Mesa Center, California Weather Forecast Discussion

240
FXUS66 KSGX 141555
AFDSGX
Area Forecast Discussion
National Weather Service San Diego CA
855 AM PDT Sun Sep 14 2025
.SYNOPSIS...
Gradual warming through mid-week, with gradual cooling for the
second half of the week. An influx of tropical moisture will bring
chances of thunderstorms for the middle to end of the week. Highest
chances of showers and thunderstorms will be in the mountains and
deserts, with non-zero chances west of the mountains. The marine
layer will become shallower early in the week, with the potential
for minimal or no low cloud coverage for the middle to end of the
week.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
At 8:30 AM visible satellite was showing low clouds had filled in
the entire coastal basin. Low clouds are expected to slowly clear
inland areas through the morning, with clearing for most coast and
beach locations expected by the afternoon. Weak ridging aloft early
this week will result in a shallower marine layer. Low cloud
coverage early in the week is not expected to reach further inland
than the western valleys. For the middle to end of the week, an
influx of tropical moisture from what is now Tropical Storm Mario is
expected to move northward. That influx of moisture will likely
disrupt low cloud and fog formation leaving coverage patchy to
nonexistent.
A gradual warming trend is expected for the first half of the week.
By Wednesday, most locations are expected to have high temperatures
at or slightly above average for this time of year. The second half
of the week is expected to see a gradual cooling trend. That will
bring high temperatures back to below average for most locations by
next Sunday, September 20.
Mid to upper level moisture from Tropical Storm Mario is expected to
become entrained in an upper level area of low pressure off the
coast of Southern California as early as Tuesday. Based on current
guidance, there will be a lack of a strong forcing mechanism on
Tuesday which should result in dry conditions prevailing across the
area although an increase in mid to high clouds can be expected. By
Wednesday, there is expected to be a further increase in moisture
and the environment is expected to become more unstable. Those moist
and unstable conditions are expected to continue into next weekend,
bringing chances for showers and thunderstorms. The highest chances
of showers and thunderstorms each day are in the mountains and
deserts (40-55%) but shower/thunderstorms cannot be ruled out west
of the mountains. For areas west of the mountains guidance is
currently showing Thursday and Friday having the highest chances (20-
30%) with lesser chances Wednesday and Saturday (15-20%). There is
still uncertainty surrounding the details but the majority of
ensemble members across model platforms favor a dry solution for
SoCal through Tuesday then a majority favor a wet solution for Wed
through Saturday. Conditions could begin to dry out next Sunday as
we lose access to the moisture from the south.
&&
.AVIATION...
141515Z...Coast/Valleys...Low clouds with bases 1500-2000 ft MSL,
tops around 3000 ft MSL have filled the coastal basin this morning.
Clouds are deep enough to yield patchy BR, areas of VIS 2-5SM and
additional SCT-BKN clouds at around 1000 ft MSL near the coast.
Clouds clear inland 16-17Z and for coastal areas 17-18Z, with mostly
clear skies following through this evening except for a 30% chance
for low clouds to linger in southern San Diego Co (La Jolla
southwards) through just after 19Z. Low clouds 1000-1500 ft MSL
redevelop and move inland up to about 15 miles after 15/02Z. Like
this morning, coverage will likely be patchy at first but grow more
uniform towards 05Z. Clouds not expected to be as deep as this
morning, though VIS 2-5SM is possible overnight for inland valleys
and for where clouds intersect with terrain.
Mountains/Deserts...Mostly clear and VFR conditions through Monday.
&&
.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...CO
AVIATION/MARINE...Westerink

NWS SGX Office Area Forecast Discussion