762
FXUS66 KSGX 111622
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
922 AM PDT Tue Mar 11 2025

.SYNOPSIS...
Cool, wet, and windy weather is expected for much of this week.
There will be two main periods of rain and mountain snow, the first
is today and the second Wednesday night into Friday morning.
Scattered light showers or drizzle may linger through the day
Wednesday, but some places have the potential to see mostly dry
conditions. Periods of gusty southerly winds are expected today,
with stronger and more widespread winds expected Wednesday evening
through Thursday. A few light showers may continue Friday. 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...

Radar imagery at 8 AM was showing scattered showers across the area
from the coast to the deserts. Over the past 12 hours accumulations
have been 0.10" or less across the area. At 8 AM light snow showers
were reported at Big Bear. Areas of light to locally moderate rain
will continue through the morning. As we get into the afternoon, the
cold core of the upper level low will move over Southern California,
bringing some instability and increasing chances of thunderstorms.
Highest chances for thunderstorms are in San Diego county. Rainfall
rates will be 0.30 to 0.60" per hour with a 10% chance of rainfall
rates exceeding 0.60" per hour. Localized areas of flooding are
possible where the heavier rain develops. Forecast rainfall totals
today for the coast is 0.40 to 0.60", locally up to 0.75"; for
the valleys is 0.25 to 0.50; for the mountains 0.50 to 1", locally
up to 1.5"; and for the deserts 0.20" or less. Periods of gusty
south winds are expected today, with peak gusts of 30 to 40 mph
for the mountains and deserts and up to 25 mph along the San Diego
coast. Snow levels will be 5500-6500 ft, with 3 to 6 inches of
snow expected in the San Bernardino and Riverside mountains,
locally 6 to 10 inches above 8500 ft.

Shower activity should become more isolated late tonight but light
rain or drizzle is still possible. The most likely place for
additional showers is the mountains. By Wednesday afternoon,
southwesterly winds will begin to increase 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 morning. 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 colder than the Tuesday
system with 700 mb temperatures dropping to around -10C, translating
to snow levels potentially as low as 3000-3500 ft by Thursday
night/early Friday morning. The cold nature of the storm aloft also
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. For Wednesday through early Friday, rainfall
totals could range from around one inch near the coast to 2 to 3
inches in the mountains with local amounts to around 4 inches for
the coastal slopes of the San Bernardino County mountains. For the
eastern San Gabriel Mountains for Wednesday morning through
Thursday night, there is around an 80 percent chance for local
rainfall and liquid-equivalent of 3 inches or more and a 20
percent chance for rainfall and liquid- equivalent of 5 inches or
more. For Palomar Mountain, in the San Diego County mountains,
there is around a 55 percent chance of 3 inches or more of
rainfall and liquid- equivalent.

A snow level around 6500 feet will begin to lower from the northwest
by Thursday morning, falling to 4000 to 4500 feet for Thursday
afternoon and 3000 to 3500 feet by Friday morning. Snowfall of 3 to
6 inches is possible from 5000 to 6000 feet and 12 to 18 inches from
6500 to 7500 feet.

Gusty south to southeast winds on Wednesday night will become
westerly on Thursday. The strongest winds are expected for Thursday
afternoon and evening with gusts to 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 75 mph.

Another weaker low pressure system moving inland to the north on
Friday could maintain enough moist onshore flow for more showers for
Friday afternoon through Friday night. 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...
111600Z...Clouds based 2500-4000ft MSL will bring -SHRA through the
day. Bases could drop below 2000ft and VIS 2-5SM in heavier RA,
especially with the possibility of Iso TSRA nearly everywhere 19z-
03z. These lower CIGs and VIS are more likely to prevail after 21Z.
Areas of mountains obscured in precip and FG, which prevail through
most of Wednesday. Precip to mostly move out with cigs/vis improving
after 06Z Wed everywhere but the mountains, but ongoing VCSH or -
SHRA possible with little to no impacts other than lower CIGs. Very
gusty west winds develop after 18z Wed in the mountains and deserts.

&&

.MARINE...
Strong southeast today is generating hazardous boating conditions,
but winds will diminish late this afternoon. There is a slight
chance of thunderstorms this afternoon and early evening. Any
thunderstorm could produce locally hazardous conditions. A Small
Craft Advisory is in effect today. A new storm arrives Thursday,
with strong southwest winds, turning northwest and strengthening
into possible gales Thursday afternoon. These winds will produce
hazardous boating conditions Thursday into Friday morning. There is
another slight chance of thunderstorms Thursday. Conditions improve
Friday afternoon through Saturday.

&&

.BEACHES...
A series of west to northwest swells associated with a few storms
will arrive this week. The first swell today will lead to elevated
surf of 3 to 6 feet, with sets to 7 feet, generating a high rip
current risk and potentially dangerous swimming conditions. Similar
surf is likely Thursday into Friday. There is also a slight chance
of thunderstorms and lightning strikes today, and again Thursday.

&&

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


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Flood Watch from Wednesday 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.

     Winter Weather Advisory until 10 PM PDT this evening for San
     Bernardino County Mountains.

     Winter Storm Watch from Wednesday afternoon through Friday
     morning for Riverside County Mountains-San Bernardino
     County Mountains.

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

PZ...Small Craft Advisory until 6 PM PDT this evening 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
AVIATION/MARINE/BEACHES...Zuber