066
FXUS66 KSGX 221604
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
904 AM PDT Sun Sep 22 2024

.SYNOPSIS...
Warming trend for early this week. The marine layer will become
shallower over the next two to three days, becoming confined to
the coast and portions of the western valleys. For the middle to
end of the week, minor daily fluctuations in high temperatures are
expected.

&&

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

This morning...The marine layer is shallower than yesterday at
about 2000 ft, with a stronger inversion. Low clouds have extended
up to 30 miles inland locally, reaching Rainbow in San Diego
County and almost reaching Ontario in the Inland Empire. The
clearing pattern will be more typical than what we saw yesterday
but given the strength of the inversion, clouds are still likely
to linger at the beaches into this afternoon. Temperatures are
near or a couple of degrees lower than at this time yesterday in
the coastal areas while elsewhere, temps are mostly higher. As
much as 10-15 degrees higher in some mountain locations.

Numerical models are in good agreement through Wednesday with
respect to the synoptic pattern. Cyclonic flow aloft in a
stretched trough will evolve in a relatively weak Rex Block by
Tuesday, with a closed upper low centered about 100 miles west of
San Diego and an upper high centered just off the southern Oregon
coast. By Wednesday, a low/trough deepens off the west coast as a
strong low pressure system moves into the Gulf of Alaska. This
will displace the upper high to a position near the Four Corners.
Solutions begin to diverge on Thu and the spread increases
significantly as we approach next weekend. However, it seems
likely that some form of low/trough will persist near SoCal
through the forecast period.

High temperatures today will reach the mid to upper 70s in the
coastal areas, the 80s to low 90s in the valleys, 70s to low 80s
in the mountains, low 90s in the High Desert, and 100 to 105
degrees in the low desert. Additional warming is expected for
Monday, with most places 3 to 5 degrees warmer than today. For
Tuesday, temps will be similar to Monday with only a degree or two
difference in most locations. At this time, it`s most likely that
there will be only slight day-to-day temp variations from Wed
through Friday with more of a cooling trend for next weekend.
However, the spread in model solutions continue to inject
significant uncertainty in the forecast.

The marine layer will become shallower through Wednesday, with low
clouds and fog becoming mostly confined to the coastal areas,
inland Orange County and the western portions of the San Diego
County valleys. The marine layer may recover slightly (or
significantly) for the middle to end of the week if - as some
model solutions suggest - the trough deepening off the west coast
were to shift eastward even a little. This would put Socal under
southwest winds aloft in cyclonic flow.

&&

.AVIATION...
221524Z...Coasts/Valleys...Low marine stratus (based around 1000 -
1500ft MSL, tops to near 2000ft MSL) with vis 1-3SM in BR for
higher coastal terrain and valleys. Scattering out will occur for
most locations by 18-19z, though some stratus may linger near the
beaches through the afternoon. Confidence in clearing time at KSAN
of 21/1800z is moderate.

Low stratus builds in again for coastal sites around 03-06z this
evening with bases near 800-1200ft MSL and tops to near 3000 feet.

Mountains/Deserts...Mostly clear skies with unrestricted VIS
expected through Sunday evening.

&&

.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...PG
AVIATION/MARINE...Small