Chatsworth, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

299
FXUS66 KLOX 150123
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
523 PM PST Thu Nov 14 2024

.SYNOPSIS...14/121 PM.

A cold low pressure system will bring chances of rain to the area
this evening through Friday night. Temperatures will plummet to
around 10 degrees below normal by Friday, with gusty west to
northwest winds in the afternoon. A gradual warming trend is
expected Sunday into next week with moderate to strong Santa Ana
winds returning Tuesday through Thursday.

&&

.SHORT TERM (TDY-SUN)...14/154 PM.

After a warm day Wednesday temperatures have fallen several
degrees today with the return of onshore flow ahead of the
approaching upper low. Really not much change to the forecast
through Saturday as models have remained more or less steady with
the track and speed of the low. While the system is quite cold for
this time of year, noted by the large area of open cell cumulus
between 125-130w, precipitable waters are under .5" so there
isn`t much moisture with this. And given the more inland
trajectory, most areas south of Pt Conception will be
significantly rain-shadowed. Even going with the high end 90th
percentile precip forecast from the GEFS, ENS, and GEPS, rain
totals from this system are expected to be under a quarter inch
across for roughly 90% of the area (basically just the Grapevine
region and right around Pt Conception) and under a tenth of an
inch for about 75% of the area. Most of that falling later tonight
into Friday. So this won`t be a wetting rain for most areas, and
for the rain-shadowed areas south of Pt Conception, roughly from
Goleta to the western San Fernando Valley, likely just a trace of
rain or possibly as much as 0.02".

The cold air with this system is already helping to generate some
isolated lightning strikes a few hundred miles offshore. Not
expecting these to move onshore but could see a couple strikes
over the coastal waters mostly north of Pt Conception tonight into
Friday morning. In addition, gusty west to winds will develop as
early as Friday morning across the coastal waters and elsewhere
Friday afternoon, though strongest near the coast where wind
advisories may be needed.

Cool but dry Saturday with highs only in the lower to mid 60s at
lower elevations. Several degrees of warming expected Sunday with
clear skies and light offshore flow in place. Gusty north winds
expected across the Grapevine region Sunday night. EPS ensembles
indicating winds gusting to 50 mph in that area, some of which
will likely filter down into the valleys through Monday morning.

.LONG TERM (MON-THU)...14/218 PM.

Aside from some gusty north winds Monday morning across the
Grapevine region down through west LA, Monday should be a quiet
weather day. Slightly cooler most areas as onshore flow briefly
returns.

Offshore expected to return Tuesday through Thursday, though there
remains quite a bit of uncertainty on the strength. Deterministic
forecast gradients have been fluctuating quite a bit, lately
trending down, which seems more reasonable given the lack of upper
support. There are still some ensemble solutions supporting a
slower and more westward trough the Great Basin, though most of
the solutions are faster and warmer with more ridging over
California. Still very dry, likely even drier than the last
Santa Ana event, with some wind, but at this time leaning more
towards and advisory level event with gusts at or below 50 mph
through the usual Santa Ana wind corridor. Will see how the models
evolve over the next few days. Current temperature forecast is
straight from the NBM and seems several degrees too cool for mid
week. Local historical based guidance suggest high temperatures at
least in the upper 70s for coast/valleys and likely into the 80s.

&&

.AVIATION...15/0055Z.

At 0002Z at KLAX, there was a marine layer up to 1000 ft AGL. The
top of the inversion was around 2000 ft with a temperature of 16
C.

VFR conds are expected in most areas through the evening between
03Z-08Z, when MVFR CIGs move over the area along with a frontal
system. MVFR conds will affect northern areas beginning this
evening, spreading into areas S of Pt. Conception around or after
midnight. There will be local IFR/LIFR cigs in the foothills/mtns.
This front will bring a chance of light rain to much of the area,
especially to areas N of Pt Conception and to the northern slopes
of the mtns.

KLAX...Moderate to high confidence in the 00Z TAF with VFR conds
expected through around 09Z. The arrival time of MVFR cigs
could differ by +/- 3 hours from TAF time. The best chance of
light rain will be between 09Z to 16Z. No significant east wind
component is expected.

KBUR...Moderate to high confidence in the 00Z TAF with VFR conds
expected through the period, but there is a a 30-40% chance that
MVFR CIGs between 06Z to 15Z.

&&

.MARINE...14/154 PM.

In the outer waters, buoy observations confirm that Small Craft
Advisory (SCA) conds are occuring. Winds and seas will remain at
SCA levels thru Sat evening, then will drop below SCA levels by
late Sat night. There is a 30% chance of Gale force winds Fri
afternoon into Fri night, mainly in PZZ 676. There will likely be
a break in the SCA conds Sun. SCA conds are likely (70-80%
chance) Sun night thru Mon night, especially in PZZ 676 and 673.

For the inner waters N of Pt. Sal, buoy observations indicate that
SCA conds are beginning to enter western portions of PZZ 645.
These conds will continue to spread across the area and continue
thru late Fri night. Winds may drop below SCA levels for a few
hours late tonight and Fri morning. There is a 20% chance of SCA
conds Sat afternoon and evening, especially for Point San Luis.
SCA conds are not expected late Sat night thru Mon morning, then
are likely (60-70% chance) Mon afternoon/evening.

