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WWUS86 KLOX 182016
RFWLOX

URGENT - FIRE WEATHER MESSAGE
National Weather Service Los Angeles/Oxnard CA
116 PM PDT Mon Aug 18 2025

...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.

CAZ288-375>382-240400-
/O.UPG.KLOX.FW.A.0006.250820T1600Z-250824T0400Z/
/O.NEW.KLOX.FW.W.0005.250820T1600Z-250824T0400Z/
Santa Clarita Valley-Santa Susana Mountains-
Southern Ventura County Mountains-
Northern Ventura County Mountains-Interstate 5 Corridor-
Western San Gabriel Mountains and Highway 14 Corridor-
Eastern San Gabriel Mountains-Western Antelope Valley Foothills-
Eastern Antelope Valley Foothills-
116 PM PDT Mon Aug 18 2025

...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...

The National Weather Service in Los Angeles/Oxnard has issued a
Red Flag Warning for wind and low relative humidity, which is in
effect from 9 AM Wednesday to 9 PM PDT Saturday.

* TEMPERATURES...Unseasonably hot high temperatures, generally
  95-110 degrees and highest Thursday through Saturday, producing
  unseasonably unstable conditions.

* RELATIVE HUMIDITY...Minimum relative humidity 8-20 percent,
  lowest Wednesday and Thursday.

* THUNDERSTORMS...Isolated thunderstorms will be possible Friday
  through the weekend, and accompanying lightning strikes will be
  capable of starting new fires on the peripheries of rain cores.

* WINDS...Southwest at 10-20 mph gusting to 20-25 mph over the
  western Antelope Valley Foothills and vicinity and in other
  wind-favored areas such as through passes and canyons. Lighter
  winds elsewhere. Passing outflow boundaries could bring sudden
  wind-shifts and increased fire-spread rates, even from distant
  thunderstorms.

* IMPACTS...If fire ignition occurs, conditions are favorable
  for extreme fire behavior and rapid fire growth, which could
  threaten life and property. Be aware of sudden re-direction of
  fires in response to passing outflow boundaries.

* ADDITIONAL DETAILS...Fire-weather headlines may eventually need
  to be extended into Sunday.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A Red Flag Warning means that fire-weather conditions are expected
to be favorable for the development of explosive fire behavior.
Use extreme caution with anything that can spark a wildfire.
Residents near wildland interfaces should be prepared to evacuate
if a wildfire breaks out. See readyforwildfire.org and
wildfirerisk.org for information.

&&

$$

CAZ238-345-351>353-240400-
/O.NEW.KLOX.FW.A.0007.250821T1600Z-250824T0400Z/
Cuyama Valley-San Luis Obispo County Mountains-
Santa Ynez Mountains Western Range-
Santa Ynez Mountains Eastern Range-
Santa Barbara County Interior Mountains-
116 PM PDT Mon Aug 18 2025

...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 National Weather Service in Los Angeles/Oxnard has issued a
Fire Weather Watch for wind and low relative humidity, which is
in effect from Thursday morning through Saturday evening.

* TEMPERATURES...Unseasonably hot high temperatures, generally
  95-105 degrees, producing unseasonably unstable conditions.

* RELATIVE HUMIDITY...Minimum relative humidity 8-20 percent.

* THUNDERSTORMS...None expected.

* WINDS...Diurnal wind patterns with speeds of 5-10 mph gusting to
  10-15 mph, locally higher in wind-favored areas such as through
  passes and canyons.

* IMPACTS...If fire ignition occurs, conditions are favorable
  for extreme fire behavior and rapid fire growth, which could
  threaten life and property. Be aware of sudden re-direction of
  fires in response to passing outflow boundaries.

* ADDITIONAL DETAILS...Fire-weather headlines may eventually need
  to be extended into Sunday.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A Red Flag Warning means that fire-weather conditions could
potentially become favorable for the development of explosive
fire behavior in the coming days. Use extreme caution with
anything that can spark a wildfire. Residents near wildland
interfaces should be prepared to evacuate if a wildfire breaks
out. See readyforwildfire.org and wildfirerisk.org for
information.

&&

$$

Cohen/Gomberg