Chino Hills, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

029
FXUS66 KSGX 240510
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
910 PM PST Tue Dec 23 2025

.SYNOPSIS...
Widespread heavy rain is expected Wednesday across Southern
California. Scattered locally heavy showers are expected to
continue across much of the area Wednesday night into Christmas
day. Snow levels will remain high through the duration of the
event increasing the flood threat for the mountains, particularly
in San Bernardino County. Gusty southerly winds are expected for
the coast, valleys, San Bernardino mountains, and High Desert.
Another round of more widespread moderate to heavy rain is
expected sometime on Friday. Drier conditions are looking more
likely for Saturday and Sunday.

&&

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

Key Points:

* Widespread moderate to heavy rainfall Christmas Eve with the
  potential for roadway flooding and localized flash flooding from
  the coast to deserts. Rapid rises in small streams and increased
  flow in main stem rivers expected.

* The highest risk for flash flooding on Christmas Eve is for the
  San Bernardino County mountains with a high risk for excessive
  rainfall that could result in damaging and potentially life-
  threatening flash flooding, mud slides, and debris flow. The
  threat will be highest during the day on Wednesday.

* Gusty south winds will develop tonight and continue through
  Wednesday evening with gusts 30 to 40 mph, locally up to 45 mph
  near the coast and to 55 to 75 mph along and below the desert
  slopes of the San Bernardino County mountains. Make sure to secure
  outdoor furniture. Tree damage is possible.

* Scattered showers will continue on Christmas Day with another
  round of more widespread showers on Friday. Snow levels will
  lower to around 7000 feet for Thursday into Thursday evening,
  then lower to around 6000-6500 feet by late Friday creating
  slick conditions on mountain highways.

* There is the potential for another storm system around New
  Years, but confidence is extremely low with regards to timing.

Evening update...

A weak short wave is beginning to lift north across the region
this evening, producing scattered light showers across San Diego
County northeastward into the Coachella Valley. Rainfall rates
with these showers are expected to remain below 0.10"/hr tonight
with no impacts expected. More moderate and steady rainfall will
begin across the San Gabriel Mountains late tonight into early
Wednesday morning as orographic lift strengthens and deeper
moisture begins to move in from the west. Main impact tonight will
be gusty south winds strengthen across the San Bernardino County
Mountains and adjacent desert foothills with gusts increasing to
around 50-60 mph, locally higher where any mountain waves surface
just north of the mountains, potentially including the Lucerne
Valley and Phelan areas. Only thing to note this evening is that
the timing of heaviest precipitation on Wednesday has shifted a
couple hours later, beginning around 8 AM near the LA County
border and spreading southeast through the afternoon and evening,
beginning to taper off after about 8 PM. Timing for the next band
of heavier precipitation may be slightly delayed as well,
potentially holding off until Friday morning.

Previous discussion issued 151 PM Tuesday...

An Atmospheric River is still on track to impact Southern California
on Wednesday.  The heaviest and most widespread rain is expected
through the day Wednesday, with the heavy rain moving northwest to
southeast from Orange County to San Diego County deserts. After
the rain band passes, scattered showers are expected to continue
with locally heavy rain into Thursday (Christmas Day). Latest
guidance shows a significant decrease in IVT (atmospheric
moisture) during the day Thursday, bringing the potential for
periods no precipitation for some areas. Snow levels are expected
to remain quite high through the duration of the heaviest
precipitation, but are expected to lower later in the week. Please
see the Hydrology section below for more information on expected
rainfall rates, totals, and snow level information.

In addition to periods of heavy rain, gusty south winds are
expected. Strongest winds expected during the day Wednesday. Peak
wind gusts of 60-70 mph, locally up to 75-80 mph possible on the
desert slopes of the San Bernardino County mountains with gusts 45-
60 mph into the High Desert. Winds will stay elevated in San
Bernardino county mountains and High Desert into Thursday. For the
coasts and valleys gust of 30-45 mph are expected, with the
strongest winds expected with the main band of rain.

Models are coming into better agreement that the next round of
widespread moderate to heavy rain. Guidance is indicating a more
organized band of rain will move across the area sometime late
Thursday into Friday, with some lingering scattered showers
through the day Friday eventually tapering off some time Saturday.
Snow levels remain near 7000 ft Thursday, falling to 6000-6500 ft
Friday evening. In addition to rain and mountain snow, winds are
expected to increase over the mountains and into the deserts, with
timing of the strongest winds shaping up to be sometime Thursday
night into Friday. Overall, rainfall rates and amounts are
starting to shape up to look less than what is expected for
Wednesday, but additional rainfall on already saturated soils may
result in additional areas of flooding.

&&

.AVIATION...
230430Z...Low clouds with bases 1500-5000ft MSL are expected to push
in along the coast with inland overnight, with some areas getting as
low as 300-700ft MSL after 12-14Z Wednesday. Rain chances will
increase overnight. Vis reductions 1-4 SM are expected as rain
chances increase, especially between 21Z Thur and 06Z Fri, when the
heaviest band of precipitation is anticipated to move through. The
main rain band will be moving in from the northwest to the
southeast, and with moderate to heavy precipitation with vis
reductions 1-3 SM along with strong south to SE winds during this
time. Rain showers will become more intermittent after 06Z Fri, and
throughout the rest of the forecast period. Embedded thunderstorms
will also be possible, with vis restrictions of less than 1SM, and
occasional cloud-to-ground lightning, if this occurs. Small hail and
gusty winds will also be possible with some of these storms, as well
as an isolated waterspout or two as they move in towards the
coastline.

