Acton Weather

000
FXUS66 KLOX 251924
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
1224 PM PDT Mon Sep 25 2023

.SYNOPSIS...25/225 AM.

Skies will be mostly clear through the period save for coastal
night through morning low clouds and fog. Temperatures will
gradually warm in most areas through mid week. Max temps will
approach normal values Tuesday or Wednesday. Gusty Sundowner winds
are expected to peak over southern Santa Barbara County on
Tuesday into Wednesday. Cooler conditions are forecast towards the
end of week. A slight chance of rain will develop on Saturday.

&&

.SHORT TERM (TDY-THU)...25/937 AM.

***UPDATE***

Visible satellite imagery indicates the recent development of an
eddy just off the LA coast. This feature is maintaining widespread
marine stratus across the LA County coast and beaches, and should
continue to do so into the early afternoon. The updated forecast
reflects a somewhat slower clearing trend in these areas. However,
the marine layer is quite shallow, and partial clearing is
anticipated later this afternoon. No other appreciable changes
have been made to the ongoing forecast. High temperatures today
are expected to be a few to several degrees below normal in most
areas, and may not rise above 80F in the portions of LA County
where marine stratus is slowest to erode.

***From Previous Discussion***

The marine layer is about 1000 ft deep and the onshore gradients
are weak and similar to ydy. Marine layer stratus has been slow
to develop and currently is mostly confined to the Central Coast.
Short Range high rez ensemble based fcsts still show a good chc
(70 percent) of low clouds covering most of the LA/VTA csts/vlys a
little after dawn. The low clouds will clear later this morning
and skies will be sunny. Max temps were supposed to warm today but
warming is now going to be confined the coast where there will be
a little less marine influence. A little south push will bring
several degrees of cooling to most of LA county. Moderate onshore
flow to the east will bring local gusts to 45 mph to the Antelope
Vly foothills this afternoon.

High pressure building in behind a weak and dry front will create
a decent northerly gradient and gusty northwest to north winds
for southern Santa Barbara County and the mountains near the I-5
corridor. There may be a need for a low end advisory across the
western SBA south coast tonight.

Tuesday will see a big warm up as rising hgts combine with much
weaker onshore flow to the east and actual offshore flow from the
north. This offshore push will limit the morning low clouds. Max
temps will rise 3 to 6 locally 8 degrees under sunny skies and the
offshore flow. The exception to the warming will occur near he
Kern county line where the offshore flow will usher in some cooler
air from the interior. Despite the warming most of the area will
see below normal max temps with only the SBA south coast and Santa
Ynez Vly will have above normal temps.

Even stronger north to south flow will occur Tuesday night with
advisory level winds likely (70-80 percent chance) for the Santa
Ynez mountains and possibly extending into portions of the South
Coast, especially near Gaviota. There is a 30-40 percent chance
of advisory level gusts (45-50 mph) through the the I-5 corridor.

Wednesday will be the warmest day of the next 7 and it will be the
first day of above normal temps for many areas after 14
consecutive days of below normal max temps. There will be offshore
flow from both the east and north in the morning with the
northerly gradient remaining offshore through the afternoon. Look
for 2 to 4 degrees of warming with the warmer vly locations
topping out in the lower 90s. The offshore flow should eliminate
any marine layer clouds.

.LONG TERM (FRI-MON)...25/328 AM.

The deterministic GFS and EC are in good agreement through Sunday
and their respective ensembles also exhibit good cohesion. So
there is pretty good confidence in the xtnd fcst.

The warm up will come to a screaming halt on Thursday as a west
coast trof deepens and moves into the state. Onshore flow will
increase through the day. The marine layer will begin to reform.
The falling hgts and stronger onshore flow will combine to lower
max temps by 5 to 10 degrees.

More of the same on Friday. The trof will be deeper. The gradients
will be more onshore. The marine layer clouds will be more
extensive. Max temps will fall another 3 to 6 degrees. Max temps
will end up 6 to 12 degrees blo normal.

The trof will develop into a cut off low and move into the
northern half of the state. Hgts will fall to about 565 dam and a
decent lobe of PVA will sweep over Srn CA. The combination of lift
from the upper low and the moisture from a deep marine layer has
about a 20 percent chc of creating some light rain or drizzle
through the day across the csts/vlys/cstl slopes south of Pt
Conception. It will probably a mostly cloudy day south of Pt
Conception. It will be the coolest day of the next 7 with 3 to 6
locally 8 degrees of additional cooling. The warmest temps will
only be in the mid 70s and max temps will end up 8 to 16 degrees
blo normal.

