Fontana, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

104
FXUS66 KSGX 202030
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
130 PM PDT Sun Jul 20 2025

.SYNOPSIS...
Monsoonal moisture will move out of the area this week, bringing a
cooler and drier weather pattern to Southern California.
Temperatures will be up to ten degrees below normal in some inland
areas along with a deeper marine layer with low clouds each
evening into the morning west of the mountains. Elevated south and
west winds will occur each afternoon across the mountains and
desert slopes.

&&

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

Low clouds will continue to be intermittent across the coastal
areas before moving ashore this evening, covering the coastal
basin overnight into Monday morning. Cumulus clouds have built up
along the mountain chain this afternoon, but as mentioned this
morning, the noted mid-level inversion has proven to be too strong
for any storms to form as seen on GOES imagery and out our window.
If any weak showers form later today, they would be across the
San Diego or Riverside County mountains.

A trough over the Pacific Northwest will push southward by Monday.
This will set the stage for a cooler and drier weather pattern as
monsoonal moisture is shifted to the east. The trough will break
away from the upper level flow, becoming a closed low that will
sit off the California coast for much of the week. These factors
will contribute to only minor day to day changes in the forecast.
High temperatures will be up to 5 degrees below normal across the
lower deserts and coast, with highs near 10 degrees below normal
across western valleys and mountain areas this week. The troughing
pattern will keep winds elevated each afternoon and evening
across the mountain passes and desert slopes with winds 20-35 mph.
The marine layer will also maintain a deeper depth, with low
clouds moving into areas west of the mountains each evening
through the morning. Ensemble models are in fair agreement of the
trough lingering into next weekend with the possibility of a ridge
moving closer to the region early next week, which would bring a
warmer weather regime.

&&

.AVIATION...
202030Z....Coast/Valleys...Low clouds based 1500-2000 feet MSL along
parts of the coast will begin to push inland after 00Z, filling the
coastal basin overnight. Vis reduced 3-5SM along higher valley
terrain. Scatter out Monday 17-19Z.

Mountains/Deserts...VFR conditions expected through Monday. SCT
cumulus based around 9000 feet MSL will continue over the ridges
through 01Z with a slight chance (10% probability) of SHRA/TSRA.
Cumulus based at 9000 feet MSL over ridges Monday after 18Z.

&&

.MARINE...
No hazardous marine weather is expected through Thursday.

&&

.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...APR
AVIATION/MARINE...MM