Spring Valley Lake, California Weather Forecast Discussion

678
FXUS66 KSGX 200432
AFDSGX
Area Forecast Discussion
National Weather Service San Diego CA
932 PM PDT Fri Sep 19 2025
.SYNOPSIS...
Warm and dry Saturday. Tropical moisture returns Sunday morning
with periods of light to moderate rain showers into Sunday
evening, most widespread across San Diego County and the
mountains. Storm chances become confined to the mountains on
Monday, followed by the potential for more widespread
precipitation Tuesday or Wednesday depending on the track of the
upper low. Dry and slightly warmer Thursday and Friday.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
Evening update...
A couple small showers developed over the Mojave Desert this
afternoon. No precipitation expected overnight into Saturday as
drier air moves into the region. Otherwise low clouds will develop
over the coastal areas and western valleys tonight, clearing by
mid-morning Saturday. Only thing of note is that when then cut-
off low moves back towards the area sometime in the Tue-Wed time
frame, there is the potential for another round of more widespread
precipitation, though there is currently little ensemble consensus
on the timing and track of this low.
Previous discussion...
Given lower dew points and less cloud cover tonight and tomorrow,
more seasonable temperatures ensue, with highs in the 70s and 80s
for coasts/valleys, 60s and 70s for the mountains, and upper 90s for
the deserts. On Sunday, tropical moisture once again pushes up into
Southern California from a developing system off of Baja. Hi-res
models are pulling the moisture up as early as Sunday morning,
spreading over San Diego County and then up into Riverside, Orange,
and San Bernardino counties by the afternoon. Soundings show
significantly drier air in the lower levels with most of the
moisture elevated, indicating better rainfall chances will be in the
mountains, but isolated spots of 0.50" rainfall totals throughout
the day Sunday are not out of the question. This pattern is
especially difficult to resolve and confidence in how far north the
moisture makes it as well as the drier air at the lower levels will
make or break this event. Regardless, better moisture and ample
cloud cover should make for slightly cooler temperatures on Sunday
compared to Saturday.
Additional moisture will surge into the region Monday-Wednesday,
with less confidence in the overall upper level pattern. Rain
showers will be possible during this time, with thunderstorm chances
returning primarily for the mountains by Monday afternoon and
becoming more widespread on Tuesday. At this point the spread in
models is a bit too great to nail out the details, but confidence in
precipitation/storm chances will be highest in the mountains for the
Mon-Wed time frame. With the incoming clouds and moisture,
temperatures will hold fairly steady into the end of next week.
&&
.AVIATION...
200345Z....Coast/Valleys...Low clouds based 900-1300 ft MSL are
forming along the San Diego coastline. These will gradually make
their way north, likely impacting the Orange County coast by 12Z
(70% chance for CIGs by this point, including at KSNA), as well as
inland up 10-15 miles. CIGs will lower slightly overnight, likely to
below 1000 ft MSL for the majority of sites, along with vis lowering
to 3-6 SM over coastal highlands. Clouds scatter to beaches 16-18Z.
Patchy clouds with lower bases 600-900 ft MSL will form in areas
along the San Diego coast after 21/03Z, then gradually spread into
coastal sites through about 09Z.
.Mountains/Deserts...VFR conditions and mostly clear skies through
Saturday.
&&
.MARINE...No hazardous marine conditions are expected through
Wednesday morning.
&&
.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...SS/Zuber
AVIATION/MARINE...CSP

NWS SGX Office Area Forecast Discussion