995
FXUS66 KLOX 220300
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
800 PM PDT Thu Aug 21 2025

.SYNOPSIS...21/119 PM.

A significant multi-day heat event will continue today and will
last through the weekend with many areas likely to see near record
temperatures. There will be a chance of thunderstorms over the
Los Angeles and Ventura County mountains, and portions of the
Antelope Valley, during the afternoon hours Friday through Monday.
Cooler conditions are expected next week.

&&

.SHORT TERM (THU-SUN)...21/800 PM.

***UPDATE***

As expected, a very hot day across the area. Beaches topped out in
the 80s to lower 90s across many areas with inland area climbing
into the upper 90s to 109. As for winds, there are still some
lingering onshore/southwesterly winds, gusting 15-25 mph.

Forecast-wise for the immediate short term, no significant issues
are expected. Overnight lows will remain quite warm, generally in
the 60s to mid 70s although some foothill areas may only cool to
around 80 degrees tonight. So, current suite of heat products
still very much on track, especially with Friday expected to be
warmer than today. Otherwise, no issues are expected overnight.
With only some scattered high clouds drifting overhead, and no
stratus/fog, skies will remain mostly clear overnight.

Overall, current forecast has great handle on the immediate short
term. So, no significant updates are planned.

***From Previous Discussion***

The hot weather has arrived with highs of 105 or higher across the
western San Fernando Valley and the deserts and very close to 100
in San Luis Obispo and the Santa Ynez Valley. Expecting a very
similar day tomorrow in most areas, except across the Central
Coast where a reversal of the winds from northeast to south will
likely bring temperatures down at least 3-6 degrees. Heat
advisories and Extreme heat warnings remain in effect at least
through Friday, with most areas except the Central Coast in effect
through Saturday. Most of the forecast models show 2-4 degrees of
cooling area-wide on Saturday, but given the warm overnight
temperatures and daytime highs still 5-10 degrees above normal
heat risk values remain quite high. In fact, models continue to
indicate very little change in temperatures between Saturday and
Sunday so there`s a greater than 50 percent chance that many, if
not all, the heat hazards will be extended into Sunday.

The one fly in the ointment with regard to temperatures as we
move into the weekend is the expected arrival of monsoon moisture.
Models continue to show PW`s increasing Friday and peaking
Saturday at around 1.5". If cloud cover ends up being more than
expected that could cut into the afternoon temperatures so will
have to see how that develops Saturday. Moisture is expected to be
fairly high based, at least 10,000 feet, but still could see some
brief heavy rain in the LA/Ventura mountains, with some of that
drifting north into the Antelope Valley. Max rain rates are
expected to be under a half inch per hour. Still can`t completely
rule out a shower or storm over the lower elevations but given the
lack of any triggers aloft most of these storms should initiate
over the mountains and move north.

.LONG TERM (MON-THU)...21/212 PM.

The cooling trend will become more pronounced Monday with most
areas cooling 3-6 degrees as the high begins to retreat to the
east. Most areas will fall back to within 2-4 degrees of normal
for this time of year with a possible return of the marine layer
to some coastal areas. Additional cooling Tuesday and Wednesday
will bring temps down to slightly below normal.

Many of the ensemble solutions are indicating the monsoon pattern
will continue through the middle of next week as a convective
activity over central Mexico increases and a favorable upper level
pattern brings that moisture into southern California. For that
reason shower and thunderstorm chances continue through Wednesday,
again mainly over the mountains and deserts.

&&

.AVIATION...22/0247Z.

At 00Z over KLAX, no marine layer was present. There was a surface
based inversion present. The top of the inversion was 3600 feet
with a temperature of 30 degrees Celsius.

There is a 10-20 percent chance of LIFR/IFR ceilings at any
coastal airport 07-15Z Friday, but KOXR and KSMX seem to have the
highest chances. Otherwise high confidence in VFR conditions
continuing through at least Friday.

KLAX...There is a 15 percent chance of LIFR to IFR conditions
Friday 11-16Z. Otherwise high confidence in VFR conditions
continuing. High confidence in any early morning easterly winds
staying below 06 knots.

KBUR...High confidence in VFR conditions through at least Friday
with seasonal winds.

&&

.MARINE...21/154 PM.

High confidence in winds staying below Gale Warnings everywhere
through at least Tuesday. Moderate confidence in Small Craft
Advisories (SCA) being common each day through at least early next
week for the waters beyond 20 miles from shore from the Central
Coast the Santa Rosa Island. Those winds however will likely not
last as long as usual with longer lulls in the morning and early
afternoon hours. The waters from Santa Rosa to San Nicolas will be
weaker than usual, and likely not SCA starting tonight or Friday
and lasting through at least the weekend. Very low-end SCA in
affect for the nearshore waters of the Central Coast today, but
the winds very nearshore will likely be more typical. The rest of
the area will stay under SCA, except for brief and localized gusts
of 20-25 knots each afternoon in the typically windiest
locations.

There is a non-zero chance of isolated thunderstorms over the
waters over the weekend. While a monsoonal surge is likely during
this time, confidence is very low on if, where, and exactly when
any thunderstorms may form.

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...21/208 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 LOCALLY BREEZY 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, so far, has
begun and will continue through Sunday. Expect temperatures to
soar into the 95-105 degree range over interior areas, locally
reaching near 110 degrees over some mountain valley and desert
locations, peaking Today and Friday. The intense surface heating
will bring strong vertical mixing to depths extending over 15-17
thousand feet -- highest Today and Friday. 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 coming this week into 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 overlie Los Angeles and Ventura Counties,
which will contribute to the development of atmospheric buoyancy
by Friday and this weekend without significantly moistening the
air mass -- i.e., displaced away from the core of the moisture
source. While lightning-induced fire ignitions are a distinctive
possibility on the peripheries of rain cores, 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 will become especially volatile
through Saturday, warranting the issuance of a 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 Saturday for
      zones 38-88-342>345-348-351>353-368>383-548. (See LAXNPWLOX).
     Heat Advisory remains in effect until 9 PM PDT Friday for
      zones 341-347-367. (See LAXNPWLOX).
     Heat Advisory now in effect until 9 PM PDT Saturday 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 9 PM PDT this evening
      for zone 645. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PDT Saturday for
      zones 670-673. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PDT Friday for zone
      676. (See LAXMWWLOX).

&&

$$

PUBLIC...MW/Thompson
AVIATION...Phillips/Kittell
MARINE...Kittell
FIRE...Cohen/Gomberg/Lund
SYNOPSIS...MW

weather.gov/losangeles

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