Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 07/23/19

Area Forecast Discussion...UPDATED

National Weather Service Los Angeles/Oxnard CA

 859 PM PDT Mon Jul 22 2019

.SYNOPSIS...22/730 PM.

Temperatures will warm to above normal across much of the region
this week. There is a slight chance of afternoon thunderstorms
over Ventura and Los Angeles County mountains and deserts through
Wednesday. Overnight and morning low clouds will weaken but
continue along the coast most days this week.

&&

.SHORT TERM (TNT-THU)...22/859 PM.

The marine layer continues to thin this evening. The latest AMDAR
soundings from KLAX indicate a marine layer depth near 700 feet
deep. High pressure aloft over the Four Corners Region continues
to weaken onshore flow and thin the marine layer. Tonight`s
stratus forecast will be tricky as the axis of monsoonal moisture
sits near the eastern Los Angeles County line. Middle and high
level cloudiness will play tricks with the marine inversion and
low confidence exists in the stratus coverage tonight through
Tuesday morning, especially south of Point Conception. Model
solutions have a poor handle on the axis of the moisture and lack
run-to-run consistency. NCEP WRF solutions seem to be the most
plausible. A few showers cannot be ruled out overnight tonight and
into Tuesday morning, especially over the Los Angeles and Ventura
County Mountains. PoPs and sky coverage were increased in an
earlier update to account for the moisture axis coming close to
the area.

A warming trend will continue across the region into Tuesday and
Wednesday. Temperatures were tweaked slightly across the interior
portions of the area over the coming days in the upcoming updates.

An update to the forecast will be issued shortly

***From Previous Discussion***

A large four-corners upper level high pressure system will remain
in place through Wednesday. The center of the upper level high is
then expected to drift S along the AZ/NM border Wed night and
Thu. The western periphery of this upper level high will be over
srn CA thru the period, with H5 heights in the 590-593 DM range
over the forecast area. The upper level flow will be out of the S
and SE thru Thu, which will help to draw additional monsoonal
moisture into the area especially Tue and Wed. PWAT values should
be in the 1.00 to 1.50 inch range for the most part during the
period. H850 dewpoints are forecast to be in the 8-10 deg C range
each day thru Wed then drop to about 6 to 8 deg C on Thu.

The marine inversion should increase to around 1200-1300 feet
deep tonight then lower to 700 feet or less Tue night thru Thu.
Night and morning low clouds and fog are expected to linger along
the Central Coast tonight through Thu morning, and along the L.A.
County coast tonight into Tue morning and again Wed night into
Thu morning. Otherwise, mid-level moisture with some cloudiness
will bring partly cloudy skies at times to the forecast area
through Thu.

There will be enough moisture and instability on Tue for a slight
chance of afternoon and evening thunderstorms over the L.A/VTU
County mtns and Antelope Vly. By Wed, there will be a slight
chance of afternoon thunderstorms over the eastern San Gabriel mtns.
There will be just an outside shot at an afternoon thunderstorm over
the eastern San Gabriels Thu afternoon, but the chance of this is
less than 15 percent and is not reflected in the current forecast.

Onshore gradients will turn weaker Tue and Wed, which should help
coastal areas warm up a bit. With slightly stronger onshore flow
Thu, temps along the coast should drop slightly. Away from the
coast, temps will be several degrees above normal with temps in the
warmest vlys and lower mtns expected to reach the 90s to about 102
on Tue, and mid 90s to 105 on Wed, then drop back into the 90s for
the most part on Thu. The combination of the daytime heat, warmer
nighttime lows, and somewhat higher humidities may prompt the
issuance of Heat Advisories by Wed for the vlys and mtns. Some
locations on Wed could even approach Excessive Heat Warning
thresholds.

.LONG TERM (FRI-MON)...22/232 PM.

The EC and GFS are in general agreement that the large upper level
hi will drift W on Fri then build into srn CA on Sat. The upper
level high should persist over the region Sun before drifting back
E into AZ for Mon. H5 heights over swrn CA will peak around 596
DM on Sun.

It looks like the deeper monsoonal moisture will be largely
shunted back to the E of the region during the extended period,
with no afternoon convection expected. The marine inversion will
remain very shallow thru the period, with some night and morning
low clouds and fog possible for the immediate Central Coast and
just along the L.A. County coast. There may also be some night
and morning low clouds and fog along the VTU County coast Fri thru
Sat. There may be a few mid or hi level clouds at times over the
region as well, otherwise mostly clear skies should prevail for
the most part Fri thru Mon.

Temps will remain several degrees above normal for most areas thru
the extended period. The warmest vlys and lower mtns are expected
to be in the mid 90s to 103 Fri thru Sun, then cool a degree or
two for Mon.

&&

.AVIATION...23/0016Z.

At 21Z, the marine layer depth was around 650 feet deep at KLAX.
The top of the inversion was near 3100 feet with a temperature of
27 degrees Celsius.

Low confidence in the current forecast. There is higher
confidence in sub-VFR conditions for coastal terminals north of
KSBA. Less confidence exists in sub-VFR conditions for coastal
terminals south and east of KSBA. LIFR to IFR conditions will
likely become prevalent through 10Z at coastal terminals. There is
a chance that VFR conditions may occur throughout the period,
especially south of KNTD. VFR conditions should redevelop between
14Z and 19Z.

For desert terminals, there is a slight chance of a thunderstorm
with gusty and erratic winds between 02Z and 04Z, then again after
20Z Tuesday.

KLAX...IFR conditions will likely spread in between 07Z and 11Z.
There is a 30 percent chance of VFR conditions may occur
throughout the period, especially south of KNTD. VFR conditions
should redevelop between 14Z and 19Z.

KBUR...VFR conditions are expected throughout the period.

&&

.MARINE...22/842 PM.

For the Outer Waters...Winds will increase through Tuesday
afternoon or evening to Small Craft Advisory (SCA) levels across
the outer waters, then winds will likely linger into Wednesday.
SCA winds and steep seas should continue across the outer waters
through at least late Wednesday night or early Thursday morning.

For the Nearshore waters between Point Piedras Blancas to Point
Sal...Winds should remain below SCA levels through at least
Tuesday morning. There is a 50 percent chance for SCA level
gusts, mainly across the western portions through Tuesday evening.
There will be a 60 percent chance for more widespread SCA level
gusts Wednesday afternoon through Wednesday eve.

For the inner waters south of Point Conception, conditions should
remain below SCA levels through at least Thursday. However, there
is a 30 percent chance of SCA level winds in the western Santa
Barbara Channel each afternoon and evening Tuesday and Wednesday.

&&

.BEACHES...22/515 PM.

A marginally long period southerly swell could bring the
possibility of strong rip currents to area beaches Wednesday and
Thursday. A Beach Hazards Statement might be needed for the
middle portion of the week.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory in effect from 2 AM Tuesday to 3 AM PDT
      Thursday for zone 670. (See LAXMWWLOX).
     Small Craft Advisory in effect from 9 AM Tuesday to 3 AM PDT
      Thursday for zone 673. (See LAXMWWLOX).
     Small Craft Advisory in effect from 3 PM Tuesday to 3 AM PDT
      Thursday for zone 676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (THU-MON).

No significant hazards expected.

&&

$$

PUBLIC...Hall/Sirard
AVIATION...Hall
MARINE...Hall
BEACHES...Hall
SYNOPSIS...Kj

weather.gov/losangeles