FXUS66 KLOX 281544
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
844 AM PDT Sat Sep 28 2024

.SYNOPSIS...28/417 AM.

Some cooling will occur today as a weak low pressure area off the
coast meanders toward the region and strengthens onshore flow. A
persistent marine layer will keep the coastal areas below normal
through Sunday with areas of morning dense fog. Warmer than normal
conditions will continue away from the coast through Sunday.
A warming trend will develop for early next week as onshore flow
will weaken beneath a building ridge high pressure.

&&

.SHORT TERM (TDY-MON)...28/417 AM.

Low clouds and fog are well-entrenched early this morning across
the coastal and lower valley areas as stronger onshore flow
continues to establish. Onshore flow and a persistent marine
layer are likely to remain in place across the region through
Sunday as an upper-level trough, sitting about 275 miles
southwest of Point Conception, advances on the southern portion
of the state. Some cooling should develop today as the trough
approaches. Earlier AMDAR soundings from KLAX indicated the marine
layer depth around 1300 feet deep, but it is likely lower than
that along the Central Coast due to the trough positioning. Clouds
are generally a little more extensive across the Southland versus
this time last night, and less extensive along the Central Coast.
The thinner marine layer depth along the Central Coast will
permit dense fog to develop. A dense fog advisory was expanded
from the Central Coast beaches to encompass all of the broader
Central Coast sections and the Santa Ynez Valley. This advisory is
in effect until 9 am PDT this morning. If you encounter dense fog
on your morning travels this morning, slow down, use low beam
headlights, and increase the space cushion around your vehicle.

A blocking upper-level ridge of high pressure over the Sonoran
Desert this morning will strengthen over the coming days and
inhibit the trough's eastward movement. The trough will run into
the ridge on Sunday over Los Angeles County and be turned back.
500 mb heights will climb and onshore flow will weaken as the
trough retreats to the southwest of the region for early next
week. Some semblance of an onshore flow could remain intact for
early next week, albeit much weaker than it has been. The
forecast continues to take a warmer than NBM stance for Monday
and beyond to account for most of the warming taking place across
the interior.

.LONG TERM (TUE-FRI)...28/425 AM.

A warming trend will continue into Tuesday and possibly Wednesday
as high pressure aloft to the east will continue to win the
battle, pushing the trough to the southwest and warming the air
mass. An offshore low-level flow component will set up between
Monday and Wednesday, potentially pushing temperatures higher than
forecast. Temperatures break away from NBM mean values and
emphasize values closer to the 75th-90th percentiles, and buying
more heavily into EPS temperature means, which have consistently
advertised a warmer pattern developing in weak offshore flow.
There is a moderate chance that Tuesday and Wednesday could be
warmer than forecast as fair amount of the higher resolution EPS
perturbations advertised much warmer temperatures than forecast.
Much will depend upon how much monsoonal moisture and additional
clouds seep into the area.

A southeast low-level flow pattern develops between Monday night
and Wednesday. The forecast ensemble members suggest precipitable
water value means approaching between 0.8 and 0.9 inch across the
region, which is on the order of 125 to 150 percent of normal for
this time of year across the southern portion of the area. EPS
members suggest a few solutions with QPF at sites across the
region, but this would rely on convective model processes working
as advertised. PoPs remain above NBM values across the terrain of
the region as there is a non-zero chance of afternoon and evening
showers and thunderstorms between Tuesday and Wednesday.

The forecast ensemble spreads increase substantially for late
next week. While temperature means suggest some cooling across
the region as the trough will move back once again, the trough's
movement remains in question at this point. The forecast goes with
NBM values for late next week and reintroduces a broader low
cloud field into the forecast.

&&

.AVIATION...28/1239Z.

At 12Z at KLAX, the marine layer was 1400 ft deep. The top of the
inversion was at 2800 ft with a temperature of 24C.

High confidence in the TAFs for KWJF, KPMD, and KPRB.

Otherwise, nearly a repeat of yesterday morning at this time.
Low clouds were widespread in all coastal areas and the Santa
Ynez and San Gabriel Valleys. Clouds have pushed into the portions
of the valleys of VTU County and the southeastern San Fernando
Valley as well. Conds were mostly LIFR to VLIFR, except IFR across
coastal sections of L.A. County. Skies should clear by mid
morning in the valleys, and by noon on most of the coastal plain.
However, clouds will likely linger into the afternoon near the
beaches, especially across southern SBA County and Ventura County.

Expect clouds to overspread the coastal plain this evening, and
push into most valley locations after midnight. Conds should be
mostly IFR to LIFR, except locally VLIFR on the Central Coast and
in the valleys.

KLAX...Low to moderate confidence in the 12Z TAF. There is a 30%
chance that cigs will linger until as late as 22Z. There is a 20%
chance that cigs will not clear at all. There is a 20% chance
that cigs will arrive as early as 01Z. Good confidence that
any east wind component will remain under 6 kt.

KBUR...Moderate confidence in the 12Z TAF. There is a 20% chance
that cigs will clear by 15Z. There is a 20% chance that LIFR to
VLIFR conds will arrive as early as 10Z.

&&

.MARINE...28/843 AM.

In the Outer Waters (Central Coast to San Nicolas Island), high
confidence in the forecast thru Sun morning, with winds expected
to remain below Small Craft Advisory (SCA) levels. There is a 20%
chance of a brief period of SCA level winds around Pt. Conception
this afternoon/eve. SCA level winds are likely (60-70% chance)
for Sun afternoon thru evening. Steep seas are likely this
afternoon thru late Sunday, however, they will likely not have a
short enough period to meet SCA thresholds. Then, moderate
confidence in sub advisory winds Monday thru late Wednesday.

For the inner waters north of Pt Sal, the Santa Barbara Channel,
and inner waters off the LA and OC Coast, moderate to high
confidence that winds and seas will remain below SCA levels thru
Wed night. However, there is a 30-50% chance of SCA level winds
Sun afternoon thru evening across the inner waters north of Pt.
Sal, and a 20-30% chance in the western and southern portions of
the Santa Barbara Channel, from Anacapa Island to Point Dume, and
thru the San Pedro Channel.

Areas of dense fog with vsbys 1 NM or less will affect the waters
thru at least tomorrow morning in the evening thru early morning
hours, most widespread off the Central Coast.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Dense Fog Advisory remains in effect until 9 AM PDT this
      morning for zones 340-346. (See LAXNPWLOX).
     Dense Fog Advisory in effect until 9 AM PDT this morning for
      zones 341-347-348. (See LAXNPWLOX).
PZ...NONE.

&&

$$

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

weather.gov/losangeles

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