000
FXUS66 KLOX 252129
AFDLOX

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

.SYNOPSIS...25/225 PM.

Other than patchy low clouds and fog in coastal areas tonight and
Tuesday morning, skies will be mostly clear through mid-week.
Temperatures are forecast to warm to near to above-normal
readings by Wednesday. Gusty Sundowner winds over southern Santa
Barbara County are expected to begin late this afternoon and
evening, and then peak for Tuesday into Wednesday. Cooler
conditions are expected from the end of this week into the
weekend, when there will be a slight chance of rain.

&&

.SHORT TERM (TDY-THU)...25/210 PM.

Marine stratus over LA County earlier today has eroded, giving way
to sunny skies areawide this afternoon. With shallow marine-layer
depths (less than 1000 ft), and near-neutral pressure gradients
turning offshore tonight, night and morning low clouds and fog
appear to be unlikely through the middle of the week. The
exception would be coastal LA County vicinity tonight and Tuesday
morning, especially if an eddy were to form over the nearshore
waters. And with the offshore gradients more substantially
strengthening in response to surface ridging north of the area
going forward early this week -- the trend toward offshore flow,
warming temperatures, and gusty Sundowner winds is already
initiating.

This pattern will facilitate more substantial warming for Tuesday
and Wednesday, especially with modest midlevel height rises
expected. Temperatures are forecast to be rising to near to above-
normal readings Tuesday and Wednesday afternoons. By Wednesday,
many locations are expected to experience their first above-normal
high temperatures after 14 consecutive days. High temperatures
Wednesday will by in the 80s and lower 90s in most areas, with
mid 90s possible in some of the interior valleys, and then cooler
closer to the coast and in the mountains. On Thursday, slight
midlevel height falls within the southern extent of a longwave
trough positioned over the western CONUS will result in
temperatures falling around 5 degrees at most locations for highs.

Regarding the Sundowner winds -- even with the near-neutral
pressure gradient thus far, gusts at Gaviota held in the 35-40-mph
range for much of the morning. And with SBA-SMX and SBA-BFL
offshore gradients strengthening to 2.5-3.5 mb tonight, confidence
in gusts exceeding 45 mph has become high enough to start a Wind
Advisory for SBA County SW Coast and the western Santa Ynez Range
at 5PM this afternoon for the first round of Sundowner winds.
Gusts of 45-55 mph will be possible in these areas through early
morning Tuesday, before winds undergo typical diurnal weakening,
temporarily. Then with these gradients strengthening in magnitude
by another 1.0-1.5 mb Tuesday night into Wednesday, an expansion
of strong northwest to northeast winds is expected. During those
time periods, isolated gusts of 55-60 mph will be possible,
especially in wind-prone areas around Gaviota and Refugio.

The Wind Advisory includes all three episodes of Sundowner winds
(starting late afternoon each day Monday, Tuesday, and
Wednesday), given short time durations between individual
episodes. In addition, there is a 50-percent chance for eastward
expansion of the Wind Advisory to account for more widespread
strong winds -- potentially encompassing eastern parts of the
Santa Ynez Mountains, SBA County SE Coast, and perhaps the I-5
corridor. Also of note, vertical cross sections indicate a low
chance (20 percent probability) for mountain-wave development to
bring even stronger wind gusts of 60-70 mph in spotty locations
along the southern SBA coastal ranges and adjacent foothills
including the Montecito area. Overall, the strongest winds are
expected Tuesday into Wednesday, Sundowner winds those days will
combine with a dry air mass to create potentially critical fire-
weather conditions -- please reference the Fire Weather Watch for
more details.

.LONG TERM (FRI-MON)...25/222 PM.

A significant pattern shift is expected to close out the week, as
a large and deep upper trough undergoes substantial amplification
over the western CONUS. Deterministic/ensemble model guidance
offer strong confidence in a deep low closing off over the
central Great Basin, with much cooler air overspreading the area.
This pattern favors strengthening onshore flow and a deepening
marine layer late in the week and during next weekend. High
temperatures could be 5-15 degrees below normal next weekend,
perhaps even cooler. The increased cold advection will likely
mitigate the development of marine stratus, however substantial
cooling aloft will contribute to enough steepening in lapse rates
to foster slight chances of showers Friday night into Sunday.

&&

.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...25/107 PM.

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...25/101 PM.

There is a 50 percent chance that high surf conditions develop
between Tuesday evening and Thursday as a moderately long- period
northwest swell building off the California coast. Surf will be
the highest at west and northwest facing shores along the Central
Coast. For theses beaches expect surf of 9 to 12 ft with local
sets to 14 feet possible.

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, expect surf
of 4 to 6 feet with local sets to 7 feet possible.

Nuisance coastal flooding and minor beach erosion may occur
Tuesday evening due to high surf for the Central Coast and
Ventura County beaches.

&&

.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 until 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).
Fire Weather Watch in effect from Tuesday afternoon through
late Wednesday night for zones 349>353. (See LAXRFWLOX).
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
AVIATION...Hall/Schoenfeld
MARINE...Hall/RS
BEACHES...Hall/RS
SYNOPSIS...Cohen

weather.gov/losangeles

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