549
FXUS66 KSGX 121534
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
834 AM PDT Mon Aug 12 2024

.SYNOPSIS...
Monsoonal moisture will decrease today, with a lingering slight
chance of thunderstorms for the southern mountains and deserts
this afternoon. This will be followed by dry and seasonal weather
through the week as a trough to the north brings in cooler and
drier air. The marine layer will provide more consistent low
clouds and fog to coastal areas each night and morning.

&&

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

Residual monsoonal moisture will hang in the southeastern part of
our region one more day, and that will bring a slight chance of
thunderstorms this afternoon, mainly in the mountains and Anza
Borrego Desert. Low clouds and fog were on the patchy side this
morning, tickling parts of the coast. An upper level trough of
low pressure off the Pacific Northwest coast will complete its
breakdown of our hot ridge of the weekend. That will bring
temperatures back to normal today and it will also sweep eastward
the lingering monsoonal moisture today and tonight. The moisture
decreases during the day, so there will be a race between the
increasing convective trigger mechanism (surface heating) and the
decreasing moisture. Will the two trending forces overlap enough
to produce a thunderstorm or two? Hence, the slight chance in
southern and eastern parts of our region. The trough will boost
onshore winds during the afternoons and nights today through
Tuesday night. Strongest winds will blow through mountain passes
into adjacent deserts, where top gusts could exceed 40 mph. With
no more monsoon disruption, the marine layer will rebound so that
coastal low clouds and fog will become more uniform, extensive and
longer lasting. But the marine layer doesn`t appear to deepen
enough for clouds/fog to extend beyond the westernmost valleys
each night and morning. A coastal eddy could enhance the marine
layer and cloud coverage Wednesday and Thursday. Counterintuitively,
high pressure aloft actually strengthens those days, so inland
temperatures will be a few degrees higher. Monsoon moisture
appears to increase this coming weekend, leading to a very small
but increasing chance of thunderstorms for mountains and deserts
by Sunday or Monday. Not enough to make our forecast yet, but
something to watch and fine tune in coming days. The low pressure
to our northwest and a growing high pressure to our east seem to
set up a stationary pattern with SoCal right in between the two.
Some guidance indicates the trough dominating while other guidance
suggests the ridge taking precedence. For now we have a fairly
persistent forecast in our fair weather pattern.

&&

.AVIATION...
121530Z...Coast/Valleys...Patchy low clouds with bases 400-800ft MSL
were slow to build in this morning, briefly impacting coastal sites,
and clearing is starting to occur. SCT-BKN high clouds with bases to
15000ft-20000ft MSL possible through the afternoon. Redevelopment of
patchy low clouds at coastal sites expected again tonight as early
as 06z, with bases to 1000ft MSL and localized VIS reductions down
to 3-5SM for higher coastal terrain and valleys.

Mountains/Deserts...Unrestricted VIS with FEW-SCT to 20000ft MSL
through the evening. FEW Cu with bases to 12000ft MSL near the
mountains this afternoon with iso TSRA (10%-15% chance) which may
bring gusty and erratic winds. Mod up/downdrafts near the mountains
this afternoon. Impacts from storms not expected at any TAF sites,
and storms diminish by sunset.

&&

.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...MM
AVIATION/MARINE...Zuber