Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 08/15/23

Area Forecast Discussion

National Weather Service Los Angeles/Oxnard CA

 849 PM PDT Mon Aug 14 2023

.SYNOPSIS...14/207 PM.

Skies will be mostly clear through late this coming week, with
the exception of night through morning low clouds at the coasts.
A warming trend is expected through Wednesday, then cooling going
into the weekend. Showers are possible early next week as moisture
from a tropical system over Mexico moves into the area.

&&

.SHORT TERM (MON-THU)...14/849 PM.

A few convective showers developed this afternoon across the interior,
mainly in Santa Barbara and San Luis Obispo counties, with a few
lightning strikes near the Cuyama Valley. Otherwise, satellite
imagery showing low clouds and fog surging quickly inland across
the coastal plain this evening. With the marine layer depth
shrinking, we are starting to see lower ceiling and visibilities
this evening as compared to the last couple of nights. Latest
ACARS sounding showing the marine layer depth around 1200 feet
across the LA Basin this evening. There is the potential for
patchy dense fog overnight across portions of the coast,
especially north of Point Conception where a dense fog advisory
may be needed. There is the high likelihood of low clouds and fog
reaching the lower valleys overnight into Tuesday morning such as
the Santa Ynez and San Gabriel valleys, with the latest HREF
ensemble guidance showing a slight chance of low clouds and fog
reaching parts of the San Fernando Valley. With the marine
inversion lowering and strengthening, there is the chance of low
clouds lingering near some of the beaches on Tuesday afternoon.

Upper level closed low will continue to spin off the Central Coast
the next couple of days, with a slight northwestward track,
resulting in gradually rising heights over the region. Despite
some lingering instability across the interior, model soundings
not showing much in the way of moisture, so thunderstorm chances
the next couple of afternoons will remain minimal (5-10%).

Already saw some warming occur today across the interior, with
highs climbing above 100 degrees across the warmest valleys and
deserts. With a gradual increase in boundary layer temperatures,
and a slight weakening of the onshore pressure gradients, looking
for temperatures to continue to warm a few more degrees in most of
the interior. Wednesday still looking on track to be the hottest
day of the week, with Woodland Hills forecasted to reach 106
degrees. Later shifts may need to consider the issuance of a heat
advisory for a few zones on Wednesday as forecasted temperatures
are expected to be near advisory thresholds. The greatest chance
of reaching the heat advisory thresholds will be the western
San Fernando valley, Santa Clarita Valley, Calabasas zone, and
the Santa Monica mountains.

A cooling trend will begin Thursday that will continue through
the weekend.

.LONG TERM (FRI-MON)...14/209 PM.

The cooling trend that will begin Thursday is expected to continue
through the weekend as a long wave trough develops along the West
Coast. A deeper marine layer is expected that will spread at least
partly into the coastal valleys. Highs expected to be 4-8 degrees
below normal by Saturday.

Still very closely monitoring the development of the next tropical
system (likely Hillary) for possible impacts locally early next
week. Models are coming into better agreement on the track of the
system, now favoring more of a westerly trajectory, especially
after it passes central Baja. However, all the ensemble solutions
now are indicating fairly high chances for significant moisture
advection into the area, perhaps as early as Sunday, but more
likely Monday and Tuesday. The GEFS is still leading the charge
but the EPS has definitely increased the number of wetter
solutions, especially south of Pt Conception. While most of the
members are generally on the lighter side in terms of rain
amounts, there are still a few that are much higher so will
certainly have to be keeping a close eye on the development and
track of this system. A slight chance of showers has been added to
most areas starting Sunday, and as confidence grows in timing
those rain chances will likely increase as we get closer.

&&

.AVIATION...15/0021Z.

At 0010Z at KLAX, the marine layer was 1300 ft deep. The top of
the inversion was at 2800 ft with a temperature of 27 C.

Low to moderate confidence in 00Z coastal/valley TAFs due to
uncertainties in marine layer. Arrival times of cig/vsby
restrictions could be +/- 3 hours of current forecasts and flight
categories could vary between IFR and low MVFR. There is a 20-40
percent chance of LIFR cigs for coastal TAF sites -- highest at
KSBP, KSMX, and KSBA where there is a 70-90 percent chance for
MVFR vsbys and a 30-50 percent chance of IFR vsbys in BR.

KLAX...Moderate confidence in 00Z TAF. High confidence that
mostly IFR cigs will now persist through at least Tuesday morning,
with a 20-30 percent chance of cigs lingering through the
afternoon hours. There is also a 20 percent chance that cigs could
lower to LIFR category overnight into early Tuesday morning.
No significant easterly wind component is expected.

KBUR...Moderate confidence in 00Z TAF as VFR conditions are
generally expected through the period. There is a 10 percent
chance of brief IFR/LIFR cigs early Tuesday morning.

&&

.MARINE...14/226 PM.

Confidence is increasing in more widespread fog development
starting this evening and continuing through at least Tuesday
morning across portions of the marine zones. The greatest chance
for visibilities to fall below 1 mile (60-80 percent) will be
north of Point Sal and elsewhere across the Outer Waters
particularly during the overnight and early morning hours. A
Marine Weather Statement has been issued to address the dense-fog
potential into Tuesday, and additional periods of dense fog will
be possible later this week over the coastal waters.

Regarding winds and waves...

For the Outer Waters, moderate to high confidence in
current forecast. High confidence in winds and seas remaining
below Small Craft Advisory (SCA) levels through Tuesday morning.
West-northwest to northwest winds should increase by the middle
of this week. Across PZZ673/PZZ676, there is a 40-60% chance of
marginal SCA winds from Tuesday afternoon into Wednesday, with a
20-30% chance of marginal SCA winds Thursday and Friday.

For the Inner Waters north of Point Sal, high confidence in
current forecast. Winds and seas are expected to remain below SCA
levels through late this week.

For the Inner Waters south of Point Conception, moderate to high
confidence in current forecast. With the increase in west-
northwest winds, there is a 30-40% chance of SCA level winds
Tuesday and Wednesday during the late afternoon and evening hours
over the western half of the Santa Barbara Channel, and across
PZZ655. Otherwise, there is high confidence in winds and seas
remaining below SCA levels through late this week.

Starting Thursday or Friday, there will be the potential for
increasing southerly to southwesterly swell to bring hazardous
marine conditions across all of the coastal waters. This will be
in conjunction with the continued evolution of tropical systems
presently tracking well south of Baja California. While any
wind/weather impacts from these systems over the local area are
highly uncertain, long-period swells consisting of steep waves
with high surf will be possible starting late this week and
especially during the upcoming weekend and beyond. Marine
interests over the southern California waters are encouraged to
continue monitoring the latest forecast information from the
National Weather Service.

&&

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

&&

$$

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

weather.gov/losangeles

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