Harbison Canyon, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

453
FXUS66 KSGX 221219
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
419 AM PST Mon Dec 22 2025

.SYNOPSIS...
Onshore flow will bring cooling to the coast into the valleys
today with high temperatures for inland areas still 10 to 15
degrees above average. Lighter rain could develop as early as
Tuesday in advance of a low pressure system off the California
coast. Heavier rainfall will develop and spread southward across
the area Tuesday night and early Wednesday with widespread heavy
rainfall for Wednesday and Wednesday night. Gusty south winds will
also occur Tuesday night through Wednesday evening with gusts to
40 mph near the coast and to 50 to 70 mph along and below the
desert slopes of the San Bernardino County mountains. Showers
with locally heavy precipitation could continue for Thursday and
Thursday night with decreasing chances for showers through
weekend. Snow levels above 9000 feet for Wednesday will fall to
around 7000 feet on Thursday to around 5000 feet for early
Saturday.

&&

.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. 27 percent chance of the San
  Diego River reaching minor flood stage.

* Snow levels are forecast to remain above 8000 feet into
  Christmas morning, increasing potential for rock and mudslides
  along mountain highways, and debris flows in and below burn
  scars, especially in the San Bernardino County mountains.

* Gusty southerly winds are expected across the area with 70-90
  percent chance of wind gusts exceeding 35 mph along the coast
  Tuesday night into Wednesday. Make sure to secure outdoor
  furniture. Tree damage is possible.

* Additional chances of showers Thursday through Sunday. Snow
  levels are expected to lower to 6500 to 7000 feet by Friday
  morning, creating slick conditions on mountain highways.

.SHORT TERM (Today through Wednesday)...
Satellite imagery shows coastal low clouds extending inland into
the western valleys early this morning with surface reports
generally showing the lowest visibilities in fog in San Diego
County near higher coastal terrain into the western valleys with
the lowest visibilities in Orange County generally from near the
coast inland to around Interstate 5. A Dense Fog Advisory is in
effect for these areas through 10 AM this morning.

Onshore flow will bring cooling for the coast into the valleys
today with high temperatures for inland areas still 10 to 15
degrees above average. High temperatures for today will range
from the lower to mid 60s near the coast to the 70s for the Inland
Empire with the mid to upper 70s for the lower deserts.

Lighter rain could develop as early as Tuesday in advance of a
low pressure system off the California coast. Heavier rainfall
will develop and spread southward across the area Tuesday night
and early Wednesday with widespread heavy rainfall for Wednesday
morning through Wednesday evening.

Ensemble support for heavier rainfall with greater amounts and
less spread among ensemble members is greatest for Orange and
southwestern San Bernardino Counties with decreasing amounts and
increasing spread going from north to south across San Diego
County.

Gusty south winds will develop Tuesday night and continue through
Wednesday evening with gusts to 40 mph near the coast and to 50
to 70 mph along and below the desert slopes of the San Bernardino
County mountains.

&&

.LONG TERM (Thursday through Sunday)...
The greatest chances for additional precipitation will be for
Thursday and Friday, though with increasing spread in potential
amounts. There is not much overlap among the members of each of
the ECMWF, GFS, and Canadian model ensemble systems. This would
usually imply greater uncertainty, at least in the details. While
chances for measurable precipitation each day for Saturday into
early next week decrease to around 15 to 25 percent, there remain
at least small chances for heavier amounts.

&&

.AVIATION...
221030Z....Coast/Valleys...Patchy low clouds based 400-800 ft MSL
with tops to 900 ft are present from the coast to 15-20 miles
inland. Widespread vis restrictions 2-6 SM in BR, 0-2 SM where
clouds intersect with higher inland terrain, will continue
overnight. Occasional scatter outs will continue as high cloud layer
occasionally disrupts the low clouds, with fuller clearing to the
coast 17-20Z. Low clouds will linger along the immediate coast in
areas through the afternoon, before moving back onshore after
23/00Z. Bases initially 700-1200 ft MSL will steadily rise
overnight, likely to above 2000 ft MSL by 23/12Z, and clouds will
spread to cover the coastal basin. Areas of DZ early Tues morning
will locally lower cigs/vis.

Otherwise...SCT-BKN high clouds with unrestricted VIS continues
through today.

&&

.MARINE...
No hazardous marine conditions through Tuesday morning. An
approaching storm system will lead to strengthening winds and
building seas starting Tuesday afternoon. Winds initially 15 to 20
knots gusting to 25 knots Tuesday afternoon will strengthen further
late Tuesday night, potentially to gale force with wind gusts
upwards of 30-35 knots. This will bring steep seas 7-10 feet.
Additionally, periods of moderate to heavy rain Wednesday will lead
to areas of poor visibility. Strong winds and steep seas continue
through early Thursday morning. Winds weaken slightly Thursday
morning, but likely remain hazardous to small craft through most of
the day. Winds weaken and turn northwesterly Friday.
&&

.HYDROLOGY...
Lighter rain could develop as early as Tuesday in advance of a
low pressure system off the California coast. Heavier rainfall
will develop and spread southward across the area Tuesday night
and early Wednesday with widespread heavy rainfall for Wednesday
morning through Wednesday evening. Showers will continue for late
Wednesday night through Thursday night, but with additional
precipitation amounts not as heavy.

Through Wednesday evening, for Orange and southwestern San
Bernardino Counties, rainfall could range from 3 to 3.5 inches
near the coast to 4 to 6 inches on the coastal slopes of the San
Bernardino County mountains with isolated totals exceeding 8
inches. This will decrease from north to south with around 2
inches across far southern San Diego County. For the high desert,
2 to 3 inches is expected with 0.75 to 1.5 inch for the lower
deserts.

For late Wednesday night through Friday afternoon for Orange and
southwestern San Bernardino Counties, additional rainfall and
liquid equivalent above the snow level for Orange and southwestern
San Bernardino Counties could range from around 1 inch near the
coast to 1.5 to 2.5 inches on the coastal slopes of the San
Bernardino County mountains. This will decrease from north to south
with around one-quarter to one-half inch across far southern San
Diego County. For the high desert, one-quarter to one-half inch
is expected with one-quarter inch or less for the lower deserts.

Through Wednesday night for Lytle Creek in the San Gabriel
Mountains to the west of the Cajon Pass, the chance for 5 inches
or more of rainfall is 85 percent with the chance for 8 inches or
more of rainfall 22 percent.

Through Wednesday night for southwestern California, chances for 2
inches or more of rainfall range from 90 to 100 percent for the
coast to the mountains for areas bordering Los Angeles County to 25
to 35 percent across far southern San Diego County.

Snow levels will rise above 9000 feet on Wednesday morning, then
fall to around 7000 feet on Thursday and 5000 feet for early
Saturday.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Flood Watch from late Tuesday night through late Wednesday night
     for San Diego County Coastal Areas-San Diego County Deserts-
     San Diego County Mountains-San Diego County Valleys.

     Flood Watch from Tuesday afternoon 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.

PZ...Gale Watch from Tuesday afternoon through Wednesday afternoon
     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...17
AVIATION/MARINE...CSP