Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 11/04/23

Area Forecast Discussion

National Weather Service Los Angeles/Oxnard CA

 837 PM PDT Fri Nov 3 2023

.SYNOPSIS...03/824 PM.

A cooling trend will intensify over the weekend as onshore flow
returns and areas of low clouds and dense fog develop near the
coast. The cooling trend will continue through early next week,
with periods of gusty northwest to north winds across southern
Santa Barbara County and through the Interstate 5 Corridor.

&&

.SHORT TERM (FRI-MON)...03/836 PM.

Another warm early November day today with some lingering, though
lighter offshore flow in place and a weak ridge of high pressure
over Southwest California. With weak upper level ridge weakening
tonight (upper flow becoming more zonal)and pressure gradients
trending slightly onshore, conditions are favorable for low clouds
and fog to return to some coastal areas tonight into Saturday
morning. Current satellite imagery already showing some low clouds
and fog moving into portions of LA/Ventura county coastal areas
this evening.

ACARS data showing a very shallow 500 foot marine layer
depth over the LA Basin this evening. Areas that do see low
clouds and fog tonight will have the potential for dense fog due
to the very low and strong marine inversion and weak pressure
gradients. As a result, a Dense Fog Advisory may need to be issued
for portions of the coast tonight into Saturday morning.

*** From previous discussion ***

Going forward, offshore flow will continue to decrease through the
weekend as the west coast ridge weakens and shifts east. The ridge
will be followed by a series of upper lows that will continue
throughout the next week to 10 days, most of which will pass too
far north to bring rain to southern California. Initially this
weekend, the biggest impacts of this shift will be along the coast
where increasing areas of dense fog are expected, especially
during the night and morning hours. Temperatures will be cooling
as well as gradients shift towards onshore, but staying above
normal in most areas away from the immediate coast as the marine
inversion remains under 800 feet based on the latest forecast
soundings.

The biggest temperature drop for inland areas will be Monday where
highs will fall 3-6 degrees and be within a degree or two of
normal in most areas.

Northerly flow will be increasing across western areas later in
the weekend with some breezy northwest winds by Sunday.

.LONG TERM (TUE-FRI)...03/148 PM.

Somewhat lower confidence than usual next week as the track of the
incoming upper lows has been quite variable from run to run and
EPS/NAEFS ensembles are still showing quite a a bit of spread in
the solutions. There is a small chance of light rain across far
northern SLO County late Monday into Tuesday and a somewhat better
chance (though very light intensity) across the Grapevine area
Tuesday morning as northerly flow generated some upslope flow
there that will enhance precip chances. Snow levels expected to
mostly stay above 8000 feet and rain amounts mostly under a tenth
of an inch. Elsewhere Tuesday, just continued cooler temperatures
with likely some breezy winds, especially coastal areas and
mountains.

Latest NAEFS forecast pressure gradients still leaning towards a
brief offshore wind event Wednesday into Thursday. So far this
appears to be much weaker than the Santa Ana event this last week
as the track of the low is most east/west rather than north/south
but could provide some breezy offshore winds in places and slight
warming.

Chances for precip area-wide are a little higher as we get into
later in the week as today`s models were a little more in
agreement on a sharp trough moving through later Friday into
Saturday. However, this one, at least so far, appears to be
extremely moisture starved with PW`s well under a half inch so any
rain from this one would be on the lighter side.

&&

.AVIATION...03/1957Z.

Around 1758Z, the marine inversion at KLAX was based around 300
feet. The top of the inversion was 1300 feet with a temperature
of 22 degrees Celsius.

Overall, moderate to high confidence in 18Z TAF package. For
tonight, moderate confidence in current forecast of the return of
CIG/VSBY restrictions with likely LIFR/VLIFR conditions in many
coastal locations.

KLAX...Low to moderate confidence in 18Z TAF. For tonight, there
is a 30-40% chance that CIG/VSBY restrictions will not develop. No
significant easterly wind component is expected.

KBUR...High confidence in 12Z TAF as CAVU conditions are expected
through the period.

&&

.MARINE...03/808 PM.

For the Outer Waters, moderate to high confidence in current
forecast. Through Saturday morning, high confidence that winds
and seas will remain below Small Craft Advisory (SCA) levels. From
Saturday afternoon through Monday, there is a 70-90% chance of
SCA level winds across PZZ673/676 and a 30-40% chance across
PZZ670. On Tuesday, high confidence in SCA level winds across all
the Outer Waters.

For the Inner Waters north of Point Sal, moderate to high
confidence in current forecast. Through Saturday morning, high
confidence in winds and seas remaining below SCA levels. From
Saturday afternoon through Tuesday, there is a 40-60% chance of
SCA level winds, mainly in the afternoon and evening hours.

For the Inner Waters S of Point Conception, moderate to high
confidence in current forecast. Through Saturday afternoon, high
confidence in winds and seas below SCA levels. For Saturday
through Sunday night, there is a 50-60% chance of SCA level winds
across the western half of the Santa Barbara Channel. For Monday
through Tuesday, there is a 40-60% chance of SCA level winds
across the western portion of the entire southern Inner Waters.

Low clouds and fog will develop over the coastal waters tonight,
with a 60 percent chance of low visibilities down to 1 NM or
less. Once dense fog develops, chances will be ongoing over the
next few days, especially during the early morning hours.

&&

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

&&

$$

PUBLIC...Gomberg/MW
AVIATION...Sweet/RAT
MARINE...Sweet/RAT/Smith
SYNOPSIS...MW/Smith

weather.gov/losangeles

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