257
FXUS66 KLOX 081718
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
918 AM PST Fri Nov 8 2024

.SYNOPSIS...08/916 AM.

Offshore flow in place the last several days will break down
today and allow onshore flow to develop through Saturday. High
pressure aloft will bring warmer temperatures through Saturday,
then a cooling trend should develop. Gusty northerly winds and
a chance of rain are on tap for early next week a weak weather
system moves over the region. Offshore flow should establish
for the middle portion of next week and bring some warming.

&&

.SHORT TERM (TDY-SUN)...08/915 AM.

***UPDATE***

Freeze Warnings in the interior have expired as daytime heating
is ongoing, and the forecast has been updated to reflect this. No
other changes have been made to the ongoing forecast.

***From Previous Discussion***

The latest satellite imagery show clear skies over the region
this morning as an upper-level ridge sitting near about 200 miles
southwest of Point Conception builds into the state early this
morning. A weak offshore flow pattern remains in place across the
region this morning, but today looks to be the last offshore day
for the stretch. Red Flag Warnings remain in place across the
mountain areas this morning, but these warnings will likely be
allowed to expire later today as the offshore winds wane. With
less wind and the ridge building in aloft, the dry air mass will
stagnate with less mixing, and air mass will warm for today.
Today should be the warmest day of the week for the northern
areas, but a warming trend will continue into Saturday across
the Southland. Daytime temperatures maxing out in the 70s to
lower 80s will be common up north today, spreading south into
the Southland on Saturday.

A cold air mass in place across the interior and in some
wind-sheltered areas over the last several days will modify as
the ridge builds in. It will frigid start to the day this
morning with freeze warnings in effect until 9 am across the San
Luis Obispo County Interior Valleys, and the Cuyama and Antelope
Valley. Several sites in the interior valleys have dipped into
the upper 20s and 30s this morning. The warming trend will
filter in today, with the interior portions warming to near
normal by Saturday then above on Sunday.

Smoke impacts from the Mountain Fire will likely remain in the
forecast for the near-term. Experimental HRRR and high-resolution
multi-model ensembles suggest the smoke concentration remaining
an issue for today, shifting to a more inland trajectory today.
It is not surprising to see South Coast AQMD and Ventura County
APCD highlighting the eastern Ventura County and western Los
Angeles County for air quality alerts due to smoke impacts. As
firefighting personnel heroically get a better handle on the
Mountain Fire, smoke impacts could get better sooner and improve
the air quality for particulate matter.

The forecast ensembles have really good agreement on 500 mb heights
falling through the weekend and into Tuesday as series of weak
weather systems drop into the region. A cooling trend will likely
develop across the coastal and valley to start the week, but there
are some questions on how much cooling will filter into the interior
valleys as the developing onshore flow pattern downslopes into these
areas. EPS ensemble members seems to inhibit the cooling from taking
place, but it does not make much sense given the weak GEFS KLAX-KDAG
surface gradients and deterministic NAM and GFS surface pressure
gradients. For now, NBM values will left in the forecast in hopes
some clarity arrives on this issue as EPS ensemble means could be
picking up on weak shortwave ridging as the pattern amplifies ahead
of the broader stronger troughing taking place offshore.

.LONG TERM (MON-THU)...08/915 AM.

The latest forecast ensembles are trending slightly wetter with the
second system of the series to affect the region between Veterans Day
and Tuesday. Confidence remains high for cooler temperatures and gusty
northerly winds across the area, especially through the Interstate 5
Corridor and across southern Santa Barbara County, but EPS precipitable
water value means climb across the region on Veterans Day. The forecast
goes with NBM values for PoPs, which is probably the best approach for
the situation, but the forecast ensembles do favor the northern areas
and the northern slopes of the mountains. EPS ensemble members indicate
almost all perturbations for KSDB with QPF, and more solutions than the
several runs across the area. As stated previously, northerly winds
will likely be the main story for the typical wind prone areas as rain
amounts will be light. Any snowfall will likely be confined to the
ridgetops or the resort-level with this system, but amounts should fall
between a dusting an an inch at best up at this level.

Offshore flow will likely develop in the wake of the system on Wednesday.
While Sundowner winds across southern Santa Barbara County seems the most
likely, Santa Lucia and Santa Ana winds cannot be ruled out between
Tuesday night and Thursday. For the current time, the forecast ensembles
advertise a much weaker Santa Ana wind event as EPS members suggest
sub-advisory wind gust means for KCMA and K3A6.  For all indications at
this time, any advisory level winds will likely remain confined to the
mountains between Wednesday and Thursday. A warming and drying trend
will likely develop during this period and marginal critical fire
weather conditions could develop as the air mass compressionally heats
and dries.

Lurking out in the extended period is a decent chance of rain sometime
late next week or into following week. Just about every solution indicates
rain in the EPS and CMC ensemble members at this point, but the issue is
the timing in the period. GEFS members offer up a mix of solutions at this
time, but the operational ECMWF and GFS solutions fall inline with this
idea. For now, stay tuned as this could be the first significant storm of
fall season.

&&

.AVIATION...08/1651Z.

At 1612Z, there was no marine layer depth at KLAX. There was
surface-based inversion up to around 1500 feet with a temperature
near 16 degrees Celsius.

High confidence in TAFs for all sites. CAVU conditions for all
sites except KOXR and KCMA due to FU from a fire in the area.

KLAX...High confidence in 18Z TAF. Any east wind component between
12Z and 18Z Saturday should remain below 6 kt, but there is a 20%
chance for a very brief 8 kt east wind component between 14Z and
16Z.

KBUR...High confidence in 18Z TAF.

&&

.MARINE...08/752 AM.

For the Outer Waters, seas are expected to remain well below
Small Craft Advisory (SCA) levels through early Monday, before an
abrupt increase to upwards of 15 ft on Tuesday. There is a 50%
chance for marginal SCA winds this afternoon through at least this
evening, especially from Pt Sal south to San Nicolas Island, thus
an SCA was issued for all Outer Waters zones. There is a 30%
chance SCA winds continue through tomorrow, then there is another
50% chance of SCAs beginning in the afternoon, mostly from Pt
Conception to San Nicolas Island. Similar chances of SCA winds
Sunday, but higher confidence in at least SCA level winds Monday
and Tuesday, with a 20% chance for GALES.

For the Inner Waters along the Central Coast, there is a 40-50%
chance for brief SCA`s this afternoon thru evening, but a SCA was
issued. Similar chances Saturday and Sunday night, then higher
confidence for Monday and Tuesday.

For the Santa Barbara Channel, expecting below SCA level
conditions through this morning. There is a 20-30% chance for SCA
level winds this afternoon thru evening, and again during the
afternoon/evening hours Saturday and Sunday, but winds will likely
remain in the far western portion of the zone. There is a 40-50%
chance for SCA winds Sunday afternoon, and higher confidence
Monday and Tuesday.
For the Southern Inner Waters, conditions are expected to be
below SCA levels through Sunday night. There is some uncertainty
with Monday and Tuesday, but chances for SCA winds are roughly
30-50%.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Red Flag Warning in effect until 11 AM PST this morning for
      zones 375>380. (See LAXRFWLOX).
PZ...Small Craft Advisory in effect from 3 PM this afternoon to 9
      PM PST this evening for zone 645. (See LAXMWWLOX).
     Small Craft Advisory in effect from 3 PM this afternoon to 3
      AM PST Saturday for zones 670-673-676. (See LAXMWWLOX).

&&

$$

PUBLIC...Cohen/Hall
AVIATION...Lewis
MARINE...Lewis
SYNOPSIS...Hall

weather.gov/losangeles

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