113
FXUS66 KLOX 010724
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
1224 AM PDT Mon Sep 1 2025

.SYNOPSIS...31/823 PM.

A hot air mass will persist over the region through mid week as
high pressure aloft remains anchored near the Four Corners
area. Monsoonal moisture will arrive again on Monday night and
Tuesday and keep a low but present risk of showers and thunderstorms
through the remainder of the week. A cooling trend is possible by
the upcoming weekend.

&&

.SHORT TERM (SUN-WED)...31/855 PM.

***UPDATE***

Temperatures were quite warm today through much of the area today,
with a few cooler spots near the coasts as clouds lingered over
portions of LA County late in the day. Areas are starting to see
more low clouds and fog as high pressure builds, and will need to
monitor for dense fog overnight tonight.

Currently a lot to examine regarding the moisture return Monday
night into Tuesday. Guidance seems to differ on intensity and
coverage, with the HRRR being fairly liberal with showers and
thunderstorms from the Santa Barbara Ventura border eastward, and
other high resolution guidance more sparse. However, the GFS and
NAM agree with more shower activity occuring from the Santa
Barbara Ventura county border southward supported by vorticity
advection so shower chances were expanded westward. Thunderstorm
chances may need to also be expanded.

Heat will continue to build each day, with the trickiest forecast
for tomorrow at the immediate coasts where clouds could hamper
heating. However, somewhat higher confidence in warm values for
the coasts Tuesday as gradients suggest offshore flow. The Heat
Advisory was extended into Tuesday for the Ventura coastal plains
to reflect this trend.

***From Previous Discussion***

Another very warm to hot day over the forecast area, with many
areas away from the coast expected to top out between 95 and 105
deg this afternoon. Even the inland coastal plain should reach
into to low 90s. With the hot conditions, Heat Advisories are in
effect for most of the region.

Some low clouds and patchy dense fog were noted over the coastal
waters S of Point Conception early this afternoon, with some fog
along the VTU County beaches to the Malibu Coast. These low clouds
should diminish in coverage through sunset. Some cu buildups have
been noted over the mtns early this afternoon as well. An
isolated shower is possible this afternoon in these areas but
overall any chances of thunderstorms is about 5 percent or less.

A broad southerly flow aloft over the forecast area between an
upper level high near the Four Corners region and a weak upper
level low just off the Central Coast can be expected through Mon
night. However, a weak disturbance aloft embedded in this flow
is forecast to move into the area later Mon night. This system,
combined with significant amounts of mid-level moisture and some
instability aloft is expected to develop an area of showers with a
slight chance of thunderstorms over a good portion of VTU/L.A.
Counties generally after midnight Mon night into Tue morning.
Lingering mid-level moisture and instability will keep the slight
chance of showers and thunderstorms mainly over the mtns and
deserts Tue afternoon and early evening.

Upper level ridging will persist over srn CA Tue night and Wed.
It looks like enough mid-level moisture and increasing afternoon
instability will prevail over the VTU/L.A. County mtns for a
slight chance of thunderstorms Wed afternoon as well.

Otherwise, there will some low clouds and patchy dense fog along
some coastal areas each night and morning through Wed, with mostly
clear skies for the most part expected through the period except
for mostly cloudy skies over VTU/L.A Counties on Tue.

Temperatures will remain quite warm to hot away from the
immediate coast through Wed, with the aforementioned Heat
Advisories in effect through Tue for many areas. The Heat
Advisories may need to be extended into Wed for some areas as
well. However, cloud cover may affect the highs over VTU/L.A.
Counties on Tue, so the confidence in these forecast highs is
moderate.

Highs Mon thru Wed are forecast to be in the 95 to 105 degree
range away from the coast. Warm overnight lows in many areas will
contribute to the heat stress.

.LONG TERM (THU-SUN)...31/154 PM.

Models are in generally good agreement in the extended. It looks
like weak upper level ridging should build into the are on Thu
followed by weak upper level troffiness Fri thru Sun, with a broad
WSW flow aloft.

