366
FXUS66 KLOX 011242
AFDLOX

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

.SYNOPSIS...01/444 AM.

High pressure aloft centered near the Four Corners region will
keep a very warm to hot air mass across the region through mid
week. Monsoonal moisture will arrive again on Monday night and
Tuesday and keep a risk of showers and thunderstorms through the
remainder of the week. A cooling trend is possible by the upcoming
weekend.

&&

.SHORT TERM (TDY-WED)...01/444 AM.

The latest satellite imagery shows a ridge of high pressure aloft
over the Four Corners region this morning. Another very warm to
hot day is expected over the area today, but temperatures will be
much more problematic across the coastal areas as onshore flow is
a little more strongly in place this morning. To the north, the
latest forecast ensembles are trending warmer along the Central
Coast with values several degrees above the latest deterministic
forecast model output. The forecast leans warmer along the Central
Coast, but south of Point Conception, the stronger onshore flow
combined with the presence of low clouds and fog is causing a bit
more uncertainty in the heat advisories across the interior
coastal sections. Low cloud coverage and onshore pressure
gradients will need to watched closely today. It is possible the
interior coastal sections south of Point Conception could end up
cooler. Thus, there is a moderate chance that the heat advisory
headlines could be ended early.

All eyes are on the convection blowing up over Baja California
this morning. The high-resolution ensemble members and
deterministic solutions move this area of convection over eastern
Santa Barbara, Ventura, and Los Angeles Counties between this
evening and Tuesday. There is a non-zero chance of showers and
thunderstorms over the Los Angeles and Ventura County mountains
this afternoon, but the most of the emphasis will be placed on
tonight and into Tuesday as monsoonal moisture moves over the
region. A warm and humid air mass will move into the region
through Tuesday with embedded sprinkles or showers. PoPs were
trended much higher inline with NBM values, but the forecast
modifies PoPs to emphasize more favorable areas in the convective
air mass. The one wrinkle could be the cloud shield putting a
damper on convective development. Typically, cloudy skies can
inhibit shower development with monsoonal surges northward. This
could also cut into temperatures to keep the heat advisory on the
cooler side of normal. That being said, mid-level CAPE values are
elevated enough to produce chances for showers and thunderstorms
over the next several days. With EPS precipitable water value
means approaching 1.50 inches overnight tonight at KLAX, there is
some concern for brief heavy downpours with any showers and
thunderstorms. WPC is highlighting eastern Los Angeles County with
a marginal area for excessive rainfall on Tuesday and Tuesday
night. While the steering flow looks strong enough to move storms,
an isolated storm producing flash flooding cannot be ruled out.

Between Tuesday night and Wednesday, the latest model solutions
want to push a shortwave trough through Mexico and potentially
develop it into a mesoscale convective complex over the Mojave
Desert. This feature will hang out over the California desert
into late week and potentially create a mechanism for firing
convection each afternoon on Wednesday and Thursday. A warm and
humid air mass is likely to remain in place through late week.
With a little more solar insolation and a lighter steering flow
on Wednesday, there is some concern that Wednesday could end up
being the more convective days with slower moving storms.

With the monsoonal moisture moving into the area, low confidence
should be placed in temperatures and the low cloud forecast
through Wednesday. Any cloudiness with the monsoonal flow, could
play tricks on the marine inversion and mess with low cloud
formation processes. There is a decent chance that low clouds and
fog could be patchy at best through late week. In addition, any
clouds with the monsoonal pattern could mess with the radiative
cooling properties and daytime solar insolation. Overnight low
temperatures could be warmer than forecast, while daytime
temperatures could be cooler than forecast.

.LONG TERM (THU-SUN)...01/440 AM.

Chances for showers and thunderstorms could linger into Thursday
and Friday across the mountains and desert as instability remains
in place and the shortwave trough lingers. A warm and humid
pattern is likely to persist into Thursday or Friday.

Southwest flow aloft should establish between Friday and Saturday
and finally kick out the warm and humid pattern and bring in a
more stable and drier air mass. A return to maritime source region
should allow for low clouds and fog to make a more pronounced
return to the coastal areas over the weekend. As a result, a
cooling trend should be expected.

&&

.AVIATION...01/1241Z.

At 1135Z at KLAX, the marine layer was 800 ft deep. The top of
the inversion was at 3200 ft with a temperature of 28 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%). If cigs do arrive, they will likely scatter
and reform frequently. 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, they
may scatter and reform frequently. Additionally, 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...01/208 AM.

There is a slight chance of thunderstorms over the Inner Waters
south of Point Conception tonight 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
today. Moderate confidence in the remaining Outer Waters
remaining below Small Craft Advisory (SCA) criteria through this
morning, with a 30% chance of winds increasing to SCA levels
during the afternoon and evening hours today and Tuesday.
Wednesday through Friday, 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.

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 each afternoon
and evening Wednesday through Friday, 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 today. Winds will increase in speed and coverage Tuesday
through Thursday, with a chance of SCA conds Wednesday and
Thursday during the afternoon and evening across western portions
of the waters, as well as near Point Dume and into the San Pedro
Channel.

&&

.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...Hall
AVIATION...Lund
MARINE...Ciliberti/Lund
SYNOPSIS...Hall

weather.gov/losangeles

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