Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 06/29/20

Area Forecast Discussion...UPDATED

National Weather Service Los Angeles/Oxnard CA

 904 PM PDT Sun Jun 28 2020

.SYNOPSIS...28/750 PM.

Overnight and morning low clouds and patchy fog will continue
through the week along the coast and into adjacent valleys with
slow clearing each day. There is a chance of light rain or drizzle
tonight through Monday morning south of Santa Barbara. Temperatures
will be cool through Monday then will warm into the weekend.

&&

.SHORT TERM (SUN-WED)...28/902 PM.

The latest AMDAR soundings from KLAX indicate a 3700 foot deep
marine layer in place this evening, which agrees well with the
current satellite imagery. Clouds are pushing well into the
coastal slopes of the mountains already and filling back into the
patches of clearing across the coastal and valley areas where they
cleared from earlier. The marine layer remains well-entrenched as
strong onshore flow continues across the area. Based upon the
latest NAM-WRF time height sections, the marine layer should
deepen to around 2700 feet north of Point Conception and close to
4200 feet south of Point Conception. With instability moving over
the area tonight from an upper-level trough of low pressure
entering the Great Basin, current forecast of drizzle or light
rain makes sense.

A wind advisory remains in effect for the Los Angeles County
mountains and the Antelope Valley, and the San Luis Obispo County
Valleys this evening. Winds are starting to drop-off for the San
Luis Obispo County Valleys and there is a chance that this
advisory could be cancelled before its expiration.

Onshore flow should start to weaken throughout Monday as the upper-
level trough lifts out into the northern intermountain Region and
the northern Rockies. High pressure aloft over the eastern
Pacific Ocean will nose into the region behind the trough and
bring a warming trend through Tuesday.

A few tweaks will be made for the forecast tonight and into
Monday, otherwise the forecast is in reasonably good shape.

***From Previous Discussion***

Overall, 12Z models in very good synoptic agreement for the short
term. At upper levels, low will spin over southern Idaho through
Monday then move eastward with broad cyclonic flow remaining over
the area through Wednesday. Near the surface, strong onshore flow
will prevail today then will weaken Monday/Tuesday before
increasing a bit again on Wednesday.

In fact, there is a decent chance of some drizzle or light
showers south of Point Conception tonight and Monday morning. So,
will keep inherited POPs as is for the area tonight and Monday
morning. Most areas will likely see trace amounts or a couple
hundredths of an inch. However, in upslope areas, upwards of 0.20
inches will be possible by Monday morning. By Monday afternoon,
expect better clearing, but still likely partly cloudy conditions
for most areas west of the mountains. For Monday night through
Wednesday, will anticipate a gradually shrinking marine inversion
due to rising H5 heights and weakening onshore gradients. So,
inland extent of stratus should become less Monday night and
Tuesday night.

As for temperatures, today will likely be the coolest day of the
forecast. For Monday through Wednesday, expect a gradual warming
trend with less marine influence and rising thicknesses/H5
heights.

.LONG TERM (THU-SUN)...28/140 PM.

Overall, 12Z models continue to exhibit good synoptic agreement
through the long term. At upper levels, main feature will be the
gradual building of a ridge over the desert SW. Near the surface,
onshore flow will weaken through the period.

Forecast-wise, pretty straightforward through the period. With
building H5 heights (as upper ridge develops) and weakening
onshore gradients, the marine inversion will become more shallow
and less extensive during the night/morning hours from day-to-day.
Daily clearing of said stratus should be very good. Other than the
stratus, skies are expected to remain mostly clear.

As for temperatures, will expect a warming trend through the
period. In fact, by the weekend, most areas should experience
temperatures a few degrees above seasonal normals.

&&

.AVIATION...29/0107Z.

At 00Z, the marine layer depth was around 3300 feet deep at KLAX.
The top of the inversion was near 6000 feet with a temperature of
around 17 degrees Celsius.

Low-to-moderate confidence in the current forecast, except high
confidence for desert terminals. Higher confidence in flight
categories, less confidence in timing. Conditions be predominantly
MVFR, but there is a chance of IFR conditions between 06Z and 15Z,
especially with any drizzle or light rain. MVFR conditions could
scatter out up to two hours earlier than forecast or up to three
hours later than forecast.

KLAX...MVFR conditions are likely through the period. There is a
30 percent chance of IFR conditions between 09Z and 13Z,
especially with any drizzle or light rain. VFR conditions could
develop as soon as 16Z, or as late as 21Z. No wind impacts are
expected at this time.

KBUR...MVFR conditions are likely through the period. There is a
50 percent chance of IFR conditions between 09Z and 15Z,
especially with any drizzle or light rain. VFR conditions could
develop as soon as 16Z, or as late as 20Z. No wind impacts are
expected at this time.

&&

.MARINE...28/902 PM.

Moderate-to-high confidence in the current forecast. Higher
confidence in seas, less confidence in winds.

For the waters from southwest through northwest of the Channel
Islands, marginally gusty winds will affect the area tonight, then
winds should remain below Small Craft Advisory (SCA) levels
through early Friday. There is chance of SCA level winds Tuesday
afternoon and evening. Winds should increase on Friday to SCA
levels.

Inside the southern California bight, conditions will likely remain
below SCA levels through the forecast period.

Short period and locally choppy seas will continue at times
through Friday, especially inside the Southern California Bight.
Then, a long-period southerly swell will build over the coastal
waters between Friday and Sunday.

&&

.BEACHES...28/902 PM.

Elevated surf and strong rip currents are possible next weekend
at southern California beaches as a swell generated from a storm
system currently near 44S and 118W will move north into the
northern hemisphere. The latest swell models indicate long-period
southerly swell arriving between Friday and Saturday around 3-4
feet at 17-18 seconds to the adjacent coastal waters. A high surf
advisory or a beach hazards statement might be needed once the
finer details (timing, height and period) become clearer.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory in effect until 3 AM PDT Monday for zones
      37-54-59. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 3 AM PDT Monday for
      zones 670-673. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (WED-SUN).

Gusty southwest winds are likely early next week for the Antelope
Valley which may lead to hazardous driving conditions. Early next
week there will likely be strong rip currents across all beaches.

&&

$$

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

weather.gov/losangeles