National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS66 KSGX 211028
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
325 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...

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 early afternoon.

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...
210930Z...Coast/Valleys...Low clouds with bases 1300-1600 ft MSL and
tops to 2000 ft MSL will continue through 16Z-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 16Z. 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 Mon 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.

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

&&

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

&&

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

&&

$$

PUBLIC...Moede
AVIATION/MARINE...Maxwell