090
WWUS86 KLOX 172019
RFWLOX

URGENT - FIRE WEATHER MESSAGE
National Weather Service Los Angeles/Oxnard CA
119 PM PDT Sun Aug 17 2025

...FIRE WEATHER WATCH IN EFFECT FROM WEDNESDAY 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 LOS ANGELES AND VENTURA
COUNTIES...

.The most significant heatwave of the summer season, so far, is
on the way middle to latter parts of this week and into next
weekend, especially Wednesday through Saturday. Expect
temperatures to soar well over 100 degrees 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 Fire Weather Watch area covers portions of the mountains and
foothills of Los Angeles and Ventura Counties, which have been a
climatologically notorious area for large plume-dominated fires in
similar weather patterns to what is coming later this week. 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 -- southwest at 10-20 mph
gusting to 25-30 mph. 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 Saturday 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 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 both the Station Fire,
the Bobcat Fire, and the Bridge Fire that burned significant
portions of the Angeles National Forest in 2009, 2020, and 2024,
respectively. 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 Fire
Weather Watch area 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.NEW.KLOX.FW.A.0006.250820T1600Z-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-
119 PM PDT Sun Aug 17 2025

...FIRE WEATHER WATCH IN EFFECT FROM WEDNESDAY 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 LOS ANGELES AND VENTURA
COUNTIES...

The National Weather Service in Los Angeles/Oxnard has issued a
Fire Weather Watch 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, which is in effect from Wednesday morning through
Saturday evening.

* 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 Thursday
  through Saturday, 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 and into portions of interior Santa
  Barbara and San Luis Obispo Counties.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A Fire Weather Watch means that critical fire weather conditions
are likely to occur in the coming days. Residents near wildland
interfaces should prepare now on what to do if a wildfire breaks
out. See readyforwildfire.org and wildfirerisk.org for
information.

&&

$$

Gomberg/Cohen