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000
FXUS66 KSGX 212040
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
140 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...

A strengthening ridge is centered over California and the Great
Basin today and the strongest positive height anomalies of the
week are present over California. Today will likely be the warmest
day of the week away from the coast, with highs topping out 4-7
degrees above normal across the inland valleys of Orange and San
Diego Counties, and 8-12 degrees above normal in the Inland
Empire, mountains and deserts. Coastal areas will remain generally
cool today as low clouds struggle to clear out at the beaches.

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 temperatures
spread 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 temperatures and stronger onshore winds next
weekend.

&&

.AVIATION...
212115Z...Coast/Valleys...Low clouds with bases 1200-1600 ft MSL and
tops to 2000 ft MSL will push inland after about 02Z Sunday
afternoon. The low clouds should deepen overnight reaching the
valley areas of KONT and KRNM around 09Z-12Z Monday morning with
higher terrain obscured. Local VIS 3-5 miles in BR will occur in the
valleys through 18Z. Confidence in BKN-OVC low clouds at KSAN the
remainder of this afternoon through at least midday Monday is
moderate to high. For Monday, clearing times should be an hour or so
slower than today in locations that cleared today.

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...EA
AVIATION/MARINE...Small