564
FXUS66 KLOX 190619
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
1119 PM PDT Mon Aug 18 2025

.SYNOPSIS...18/512 PM.

Gusty Sundowner winds and northerly winds through the Interstate 5
Corridor will continue nightly through Wednesday. A significant
multi- day heat event is expected Wednesday through Saturday with
many areas likely to see near record temperatures. There will be
a slight chance of thunderstorms over the Los Angeles and Ventura
County mountains, and portions of the Antelope Valley, during the
afternoon hours Friday through Sunday.

&&

.SHORT TERM (MON-THU)...18/830 PM.

***UPDATE***

***A SEVERAL DAY HEAT EVENT is coming Wednesday through next
 weekend, with a HIGH RISK FOR HEAT ILLNESS AND FIRE DANGER. Now
 is the time to adjust any plans for strenuous outdoor activities
 in the valleys and mountains to the cooler morning hours or for
 another week. If you live in a high fire danger area in the
 mountains or foothills, review your evacuation plans and route
 and stay tuned to your local emergency officials.***

High temperatures today peaked in the mid 80s to 90s away from the
coast, with upper 70s to mid 80s for the interior coastal basins
and 60s to low 70s along the beaches. Further warming is expected
through the work week, peaking Thursday and Friday as described in
the previous discussion below.

Gusty northerly winds are affecting Southwest Santa Barbara County
this evening, expected to increase over the next few hours to
Advisory Levels, with gusts up to 50 mph. The Interstate 5
Corridor will also see increasing north winds after 8-9 pm, but
gusts should remain near or below 35 mph (below Advisory level).
At the same time, onshore/southwest winds are blowing through the
interior passes and canyons of LA County into the Antelope Valley.
These wind patterns are expected to persist each day through
Wednesday night or early Thursday morning.

The marine layer will become increasingly shallow as high pressure
aloft builds over the region. The coastal areas of LA and Ventura
Counties and western Santa Barbara County should see low clouds
moving over the near-coastal areas this evening through late
tonight. There is a chance of stratus forming only briefly for the
LA and Ventura Coasts with early burn off, and a chance of patchy
dense fog in the Santa Maria Valley.

***From Previous Discussion***

A high pressure ridge that is currently over the central US will
migrate westward over the four corners area and build to about 598
dam by Tuesday. This feature will remain fairly constant through
early Sunday when it will begin to weaken and move to the south.
The ridge will drive our extended heat event and associated
impactful fire weather conditions.

Hgts will rise to 592 dam on Tuesday as the upper high migrates
westward. Most areas will warm another 1 to 3 degrees with the
exception of the Central Coast which will cool a few degrees as a
there will be a slightly stronger sea breeze. Max temps will near
seasonal normal. 2 to 3 mb of offshore flow will develop from the
north Tuesday night, likely generating advisory level gusts
stronger than on Monday, 45 to 55 mph, across the western SBA
county south coast but the I-5 corridor as well. The north winds
will keep the low clouds away from the SBA south coast and there
is a chc that they could eliminate many of the coastal low clouds
currently fcst for the LA/VTA coasts.

Hgts climb to 594 dam (or higher) on Wednesday. These hgts will
squash the marine layer down to 600 or 700 ft and place a very
strong capping inversion on top of it. This could create some
dense fog in the morning (most likely across the SBA western
coast) as well as delaying or preventing low cloud clearing at the
beaches in the afternoon. The afternoon gradients will be weaker
than Tuesday and combined with the actual offshore flow in the
morning and the rising hgts will bring 4 to 8 degrees of warming
to most areas. This warming will bring most areas up to 4 to 8
degrees over normal. This heat wave will bring fire weather dangers
as well. Please see the Fire Weather Products and the Fire
Weather discussion section below for additional information.

An EXTREME HEAT WATCH is effect for all of the non-coastal areas.
A watch means that there is the potential for dangerous heat
conditions to develop and is intended to help people prepare for
dangerous heat conditions.

Thursday will warm 3 to 6 degrees. Almost all areas away from the
coast will have triple digit temps with 106 to 109 degree temps
possible in the western San Fernando Vly and Antelope Vly. In
addition to the day time heat, overnight lows in areas above the
strong marine inversion (the vlys and foothills) will have well
above normal overnight lows (some lows may end up in the mid 80s).

.LONG TERM (FRI-MON)...18/147 PM.

The upper high will remain over the four-corners area through
Sunday. The high temperatures will remain in effect, and the
pattern will also bring the potential of afternoon thunderstorm
activity.

Friday will be very similar to Thursday and they will be the
warmest two days of the next 7. Max temps will end up around 10
degrees over normal for the two days. The EXTREME HEAT WATCH
covers both days and the watch will be converted into many
warnings and advisories. High temperature records are possible.
Expect a sharp temperature gradient from the immediate coast
where onshore breezes should keep temperatures down, and just a
few miles inland where where conditions will be very hot.

On Friday the monsoonal flow will raise PWATs to between 1.25 and
1.50 inches and this is enough to bring a slight chc of TSTMs to
the mtns of VTA and LA counties as well as the Antelope Vly. This
brings the risk of both dry lightning, or flash flooding.

