981
FXUS66 KLOX 181553
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
853 AM PDT Sat May 18 2024

.SYNOPSIS...18/844 AM.

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 (TDY-MON)...18/852 AM.

***UPDATE***

Our deep marine layer pattern continues this morning with the
cloud tops 4000-4500 feet. Clouds even made it all the way
through the Cuyama Valley as well as Sandberg at 4500 ft near the
LA/Kern County line. As mentioned yesterday, when the marine layer
gets this deep we often start seeing a reverse clearing pattern
and there have been hints of this the last couple days. Visible
satellite imagery is also showing it this morning with significant
thinning of the stratus from western Ventura County and out
across the SB Channel. So there may be more sunshine in these
areas than we`ve seen the last week or so. Still well below normal
temperatures in most areas except the far interior. Little change
expected Sunday.

***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.

.LONG TERM (TUE-FRI)...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...18/1300Z.

At 12Z at KLAX, the marine layer was 3500 ft deep. The top of the
inversion was at 4900 feet with a temperature of 18 C.

Nearly a repeat of the past few mornings. Clouds were widespread
across the entire area with the exception of the Antelope Valley,
most mountain locations and the far interior valleys of SLO
County. Conds were mostly MVFR, except locally IFR across SLO and
SBA Counties, and widespread LIFR to VLIFR in the foothills and
mtn slopes. Expect slow clearing again today, with skies clearing
by noon or early afternoon in the valleys, and early to mid
afternoon across the coastal plain. Once again, it will likely
stay cloudy at some beaches. Cigs will probably rise into the VFR
category on the coastal plain this afternoon. Expect a repeat
tonight, with clouds in all coasts, valley and mtn slope areas.
Conds will be mostly MVFR, except IFR n of Pt Conception, and
LIFR to VLIFR in the foothills and mtns.

KLAX...Moderate confidence in TAF. There is a 20-30% chance that
cigs will linger all day, though they should rise into the VFR
category. There is a 20% chance that if cigs do clear, they will
not arrive until 06Z. No significant E wind component expected.

KBUR...Moderate to high confidence in TAF. There is a 20-30%
chance that cigs tonight will not arrive until as late as 09Z.

&&

.MARINE...18/832 AM.

In the Outer Waters, high confidence in the forecast. Winds and
seas will remain below Small Craft Advisory (SCA) levels thru Sun
morning. There is a 30% chance of SCA level winds late Sun in the
northern zone (PZZ670). SCA conds are likely there Sun night, with
a 40% chance elsewhere. SCA level winds and seas are likely across
the entire outer waters Mon thru Tue night, with a 40% chance Wed.

For the Inner Waters N of Pt. Sal, moderate to high confidence in
the forecast. Through Sun morning, winds and seas will remain
below SCA levels. From Sun afternoon thru Wed, there is a 30%
chance of SCA level winds each afternoon/eve.

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 Wed. However, in western
portions of the SBA Channel, there is a 30-40% chance of SCA
level winds during the afternoon/eve hours Mon thru Wed.

&&

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

&&

$$

PUBLIC...MW/Kittell
AVIATION...DB
MARINE...DB/Sirard
SYNOPSIS...MW

weather.gov/losangeles

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