Ontario, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

073
FXUS66 KSGX 051915
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
1215 PM PDT Sun Apr 5 2026

.SYNOPSIS...
Patchy fog may develop tonight into Monday morning along the coast,
with the potential for locally dense fog on the coastal mesas. Low
clouds and fog will continue most nights and mornings this week, but
the marine layer will become deeper, lessening the chances for dense
fog. Temperatures will fluctuate a few degrees each day through mid-
week, but mostly stay above average for this time of year. Pattern
change expected for the end of next week, with cooler, windier, and
wetter conditions expected.

&&

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

Areas of high clouds continue to stream west to east across the area
as of noon today. Periods of high cloud coverage are expected to
continue into Monday. The pressure gradient is trending more onshore
compared to noon yesterday with the pressure gradient -1.1 mb from
SAN-DAG. The trend is expected to continue to skew more onshore,
which may allow for patchy low clouds and fog to develop tonight
into Monday morning. One potential hiccup to fog development could
be how widespread the high cloud coverage is. More widespread high
clouds will lessen fog chances and less will increase them. If fog
develops, it may be locally dense. The most likely place for dense
fog to develop is near higher coastal terrain. Low clouds and fog
are expected to remain present each night and morning for much of
this week but a deepening marine layer will limit chances for
coastal dense fog.

Highs on Monday are expected to be a few degrees cooler across the
area due to a passing  shortwave trough. Breezy westerly winds may
develop over the mountains and locally into the deserts, but no
impacts expected. Weak ridging will build over California on
Tuesday, which will bring a degree or two of warming to some inland
locations. The ridge will quickly be pushed aside on Wednesday as
stronger troughing sets up over the Eastern Pacific.

There remains quite a bit of uncertainty in the ensemble guidance in
regards to the timing of the low`s passage and expected
precipitation amounts. Overall, timing of the onset of precipitation
has trended later, but members of the GEFS are still showing a
quicker passages of the low with the bulk of the precipitation
centered on Friday/Saturday, while the majority of the ensemble
members of the ECMWF are showing a slower progression and the bulk
of the precipitation centered Saturday/Sunday. Both of the global
models have quite a bit of spread in precipitation amounts as well.
NBM probabilities of 48 hour rainfall totals (5 am Friday-5am
Sunday) exceeding 0.50" are highest in the mountains at 50-60
percent and around 20 percent for the coast and valleys. The High
Desert has about a 10 percent chance with less than 5 percent chance
for the low desert. In addition to timing of rainfall, the forward
progression of the low will influence when the strongest winds and
coldest conditions will occur. Some snow is expected out of this
system but there still remains considerable uncertainty in snow
levels. The spread in snow level guidance from the NBM ranges from
7000-9000 ft on Friday and 6500-7500 ft on Saturday and Sunday.

&&

.AVIATION...
051800Z...Generally VFR with increasing clouds AOA 15k ft today.
There is higher confidence in more widespread low clouds 800-1200 ft
MSL spreading inland tonight after 08Z later this evening, vis
restrictions 2-5 SM over higher valley terrain. These low clouds
will begin to scatter out tomorrow from 16-18Z Monday. Clouds AOA
15k ft will also decrease tomorrow.

&&

.MARINE...
No hazardous marine conditions expected through Thursday. Winds and
seas may increase late week due to an incoming weather system. Low
confidence in details at this point.

&&

.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...Stewey