902
FXUS66 KLOX 202012
AFDLOX

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

.SYNOPSIS...20/226 AM.

A weak upper level trough will move over the area today 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 (TDY-WED)...20/924 AM.

***UPDATE***

The upper low is moving closer to the coast, inline with previous
forecasts. High cloud coverage is more robust than expected but
will have zero impact other than cutting down on the solar energy
reaching the surface. Otherwise, forecast on track for some
cooling today and Monday. Satellite based convection detection
not showing much with the upper low, and latest CAMs indicating
even less of a chance for any convective activity. However,
forecast soundings indicate a rapidly increasing marine layer
tonight and Monday, likely up to 4000 feet across LA County, and
close to 2000 feet along the Central Coast. So there`s a strong
possibility for some drizzle or even some very light rain Monday
morning, especially in the upslope areas of LA County,
particularly the south facing San Gabriel Mountains.

***From Previous Discussion***

Current mid and high clouds streaming into the region are
indicative of the low pressure system currently centered around
400 miles off the coast, that will move across the region through
Wednesday. Falling 500 mb heights, an increase in onshore surface
pressure gradients, and an influx of light moisture and clouds
will yield a cooling trend through Monday. Highs in the 70s will
be common on Monday, as temperatures will be around 5 to 10
degrees below normal.

Current marine layer clouds are being disturbed by the high
clouds, thus will be patchy and scatter and reform. Overall
however, clouds are likely to be rather slow to clear, with a
very fall inland extent today. A similar messy cloud situation
is expected for tomorrow.

Little moisture is associated with the upper level trough,
however there is some instability. As a result, there is a 5 to 10
percent chance of thunderstorms/showers Sunday into Monday,
focused over the inland mountains. The main threats with a storm
will be dry lighting strikes and gusty and erratic winds.

.LONG TERM (THU-SUN)...20/340 AM.

Wednesday looks to be the main peak of heat for next week. The low
pressure system will have cleared out of the area and higher
pressure will build over the region. Perhaps one of the most
important factor`s contributing to warmer temperatures will be
weaker onshore flow and at times even brief offshore flow on
Wednesday. The coastal valleys are favored to see highs in the
90s, with around a 25 percent chance of 100 degrees in the
western San Fernando Valley and portions of the San Gabriel Valley.
Up north, there is around a 50 percent chance of 100 degrees or
higher across inland SLO and Santa Barbara Counties, and 15
percent chance for the City of San Luis Obispo.

There is around a 30 percent chance of a few Heat Advisories being
needed for coasts and valley for Wed-Thu, and there is some
indication than elevated temperatures may continue for Friday
into next weekend.

&&

.AVIATION...20/2007Z.

At 2000Z at KLAX, the marine layer was 2700 ft deep. The top of
the inversion was at 4000 ft with a temperature of 21 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 3 hrs and flight
minimums by one category. High clouds may disturb the marine layer
and sites with cigs may bounce between categories at times. There
is a 5-10 percent chance of -DZ/-SHRA focused through 18Z. There
is a 20-30 percent chance that VFR conds prevail.

KLAX...Low to moderate confidence in TAF. Flight cat changes may
be off by 3 hours. Any east wind component is expected remain
less than 6kt.

KBUR...Low to moderate confidence confidence in TAF. Flight cat
changes may be off by 3 hrs.

&&

.MARINE...20/110 PM.

For the outer waters, moderate confidence in the current
forecast. Small Craft Advisory (SCA) level winds are likely (50-80
percent chance) for the waters mainly west and northwest of Point
Conception through tonight or Monday night. The SCA winds will be
most persistent around Point Conception. 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 Tuesday 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 likely (50-60 percent chance)
during this afternoon and evening, and again Tuesday. Conds are
otherwise expected to be below SCA levels Monday 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 40%-50% chance
Monday afternoon/evening and Tuesday afternoon/evening.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory in effect until 3 AM PDT Monday for
      zones 645-670. (See LAXMWWLOX).
     Small Craft Advisory in effect until 5 AM PDT Tuesday for
      zone 673. (See LAXMWWLOX).

&&

$$

PUBLIC...MW/Schoenfeld
AVIATION...RM
MARINE...Ciliberti/RS/RM
SYNOPSIS...MW/CC

weather.gov/losangeles

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

NWS Los Angeles (LOX) Office