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000
FXUS66 KSGX 220354
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
854 PM PDT Sun Apr 21 2024

.SYNOPSIS...
Warm conditions will continue across Southern California today,
with cooling spreading inland through the mountains on Monday,
reaching the lower deserts by Tuesday. Patchy drizzle will be
possible west of the mountains Tuesday morning. More noticeable
cooling along with stronger onshore winds and scattered showers
will be possible Thursday into next weekend.

&&

.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...

.Evening update...
Marine layer stratus, which stuck to many of the beaches this
afternoon, made a swift push inland this evening, filling in
across Orange County and even pushing into the far southern
portions of the Inland Empire. The 00Z KNKX sounding shows a 9C
inversion based near 1700 ft MSL. Clouds will spread slightly
further inland overnight. Elsewhere skies remain clear with sea
breeze winds weakening through the evening. Forecast remains
mostly unchanged through midweek, with ensembles becoming more
aligned with regards to timing of the Wed/Thu trough. Made some
adjustments to PoPs later in the week as the track of the second
trough appears to take a more inland (drier) track and moves out
quicker.

.Previous discussion...
The ridge axis weakens and moves eastward and Monday, and a
strengthening closed upper low quickly moves into the eastern
Pacific. The marine layer will deepen and cooler weather spreads
inland, with highs on Monday 2-6 degrees cooler than today.
Further cooling is expected on Tuesday and Wednesday as the upper
low approaches Southern California, and a coastal eddy spins up.
The marine layer may be deep enough to produce some patchy drizzle
west of the mountains Tuesday morning, and clouds will be hard
pressed to clear across the coast and western valleys that day. An
uptick of winds will occur over the mountains and deserts Tuesday
afternoon and evening, with a stronger push Wednesday into
Thursday as the low passes overhead.

The forecast becomes murky for late this week into the weekend.
Ensemble cluster analysis shows a general troughing pattern
covering much of the western United States on Thursday, but with
substantial disagreement of the placement of the trough axis and
strength by Friday. This system does look to bring moisture into
Southern California however, with the ECMWF ensemble mean showing
PWAT values near 0.9" for SAN and PWAT anomalies 125-175% of
normal. We are moving toward our dry season, so most widespread
measurable precipitation could be considered "anomalous", but
this system bears watching. Regardless of the timing and intensity
of rain over the region, it looks like we will be trending
towards cooler weather and stronger onshore winds next weekend.

&&

.AVIATION...
220355Z...Coast/Valleys...Low clouds with bases around 1000 ft MSL
and tops to 2000 ft MSL have already spread 10-15 miles inland at
this hour. Coastal TAF sites are experiencing CIG impacts and KSNA
has reduced VIS. There is about a 50-60 percent chance for CIG and
VIS impacts at KONT between 12Z and 15Z but impacts at KSBD are
unlikely. VIS restrictions will occur mainly inland where clouds and
terrain intersect. Bases and tops will rise slightly after 12Z.
Inland clearing is expected 17Z-19Z but there will likely be limited
clearing in the coastal areas. SCT-BKN clouds could persist at
coastal TAF sites into Monday afternoon.

Mountains/Deserts...Mostly clear skies with unrestricted VIS through
Mon morning.

&&

.MARINE...
No hazardous marine conditions are expected through Thursday.

&&

.SKYWARN...
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.

&&

$$

PUBLIC...SS/EA
AVIATION/MARINE...PG