375
FXUS66 KLOX 210558
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
1058 PM PDT Sun Sep 20 2026

.SYNOPSIS...20/812 PM.

A weak upper level trough will move over the area tonight into
Monday, cooling temperatures slightly and increasing marine layer
stratus. A warming trend will begin Tuesday and peak on Thursday,
with highs 5 to 10 degrees above normal.

&&

.SHORT TERM (SUN-WED)...20/810 PM.

***UPDATE***

The marine inversion was around 1400 ft deep and VBG and near
1800 ft deep at LAX early this evening and is expected to deepen
some overnight in response to an approaching upper level low
pressure system. Low clouds were along portions of the Central
Coast and SBA S coast this evening, with patchy low clouds
starting to form along the VTU/L.A. County coast. These low
clouds are likely to expand this evening and push inland quickly
overnight. Would not be surprised to see some drizzle develop
later tonight as well especially S of Point Conception. Current
forecast is on track and do not anticipate any zone updates this
evening.

***From Previous Discussion***

An upper low is just west of the Central Coast this afternoon. The
low is spreading lots of high clouds across the area today but the
lack of moisture below 15000 feet is preventing any precip from
developing. Can`t completely rule out a stray drop or two at
higher elevations but otherwise dry conditions are expected
through at least tonight. With the high clouds decreasing through
the night and less trapped heat overnight lows will likely be a
little cooler.

As the low moves overheat tonight, models have been consistent
indicating a rapidly developing marine layer, possibly deepening
to 4000 feet or higher by Monday morning. Given the rapid increase
there`s good chance that some drizzle will develop, especially in
the south facing foothills of LA County. Some light measurable
rain is possible in the most favored areas, namely from the
eastern San Fernando Valley into the San Gabriel Valley and
adjacent foothills.

Significant cooling will accompany the deepening marine layer
Monday with the warmest valleys barely reaching 80 and desert
areas only in the low 80s, roughly 10 degrees below normal. Skies
are expected to clear eventually Monday but it may be a reverse
clearing day where coastal areas clear before the valleys.

A warming trend will begin Tuesday and continue through at least
Wednesday, by which time most areas will be 4-8 degrees above
normal. Downtown LA still has about a 40-50 percent chance of
reaching 90 Wednesday while the warmer valleys have a similar
chance of reaching 100. Chances for heat advisories in those areas
remains around 30%

.LONG TERM (THU-SUN)...20/229 PM.

Uncertainty remains with regard to the length of the next heat
wave but there are still at least 30% of the solutions showing
little to no change in high temperatures through at least
Saturday. However, more of the guidance products suggest a slow
cooling trend after Wednesday due to a slowly deepening trough
along the West coast.

&&

.AVIATION...21/0556Z.

At 0512Z at KLAX, the marine layer was 1700 ft deep. The top of
the inversion was at 4900 ft with a temperature of 19 C.

High confidence in VFR conds for KPMD & KWJF.

Low to moderate confidence in the remaining sites. The timing of
CIG and any VSBY restrictions may be off 2 hrs and flight minimums
by one category. Cigs may bounce between categories. There is a
10 percent chance of -DZ through 18Z.

KLAX...Moderate confidence in TAF. Cigs may vary between 015 and
030 through 18Z. There is a 30 percent chc of no clearing. Any
east wind component is expected remain less than 6kt.

KBUR...Moderate confidence in TAF. There is a 30 percent chc of
BKN015 conds through 14Z.

&&

.MARINE...20/902 PM.

For the outer waters, moderate confidence in the current
forecast. Small Craft Advisory (SCA) level winds are likely
(60-80 percent chance) for the waters around Point Conception
through late tonight. There is a 40-50% chance of SCA wind gusts
west and south of Point Conception Tuesday afternoon and night as
well, otherwise conds will be below SCA levels through Thursday
night. Expect steep, choppy seas with the SCA conditions.

For the inner waters N of Point Sal, moderate confidence in the
current forecast. SCA wind gusts are possible (30-40 percent
chance) during the afternoon and evening today and again Tuesday.
Conds are otherwise expected to be below SCA levels through
Thursday.

For the inner waters S of Point Conception, moderate to high
confidence in the current forecast. Conds are expected to be below
SCA levels for the most part through Thursday night. However, for
the western Santa Barbara Channel, there is a 30-40% chance
this afternoon/evening and Tuesday afternoon/evening.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory in effect until 3 AM PDT Monday for zone
      670. (See LAXMWWLOX).
     Small Craft Advisory in effect until 5 AM PDT Tuesday for
      zone 673. (See LAXMWWLOX).

&&

$$

PUBLIC...MW/Sirard
AVIATION...Rorke
MARINE...Ciliberti/RS/RM
SYNOPSIS...MW/Sirard

weather.gov/losangeles

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