874
FXUS66 KLOX 021636
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
936 AM PDT Tue Sep 2 2025

.SYNOPSIS...02/925 AM.

Very warm conditions continue through today or Wednesday then
lower some through the week. Monsoonal moisture will remain over
the region through at least Wednesday, bringing risks of strong
winds, brief heavy downpours, lightning, and fire starts - highest
risks towards Los Angeles County.

&&

.SHORT TERM (TDY-THU)...02/935 AM.

***UPDATE***

Showers and thunderstorms were very active this morning east of
Los Angeles County. These storms produced a strong outflow with
gusts of 50 to 70 mph registered on mutiple weather stations over
primarily Riverside County. That outflow is starting to push into
eastern Los Angeles County (but of a weaker variety) which is
initiating fresh convection from the San Gabriel Valley to the
Antelope Valley. Expecting activity to increase over the next few
hours with storms possible anywhere over Los Angeles County and
possibly Ventura County. Areas to the north should stay clear this
morning. Over the afternoon hours, the action will shift to the
traditional interior areas. While the San Gabriel Mountains and
the northern Ventura County Mountains are nearly a slam dunk for
convection this afternoon, any mountain or interior valley from
Los Angeles County to San Luis Obispo County will be in the
thunderstorm window. Any storm that forms will bring risks of
strong winds, brief heavy downpours, lightning, and fire starts.
Higher elevations have a greater threat for heavy rain than lower
elevations with moderately dry air closer to sea-level. The Flood
Watch for northern Los Angeles County still looks good.

Temperatures will be very tricky with all the clouds, convection,
and outflow. With nearly all models showing easterly flow
tomorrow morning, coastal and valley areas may be just as warm
tomorrow as today. While the current plan is for no changes to
what is now a borderline Heat Advisory, will be assessing that
more and coordinating with neighboring offices. Will hopefully
make a decision if the LA and Ventura County coastal and valley
Heat Advisories need to be pushed one more day or not.

***From Previous Discussion***

Southern CA is sandwiched between a 593 dam upper high over UT
and a high hgt (582 dam) upper low just to the west of Monterey.
There is moist unstable S to N flow between the two systems.
Currently there is a narrow band of PVA that has triggered a line
of convection across eastern SBA and SLO county and extending
almost due south into the coastal waters. These storms are moving
fairly quickly and do not pose much of flood threat. As the day
progresses the area of greatest instability will shift to the east
over LA county. This is also the area which will contain the
greatest amount of moisture. These two areas will converge late
this morning and will create an environment favorable for TSTM
induced flash flooding and a flood watch is in effect for the mtns
of LA/VTA Counties and the Antelope Valley from 11 AM today all
the way to 11 PM Wed. Most of the Bridge Fire Burn Scar is
included in the watch area. In addition to the flood risk there is
also a potential for TSTM produced wind gusts to 60 mph. In
addition to the risk of TSTMs there is also a heat risk due to
the combination of warmer than normal temperatures and humidity.
Temperatures today could be tricky due to the high clouds. Still
even if temps do cool the increase in humidities will be to keep
the heat danger going.

The upper low will continue to bring pockets of vorticity to the
area tonight and the threat of TSTMs will continue. Tonight,
however, the threat will be confined to the LA/VTA mtns and AV.
Low clouds will likely form again across many of the coastal
sections, but they ma be disrupted in places from the clouds
streaming overhead.

The TSTM threat will continue Wednesday. The threat will be
confined to the LA/VTA county mtns, the AV and the eastern portion
of the San Gabriel Vly. The steering flow is weaker than it is
today and this will increase the flooding risk. Max temps will
cool 2 or 3 degrees - this may not be enough to end the heat risk
and the heat advisories may need an extension into the early
evening.

The upper high pushes to the east on Thursday and troffing will
move into the state. This will increase the odd of a more robust
coastal marine cloud layer. There will be just enough moisture for
a slight chc of afternoon TSTMs over the LA/VTA mtns. The lower
hgts and stronger onshore flow will bring 3 to 6 degrees of
cooling to the area and this will be enough to eliminate the need
for heat advisories.

.LONG TERM (FRI-MON)...02/327 AM.

Long wave troffing sets up over the west coast on Friday and
continues into Saturday. Onshore flow increases as well. This will
lead to an increase in the morning marine layer cloud layer and a
couple degrees of cooling each day.

On Sunday and continuing into Monday a ridge will nudge up from
the north. An increase in onshore flow, however, will negate any
possible warming from the rising hgts.

&&

.AVIATION...02/1317Z.

At 1233Z at KLAX, the marine layer was 1000 ft deep. The top of
the inversion was near 3200 feet with a temperature of 27 C.

Low confidence in low cloud forecast as low clouds could form,
dissipate, and reform as the high level mositure passes overhead.
There is a 25 percent chc of IFR cigs at KPRB, KBUR and KVNY
12Z-15Z.

There is a 25 percent chc of a less than 1 hour in duration shower
or TSTM at all sites through 06Z Wed except for a 30 to 40
percent chc for KPMD and KWJF.

KLAX...Low confidence in TAF. Low clouds may move into and and out
of the area through 16Z. There is a 20 percent chc of a brief
shower or TSTM through 06Z Wed. High confidence that any east
wind component will remain below 7 kt.

KBUR...Moderate confidence in TAF. There is a 25 percent chance
of showers and thunderstorms through 06Z Wed.

&&

.MARINE...02/747 AM.

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

Today through Thursday night, winds will increase across the
central and southern outer waters, with the highest chances of
Small Craft Advisory (SCA) level winds focused around Point
Conception and southward to San Nicolas Island. A relative lull
in winds will be likely each morning. There is a 40% chance of SCA
level winds across all the outer waters during the afternoon and
evening hours Friday through the weekend.

Moderate confidence in forecast for the nearshore waters along
the Central Coast. There is a 20-30% chance of SCA winds each
afternoon and evening through the weekend.

Winds will increase in speed and coverage across the nearshore
waters South of Point Conception, with a 40-50% chance of SCA
conds during the afternoon and evening hours today through
Thursday (decreasing to 30% for the same hours Friday through the
weekend) across western portions of the waters. Localized gusts to
25 kt may occur in the San Pedro Channel and near Point Dume
during these times. A SCA was issued for the Santa Barbara
Channel this afternoon into the evening, with strongest winds in
the western portion of the Channel.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory remains in effect until 6 PM PDT this evening
      for zones 38-88-344-345-352-353-355>358-368>379-548. (See LAXNPWLOX).
     Flood Watch in effect through Wednesday evening for zones
      379>383. (See LAXFFALOX).
PZ...Small Craft Advisory in effect from 3 PM this afternoon to 9
      PM PDT this evening for zone 650. (See LAXMWWLOX).
     Small Craft Advisory in effect from 3 PM this afternoon to 3
      AM PDT Thursday for zones 673-676. (See LAXMWWLOX).

&&

$$

PUBLIC...Rorke/Kittell
AVIATION...Rorke/Lund
MARINE...Lund/Lewis
SYNOPSIS...RK

weather.gov/losangeles

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