Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 06/04/23

Area Forecast Discussion

National Weather Service Los Angeles/Oxnard CA

 854 PM PDT Sat Jun 3 2023

.SYNOPSIS...03/853 PM.

A weak upper level low pressure system will bring slight cooling
on Sunday. A stronger low pressure system will bring much cooler
weather Monday through Wednesday, along with a slight chance of
showers and thunderstorms. A cooler air mass is likely to remain
through the rest of next week with extensive low clouds.

&&

.SHORT TERM (SAT-TUE)...03/850 PM.

Satellite imagery showing a return of low clouds across many
portions of the coastal plain this evening. ACARS sounding showing
a marine layer depth around 1700 feet across the LA Basin this
evening, while LAX-Daggett pressure gradient peaked at +7.3 mb. As
a weak upper level trough approaches the area on Sunday, there
will be increasing onshore pressure gradients and a slight
deepening of the marine layer which will likely lead to a slight
cooling trend. Look for low clouds to fill into most valleys by
Sunday morning, with a slower clearing trend anticipated in the
afternoon.

By late Sunday afternoon, some mid level moisture and instability
increase across the mountains. While not officially in the
forecast, there is a 10 percent chance of thunderstorms over the
mountains of Santa Barbara and Ventura counties by late Sunday
afternoon and evening, where the greatest instability and mid
level moisture are focused. The upper low will then move into the
coastal waters late Sunday night and over the mainland Monday
afternoon or possibly not until evening. At the very least the
upper low will cause the marine layer to deepen back up to at
least 3000` and possibly as high as 4500` by Tuesday with areas of
drizzle possible and minimal clearing. However, given the
placement of the low precip may fall as actual rain showers rather
than just drizzle, especially in upslope areas. Steepening lapse
rates Monday afternoon associated with the cooling aloft and some
upper level divergence will make conditions more favorable for
convective activity, mainly over the mountains but certainly not a
zero chance over lower elevations.

*** From previous discussion ***

After Monday there is some uncertainty regarding the track of the
upper low. The NAM actually drifts it north to around Monterey
Tuesday while the other deterministic models keep the low in the
vicinity of southern California through Wednesday afternoon.
Keeping showers and thunderstorms in the forecast is reasonable,
mainly in the mountains, though lower elevations will at least be
susceptible to drizzle or light showers from the lingering deep
marine layer, assuming the inversion doesn`t get so weak that the
stratus dissipates. Temperatures are expected to remain 5-10
degrees below normal

.LONG TERM (WED-SAT)...03/108 PM.

The upper low is finally expected to exit the region to the east
Thursday, however weak troughing and cyclonic flow is expected to
remain over the region through at least Saturday. Heights do rise
slowly through the period but onshore flow remains strong.
Interior areas like the Antelope Valley and interior SLO County
are expected to see a slight warming trend but coast/valley areas
will likely be mired in June Gloom with late (if any) clearing.
This mirrors the ECMWF EFI and CPC`s below normal forecast that is
expected to continue through at least the middle of the month.

&&

.AVIATION...04/0048Z.

At 2353Z at KLAX, the marine layer was 1200 feet deep. The top of
the inversion was 4800 feet with a temperature of 19 Celsius.

Overall, moderate confidence in coastal/valley TAFs and high
confidence in desert TAFs. Timing of flight cat changes could be
off by +/- 2 hours. There is a 30% chance that IFR CIGs could
spread into the valleys tonight.

KLAX...Moderate confidence
in 18Z TAF. For tonight, high confidence in return of bkn006-012
CIGs. Timing of flight cat changes could be off by +/- 2 hours.
No significant easterly wind component is expected.

KBUR...Moderate confidence in TAF. There is a 30% chance of
BKN006-008 10Z-16Z.

&&

.MARINE...03/805 PM.

For the Outer Waters, high confidence in current forecast. Small
Craft Advisory (SCA) level winds will continue through tonight.
For Sunday through Wednesday, winds and seas will remain below SCA
levels.

For the Inner Waters north of Point Sal and the Inner Waters south
of Point Conception, high confidence in current forecasts. Today
through Wednesday, winds and seas are expected to remain below SCA
levels.

For Monday afternoon and evening, there is a slight chance of
thunderstorms, mainly north of Point Conception.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory in effect until 3 AM PDT Sunday for
      zones 670-673-676. (See LAXMWWLOX).

&&

$$

PUBLIC...Gomberg/MW
AVIATION...Lund
MARINE...Sweet/Lund
SYNOPSIS...MW

weather.gov/losangeles

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