There is a non-zero chance (around 5-10 percent) of afternoon
thunderstorms over the San Gabriel Mtns Thu and Fri. Otherwise,
dry weather is expected Thu thru Sun. There should be varying
amounts of night and morning low clouds and fog for the central
Coast each day, with some low clouds developing along the L.A.
County coast next weekend. Otherwise, clear to partly cloudy skies
should prevail thru the extended. Temperatures will be near
normal to slightly above normal Thu then fall to several degrees
below seasonal norms by the weekend.

&&

.AVIATION...01/0723Z.

At 0516Z at KLAX, the marine layer was 900 ft deep. The top of
the inversion was at 2200 ft with a temperature of 29 C.

Low confidence in TAFs for KSBA, KOXR, KCMA, KSMO, KLAX, and KLGB
due to uncertainty of low clouds. There is a chance for no low
clouds at KSBA (40%), KOXR (30%), KCMA (30%), KSMO (40%), KLAX
(40%), and KLGB (40%). Otherwise, timing of flight cat changes
may be off +/- 3 hours and minimum cig heights may be off +/- 300
feet. There is a 10-30% chance for vsbys less than 1SM, highest
chances at KOXR and KCMA.

High confidence in remaining TAFs. There is a 15% chance for
VLIFR/LIFR conds between 10Z and 17Z at KSMX and KSBP.

There is a 10-15% chance of showers and/or thunderstorms at any
LA/Ventura site during the late evening hours (after 00Z).

KLAX...Low confidence in TAF through 18Z, then moderate confidence.
There is a 40% chance for no low clouds. If they do arrive, there
is a 25% chance for cigs OVC002-004 and 15% chance vsbys
1/2SM-1SM. Timing of arrival of low clouds may be off +/- 3 hours.
Additionally, there is a 10% chance of light showers and/or
thunderstorms 00Z Tue through at least 12Z Tue. High confidence
that any east wind component will remain below 7 kt.

KBUR...High confidence in TAF.

&&

.MARINE...31/832 PM.

There is a slight chance of thunderstorms over the Inner Waters
south of Point Conception Monday night through Tuesday morning,
especially the waters adjacent to the Los Angeles and Orange
County coasts. Any thunderstorm may produce frequent lightning,
rain, and gusty, erratic winds.

Moderate confidence in 20-25 kt NW winds across the Outer Waters
from Point Sal north to Point Piedras Blancas continuing through
Labor Day (Monday). Moderate confidence in the remaining Outer
Waters remaining below Small Craft Advisory (SCA) criteria through
Monday morning, then a 30% chance of winds increasing to SCA
levels during the afternoon and evening hours Monday. Wednesday
into Thursday, winds will increase across the Outer Waters, with
the highest chances for SCA winds focused around Point Conception
south to San Nicolas Island. A relative lull in winds will be
likely each morning. Winds may decrease some on Friday.

Moderate confidence in forecast for the nearshore waters along
the Central Coast. Winds and seas will remain relatively light
and small into Tuesday, but winds look to increase Wednesday
afternoon and evening with a 20-30% chance of SCA conds.

Aside from seasonal afternoon thru evening localized NW wind
gusts to 20 kts in the far Western Portion of the Santa Barbara
Channel and the San Pedro Channel, light winds and small seas will
be common for the nearshore waters south of Point Conception
through Labor Day. Winds will increase in speed and coverage
Tuesday through Thursday, with a chance of SCA conds Wednesday and
Thursday during the afternoon and evening.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory remains in effect until 6 PM PDT Tuesday for
      zones 38-88-344-345-352-353-356>358-368>379-548. (See LAXNPWLOX).
     Beach Hazards Statement in effect through this evening for
      zones 340-346-354-362-366. (See LAXCFWLOX).
     Heat Advisory now in effect until 6 PM PDT Tuesday for zone
      355. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 3 AM PDT Tuesday for
      zone 670. (See LAXMWWLOX).

&&

$$

PUBLIC...Phillips/Sirard
AVIATION...Lund
MARINE...Ciliberti
SYNOPSIS...Hall/Sirard/Ciliberti

weather.gov/losangeles

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

NWS Flagstaff Office