Ontario, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

811
FXUS66 KSGX 150353
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
853 PM PDT Wed May 14 2025

.SYNOPSIS...
Dry and warmer through Thursday. Cooler, cloudier, and windier
with chances of precipitation along and west of the mountains over
the weekend. Warmer with a shallower marine layer expected next
week.

&&

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

Evening update...
Patchy low clouds have developed along the coast with some
scattered high clouds moving east across the region this evening.
The 00Z KNKX sounding shows the marine inversion based near 2200
ft MSL, down significantly from around 3800 ft MSL this morning.
With the marine inversion strengthening, expect low clouds to be
more organized tonight, but limited to the coastal areas and
western valleys. Breezy west winds in the mountains and deserts
will weaken overnight. No changes to the forecast this evening.

Previous discussion...
Weak troughing will continue over the western United States through
Thursday. Highs Thursday are expected to be 3 to 6 degrees warmer
than today for inland locations. The marine layer is expected to get
a little shallower for Thursday and Friday, but low clouds are still
expected to reach into the western portions of the Inland Empire. On
Friday an impulse will move through the mean flow, deepening the
troughing pattern over Southern California, which will bring a few
degrees of cooling west of the mountains, a deeper marine layer, and
an uptick in westerly winds over the mountains and deserts.

A deeper troughing pattern is expected for the weekend as an upper
low pressure system digs south along the West Coast. There remain
some slight differences in how far south the trough digs but there
is fairly high confidence in cooler weather, increased cloud
coverage, and stronger winds over the mountains and deserts. NBM
chances for wind gusts reaching or exceeding 50 mph are 40 to 60
percent for the desert mountain slopes and into the deserts, with
chances closer to 95 percent in wind prone locations in those
geographic areas. A ridge of high pressure will set up over the
Eastern Pacific for the weekend. Model guidance is suggesting
subtropical moisture will be pulled over the ridge and into Southern
California as the aforementioned trough digs south. The increased
moisture will bring chances of precipitation to the area. Due to the
predominately northwesterly flow, highest chances of precipitation
are along and west of the mountains for San Diego county, with
second highest chances for precipitation on the coastal slopes of
the San Bernardino and Riverside county mountains. NBM chances of
rainfall totals exceeding 0.10" Saturday night through Sunday for
San Diego county coast, valley, and mountains and Riverside/San
Bernardino mountains are 20 to 40 percent, with the highest chances
on the coastal mountain slopes. Elsewhere chances are 10 percent or
less. For total rainfall accumulations between Saturday evening and
Sunday it looks unlikely more than 0.25" will accumulate for San
Diego coast/valleys. For the coastal mountain slopes, it is unlikely
total rainfall will exceed 0.50".

Dry conditions are expected to return to the area by Monday, as the
trough moves east and upper level ridge inches closer to the West
Coast. By Tuesday, the majority of ensemble clusters show ridging
over the West Coast. Current forecast follows the NBM with warming
temperatures for Monday through Wednesday. By Tuesday and Wednesday,
high temperatures will be around average for the mountains and
around 4 to 8, locally up to 10 degrees above average for the coast,
valleys, and deserts.



&&

.AVIATION...
150330Z...Coast/Valleys...Currently patchy low clouds 1300-1800 ft
MSL along the coast will become more widespread after 06Z this
evening, moving up to 20 miles inland overnight. Reduced vis for
higher valley terrain. Clouds scatter to the coast 16-18Z. Low
clouds with slightly lower bases move inland again after 02Z Fri.

.Mountains/Deserts...Mostly clear skies through Thursday evening.
FEW-SCT cumulus forming over the mountain ridges Thursday afternoon.

&&

.MARINE...
No hazardous marine conditions are expected today through Saturday.
Stronger winds and higher seas are expected late Saturday into
Sunday. Winds 15 to 25 kts expected in the outer coastal waters and
steep, wind-driven waves 7 to 10 feet possible for outer coastal
waters and 5 to 8 feet for inner coastal waters. Winds and waves
gradually subside late Sunday into Monday.

&&

.BEACHES...
Elevated to potentially high surf will impact beaches late Sunday
into Monday. Surf height of 4-7 feet with sets to 8 feet possible
along west-facing beaches.

&&

.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/CO
AVIATION/MARINE/BEACHES...CSP