See LAXMWWLOX).

&&

$$

PUBLIC...Phillips/Lund
AVIATION...Black
MARINE...Black
SYNOPSIS...Gomberg/Ciliberti

weather.gov/losangeles

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