Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 06/21/19

Area Forecast Discussion

National Weather Service Los Angeles/Oxnard CA

 807 PM PDT Thu Jun 20 2019

.SYNOPSIS...20/750 PM.

Low clouds will fill into the coasts and valleys tonight through
Friday morning with possible drizzle in many areas. Clouds will be
slow to clear during the day keeping temperatures cool. A warming
trend for inland areas is expected over the weekend as onshore
winds weaken leading to earlier clearing.

&&

.SHORT TERM (THU-SUN)...20/806 PM.

June gloom pattern in full swing today with little change expected
into Friday. An upper level trough centered across interior
sections of California will maintain the strong onshore flow and
deep marine layer pattern through Friday. LAX-Daggett gradient
peaked at +11.3 mb onshore this afternoon, which is unusually
strong for mid June. ACARS soundings and 00z Vandenberg
sounding showing a uniformly deep marine layer between 3500 and
4000 feet this evening. As a result, satellite imagery already
showing low clouds pushing well inland this evening across the
interior valleys and lower coastal slopes. Marine layer cloud
coverage expected to be even more widespread by Friday morning,
extending well into the coastal slopes, with a marine layer
depth over 4000 feet. This deep marine layer combined with
weak southerly low level flow will set the stage for widespread
drizzle across our forecast area tonight into Friday morning.
Light measurable rainfall will be possible, especially across
Los Angeles county and eastern Ventura county (where Pops are
ranging between 20 and 40 percent through Friday morning).

Wind advisories were extended until 9 pm Friday for the Antelope
Valley where wind gusts between 40 and 50 mph will be common, with
isolated gusts as high as 60 mph in the foothills near Lake
Palmdale. The strongest winds will be this evening, and again
Friday afternoon/evening. These gusty winds combined with
relatively low humidities will continue to bring elevated fire
weather conditions to the Antelope Valley and adjacent foothills
through Friday. As expected, temperatures took a large fall today,
especially interior sections, where we saw some areas see
temperatures 10 to 15 degrees cooler than yesterday. Another
unusually cool day expected on Friday, which will be the official
start of summer.

Those offshore trends will continue Saturday through Monday and
combine with a building ridge across the eastern Pacific to lower
the marine layer depth and bring some warming, mainly for inland
areas. Clouds still expected to linger near the coast through the
afternoon but clearing elsewhere should be much earlier.

.LONG TERM (MON-THU)...20/151 PM.

The warming trend will reverse Tuesday as the next trough arrives
on the west coast. A stronger onshore flow will develop through
Thursday with cooling temps pushing inland. Then warming expected
going Friday into next weekend as high pressure strengthens and
expands over the desert southwest. Models also hinting at some
northerly flow developing in the lower levels that would bring
more warming to coastal areas and possibly a reprieve in the June
gloom conditions.

&&

.AVIATION...21/0051Z.

At 2023Z, the marine layer depth was around 3500 feet deep at
KLAX. The top of the inversion was near 6000 feet with a
temperature around 19 degrees Celsius.

Moderate confidence in the current forecast. The latest visible
satellite imagery and observations trends show solid marine layer
coverage across much of the coastal and portions of the valleys.
However, as an upper level trough continues to dig into CA
tonight into tomorrow morning, marine layer should overspread over
much of the inland valleys and coastal slopes tonight. Latest
model forecast soundings and vertical mesoscale model profile
suggest that marine layer depth will be the greatest tonight
(Cloud tops to around 4,500-5,000 FT) and low level lifting
within the layer will be strong enough to produce light rain or
drizzle mainly across Ventura and Los Angeles Counties, leading
to MVFR vsbys tonight into early tomorrow morning. As for
tomorrow afternoon, expect better chance of clearing across the
inland valley areas. However coastal areas will see limited
clearing with a persistent eddy circulation off the coast.
Terminals over the Antelope valleys will see continued VFR
conditions with gusty SW/WSW winds tonight into tomorrow afternoon
as tight onshore pressure gradients persist.

KLAX...Moderate confidence in 00z TAF. Expect persistent MVFR
CIGs tonight into tomorrow afternoon with a chance of MVFR vsbys
in light rain or drizzle tonight.

KBUR...Moderate confidence in 00z TAF. MVFR CIGs should prevail
through the period though a brief period of partial clearing can
be seen between 00z-02z this afternoon per latest obs and visible
satellite imagery trends. There is a chance of MVFR vsbys in
light drizzle tonight. MVFR cigs should clear out tomorrow
afternoon.

&&

.MARINE...20/744 PM.

Outer Waters...High confidence with seas remaining below Small
Craft Advisory (SCA) thresholds through at least Friday morning.
Then a 60% chance for SCA level NW gusts across the northern
portion (PZZ670) and 40% chance for (PZZ673) and even lower chance
for the southern outer waters zone (PZZ676). 20% chance for SCA
across the Outer Waters this weekend.

Inner Waters N and S of Point Conception...Winds are expected to
remain below SCA thresholds through this weekend.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory in effect until 9 PM PDT Friday for zone 59. (See LAXNPWLOX).
PZ...NONE.

&&

.HAZARD POTENTIAL OUTLOOK (SUN-THU).

No significant hazards expected.

&&

$$

PUBLIC...Gomberg/MW
AVIATION...Oh/Gomberg
MARINE...Sweet
SYNOPSIS...Stewart

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