There will be slight cooling Sat, Sunday, and Monday as the high
weakens and onshore flow increases. Max temps will still be well
above normal and the monsoon flow will continue to bring higher
than normal humidities which will increase the heat risk. The
slight chc of afternoon mtn/AV TSTMs will continue as well.

&&

.AVIATION...19/0611Z.

At 0505Z at KLAX, the marine layer was 600 feet deep. The top of
the inversion was at 2000 feet with a temperature near 23 deg C.

High confidence in TAFs for KPRB, KWJF, KPMD, KBUR and KVNY.

Good Confidence in TAFs for KSBP and KSBA with only a 15 percent
chc of LIFR conds 11Z-17Z.

Low confidence in TAF for KSMX with a 40 percent chc of LIFR conds
11Z-17Z.

Moderate confidence in all other TAFs. Timing of flight cat
changes could be off by +/- 2 hours. There is a 25 percent chc of
LIFR cigs 11Z-16Z. There is a 25 percent chc of no cigs at KOXR
and KCMA.

KLAX...Moderate confidence in TAF. Low clouds could arrive any
time between 08Z and 12Z. VFR conds could arrive any time
1530Z-1730Z. There is a 25 percent chc of OVC004 conds 11Z-16Z.
Good confidence that any east wind component will be under 7 KT.

KBUR...High confidence in TAF.

&&

.MARINE...18/852 PM.

High confidence in the current forecast.

For the outer waters and the nearshore waters along the Central
Coast, Small Craft Advisory (SCA) level winds and choppy seas will
be common through Wednesday, peaking during the afternoon and
evening hours. Winds will likely fall below advisory levels at
times during the late night through morning hours. Local Gale
Force gusts to 35 knots may occur during the late afternoon and
evening hours each day through Wednesday. Winds and seas will
likely drop below SCA levels between Thursday and Friday
afternoon, but there is a moderate to high chance of SCA level
winds returning from Friday afternoon through the upcoming
weekend.

Inside the southern California bight, there is a 40-60% chance of
SCA level winds each afternoon and evening through midweek,
highest across the western portion of the Santa Barbara Channel.
The highest chances for more widespread winds to spill into the
bight will be on Tuesday evening, but there is a chance for local
SCA level wind gusts near Anacapa Island, near Point Dume, and
into the San Pedro Channel.

&&

.FIRE WEATHER...18/126 PM.

***RED FLAG WARNING IN EFFECT FROM 9 AM WEDNESDAY TO 9 PM PDT
 SATURDAY FOR AN UNSEASONABLY HOT AND UNSTABLE AIR MASS CAPABLE OF
 PRODUCING EXPLOSIVE FIRE BEHAVIOR FROM VERTICAL PLUME
 GROWTH...LOW RELATIVE HUMIDITY...AND LOCALLY BREEZY WINDS FOR
 PORTIONS OF THE MOUNTAINS AND FOOTHILLS OF LOS ANGELES AND
 VENTURA COUNTIES***

***FIRE WEATHER WATCH IN EFFECT FROM THURSDAY MORNING THROUGH
 SATURDAY EVENING FOR AN UNSEASONABLY HOT AND UNSTABLE AIR MASS
 CAPABLE OF PRODUCING EXPLOSIVE FIRE BEHAVIOR FROM VERTICAL PLUME
 GROWTH...LOW RELATIVE HUMIDITY...AND LOCALLY BREEZY WINDS FOR
 PORTIONS OF THE MOUNTAINS AND FOOTHILLS OF SANTA BARBARA AND SAN
 LUIS OBISPO COUNTIES***

The most significant heatwave of the summer season, so far, is
on the way for middle to latter parts of this week and into the
upcoming weekend, from Wednesday through Saturday. 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. The intense surface heating will bring
strong vertical mixing to depths extending over 15-17 thousand
feet -- highest Thursday and Friday. Resultant unseasonably strong
instability will create a fire environment capable of producing
explosive 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 and Fire Weather Watch 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 explosive fire
behavior. And 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 for
Wednesday through Saturday, warranting the issuance of a Red Flag
Warning and a Fire Weather Watch 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 explosive fire
behavior and the growth of large fires. Interests in the Red Flag
Warning and Fire Weather Watch 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 Watch in effect from Wednesday afternoon through
      Saturday evening for zones
      38-88-342>345-348-353-356>358-369-371>383-548. (See LAXNPWLOX).
     Wind Advisory remains in effect until 5 AM PDT Tuesday for
      zones 349-351. (See LAXNPWLOX).
     Extreme Heat Watch in effect from Thursday afternoon through
      Friday evening for zones 351-352-368-370. (See LAXNPWLOX).
     Red Flag Warning in effect from 9 AM Wednesday to 9 PM PDT
      Saturday for zones 288-375>382. (See LAXRFWLOX).
     Fire Weather Watch in effect from Thursday morning through
      Saturday evening for zones 345-351>353. (See LAXRFWLOX).
PZ...Small Craft Advisory in effect until 3 AM PDT Tuesday for
      zone 645. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PDT Wednesday for
      zones 670-673-676. (See LAXMWWLOX).

&&

$$

PUBLIC...Rorke/jld/Ciliberti
AVIATION...Rorke
MARINE...Phillips/Lund
FIRE...Cohen/Gomberg
SYNOPSIS...jld/Ciliberti

weather.gov/losangeles

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