Palomar Mountain, California Weather Forecast Discussion

820
FXUS66 KSGX 061000
AFDSGX
Area Forecast Discussion
National Weather Service San Diego CA
300 AM PDT Sat Sep 6 2025
.SYNOPSIS...
For the weekend, daytime temperatures will remain slightly above
normal for the inland valleys but near or slightly below normal
elsewhere. Decreasing monsoonal moisture and increasing stability
will reduce the chances for showers and thunderstorms this
afternoon, and all but eliminate it by Sunday afternoon. A cooling
trend is expected for Monday through the middle of the week as a
low pressure system moves through the region from the northwest.
This system will also bring breezier conditions to the mountains
and deserts, with a deeper marine layer west of the mountains.
Temperatures begin to rise as we approach next weekend.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
This morning, the marine layer is slightly deeper than yesterday
and low clouds have already spread up to 10 miles inland in some
areas. By sunrise, low clouds could spread up to 20 miles inland
with fog on the higher terrain inland.
A low pressure system currently just south of the Gulf of Alaska
will steadily move southeast with a closed upper low becoming
centered over northern CA by Wed. Model solutions are in good
agreement with respect to the timing and trajectory of this system
so forecast confidence is moderate to high. Temperatures this
weekend will change very little as we remain under the influence
of a weak high pressure ridge, with daytime high temps a few
degrees above normal for the inland valleys and near or slightly
below normal elsewhere. Monsoonal moisture is on the decrease and
conditions are becoming more stable but residual moisture could
still result in showers/tstms in the Riverside and San Diego
County mountains this afternoon. By Sunday afternoon the chances
for showers/tstms are all but eliminated.
A more noticeable cooling trend begins on Monday and continues
through the middle of next week as the low pressure system
approaches and we come under its influence. We can expect
temperatures to lower through the middle of next week with highs
5 to 15 degrees below average through Thursday. There is high
confidence in forecast high temperatures by Wednesday will be in
the 70s/80s for many areas west of the mountains into the high
desert with 90s in the lower deserts. In addition to generally
lower temperatures, this system will bring stronger onshore winds
and a deeper marine layer with more low clouds during the nights
and mornings. Between Monday and Wednesday, westerly winds gusting
25-45 mph are likely in the mountains and adjacent desert areas
during the afternoons and evenings.
Temperatures begin to rebound towards the end of next week as the
low pressure system moves inland and weak ridging returns.
However, there is significant uncertainty in forecast details by
then as model solutions diverge.
&&
.AVIATION...
060930Z...Coast...Low clouds based 900-1300 ft MSL over coastal
areas will continue to fill in and reach 10-15 miles inland by 12z.
Reduced vis over coastal high lands and higher west valley terrain 2-
5 SM. Clouds clearing to the beaches 15-17Z, with VFR conditions
following through the afternoon. Low clouds redevelop over coastal
waters Saturday evening and push into coastal land areas after 06Z
Sunday. Expecting slightly lower bases and less inland extent.
Valleys/Mountains/Deserts...Low chances (10-20%) for SHRA over
mountains and 5-10% chance of isolated TSRA Sat 20Z-01Z (mostly
mountains of San Diego and southern Riverside counties). CB bases
around 10K ft and any TSRA tops to 35K ft. Any TSRA will bring
gusty, erratic winds, blowing dust with low visibility, lightning,
and lower bases 6000-9000 feet MSL.
&&
.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...PG
AVIATION/MARINE...KW

NWS SGX Office Area Forecast Discussion