324
FXUS66 KSGX 212159
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
159 PM PST Thu Nov 21 2024

.SYNOPSIS...
Warm and fair weather will continue through Friday. An atmospheric
river to the north will push southward and weaken as it moves into
Southern California over the weekend, bringing in cooler weather
and a chance for showers. This weather pattern will stick around
into early next week low pressure hangs tight across the West
Coast. Drier weather is likely to occur by the middle of next
week.

&&

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

.SHORT TERM (Thursday through Sunday)...
Onshore flow is starting to increase across the region this
afternoon, as highs across inland valleys are reaching into the
70s and lower 80s. A trough to the north will slowly drift
southward on Friday into the weekend. This will help build the
marine layer slightly, as latest HREF probabilities show a 30-60%
chance of mostly cloudy conditions across the coast by Friday
morning.

The trough and associated atmospheric river will move into our
area over the weekend, bringing in much cooler weather for the
mountains and valleys. Highs will drop close to 10 degrees in
these areas from Friday to Saturday. In terms of rainfall, our
confidence is higher on occurrence and lower on how much rain each
of our communities see. EPS/GEFS have trended a bit drier,
especially in San Diego for this weekend. We are also in the
window of high resolution models, where local WRF is favoring a
drier scenario than the HRRR. 25-55% precip chances modified
accordingly for rain to start sometime near the noon hour on
Saturday across northern areas and in the evening for southern
areas. Heaviest rainfall will be along the coastal slopes of the
San Bernardino Mts, locally over one half inch; most coastal and
valley locations will see under one quarter of an inch in total,
some close to zero. Snow levels will be high with this system as
the weakening AR flows in from the southwest. A brief dry period
will occur starting later Saturday night or Sunday morning. Some
northern areas may see some partial clearing west of the mountains
with sunnier conditions across the deserts.

&&

.LONG TERM (Monday through Thanksgiving)...

The troughing pattern will continue into early next week, as lows
rotate inside the system. This system combined with another low
off the Pacific, will pull in greater Pacific moisture. This will
lead to another chance of rainfall. Timing and exactly how much
rain we acquire is of low confidence. Ensemble models become
wetter on sometime later on Monday into Tuesday. NBM POPs are
sufficient with low to moderate chances for precip during these
two days. Trends over the past couple days have trended a bit
drier, but the spread in totals still remains, especially for the
LA basin and northern coastal slopes. Since this shower activity
looks to be coming in more from the west instead of the north,
snow levels will likely remain high for at least the early part of
the week, where most mountain communities will stay warm enough
for rainy forecast. Snow levels may lower a bit later on, but
confidence on this is low.

Long range models are beginning to show areas of weaker areas
high/low pressure by the middle of the week. This should bring
subtle warming to the area and drying by the Thanksgiving holiday,
but still does not mean we are out of the woods on a completely
dry forecast.


&&

.AVIATION...
21530Z...Some high clouds this morning at about 28,000 ft MSL,
otherwise clear today. Patchy coastal low clouds developing early
Friday. Moderate confidence in bases around 800-1400 ft MSL. These
may cause intermittent impacts to coastal sites 10-16Z Fri. There is
a 30-40% chance for BKN or more cigs at KSAN and a 50-60% chance for
the same at KSNA after 12Z Fri. Clouds will clear after 16Z Fri.

&&

.MARINE...
No hazardous marine weather conditions expected through Monday.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.

&&

$$

PUBLIC...APR
AVIATION/MARINE...CSP