753
FXUS66 KLOX 030622
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
1122 PM PDT Tue Sep 2 2025

.SYNOPSIS...02/753 PM.

Very warm conditions will continue through Wednesday, including
overnight with fairly high humidity, then temperatures will lower
some through the week. Monsoonal moisture will remain over the
region through at Thursday, peaking through Wednesday, bringing
risks of strong winds, brief heavy downpours, lightning, and fire
starts - highest towards Los Angeles County.

&&

.SHORT TERM (TUE-FRI)...02/839 PM.

***UPDATE***

Following the overnight convection over interior San Luis Obispo
and Santa Barbara Counties, showers and thunderstorms formed over
the higher Ventura Mountains in the vicinity of Lockwood Valley
this afternoon into the early evening hours. Radar indicated
heavy downpours with likely flash flooding. The rain gauge
network is sparse in this area, but one gauge showed 0.20 inch of
rain in 30 minutes and it is likely that heavier rain fell in
other areas based on radar imagery and derived rain rates.

By 800pm this evening, activity has subsided and is not expected
to return for the overnight period through Wednesday morning. For
Wednesday afternoon and evening, showers and thunderstorms will be
possible from far SE San Luis County and eastward across the
Ventura Mountains, the Antelope Valley and the San Gabriels. The
best chances will be over the Ventura Mountains and especially
over interior LA County. There will be a chance of moderate to
heavy downpours in any thunderstorm that forms, due to precipitable
water values of 1.25 to 1.50 inches. The risk of heavy downpours,
and the resulting risk of flash flooding, will be highest over
the San Gabriels where the instability is greatest. A Flash Flood
Watch remains in effect for this area, and the Antelope Valley,
through Wednesday evening. Will also need to watch the Ventura
Mountains again due to model projections of moisture and
instability in this area.

***From Previous Discussion***

A 595 decameter (at 500 millibar) high, currently centered over
Utah, will continue to churn up monsoonal moisture through Thursday
over southwest California. A few notable impulses from convection
over Mexico, often called easterly waves, will rotate up with the
flow. These features provide the forcing for thunderstorms really
anywhere, and often in a widespread and organized manner. That is
what we saw this morning. Another wave, caused by the massive
convection currently over northern Mexico and southwest Arizona,
will rotate northward tonight. While all the projections keep the
direct impacts of this feature east of Los Angeles County, some
are a little too close to completely call the all clear. So slight
chance wording was added for overnight period for eastern Los
Angeles County. By tomorrow afternoon, expecting more convection
over the mountains and deserts in our 4 county area, with the
highest chances over Los Angeles County once again. With precipitable
water values between 1.25 and 1.50 inches once again, there remains
a moderate threat for heavy rain inducing flash flooding over the
San Gabriels and Antelope Valley...where the moisture and
instability are most abundant. We may be able to skate through
without any flash flooding, but would be totally surprise if we
did not see heavy rain somewhere in our area. So the threat is
high enough to keep the Flood Watch going. The moisture will start
to move to the east on Thursday, with a lingering chance over the
mountains and deserts. By Friday, most projections now show dry
southwest flow aloft as what is now Tropical Storm Lorena pushes
into northern Mexico and draws all the moisture to the east. As
with any tropical system, there is always some uncertainty on the
path. If the remnants veer to the west at all, we might still be
in the potential for thunderstorms, but at this point it seems
most likely that our thunderstorms will end on Thursday.

On the wind front, some fairly strong easterly winds associated
with all the convection impacted portions of our area today,
currently focused over the Antelope Valley. Most of the
projections show the east wind weakening overnight, but covering
more of the area by Wednesday as that disturbance mentioned
earlier moves northward.

While most of the area will see temperatures drop a degree or
three tomorrow, coastal and nearby valley areas of Los Angeles and
Ventura Counties likely will see similar if not warmer conditions
on Wednesday thanks to that easterly offshore flow. With humidity
values staying up and overnight temperatures tonight staying on
the order of 10 to 15 degrees above normal, decided to extend the
Heat Advisories there one more day. The rest of the area will
again remain warm, but the Heat Advisories will be allowed to
expire at 6pm tonight as temperature start to lower.

.LONG TERM (SAT-TUE)...02/211 PM.

Other than the low potential wrinkle of a more westerly track of
Tropical Storm Lorena, Friday through Monday looks fairly quiet.
Temperatures will return to around normal by Friday with a little
more marine layer. High pressure aloft with some warming looks
favorable starting Monday or Tuesday, but the risk for any Heat
Advisories or Warnings at this point is very small.

&&

.AVIATION...03/0621Z.

At 0515Z at KLAX, the marine layer was 800 ft deep. The top of
the inversion was near 1500 feet with a temperature of 30 C.

AT 0600Z there was a national METAR outage and there will be
limited or no amendments until obs are restored.

Good confidence in TAF from KSBA and south. Moderate confidence in
TAF for KSBP with a 30 percent chc of LIFR conds 11Z-16Z. Moderate
confidence in KSMX with a 25 percent chc of 1/4SM FG conds
09Z-15Z.

There is a 10 percent chc of a shower or TSTMs at all LA county
sites 20Z-02Z with the exception of a 20 percent chc at KPMD and
KWJF.

KLAX...Good confidence in TAF. There is a 10 percent chc of OVC004
conds 12Z-16Z. There is a 10 percent chc of a TSTM within 5SM of
the terminal from 20Z-02Z. Good confidence that any east wind
component will be under 6kt.

KBUR...Good confidence in TAF. There is a 10 percent chc of a
TSTM within 5SM of the terminal from 20Z-02Z.

&&

.MARINE...02/859 PM.

Moderate confidence in NW winds 20-25 kts across the Outer Waters
at times through the end of the week, especially in the afternoon
and evening hours. Winds will be initially strongest focused
south of Point Conception. Chances for Small Craft Advisory (SCA)
winds increase across the northern Outer Waters and nearshore
waters from Point Sal to Point Piedras Blancas by Wednesday.

For the Santa Barbara Channel and the Inner Waters adjacent to
Los Angeles and Orange Counties, Small Craft advisory level WNW
winds are again possible across the western SBA Channel to Santa
Cruz Island and from the Anacapa Pass south through the San Pedro
Channel during the afternoon to evening hours Wednesday, but look
lighter than today so there is a 40% chance for an SCA to be
issued tomorrow. Winds look stronger for the same area Thursday
afternoon and evening, with a 50-60% chance for SCA to be issued.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory remains in effect until 6 PM PDT Wednesday for
      zones 88-355>358-368>375-548. (See LAXNPWLOX).
     Flood Watch in effect through Wednesday evening for zones
      379>383. (See LAXFFALOX).
PZ...Small Craft Advisory in effect until 3 AM PDT Thursday for
      zones 673-676. (See LAXMWWLOX).

&&

$$

PUBLIC...Kittell/Ciliberti
AVIATION...Rorke
MARINE...Phillips/Lewis
SYNOPSIS...RK/CC

weather.gov/losangeles

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

NWS Flagstaff Office