Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 07/11/23

Area Forecast Discussion

National Weather Service Los Angeles/Oxnard CA

 900 PM PDT Mon Jul 10 2023

.SYNOPSIS...10/757 PM.

An upper level ridge of high pressure will continue to build over
the region, bringing a warming and drying trend away from the
coast. A significant heat event with elevated fire weather
conditions is forecast for areas away from the coast from mid
week into next weekend.

&&

.SHORT TERM (MON-THU)...10/859 PM.

A building upper level ridge of high pressure combined with
weakening onshore pressure gradients to the east and north
to result in a shrinking marine layer depth and less low
cloud coverage this morning. As a result, most inland areas
saw a noticeable warm-up today, with highs into the mid 90s
across the warmest valleys. As of 8 pm, ACARS data is showing
the marine layer depth around 1000 feet across the LA Basin.
Satellite imagery is showing low clouds and fog moving into
the Central Coast this evening, and is expected to overspread
most coastal areas south of Point Conception later tonight into
Tuesday morning.

For Tuesday, looking for upper level ridge of high pressure
to continue strengthening, resulting in slightly higher heights
across the region. At the same, onshore pressure gradients are
expected to strengthen to the north and east on Tuesday. While
coastal areas will see little change in temperatures on Tuesday,
inland areas are expected to climb an additional few degrees,
with warmest parts of the Antelope Valley expected to climb
to over 100 degrees. By Wednesday, and Thursday expecting a few
more degrees of warming each day across the interior with more
widespread triple digit heat. However, closer to the coast, there
will continue to be little change due to the persistent strong
onshore flow pattern. As the marine layer depth diminishes
gradually over time, there will continue to be less extensive
low clouds and fog on Wednesday and Thursday, along with the
potential for patchy dense fog. A weak sundowner wind event is
possible for southwest Santa Barbara county on Thursday evening.
Since there will be a warm and dry air mass in place across the
foothills, any downslope winds will bring the potential for warmer
and drier conditions to translate into lower foothill elevations
and wind favored canyons.

.LONG TERM (FRI-MON)...10/239 PM.

High pressure continues to strengthen over the area through the
extended, and 500 mb heights are forecast to reach impressive
values near 600 dM by Sunday. In addition, the high center shifts
to the east of the region, bringing southerly flow to southern
California. Therefore, high confidence in a long duration heat
event, although temperatures have been backed off slightly for
Thursday. Temperatures are expected to peak within the Friday
through Monday timeframe with high temperatures reaching 105-113
degrees. Overnight low temperatures for portions of the interior
will be uncomfortable, in the 70s to low 80s. Ensemble guidance
continues to forecast warmer and warmer temperatures each run over
the interior Saturday, Sunday, and through next week. Given this,
The EXCESSIVE HEAT WATCH has been extended through Sunday for the
Antelope Valley/Santa Clarita Valley and the western San Gabriel
Mountains. An EXCESSIVE HEAT WATCH has also been expanded into the
VTA mtns, and the interior valleys and mountains of SLO and SBA
counties, with an effective time for Thursday through Sunday. The
coastal valleys also look hot, but currently holding off on
expanding the heat watch for increased confidence. A tricky aspect
of the forecast for these areas will be based on the marine layer
depth and strength of onshore flow. A few hotter areas like the
Antelope Valley, Cuyama Valley, Santa Clarita Valley and Ojai
Valley may also require upgrades to heat warnings.

Will need to monitor Thursday and Friday as guidance shows
offshore flow from the north as well as weaker onshore flow to the
east. Sundowner winds are possible both nights, and Friday could
be the day where the coasts and lower vlys see a jolt in temps -
the SBA south coast will be very vulnerable to this type of
pattern.

Moderate onshore pressure gradients will continue through the
period. So, there will continue to be some gusty southwesterly
winds across interior sections each afternoon and evening, but no
widespread advisory-level winds are expected.

Many of the ensembles keep the heat going deep into next week. The
big change is that there is an increase in the onshore flow to the
north which would bring significant cooling to the vlys. The mtns
and far interior will likely to continue to sizzle.

&&

.AVIATION...11/0001Z.

At 2350Z at KLAX, the marine layer was 1000 feet deep. The top of
the inversion was 2400 feet with a temperature of 24 C.

Moderate confidence in the current forecast for coastal and valley
TAFs. IFR/LIFR cigs are expected to return to most coastal TAF
sites tonight, but uncertainty in timing. For KSMX, KSBP expect
cigs to return this evening, while coastal TAF sites will likely
be late tonight or early Tuesday morning.

High confidence of VFR conditions in the forecast for valley and
desert TAFs.

KLAX...Moderate confidence in TAF. Timing of cig arrival could be
+/- 2 hours from current TAF timing. There is a 30-40 percent
chance of VFR conditions through the period. High confidence that
any east wind component will be 5 kt or less.

KBUR...Good confidence in TAF. VFR conditions are expected through
the period.

&&

.MARINE...10/820 PM.

For the outer waters, Small Craft Advisory (SCA) level winds are
expected through at least tonight. However winds are likely to
fall below SCA level on Tuesday through Wednesday in the southern
two zones. There is a 40-60% chance of SCA level winds over the
northern outer waters through late Tue night, then redeveloping
Wednesday night. For the southern two zones, SCA winds are
expected to redevelop on Thursday, with SCA conds across all of
the outer waters through Friday.

For the inner waters N of Point Sal, conds should generally be
below SCA levels tonight through Wednesday, but are likely to
return Thursday and Thursday night, and possibly into Friday.

Inside the inner waters south of Point Conception, conditions are
expected to be below SCA levels through Saturday.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Excessive Heat Watch in effect from Thursday morning through
      Sunday evening for zones 38-343>345-353-376-377. (See LAXNPWLOX).
     Excessive Heat Watch in effect from Wednesday morning through
      Sunday evening for zones 88-378>383. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 3 AM PDT Wednesday for
      zone 670. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PDT Tuesday for
      zones 673-676. (See LAXMWWLOX).

&&

$$

PUBLIC...Gomberg/Phillips
AVIATION...Gomberg
MARINE...Smith
SYNOPSIS...Phillips/Gomberg

weather.gov/losangeles

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