The upper low will slowly pull out to the NE on Sunday. The cold
air advection from Saturday will likely not allow for any marine
layer clouds. The extra sunshine and slightly higher hgts will
likely bring a few degrees of warming but it will still be a very
chilly way to start off October.

&&

.AVIATION...25/1923Z.

High confidence in the current forecast for the desert terminals.
Low-to-moderate confidence in the current forecast for coastal
and valley terminals. Timing of arrival could be significantly
off tonight.

For coastal terminals there is a 10 percent chance of earlier
arrival of IFR to MVFR conditions (as early as 05-08Z). There is a
20 percent chance that conditions could be one category higher
than forecast at Central Coast terminals. There is a 20 percent
chance of IFR- MVFR cigs at KBUR, KVNY, and a 10 percent chance at
KSBA. There is 30 percent chance of no cigs developing at KPRB,
KSBP, and KOXR and KCMA.

KLAX... OVC008-OVC012 cigs may develop up to 4 hours earlier than
forecast. Light east winds are expected from 11Z-17Z, with a 20%
chance of an east wind component above 8 kts.

KBUR...There is a 20 percent chance of several hours of
BKN008-BKN015 cigs from 10Z-16Z. No wind impacts are expected at
this time.

&&

.MARINE...25/936 AM.

High confidence in the current forecast through Thursday, then
moderate confidence thereafter. There is a moderate chance that
winds could be stronger and seas much higher between Thursday and
Saturday.

For the waters northwest through southwest of the Channel Islands,
the chances for SCA conditions will increase each day through
Tuesday. A 50-70 percent chance of SCA conditions by this
afternoon and evening will increase to a 80-100 percent of
widespread SCA conditions by Tuesday afternoon. Widespread SCA
conditions with hazardous seas are virtually certain from Tuesday
through Thursday. There is a 40-60 percent chance of Gale Force
winds, especially during afternoon and evening hours. A Gale Watch
is in effect from Tuesday afternoon through late Wednesday night.
There is a moderate-to-high chance of SCA conditions lingering
into Friday and Saturday. Gales are possible again over the
weekend.

For the nearshore waters along the Central Coast, winds and seas
will generally remain below SCA levels through early Tuesday.
There is a 30-40 percent chance of SCA level winds this afternoon
and evening increasing to 80-90 percent chance by Tuesday
afternoon. Widespread SCA conditions are very likely to virtually
certain between Tuesday and Thursday, especially during the
afternoon and evening hours. There is a 20-30 percent chance for
Gale Force winds Tuesday afternoon and evening, increasing to
40-50 Wednesday afternoon and evening. There is a moderate chance
of SCA conditions lingering into Friday and Saturday.

Inside the southern California bight, chances for SCA level winds
will increase to 60-80 percent this afternoon and evening. There
is a 40-60 percent chance of widespread SCA conditions (winds and
seas) between Tuesday and Thursday. The highest chances are during
the afternoon and evening hours across the western portion of the
Santa Barbara Channel. Additionally for the Santa Barbara Channel
a Gale Watch is in effect for Tuesday afternoon through late
Wednesday night.

&&

.BEACHES...25/939 AM.

There is a 50 percent chance that high surf conditions could
develop between Tuesday evening and Thursday as a moderately
long- period northwest swell building off the California coast.
The highest chance for high surf is for west and northwest facing
shores along the Central Coast. For theses beaches expect surf of
8 to 12 ft with local sets to 14 feet possible.

Additionally for Ventura County beaches, there is a 50 percent
chance of elevated surf developing as soon as Tuesday evening and
lasting through Thursday. For west and northwest facing beaches, surf
of 4 to 6 feet with local sets to 7 feet possible.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory in effect from 9 PM this evening to 9 PM
      PDT Thursday for zones 340-346. (See LAXCFWLOX).
     Wind Advisory in effect from 5 PM this afternoon to 5 AM PDT
      Thursday for zones 349-351. (See LAXNPWLOX).
     Beach Hazards Statement in effect from 9 PM PDT this evening
      through Thursday evening for zone 354. (See LAXCFWLOX).
PZ...Small Craft Advisory in effect from 9 AM Tuesday to 3 AM PDT
      Thursday for zones 645-670. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 PM PDT Tuesday for
      zones 650-673-676. (See LAXMWWLOX).
     Gale Watch in effect from Tuesday afternoon through late
      Wednesday night for zones 650-673-676. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PDT Tuesday for
      zone 655. (See LAXMWWLOX).

&&

$$

PUBLIC...Cohen/Rorke
AVIATION...Hall/Schoenfeld
MARINE...Hall/RS
BEACHES...Hall/RS
SYNOPSIS...30

weather.gov/losangeles

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