Topanga, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

846
FXUS66 KLOX 212112
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
112 PM PST Sun Dec 21 2025

.SYNOPSIS...21/238 AM.

Temperatures will remain above normal through Sunday in most
areas except the coast. A cooling trend will begin Monday as a
strong storm approaches with increasing clouds. Rain will begin
Tuesday in most areas with periods of heavy rain Tuesday night and
Wednesday as well as very strong winds. Showers are expected to
continue on Christmas day and through next weekend.

&&

.SHORT TERM (TDY-WED)...21/111 PM.

***MAJOR STORM COMING WITH SIGNIFICANT HYDROLOGIC IMPACTS***

For the short term period, 12Z models in very good synoptic
agreement through the period. And with that being said,
Southwestern California will be dealing with a major winter storm.

For this afternoon through Monday night, conditions will be rather
benign. Through Monday night, there will be an increase in mid to
high level clouds across the entire area along with pretty
extensive marine layer stratus west of the mountains. With this
pattern, there will continue to be a threat of light rain across
northern San Luis Obispo county.

On Tuesday and Wednesday, things will dramatically change. Based
on deterministic and ensemble IVT guidance, a moderate to strong
atmospheric river will take "dead aim" on the area. Through
Tuesday afternoon, rain will gradually increase in coverage and
intensity across the area. For Tuesday night through Wednesday,
the first, and most impactful, surge of the AR will bring heavy
rainfall to all areas. At this time (through Wednesday evening),
2-5 inches of rain is expected across the coasts/valleys and 5-10
inches across the foothills and mountains. In terms of rainfall
rates, hourly rates of 0.75 to 1.25 inches will be possible (based
on latest high resolution data). So, needless to say, there will
be significant hydrologic issues, including widespread urban
flooding, mud and debris flows and very hazardous driving
conditions. Given this potential, a FLOOD WATCH has been issued
for all four counties from Tuesday afternoon through Wednesday
evening. START TAKING PROTECTIVE ACTIONS NOW.

Given the subtropical nature of this system snow levels through
Wednesday night will remain very high (above 7500-800 feet). So,
at least through Wednesday evening, no significant winter weather
issues are expected.

Finally, winds will also be a significant issue with this system.
From Tuesday afternoon through Wednesday, moderate to strong
southeasterly winds are expected. Many coastal and valley areas
can expect advisory-level winds, gusting 35-55 MPH. Across the
mountains and foothills, warning-level winds, gusting up to around
70 MPH, will be possible. Future shifts will likely need to issue
various wind products (both advisories and warnings).

.LONG TERM (THU-SUN)...21/111 PM.

For the extended, a wet and unsettled pattern will continue across
the area through the weekend. 12Z models agree on the details for
Christmas Day, but start to deviate Friday through the weekend.

For Christmas Day, the second surge, associated with the AR, will
impact the area. This second surge will bring additional moderate
to locally heavy rainfall to the area. At this time, additional
rainfall totals for Christmas Day are expected to range between 1
and 3 inches. So, there will continue to be flooding and debris
flow issues and the FLOOD WATCH may need to be extended into
Christmas Day. Snow levels will begin to drop on Christmas Day,
down to around 7000 feet. So, there will likely be a White
Christmas at the resort level and Winter Weather products may need
to be considered. As for winds, they will shift to more southerly
direction and decrease in intensity. However, there will still be
a chance of warning-level winds across the mountains and advisory
level winds elsewhere.

For Friday, both the GFS and ECWMF continue to indicate wet
weather continuing across the area, but the GFS is more
significant with rainfall totals than the ECMWF family. Snow
levels will drop to the 5500-6000 foot range and winter weather
conditions will likely impact more mountain communities.

For Saturday and Sunday, models diverge noticeably. The GFS is
much more bullish, keeping some decent shower activity across the
area into Sunday. However, the ECMWF is much drier. Forecast
currently leans towards the GFS and will keep that going.

IN SUMMARY...TUESDAY THROUGH SATURDAY LOOKS TO BE AN EXTENDED
PERIOD OF SIGNIFICANT RAINFALL. BY SATURDAY EVENING, RAINFALL
TOTALS WILL RANGE FROM 4-8 INCHES ACROSS COASTAL AND VALLEY AREAS
TO 8-12+ INCHES ACROSS THE FOOTHILLS AND MOUNTAINS. PLEASE TAKE
THE NECESSARY PROTECTIVE ACTIONS AS FLOODING AND DEBRIS FLOW WILL
BE A MAJOR ISSUE THIS UPCOMING WEEK.

&&

.AVIATION...21/1752Z.

At 1706Z at KLAX, the marine layer was 500 feet deep. The top of
the inversion was near 2500 feet with a temperature of 17 C.

High confidence in VFR TAFs for desert airfields (KPMD & KWJF).

Low to moderate confidence for remaining TAFs. Timing of CIG/VSBY
restrictions could be off by +/- 3 hours, and off by 2 categories
at any point. KPRB, KSBP, and KSMX may see -DZ at times through
the period.

KLAX...Low confidence in TAF. Generally expecting LIFR to MVFR
CIG/VSBY restrictions (OVC003-012) through forecast period.
Timing of flight cat changes may be off +/- 3 hours and may bounce
at times. 30% chance that CIGs clear or remain intermittent in
nature from 20Z Sun to 05Z Mon. Good confidence that any east
wind component remains below 7 kts.

KBUR...Moderate confidence in TAF. Generally expecting VFR
conditions. However, BR or HZ MVFR VSBYs are possible thru period
and CIGs could return after 12Z Monday (20% chance).

&&

.MARINE...21/1227 PM.

High confidence in the current forecast through Monday night,
then moderate confidence thereafter. Confidence lower due to
timing and seas. Winds and seas will largely remain below SCA
levels through Monday night.

On Tuesday, SE to south winds and seas will are expected to
rapidly increase to dangerous levels as a storm system approaches
the coastal waters. There is a 90+ percent chance of SCA level
southerly winds developing by Tuesday afternoon with a likely
(80-90 percent) chance of widespread Gale Force Winds through at
least Tuesday night with a 20-40 percent (highest northern waters)
chance of at least brief Storm Force Winds. Large short-period
seas are likely to develop Tuesday night and should linger
Wednesday into Thursday. There is also a 5-15% chance of
thunderstorms Tuesday night through Thursday morning.

Boaters are urged to monitor the latest weather forecasts. If
marine weather conditions deteriorate as advertised, boaters
should remain in safe harbor during this significant storm.
Unprotected south facing harbors may be especially vulnerable to
the south swell and winds.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Flood Watch remains in effect from Tuesday afternoon through
      Wednesday evening for zones 38-87-88-340>358-366>383-548. (See LAXFFALOX).
     Flood Watch in effect from Tuesday afternoon through
      Wednesday evening for zone 362. (See LAXFFALOX).
PZ...NONE.

&&

$$

PUBLIC...Thompson
AVIATION...Black
MARINE...RM/Black/RAT
SYNOPSIS...MW

weather.gov/losangeles

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