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000
FXUS66 KSGX 211615
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
915 AM PDT Sun Apr 21 2024

.SYNOPSIS...
Warm today and Monday with weak high pressure over the region. The
weather will turn cooler Tuesday through Friday as a trough of low
pressure deepens down the West Coast. Drizzle from a deep marine
layer is possible west of the mountains Tuesday morning. Friday and
Saturday will be breezy and cool with showers at times.

&&

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

Update...
The 12z Miramar sounding showed a 11.5C degree inversion based
near 1300 feet. Low clouds extend through the coast and valleys,
but are already starting to erode across the eastern valleys. With
the strength of this inversion, it may be tough to completely
clear across beach communities, but everywhere else should clear
by late morning.

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.

Previous Discussion (Issued 325 AM PDT Sun Apr 21 2024)...
The marine layer was 500 feet shallower this morning than yesterday
morning when low clouds reached all the way to the foothills. This
morning the Inland Empire and the mountain foothills were clear. Low
clouds over Orange and San Diego Counties will clear back to the
coast through late morning.

Today will be warmest day of the week with high pressure aloft
bringing sunny skies and highs from 85-90 in the Inland Empire, 68-
78 in the mountains, near 90 in the high deserts and from 96-101 in
the lower deserts.

On Monday the ridge drifts east which will allow the marine layer to
deepen a few hundred feet and bring 3-5 degrees of cooling west of
the mountains, but only 1-2 degrees of cooling in the deserts.
Further cooling takes place Tuesday as the first of two troughs
approach from the west. A coastal eddy also spins up Tuesday morning
which will deepen the marine to nearly 4000 feet, deep enough for
patchy drizzle west of the mountains.

This first trough passes SoCal Wednesday night with transient
ridging on Thursday ahead of a second, stronger and deeper trough
that will bring colder weather Thursday night through Saturday. This
trough taps into a weak Atmospheric River with IVT between 300-400
kg/m/s ahead of the trough Thursday night and Friday. This will be
followed by scattered cold core instability showers on Saturday.
Showers may persist into Sunday and that will depend on how quickly
or slowly this long wave trough ejects eastward.

&&

.AVIATION...
211530Z...Coast/Valleys...Low clouds with bases 1200-1600 ft MSL and
tops to 2000 ft MSL will continue through 18Z within 20-25 miles
of the coast, with higher terrain obscured. Local VIS 3-5 miles in
BR will occur in the valleys through 18Z. Except for local BKN
clouds around 1200 ft MSL at the beaches, skies will be clear this
afternoon. Low clouds will develop again 01Z-05Z Sun evening near
the coast and spread up to 20 miles inland by 12Z Mon with bases
1000-1400 ft MSL and local VIS 3-5 miles. Confidence in BKN low clouds
at KSAN til around 18Z today at KSAN and after about 03Z this afternoon
is moderate to high.

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