Rancho Cucamonga, California Weather Forecast Discussion

887
FXUS66 KSGX 241636
AFDSGX
Area Forecast Discussion
National Weather Service San Diego CA
936 AM PDT Wed Sep 24 2025
.SYNOPSIS...
There will be a cooling trend through Friday and Saturday with
high temperatures cooling to around 5 degrees below average for
inland areas. This will be followed by a slower warming trend
through Wednesday of next week with high temperatures warming to
slightly below average. A slow moving low pressure system from the
northwest will bring a chance of showers and thunderstorms for
Friday and Saturday, possibly lingering on Sunday during the
afternoon for the mountains and deserts. The chances are greatest
for the mountains and deserts and greatest on Saturday afternoon.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
.Morning Update...
The area of low pressure to the north has mostly cleared the area,
providing mostly sunny skies. Low clouds off the coast will
continue to dissipate over the next few hours. Since higher clouds
are departing from this system, the marine layer will be able to
build in deeper tonight. This will lead to areas of low clouds and
fog within 20 miles of the coast tonight into Thursday morning.
We continue to monitor the area of low pressure moving back
southward into the weekend with cooler weather and chances for
more rainfall.
.Previous Discussion (323 AM Wednesday)...
.SHORT TERM (Today through Friday)...
A slow-moving closed low pressure system will move to near the Bay
Area tonight, then move into southern California on Thursday
night, and then move northeast and weaken for Saturday night and
Sunday. There will be a cooling trend for today through Friday for
the coast and valleys and into Saturday for the mountains and
deserts with high temperatures on Saturday around 5 degrees below
average for inland areas. High temperatures on Saturday will
range from the lower 70s near the coast to around 80 for the
Inland Empire with the upper 80s for the lower deserts.
Dry weather will continue for today and Thursday with a chance of
showers and thunderstorms for Friday afternoon and early evening.
The greater chances are for the mountains and deserts with chances
for measurable rainfall of 15 to 25 percent.
&&
.LONG TERM (Saturday through Wednesday)...
Chances for showers and thunderstorms will increase on Saturday,
to as much as 40 to 55 percent for the mountains and deserts with
the greatest chances on Saturday afternoon. There is a slight
chance for showers and thunderstorms for the mountains and deserts
on Sunday, dependent on how long the low pressure system lingers
over southern California before moving to the northeast and
weakening. This will be followed by drying for early next week.
There will be a slower warming trend for early next week with high
temperatures for Wednesday of next week a few degrees below
average for inland areas.
&&
.AVIATION...
241530Z....Coast...Low clouds lingering at the San Diego County
coastline should quickly dissipate by late morning. VFR through the
evening with low clouds returning to coastal areas 03-06Z Thursday.
Better coverage of low clouds expected with higher bases (1000-1500
ft MSL) and extending 15-20 miles inland by 12Z. Vis reductions
possible for elevated inland valleys (2-5 SM).
Otherwise...Mostly clear and VFR conditions today and tonight,
except for SCT clouds 10000-15000 feet MSL over mountains 19-01Z.
&&
.MARINE...
No hazardous marine conditions are expected through Sunday. However,
stronger northwest winds with gusts approaching 20 knots at times
near San Clemente Island are expected in the afternoons and evenings
today and Thursday.
&&
.BEACHES...
Long period southerly swell from Hurricane Narda will reach the
coastal waters this weekend. Swell of 5-6 feet with periods 14-15
seconds will produce high surf for southern facing beaches from late
Saturday through early next week. Elevated surf and strong rip
currents can be expected along the entire coastline. More details in
the coming days.
&&
.SKYWARN...
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
&&
.SGX WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&10 to 15
$$
UPDATE...APR
PUBLIC...17
AVIATION/MARINE...KW

NWS SGX Office Area Forecast Discussion