Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 09/23/20

Area Forecast Discussion

National Weather Service Los Angeles/Oxnard CA

 821 PM PDT Tue Sep 22 2020

.SYNOPSIS...22/726 PM.

Ridging aloft will build in through Thursday and bring a slight
warm-up. Temperatures will remain above normal into the weekend,
then a significant warming trend is forecast for early next week
as high pressure aloft strengthens and becomes the dominant
weather feature across the area. Night through morning low clouds
and fog will become more confined to the coast over the next
several days.

&&

.SHORT TERM (TUE-FRI)...22/820 PM.

Satellite imagery showing low clouds and fog moving into the
Central Coast this evening, along with patches developing
across the Ventura and southern Santa Barbara coasts. 00z
Vandenberg sounding and ACARS data out of LAX showing the
marine layer depth around 1000 feet this evening. With an
upper level ridge of high pressure building over Southwest
California overnight, the marine layer depth will continue
to shrink, bring an increased threat for patchy dense fog,
especially across the Central Coast where a dense fog
advisory may be needed. Any low clouds and fog that develop
tonight into Wednesday morning are generally expected to remain
confined to the coastal plain.

The upper level ridge of high pressure combined with a slight
weakening of the onshore pressure gradients will also likely
bring a few degrees of warming across most areas on Wednesday.
Have bumped up temperatures a few degrees for tomorrow in evening
update as temperatures climbed a bit higher today than expected.

*** From previous discussion ***

The building high will help boost temps a few more degrees Wed/Thu
but nothing significant. Temps will jump back up a few degrees above
normal but nothing too unusual for this time of year. The trends
will briefly reverse Fri as a trough passes through the Pac NW
but just minor cooling at best. Some northerly winds expected in
srn SB County each evening starting Wed but so far models are
keeping wind speeds mostly below advisory levels. Marine layer
clouds will likely be confined to LA and possibly Ventura County
with the increase in northerly flow Wed/Thu.

.LONG TERM (SAT-TUE)...22/154 PM.

An even stronger ridge will start to build over the West Coast
Saturday but not really kick into gear until early next week,
though even then temps aren`t expected to come anywhere close to
the earlier heat wave that saw highs well above 110 in the coastal
valleys. There are a few extreme ensemble solutions suggesting a
hotter scenario than currently expected but not too much support
for that now. Inland areas will see a little warming Saturday but
then all areas will start warming Sunday as a 595 high sits
almost on top of us. Warmer valley temps expected to reach triple
digits by Sunday with the warmest days likely to be Mon/Tue.
Record highs are quite high through Monday. The 27th is the
anniversary of the all time Downtown LA high of 113 and the
records for Monday are only a few degrees lower so Tuesday would
probably be our best chance for record highs but even then it
would be a stretch unless some of the minority become more favored
in subsequent model runs.

&&

.AVIATION...23/0310Z.

At 01Z, the marine layer depth was around 1000 feet deep at KLAX.
The top of the inversion was near 2000 feet with a temperature
around 25 degrees Celsius.

Moderate to high confidence in the current forecast. Higher
confidence in flight categories, less confidence in timing. Timing
could up to 2 hours later or earlier than forecast.

LIFR to IFR conditions will spread into most coastal terminals
through 13Z. The best chance of LIFR conditions will be for
coastal terminals north of KSBA between 08Z and 15Z. Conditions
will improve one category between 14Z and 16Z. VFR conditions
should develop at coastal terminals by 18Z at the latest.

For valley and desert terminals, VFR conditions are expected at
this time.

KLAX...IFR conditions will spread into KLAX as soon as 06Z or as
late as 13Z. There is a 30 percent chance of LIFR conditions
between 10Z and 14Z. Conditions will improve one category between
14Z and 16Z. VFR conditions should develop between 15Z and 18Z. No
wind impacts are expected at this time.

KBUR...VFR conditions are expected at this time. There is a 30
percent chance of MVFR visibilities. No wind impacts are expected
at this time.

&&

.MARINE...22/812 PM.

For the waters southwest through north of the Channel Islands and
outside the southern California, winds will increase through
Wednesday evening, spreading south to near San Nicolas Island and
east into near shore waters along the Central Coast. Small Craft
Advisory (SCA) level winds across the far northwest portion of the
coastal waters this evening will spread southward into Wednesday.
There is a chance of gales between Thursday night and early
Saturday morning. SCA conditions will likely develop across much
of the waters west of the southern California bight and more than
10 NM offshore of the Central Coast. A moderately long-period
northwest swell building across the outer coastal waters will
contribute to SCA conditions between Thursday evening and Saturday
evening.

Inside the southern California bight, winds and seas will remain
below SCA levels. There is a 30-40% chance that SCA level winds
may develop across the western portion of the Santa Barbara
Channel Wednesday through Friday.

Patchy dense fog from a shallow marine layer could create hazards
to mariners tonight through Wednesday.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory in effect until 3 AM PDT Thursday for
      zone 670. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (FRI-TUE).

Strong high pressure is expected to build over the West Coast
Sunday and Monday. Heat stress and elevated fire weather
conditions will be possible, especially on Monday.

&&

$$

PUBLIC...Gomberg/MW
AVIATION...Hall
MARINE...Hall
SYNOPSIS...Hall

weather.gov/losangeles