499
FXUS66 KLOX 230324
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
824 PM PDT Fri Aug 22 2025

.SYNOPSIS...22/139 PM.

Near record heat will continue across the region through Sunday
as a hot air mass will remain in place through the weekend. High
pressure aloft over the Four Corners Region will linger through at
least Sunday. Showers and thunderstorms will be possible over the
Los Angeles and Ventura County mountains, and portions of the
Antelope Valley, during the afternoon and evening hours through
Monday. A few showers spilling over into the valleys and foothills
cannot be ruled out over the weekend. A cooling trend is expected
for next week as an upper-level trough approaches the West Coast.

&&

.SHORT TERM (FRI-MON)...22/824 PM.

***UPDATE***

A solid and very shallow low cloud layer is blanketing the
Central Coast beaches and ocean areas. Another smaller patch is
off the Los Angeles and Orange County coasts. With such a strong
marine inversion, dense fog with very low visibilities will be an
issue heading into Saturday.

Cloud debris from a huge area of convection over north-central
Mexico will be headed our way overnight into Saturday. For
Saturday morning, ample and widespread mid-level clouds are
certain. Virga or light big drop showers are likely. A few
thunderstorms are possible and cannot be counted out. Added that
to the forecast as a result. By the afternoon, any thunderstorm
activity will likely shift to the interior. It could be rather
active with healthy precipitable water values, instability, and a
few upper level disturbances to initiate things. With a lingering
hot and dry layer near the surface, the main threat from any storm
will be lightning (causing a fire or a danger unto itself) and/or
isolated strong winds (like what happened in Barstow this
afternoon). The higher elevations of the mountains above that dry
layer could see all that as well as an isolated brief heavy
shower.

The heat remains in play and no changes planned on our Heat
Warnings and Advisories. The extra clouds to start Saturday could
actually help make it feel like a hot day, by keeping the morning
warmer than it has been and adding some humidity feel by the
afternoon.


***From Previous Discussion***

Another very hot day south of Pt Conception with just minimal
cooling of 1-3 degrees at most, and across the far interior
temperatures were slightly warmer. Along the Central Coast, a wind
reversal from north to south ushered in much cooler air off the
ocean and some areas were more than 10 degrees cooler than
yesterday.

For Saturday south of Pt Conception, still expecting temperatures
to range from 5-10 degrees above normal, with isolated areas
10-15 above normal. Therefore, all the heat hazards currently in
effect there will continue. And with minimal if any additional
cooling expected Sunday confidence was high enough to go ahead
and extend all those hazards through Sunday. There is still a
minor concern for increasing clouds from the monsoon moisture to
cut into the temperatures somewhat but at least at lower
elevations it was felt that the impacts of that would be
negligible.

Along the Central Coast a return of the marine layer and onshore
flow will continue the cooling trend there.

Models are still showing PW`s increasing to around 1.5" Saturday
as the monsoon push reaches its peak. However, the bulk of the
moisture is expected to be at or above 700mb (roughly 10,000 ft).
With increasingly dry air below that level, it may be difficult to
get much precip below about 5000`. High res models do indicate
the potential for showers and storms to move through the LA Basin
as early as Saturday morning, but the chances for any measurable
rain is under 20%. Certainly can`t rule out a few sprinkles with
big drops reaching the surface or even a stray lightning strike.
And possibly some gusty outflow winds at times from evaporative
cooling effects. Better chances for showers and storms in the
LA/Ventura mountains but again with the high moisture bases rain
rates are expected to stay below a half inch per hour.

The cooling trend will continue into Monday with highs dropping
another 2-5 degrees and heat risk values dropping below advisory
thresholds. Still a small risk for afternoon convection over the
mountains but PW`s will be on the decrease as the upper level flow
veers to the southwest.

.LONG TERM (TUE-FRI)...22/223 PM.

Ensemble solutions continue to show high confidence in a continued
slow but steady cooling trend through middle of next week. Most
areas are expected to be at or slightly below normal by Wednesday,
then temperatures remaining fairly steady thereafter through next
weekend. However, there is a chance that monsoon flow will
continue across the area, at least the eastern mountains. Small
rain chances remain in the forecast for the mountains despite a
less than favorable upper level pattern along the West coast.

&&

.AVIATION...22/1658Z.

At 1600Z at KLAX, the marine inversion was based at 800 feet. The
top of the inversion was 3400 feet with a temperature of 29 C.

For 18Z TAF package, high confidence in desert/valley TAFs as VFR
conditions are expected through the period.

For coastal sites, moderate confidence in 18Z TAFs. For sites
south of Point Conception, there is a 20-30% chance of LIFR/VLIFR
conditions 08Z-16Z. North of Point Conception, there is a 40%
chance of LIFR/VLIFR conditions at KSBP 08Z-16Z and a 50% chance
that CIG/VSBY restrictions do not develop at KSMX.

KLAX...Moderate confidence in 18Z TAF. There is a 20% chance of
LIFR/VLIFR conditions 09Z-16Z. No significant easterly wind
component is expected.

KBUR...High confidence in 18Z TAF.

&&

.MARINE...22/124 PM.

For the Outer Waters, moderate to high confidence in current
forecast. Through tonight, high confidence in Small Craft Advisory
(SCA) level winds across PZZ670/673 with winds remaining below SCA
levels across PZZ676. For Saturday through Wednesday, there is a
30-50% chance of SCA level winds, with the best chances around
Point Conception.

