472
FXUS66 KLOX 190636
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
1136 PM PDT Sat May 18 2024

.SYNOPSIS...18/830 PM.

Low clouds will continue to be a staple of the forecast for coast
and valleys through Monday, and struggling to clear each
afternoon. Breezy onshore winds will occur across the interior
valleys and adjacent foothill areas each afternoon and evening.
More sunshine with slight warming is expected Tuesday and
Wednesday as onshore flow weakens. Then cooler with increasing
marine layer clouds again the latter half of next week.

&&

.SHORT TERM (SAT-TUE)...18/830 PM.

A long wave trough embedded along the West Coast will remain
in place through early next week, maintaining a strong onshore
flow and deep marine layer pattern. The current marine layer
depth is around 3500 feet across the LA Basin, with low clouds
already overspreading many coastal/valley areas, and locally into
the coastal slopes from Ventura county northward. The LAX-DAG
pressure gradient is expected to remain strong through Monday,
generally ranging in the +8 to + 10 mb range each afternoon. This
will translate into gusty onshore winds across the interior, with
gusts of 25 to 40 mph common, and isolated gusts as high as 50
mph in the foothills of the Antelope Valley. A wind advisory
had been issued for the Antelope Valley and western foothills
until 9 pm this evening, with winds gradually expected to
diminish overnight. With the deep marine layer, expecting
areas of drizzle overnight into Sunday morning for areas
south of Point Conception. Looking for another day of slow
or no clearing near the coast on Sunday. Temperatures will
remain at least 3-6 degrees below normal and possibly more where
clouds linger most of all of the day.

*** From previous discussion ***

On Monday a weak low pressure system, currently centered 1000
miles west of Los Angeles, will pass through extreme southern
California will drawing a deeper trough passing through the
northwest states down closer to California. This will bring some
noticeable changes. Temperatures will drop to below normal for the
interior areas. Coastal and valleys areas will also drop a few
degrees, and will likely see an even deeper marine layer and more
drizzle. Low clouds could even push into some interior valleys
like Cuyama and the Antelope Valley. Southern Santa Barbara County
and western Ventura County would be the one exception, as
increasing northwest flow will likely bring an area of low cloud
clearing in the morning or early afternoon. This would locally
counteract the cooling factor there, and form a coastal eddy to
the east. There is chance that the marine layer grows too deep to
support itself, with more clearing than we have been seeing
overall by Monday afternoon.

Models still in good agreement showing much weaker onshore flow
Tuesday as the trough passes to the east. Expecting faster and
more complete clearing in all areas, though can`t rule out some
stubborn low clouds near the coast. Coastal valleys will see the
biggest adjustment with highs bouncing back to the high 70s and
possibly low 80s. There will be some northeast breezes across the
mountains and other interior areas but those should be below
advisory levels. Otherwise, just the standard onshore sea breezes
for most coast/valleys.

.LONG TERM (WED-SAT)...18/252 AM.

As the aforementioned low pressure system moves to the east on
Tuesday and Wednesday, this will weaken the onshore pressure
gradients and flow (LAX-DAG predicted to go from +6 millibars
Monday morning to +2 millibars on Tuesday). This should cause the
marine layer to lower some and not push as far inland as it has
been. The northwest flow over Santa Barbara County and the
northern mountains will also continue to make low clouds over
southern Santa Barbara and western Ventura Counties less
favorable. As a result, Tuesday and Wednesday will likely be the
warmest over coastal and valleys areas over the last week or two
with coastal temperatures starting to sniff normal values. Beyond
that there is a fair amount of uncertainty. Several of the
ensemble members show further warming to close out the week, while
a significant amount show onshore flow strengthening and the
marine layer expanding once again. The most likely outcome is a
return to conditions like we have been seeing by Thursday or
Friday of next week, with cool and cloudy conditions on the
coastal side of the mountains, with warmer than usual and breezy
conditions over the interior.

&&

.AVIATION...19/0635Z.

At 0505Z at KLAX, the marine layer was 1900 ft deep. The top of
the inversion was at 4200 feet with a temperature of 16 C.

Good confidence in desert TAFs.

Moderate confidence in the remainder of TAFs. There is a 30
percent chc that sites with afternoon clearing will remain cloudy.
Flight Cat transitions may be off by +/- 90 minutes and cig hgts
off by +/- 300 ft.

KLAX...Moderate confidence in TAF. There is a 30 percent chc of
BKN025 conds through the afternoon. BKN025 cigs may arrive
anytime between 14Z and 16Z. No significant E wind component
expected.

KBUR...Moderate confidence in TAF. There is a 20 percent chc of
BKN025 conds through the afternoon. BKN025 cigs may arrive
anytime between 15Z and 17Z.

&&

.MARINE...18/524 PM.

In the Outer Waters, high confidence in the forecast. Winds and
seas will remain below Small Craft Advisory (SCA) levels thru Sun.
There is a 30-50% chance of SCA level winds late Sun. SCA level
winds and some SCA level seas are likely (40%-60%) across the
entire outer waters Mon thru Tue night. There is a 30%-40% chance
of SCA level winds at times Wed especially the northern waters,
then conds should be below SCA levels for Thu.

For the Inner Waters N of Pt. Sal, moderate to high confidence in
the forecast. Conds are expected to remain below SCA levels thru
Thu, except for a 20%-30% chance of SCA level wind gusts at times
mainly afternoon and evening hours Tue thru Wed.

In the Inner Waters S of Pt. Conception, moderate to high
confidence in the forecast. Winds and seas will remain below SCA
levels for the majority of the area thru Thu. However, in western
portions of the SBA Channel, there is a 30% chance of SCA level
wind gusts at times during the afternoon/eve hours Mon thru Wed.

&&

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

&&

$$

PUBLIC...Gomberg/MW
AVIATION...Rorke
MARINE...Munroe/Sirard
SYNOPSIS...MW

weather.gov/losangeles

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