San Marino, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

310
FXUS66 KLOX 140344
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
844 PM PDT Sun Apr 13 2025

.SYNOPSIS...13/843 PM.

A gradual cooling trend is expected into early this week, then
more significant cooling will take place by late week. Night
through morning low clouds and fog can be expected, pushing into
the coastal slopes of the mountains by mid week. A cold upper
level low pressure systems is forecast to bring showers to the
area on Friday, and even a thunderstorm cannot be ruled out
especially in the mountains and deserts. Dry and milder conditions
can then be expected next weekend.

&&

.SHORT TERM (SUN-WED)...13/842 PM.

Weak closed upper level low pressure system spinning off the
coast of Southwest California tonight. This in combination
with moderate onshore flow resulting in low clouds and patchy
fog making a quick return to many coastal areas this evening.
With the marine layer depth still around 1500 feet, expecting
low clouds and patchy fog to fill in across most coastal/valley
areas overnight into Monday morning, and could even see some
patchy drizzle.

Another weak upper low well west of Baja this evening is
expected to track east-northeast and open up as an upper level
trough as it comes ashore over northern Baja by late Monday
afternoon. This system will tap into some mid level moisture
and with the upper flow turning southeasterly, looking for mid
level clouds to be on the increase across Southwest California
by Monday afternoon/evening. 00Z NAM model showing an embedded
vort max in the upper level flow that could bring some additional
energy/organization to the mid level moisture field. Models also
showing some increased instability Monday afternoon into Monday
evening. While sounding profiles showing much of the moisture
rather elevated and limited, there is around a 5 percent chance
of an elevated thunderstorm on Monday afternoon/evening.

*** From previous discussion ***

The marine inversion is expected to be around 1500-1700 ft or so
for the most part tonight thru Tue, then deepen to 2500-3000 ft
Tue night into Wed morning. Overall, it looks like a marine layer
pattern will prevail across the forecast area during the period.
Night and morning low clouds and fog can be expected along the
coast and into many of the vlys, and even extending to the lower
coastal slopes Tue night into Wed morning. The low clouds will
clear back toward the coast each afternoon thru Tue with many
beaches having only partial afternoon clearing. The low clouds may
persist for many areas on Wed, even into some of the vlys. There
also should be enough of an onshore push for patchy drizzle over
the coast and vlys S of point Conception later Mon night into Tue
morning. Otherwise, clear to partly cloudy skies with mainly some
mid and hi clouds at times can be expected.

Winds through Wed should be generally weak during the night and
morning hours, with breezy to gusty S to W winds in the afternoon
and early evening. However, stronger gusty SW winds should affect
portions of the L.A. County mtns and deserts on Wed thanks to a
fcst of a +10.3 mb LAX-DAG Wed pressure gradient in the afternoon.

Temps should cool down slightly for Mon, with inland areas
remaining several degrees above normal while coastal and some
adjacent vlys continue to be around or a few degrees below normal.
For Tue, further cooling from the coast to the coastal slopes
should prevail, while the interior vlys, mtns and deserts remain a
few deg above normal. By Wed, more significant cooling is
expected, with just about all areas falling to about 4 to 10 deg
below seasonal norms. Highs on Mon for the warmest vlys and lower
mtns should be in the mid to upper 70s, except lower to mid 80s in
the Antelope Vly, then fall to the lower 70s on Tue, except to
around 80 in the Antelope Vly, and to the mid to upper 60s on Wed,
except lower 70s in the Antelope Vly.

.LONG TERM (THU-SUN)...13/206 PM.

The models are in mostly good agreement in the extended period.
On Thu, a significant and cold upper level low will move into the
northern and central Great Basin, then quickly dive S and into
southern and southeastern CA on Fri. The upper level low will move
E of the region on Sat with a broad NW to N flow aloft. H5
heights will rebound on Sun to near 573 dam with a broad NW flow
aloft.

The marine layer pattern will persist into Thu with night and
morning low clouds for the coast and vlys, possible even up to the
coastal slopes. Otherwise partly cloudy skies overall can be
expected.

For Fri, the proximity of the upper level low will bring the
slight chance to chance of showers to much of the region, mostly
in the afternoon hours. The cold air aloft (GFS fcst as low as -25
deg C at H5) will also contribute to increased instability with
the slight chance of thunderstorms introduced into the fcst for
Fri afternoon, especially over the mtns and deserts. There is
still some uncertainty on the exact track of the upper level low
and where the coldest air aloft moves to, but we should have
better confidence in this with additional model runs as we draw
closer to the middle of next week. Any leftover showers will end
Fri evening, with dry and milder conditions expected on Sat then
turning warmer on Sun with some coastal low clouds and fog in the
night and morning.

Temps are expected to cool to significantly below normal for mid-
April on Thu and Fri before turning a bit warmer on Sat and Sun,
but remaining a few deg below normal for the most part. The
warmest day overall during the extended period should be next Sun
with the warmest vlys and lower mtns reaching the low to mid 70s.

&&

.AVIATION...14/0017Z.

At 0010Z at KLAX, the marine layer was around 1500 feet deep. The
top of the inversion was around 2600 ft with a temp of 19 C.

Moderate confidence in all TAFs, except high confidence in desert
TAFs. Cigs likely to redevelop tonight across most coastal/valley
YAF sites except KPRB. Timing of flight cat changes may be off by
+/- 3 hours. Cigs may drop one flight cat lower than forecast
overnight.

KLAX...Moderate confidence in TAF. There is a 20% chc of LIFR
cigs tonight. Good confidence that any E wind component will
remain under 6 kt.

KBUR...Moderate confidence in TAF. There is a 30% chc that cigs
will arrive as early as 06Z Mon.

&&

.MARINE...13/753 PM.

Winds have subsided below Small Craft Advisory (SCA) levels,
however seas may linger around/just below 10 feet across the outer
waters into this evening. Otherwise, SCA conds are not expected
across all the coastal waters through Thursday night.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...NONE.

&&

$$

PUBLIC...Gomberg/Sirard
AVIATION...Gomberg
MARINE...Lund
SYNOPSIS...Sirard

weather.gov/losangeles

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