For the Inner Waters north of Point Sal, high confidence in
current forecast. Tonight through Wednesday, winds and seas are
expected to remain below SCA levels.

For the Inner Waters south of Point Conception, moderate to high
confidence in current forecast. For a majority of the southern
Inner Waters, high confidence in winds and seas remaining below
SCA levels tonight through Wednesday. The only exception will be
the western half of the Santa Barbara Channel, where there will be
a 20-30% chance of SCA level winds Sunday through Wednesday,
mainly in the late afternoon and evening hours.

Fog coverage will limited through the weekend, but random patches
are possible each morning. Any fog that forms will be dense with
visibilities under one mile.

&&

.FIRE WEATHER...22/333 PM.

***RED FLAG WARNING IN EFFECT UNTIL 9 PM PDT SATURDAY FOR AN
 UNSEASONABLY HOT AND UNSTABLE AIR MASS CAPABLE OF PRODUCING
 EXTREME FIRE BEHAVIOR FROM VERTICAL PLUME GROWTH...LOW RELATIVE
 HUMIDITY...AND RISK OF DRY LIGHTNING FIRE STARTS WITH GUSTY
 ERRATIC WINDS FOR PORTIONS OF THE MOUNTAINS AND FOOTHILLS OF LOS
 ANGELES, VENTURA, SANTA BARBARA, AND SAN LUIS OBISPO COUNTIES***

The most significant heatwave of the summer season will continue
through Sunday. Expect temperatures to soar into the 96-106
degree range over interior areas, except locally reaching near
110 degrees today. The intense surface heating will bring strong
vertical mixing to depths extending over 12-18 thousand feet
through the weekend. Resultant unseasonably strong instability
will create a fire environment capable of producing extreme fire
behavior through significant vertical plume growth, as minimum
relative humidity ranges from 8 to 20 percent in the dry air mass.
Overnight relative humidity recovery will be poor to moderate,
while the shallow marine layer generally remains displaced closer
to the beaches.

The Red Flag Warning areas cover portions of the mountains and
foothills of Los Angeles, Ventura, Santa Barbara, and San Luis
Obispo Counties, which have been a climatologically notorious area
for large plume-dominated fires in similar weather patterns to
what is happening through the weekend. While background surface
winds are not expected to be strong, or even close to reaching
nominal Red Flag Warning criteria, they will be locally breezy in
the afternoon and evening over the western Antelope Valley
Foothills and vicinity and in other wind-favored areas such as
through passes and canyons -- sustained winds 10-20 mph gusting to
25-30 mph following diurnal- wind patterns. These winds will
exacerbate the spread of any plume-dominated fires, and add to the
potentially dangerous fire- weather environment.

Moreover, the western edge of a southwest-states monsoonal
moisture influx will overspread the area through the weekend.
The main threat (20-40% chance) of thunderstorms will be across
the mountains of LA/Ventura counties and Antelope Valley, there
is a 5-15% chance for remaining areas (starting Saturday),
including coasts and valleys. This will mostly be high based
convection, with the main threats being isolated dry lightning
strikes and strong/erratic outflow/downburst winds. In fact, many
of the model sounding show an inverted-v structure, indicative of
the dry lightning and gusty downburst risks. The influx of mid
level moisture will bring a better threat of wetting rain across
the higher mountains, with a small but non-zero threat of
localized flash flooding/debris flow concerns (including the
Bridge Fire burn scar). The increase in buoyancy will further
aid in vertical plume growth accompanied by potential pyrocumulus
development and related extreme fire behavior. Combined with
significant fuel loading of exceptionally dry fuels, the fire
environment in the mountains and foothills of Los Angeles and
Ventura Counties remains especially volatile through Saturday,
warranting the Red Flag Warning upon collaboration with local
area National Weather Service Core Partners.

Analogs to the forthcoming, highly volatile fire-weather
environment in Los Angeles County include the Station Fire in
2009, the Bobcat Fire in 2020, the Lake Fire in 2024, and the
Bridge Fire in 2024, which burned significant portions of
forested areas. In each case, winds were generally below Red Flag
Warning criteria, yet the extreme heat combined with buoyancy
greatly offset the sub-marginal wind to create extreme fire
behavior and the growth of large fires. Interests in the Red Flag
Warning areas should be prepared for similar activity if fires
were to start. Also, be aware of passing outflow boundaries that
could bring sudden wind-shifts and increased fire-spread rates,
even from distant thunderstorms.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Extreme Heat Warning in effect until 9 PM PDT Sunday for
      zones 38-88-342>345-348-351>353-368>383-548. (See LAXNPWLOX).
     Heat Advisory remains in effect until 9 PM PDT Saturday for
      zones 87-349-350-354-355-362-366-367. (See LAXNPWLOX).
     Heat Advisory remains in effect until 9 PM PDT this evening
      for zones 341-347. (See LAXNPWLOX).
     Heat Advisory remains in effect until 9 PM PDT Sunday for
      zones 356>358. (See LAXNPWLOX).
     Red Flag Warning in effect until 9 PM PDT Saturday for zones
      288-345-351>353-375>382. (See LAXRFWLOX).
PZ...Small Craft Advisory in effect until 3 AM PDT Saturday for
      zones 670-673. (See LAXMWWLOX).

&&

$$

PUBLIC...MW/Kittell
AVIATION...RAT
MARINE...RAT
FIRE...Cohen/Gomberg/Lund
SYNOPSIS...MW/Hall

weather.gov/losangeles

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