In the Santa Barbara Channel, buoy observations indicate that
SCA conds are beginning to enter western portions of PZZ 650.
These conds will continue to spread across the area and continue
thru late Fri night. Winds may drop below SCA levels for a few
hours late tonight/Fri morning, especially in eastern sections.
SCA level winds are likely (60% chance) Sat afternoon/eve. Winds
and seas should be below SCA levels late Sat night thru Mon
morning, then are likely (60% chance) Mon afternoon/eve, mainly
western sections.

In the southern inner Waters, SCA level winds will develop this
afternoon from west to east, then continue thru late Fri night.
Winds may drop below SCA levels for a few hours late tonight/Fri
morning, especially in eastern sections. Winds and seas should be
below SCA levels late Sat eve thru Mon night.

&&

.BEACHES...14/220 PM.

Large W to NW swell will likely bring High Surf to Central Coast
beaches beginning this afternoon then continuing thru Sat
morning, with surf peaking late tonight/Fri. Surf heights of 9 to
13 ft are expected at the peak of the event, with local sets to
15 ft. Surf will be highest on exposed W and NW facing beaches.

High surf will likely affect the beaches of VTU County this
evening thru Sat morning. Surf is expected to peak at 6 to 8 ft
late tonight/Fri, with local sets to 10 ft possible. Elsewhere on
the beaches S of Pt. Conception, elevated surf is likely this
evening thru Sat morning, with surf heights of 3 to 6 ft and local
sets up to 7 ft. There is a chance that High Surf Advisories will
have to be expanded to the L.A. County Coast Fri into Sat.

Minor coastal flooding is possible on west and northwest-facing
beaches during the high tides Fri morning and Sat morning, with
nuisance coastal flooding possible on exposed west-facing beaches
south of Pt. Conception. High tides are between 800 AM and 830 AM
PST Friday morning, and 830 AM to 900 AM PST Sat morning.

&&

.FIRE WEATHER...14/523 PM.

***CRITICAL FIRE-WEATHER EVENT INCLUDING *** POTENTIAL HIGH-END
 RED FLAG*** CONDITIONS FROM A MODERATE TO POSSIBLY STRONG SANTA
 ANA WIND EVENT BECOMING LIKELY BETWEEN NEXT TUESDAY AND
 THURSDAY***

***FIRE-WEATHER HEADLINES LIKELY BETWEEN NEXT TUESDAY AND
 THURSDAY-- GREATER THAN 80 PERCENT CHANCE***

Between next Tuesday and Thursday, a moderate to possibly strong
Santa Ana wind event is likely to develop. This will bring an
increasing likelihood for critical fire-weather conditions
including ***POTENTIAL HIGH-END RED FLAG*** conditions.

At the synoptic scale, the key feature that we will be watching
is the proximity of the closed low that develops near the four
corners area and how quickly it ejects eastward. Current 12z
operational models are trending further east with this low,
which would likely result in less upper level wind support than
previous model runs. As a result, the Santa Ana wind event that
develops between and Thursday will likely be a moderate event.
However, there model ensemble solutions show around a 20 percent
chance of a strong Santa Ana wind event.

The next Tuesday through Thursday Santa Ana event will likely be
a warmer and drier Santa Ana wind event compared to the event from
last week. Relative humidities may be 5% drier over the coastal
slopes and valleys for next Tuesday through Thursday
-- with potential for widespread single digit relative humidities
at times -- as temperatures warm well into the 70s and 80s
(enhancing the fire-plume growth- potential component). Latest
LAX-Daggett offshore pressure gradients are projected to be in the
-5 to -6 mb range, somewhat weaker than previous model solutions.
The strongest winds will likely be focused in the typical Santa
Ana wind prone areas of western LA and eastern Ventura counties.

One notable difference between the next Tuesday through Thursday
event compared to the event from last week is that the stronger
upper support for next Tuesday through Thursday should be
displaced much farther east, owing to the synoptic-scale
interactions discussed above. As a result, present indications
are that winds will not be quite as extreme for next Tuesday
through Thursday (modestly reducing the extent of long-range
spotting potential). Nevertheless, moderate to possibly strong
Santa Ana winds are likely between Tuesday and Thursday, and there
is a greater than 80% chance that fire-weather headlines will
become necessary across much of Los Angeles and Ventura Counties
for Tuesday through Thursday of next week. With very poor overnight
relative humidity recovery expected, this will have the potential
to be a long- duration Red Flag event, adding to the potentially
very favorable fire-weather environment for large fire development.

Also of note, spotty elevated fire-weather conditions cannot be
ruled out over the interior mountains of Santa Barbara and San
Luis Obispo Counties next week, though the focus for stronger
winds will be in Los Angeles and Ventura Counties.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory in effect until noon PST Saturday for
      zones 340-346. (See LAXCFWLOX).
     Wind Advisory remains in effect until 10 AM PST Friday for
      zones 349-351-352. (See LAXNPWLOX).
     High Surf Advisory in effect from 9 PM this evening to noon
      PST Saturday for zone 354. (See LAXCFWLOX).
PZ...Small Craft Advisory in effect until 3 AM PST Saturday for
      zones 645-650-655. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PST Sunday for
      zones 670-673-676. (See LAXMWWLOX).

&&

$$

PUBLIC...MW
AVIATION...Smith
MARINE...RAT/Black
BEACHES...DB/Black
FIRE...Gomberg/Cohen
SYNOPSIS...MW/Schoenfeld

weather.gov/losangeles

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