&&

.MARINE...
The approaching storm system has increased winds out of the south to
southeast and will build seas this afternoon. Winds initially around
15-20 kts gusting to 25 kts will increase early Wednesday to gale
force, with wind gusts upwards of 35 kts. This will bring steep
combined seas of 6-9 feet. Additionally, periods of moderate to
heavy rain Wednesday will lead to areas of poor visibility. Winds
diminish slightly late Wednesday through early Thursday, but winds
and seas will remain hazardous to small craft. Another round of
stronger southwest winds expected late Thursday into early Friday,
with gusts around 25 kts. Winds weaken and turn northwesterly
Friday. Thunderstorms will be possible out over the open waters,
especially for tomorrow between 21Z Thur and 06Z Fri. Some of these
may contain small hail, gusty winds, and even a waterspout or two
will be possible.

&&

.BEACHES...
Strengthening south winds tonight into Wednesday will lead to
elevated surf 5 to 8 feet with sets to 9 feet, highest for south-
facing beaches. This will lead to hazardous swimming conditions, as
well as possibly minor tidal overflow for south-facing beaches from
a combination of winds and elevated surf through Wednesday,
especially during high tides. Winds diminish along with surf late
Wednesday, but more breezy winds along with large fresh swell will
lead to surf building again Friday-Saturday. A Surf Advisory is in
effect from tonight to Saturday afternoon. Thunderstorms will be
possible, especially for tomorrow between 21Z Thur and 06Z Fri. Some
of these may contain small hail, gusty winds, and even a waterspout
or two will be possible for some of these storms just offshore.

&&

.HYDROLOGY...
Isolated light showers will redevelop overnight, with locally
moderate and steady rainfall along the coastal slopes of the San
Gabriel Mountains. Rain is expected to become heavy at times
Wednesday morning along the south slopes of the San Bernardino
County mountains with heavy rainfall spreading southward across
the area Wednesday morning through Wednesday evening. Showers
will continue on Thursday with another round of more widespread
showers for Thursday night into Friday. The snow level will rise
to above 9000 feet for early Wednesday morning, fall to around
7000 feet on Thursday and Thursday night, then fall to around
5000 feet for early Saturday morning.

Through Wednesday night, for Orange and southwestern San
Bernardino Counties, rainfall could range from 2.5 to 3 inches
near the coast to 6 to 8 inches on the coastal slopes of the San
Bernardino County mountains with isolated totals to around 12
inches on the coastal slopes to the west of the Cajon Pass.
Rainfall will decrease from north to south with rainfall across
far southern San Diego County around 1 inch near the coast to 2
inches in the mountains with local amounts near 4" near Palomar.
For the high desert, 1.5 inch to 3.5 inches near the foothills of
the San Gabriel Mountains is expected with 0.50 to 1.5 inch for
the lower deserts.

The San Bernardino County mountains are part of a high risk area
for excessive rainfall for Wednesday morning through Wednesday
night, areas with a heightened risk for damaging and potentially
life-threatening flash flooding. Hourly rainfall rates of around
0.50 inch are likely for several hours on the coastal slopes of
the eastern San Gabriel Mountains from before dawn on Wednesday
through Wednesday afternoon, locally to around 1 inch per hour
or more from thunderstorms or where stronger orographic
precipitation occurs.

Additional rainfall during the day on Thursday from showers will
range from around 0.50 inch north to 0.15 inch south, locally to
around 0.50 inch on the coastal slopes of the San Bernardino
County mountains.

The Santa Margarita River at Ysidora is currently expected to
reach Action/Monitor stage, while the latest forecast for the San
Diego River at Fashion Valley now forecast to remain below Monitor
Stage. See the RVSSGX for details. If heavier rain develops over
either of those two river basins, the rivers may exceed their
currently forecast peaks.

For Thursday night and Friday, a weaker atmospheric river will
bring another round of more widespread showers with a slight
chance of thunderstorms. For Orange and southwestern San
Bernardino Counties, rainfall could range from around 0.75 inch
near the coast to 1 to 2 inches on the coastal slopes of the San
Bernardino County mountains with isolated totals to around 3
inches on the coastal slopes to the west of the Cajon Pass.
Rainfall will decrease from north to south with rainfall across
far southern San Diego County around 0.25 to 0.50 inch. For the
high desert, 0.25 to 0.50 inch is expected with less than 0.25
inch for the lower deserts.

&&

.SKYWARN...
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory until 11 AM PST Saturday for Orange County
     Coastal Areas-San Diego County Coastal Areas.

     Wind Advisory from 3 AM to 10 PM PST Wednesday for Orange County
     Coastal Areas-Orange County Inland Areas-San Bernardino and
     Riverside County Valleys-The Inland Empire-San Diego County
     Coastal Areas-San Diego County Valleys-Santa Ana Mountains
     and Foothills.

     Flood Watch from 4 AM PST Wednesday through late Wednesday night
     for San Diego County Coastal Areas-San Diego County Deserts-
     San Diego County Mountains-San Diego County Valleys.

     Flood Watch through Wednesday evening for Apple and Lucerne
     Valleys-Coachella Valley-Orange County Coastal Areas-Orange
     County Inland Areas-Riverside County Mountains-San
     Bernardino County Mountains-San Bernardino and Riverside
     County Valleys-The Inland Empire-San Gorgonio Pass near
     Banning-Santa Ana Mountains and Foothills.

     High Wind Warning until 3 PM PST Thursday for Apple and Lucerne
     Valleys-San Bernardino County Mountains.

PZ...Gale Warning until 4 PM PST Wednesday for Coastal Waters from
     San Mateo Point to the Mexican Border and out to 10 nm-
     Waters from San Mateo Point to the Mexican Border Extending
     10 to 60 nm out including San Clemente Island.


&&

$$

PUBLIC...SS/CO
HYDROLOGY...SS
AVIATION/MARINE/BEACHES...Stewey