Ontario, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

383
FXUS66 KSGX 220933
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
233 AM PDT Tue Sep 22 2026

.SYNOPSIS...
High temperatures will warm several degrees for today and
Wednesday to within a few degrees of average on Wednesday with
the greatest warming for the inland valleys. Monsoonal moisture
from the south on Thursday will bring a slight chance of showers
and thunderstorms during the afternoon. Drying aloft with not
much change in temperatures for Friday and Saturday with a low
pressure system moving inland along the West Coast bringing
cooling for Sunday and Monday.

&&

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

.SHORT TERM (Today through Thursday)...
A weak low pressure system will develop off the coast of northern
Baja today and linger into Thursday with weak lower-level easterly
flow and east winds for the mountains at times on Wednesday and
Thursday. High temperatures for today will warm a few degrees
near the coast to 5 to locally 10 degrees for the inland valleys
onto the coastal slopes of the mountains. Similar warming will
occur again on Wednesday from the coast to the mountains with
warming also spreading into the deserts. There will be little
additional warming on Thursday.

High temperatures on Wednesday will be within a few degrees above
or below average for most areas with high temperatures ranging
from the mid to upper 70s near the coast to the upper 80s to mid
90s for the Inland Empire with the lower deserts around 100.

On Thursday, that weak low pressure system off the northern Baja
coast could draw some mid-level monsoonal moisture northward into
southwestern California with a slight chance of showers and
thunderstorms for the mountains during the afternoon.

The marine layer is still around 4500 feet deep with low clouds
over the coastal waters extending well inland across the coast and
valleys and onto the lower coastal slopes of the mountains. The
marine layer is expected to decrease in depth for Wednesday and
Thursday with night and morning coastal low clouds not spreading
as far inland.

&&

.LONG TERM (Friday through Monday)...
That weak low pressure system off the northern Baja coast will
weaken and move inland on Thursday with drier westerly flow aloft
for Friday and Saturday. High pressure aloft over northern Mexico
and southern Texas will expand westward across Baja during the
weekend with Hurricane Polo remaining on a west-northwest track
along the southern edge of the upper high.

Not much change in high temperatures is expected for Friday and
Saturday with a low pressure system moving inland across the
western states bringing cooling for Sunday and Monday.

&&

.AVIATION...
220530Z...Coast/Valleys...Low clouds with bases 1800-3800 feet MSL
will gradually increase to produce cigs around 2000-2500 feet MSL
over most of the coastal basin. Relatively early scatter out vcnty
KSAN 14-16Z Tuesday, and 15-18Z elsewhere. Low clouds based around
1500-2000 feet MSL to develop vcnty KSAN after 03Z Tuesday evening.

Otherwise...mostly clear skies through Tuesday.

&&

.MARINE...
No hazardous marine conditions are expected through Saturday.

&&

.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...17
AVIATION/MARINE...MM