067
FXUS66 KSGX 121619
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
919 AM PDT Wed Mar 12 2025

.SYNOPSIS...
Cool, wet, and windy weather is expected through Friday.
Scattered light showers or drizzle may occur today, but some
places have the potential to see mostly dry conditions. An
additional round of more widespread precipitation is expected late
tonight into early Thursday morning, with additional scattered
locally heavy rain continuing through Thursday afternoon.
Widespread gusty winds expected Wednesday evening through Thursday
from the coast to the deserts. Additional rounds of light rain
and snow will continue Friday. Dry conditions are expected over
the weekend. There is the potential for yet another system
sometime early next week.

&&

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

Scattered areas of light rain or drizzle may occur through the day
from the coast to the mountains. Some areas may be mostly dry
through the afternoon. Southwesterly winds will begin to increase
this afternoon ahead of another approaching upper level trough,
especially for the mountains and deserts.

An atmospheric river with near 500 kg of IVT will reach Southern
California Thursday. The most likely time for widespread and heavier
precipitation is very late Wednesday night into Thursday morning
with a passing cold front providing lift in a saturated environment.
This system is expected to be quite cold aloft which increases the
chances of thunderstorms across the area, leading to an increased
threat of flooding. High resolution guidance is indicating rainfall
rates of 0.50 to 0.75" per hour, locally up to 1" per hour where
thunderstorms develop and in the mountains below the snow level.
Through Thursday night, rainfall and liquid-equivalent above the snow
level is expected to range from around one inch near the coast to 2
to 3 inches in the mountains with local amounts to around 5 inches
on the coastal slopes of the San Bernardino County mountains. For
the Apple and Lucerne Valleys, one-half to one inch is expected with
one-quarter to one-half inch for the lower deserts.

A snow level around 6000-6500 feet through tonight, will lower to
4000 feet by Thursday afternoon and 3500 feet by late Thursday
evening with snowfall of 4 to 8 inches from 5000 to 6000 feet, 8 to
14 inches from 6000 to 7000 feet, with local snowfall of 24 inches
or more on the higher peaks above 8000 feet.

Gusty southerly winds this afternoon and evening will become
westerly on Thursday. For the coast and valleys, there will be a
round of gusty southerly winds with the front passage Thursday
morning with additional gusty westerly winds Thursday afternoon.
Gusts Thursday afternoon of 30 to 40 mph for the coast and valleys
with the stronger gusts along the desert slopes of the mountains to
50 to 60 mph with isolated gusts to 65 mph on the desert mountain
slopes.

A weaker weather system moving inland to the north is expected to
bring another round of showers for Friday afternoon and evening but
with less totals, around one-tenth inch near the coast to one-
quarter inch in the mountains. Then drier with warming for the
weekend with Sunday high temperatures warming to near average. For
late Monday into Tuesday, another Pacific low pressure system could
bring additional precipitation.

&&

.AVIATION...
120930Z...Mostly cloudy conditions will prevail today and tonight.
Isolated -SHRA this morning increasing in coverage and frequency
this afternoon into tonight from north to south. Cloud bases will
vary between 1200-3500 feet MSL, and vis reduced to 3-5SM in SHRA.
Intermittent higher terrain obscurations. Little if any scatter out,
most likely on the coast briefly this afternoon. Cloud bases in the
deserts mostly 4000-10000 feet MSL. Gusty south to west winds will
increase after 19Z, highest in the San Bernardino County mountains
into deserts where gusts 25-45 kt will occur with gusts 20-35 kt in
other mountain/desert locations. Areas of strong up/downdrafts will
occur in lee of mountain ridges into deserts. Winds decrease
slightly for the coastal basin this evening before picking up again
ahead of the cold frontal passage between 6-10Z for Orange County/
Inland Empire and 9-14Z for San Diego County. +RA with a slight
chance of TS with the cold front Thursday morning.

&&

.MARINE...
Strong south winds will develop late tonight, then turn west to
northwest Thursday morning with winds approaching gale force. These
winds will produce hazardous boating conditions late tonight through
Thursday night. A Small Craft Advisory has the details. There is a
slight chance of thunderstorms Thursday. Hazardous conditions will
diminish Friday, but brisk northwest winds return Friday night.
Conditions will rapidly improve Saturday and continue Sunday.

&&

.BEACHES...
Surf will increase Thursday, reaching 3 to 6 feet, with sets to 7
feet in San Diego County in the afternoon and evening. There is also
a slight chance of thunderstorms and lightning strikes Thursday.

&&

.HYDROLOGY...
The San Diego and Santa Margarita rivers are forecast to reach
monitor/action stage on Thursday. The San Diego River at Fashion
Valley will reach Monitor Stage at 7.5 around 11 AM Thursday the
13th, peaking in the afternoon around 8.5 ft. The river is
forecast to fall to below monitor stage by Friday morning. The
Santa Margarita River will reach Monitor Stage at 8.2 ft by
Thursday afternoon. The river is expected to peak at 9.3 ft by
Thursday evening. The river is expected to fall back below monitor
stage by Friday morning. Additionally, areas of urban flooding
are possible Thursday morning, with a band of rainfall moving
northwest to southeast across the area producing rainfall rates of
mainly 0.50 to 0.75" per hour, locally up to 1" in the mountains.
Additional chances of more localized flooding are possible
Thursday afternoon.

Stay informed on the latest forecast and conditions. Do not drive
through flooded areas or around barricades.

&&

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


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Flood Watch from this evening through Thursday afternoon for
     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 Diego County Coastal Areas-San Diego County
     Mountains-San Diego County Valleys-Santa Ana Mountains and
     Foothills.

     Wind Advisory from noon to 8 PM PDT Thursday 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.

     Winter Storm Warning from 4 PM this afternoon to 11 PM PDT
     Thursday for Riverside County Mountains-San Bernardino
     County Mountains.

     Winter Weather Advisory from 6 AM to 11 PM PDT Thursday for San
     Diego County Mountains.

     Winter Storm Watch from Thursday morning through Friday morning
     for San Diego County Mountains.

     Wind Advisory from 5 PM this afternoon to 5 AM PDT Friday for
     Apple and Lucerne Valleys.

     Wind Advisory from 7 PM this evening to 11 PM PDT Thursday for
     San Diego County Deserts.

     Wind Advisory from 7 PM this evening to 5 AM PDT Friday for San
     Gorgonio Pass near Banning.

PZ...Small Craft Advisory from 10 PM this evening to 2 AM PDT Friday
     for Coastal Waters from San Mateo Point to the Mexican
     Border and out to 30 nm-Waters from San Mateo Point to the
     Mexican Border Extending 30 to 60 nm out including San
     Clemente Island.


&&

$$

PUBLIC...CO/17
AVIATION/MARINE/BEACHES...Westerink