987
FXUS66 KSGX 210504
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
904 PM PST Thu Nov 20 2025

.SYNOPSIS...
Periods of rain and mountain snow are expected tonight into
Friday afternoon. Up to an inch of rainfall possible for
coast/valleys, higher in the foothills and mountains. Periods of
heavy snowfall in the mountains, especially early Friday morning,
with snow levels around 6000-6500ft where 5-10+ inches of snow may
accumulate. Precipitation will linger into Saturday. Drier
weather with a very slow warming trend sets in for the end of the
weekend into early next week, warming to above normal by Thursday.

&&

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

Widespread rain and mountain snow above 6500 ft have been falling
through this afternoon and evening. Periods of moderate to locally
heavy rain occurred earlier this evening in portions of the High
Desert and Orange County, with lighter showers observed elsewhere.
Rainfall rates as of 9 PM have been mainly light, 0.10 inch per
hour or less, with some local rates up to 0.20 inches per hour in
southern Orange County. The latest rainfall totals have been
headlined on our weather.gov/sandiego website. Forecast remains on
track for periods of additional heavy rain, with rainfall rates
around 0.50 inch per hour overnight tonight. Latest high
resolution guidance indicates the timing of heavier rain will
occur after 10 PM. Scattered showers can be expected much of the
day Friday, with shower coverage becoming more confined to the
mountains and deserts for late Friday into Saturday. Periods of
gusty east to northeast winds can be expected Friday night into
Saturday as well.

From previous discussion issued 2 PM November 20...

Water vapor imagery shows a deepening low off the coast of Monterey,
quickly moving southward where it is scheduled to set up off the
coast of Southern California tonight. It will follow a very similar
track to the last system, bringing cooler weather, ample moisture,
and periods of gusty winds to the mountains and deserts. Upper
levels remain quite chilly with limited time to warm in between
systems, indicating snow level will be cooler with this event than
previous. Snow levels begin today around 6500ft, falling to around
6000ft as the main moisture moves in late tonight/early Friday.
Heavy rain bands with periods of 0.50"/hr rainfall rates expected
this evening and into Friday morning, although there will also be
around a 20-40% chance of thunderstorms region-wide that may result
in briefly higher rates. While still looking at significant wetting
rain, the lower rain rates with this system mean the flooding threat
is somewhat less compared to what occurred over the weekend. Still,
half an inch or greater with any thunderstorm in the vicinity of
recent burn scars may allow moderate flooding to occur at times,
primarily tonight into Friday morning. Always monitor the forecast
and listen to local emergency managers in you live in a flood-prone
region.

Rainfall totals haven`t changed much from the previous forecast
package, still looking at Thur-Fri totals of around 1-1.25" for
coast/valleys and low-lying areas with around 2" for foothills and
lower elevations of the mountains. With snow levels around 6000-
6500ft coinciding with the heaviest precipitation, elevations above
6000ft will likely see at least some snow accumulations, and those
above 6500ft will see around 5-10". The greatest accumulations will
be above 7500ft, which may be around 15-17" in total through early
Saturday morning. The greatest uncertainty with precipitation
remains on Saturday as the low pivots into Arizona. Even only 60
hours out, there is significant issues with model alignment for the
center of the low and its progression, giving decent spread in
amounts of wrap around moisture as the low moves east. As we enter
the hi-res model window for Saturday morning, QPF amounts for
Saturday range from 0.10"/6hr time frame to around 1"/6hr time
frame, all dependent on the position of the low. For now, the wrap-
around moisture looks to be most prevalent in San Diego County, in
particular the mountains and deserts. Bands of 0.20-0.25"/hr rates
won`t be out of the question, especially before sunrise on Saturday.
Further north, additional moisture being pushed into the Riverside
and San Bernardino Mountains may lead to additional snowfall as
those snow levels slowly rise from 6500ft to 7000ft, but chances are
lower there than in San Diego County. Regardless of how the wrap
around moisture shakes out, gusty winds as the low pivots across
will begin Friday morning and spread across the High Deserts and
higher terrain Friday afternoon into early Saturday morning. Gusts
may exceed 30 mph at times, higher in mountain passes and along
terrain, especially early Saturday morning.

As the low moves out Saturday, weak ridging will take its place and
return us to a drier pattern with a slow warming trend through at
least Thanksgiving. Highs will return to near normal by Wednesday,
and slightly above by Thursday. The next system may arrive next
week, but its a bit too early to tell if it will make it far enough
south for us to benefit from. Stay tuned.

&&

.AVIATION...
210400Z...SCT-BKN low clouds 2500-5000 feet MSL through the coastal
basin this evening through 01-02z Saturday. Widespread precipitation
will continue to move across the region through 12-14z before
becoming more scattered. Expect widespread MVFR cigs/vis through
the coastal basin and deserts with brief periods of IFR conditions
in the coastal basin (cigs below 1000 ft and VIS 1-3SM) as the
heaviest precip passes through around 05-11Z. Slight chance TSRA
(10- 20%) from the coast to the mtns. Mtns shrouded in FG through
the night. Lingering SCT SHRA and ISO TSRA will create
intermittent MVFR conditions for all areas. Easterly winds gusting
20-30 knots along west facing slopes and downwind of mountain
passes into the coastal foothills after 18Z.

&&

.MARINE...
Strong southerly winds becoming westerly winds 10-20 knots this
evening with gusts to 25 knots, generating choppy seas. Check the
Small Craft Advisory for details. There is also a slight chance of
thunderstorms tonight through Friday afternoon. Any thunderstorm
could bring lightning, gusty winds, choppy seas, and a waterspout.

&&

.BEACHES...

There is a slight chance for lightning (20-30%) at the beaches
tonight through Friday afternoon.

&&

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


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Winter Storm Warning until 4 PM PST Friday for Riverside County
     Mountains-San Bernardino County Mountains.

PZ...Small Craft Advisory until 2 AM PST Friday 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...CO/Zuber
AVIATION/MARINE/BEACHES...Villafane