000
FXUS66 KSGX 111646
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
846 AM PST Mon Dec 11 2023

.SYNOPSIS...
High pressure will give way to developing low pressure aloft
through Wednesday. This will draw marine air inland over Southern
California, with areas of low clouds and patchy fog likely to return
west of the mountains. It will also produce some locally gusty
northerly winds on Wednesday. The days will be slightly cooler, but
nights shouldn`t be quite as cold, due to the added moisture. Warmer
days return on Thursday, and continue into the weekend, as a strong
ridge reemerges over the Southwest with weak offshore flow. The
weather will remain dry, with warmer than average days and cool
nights through next weekend.

&&

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

We are off to another chilly start this morning with widespread
temperatures in the 40s at 8 AM PST. High clouds were streaming east
across the area, and were fairly thick. The north edge of the cloud
shield was near Pt. Conception, so these could be with us much of
the day, with a few breaks. This is inferred from the global models
as well. The winds have decreased considerably from yesterday, and
were light this morning. Our 12Z Miramar sounding actually showed
another temperature increase of 2-4C between 1000 and 4000 FT MSL,
so provided we get a little sun, we could warm up quickly this
afternoon so no forecast updates are planned this morning.

From previous discussion...

Increasing high clouds and pockets of offshore breezes are in the
weather picture this morning. Isolated gusts in the foothills
are around 20 mph, but winds will be lighter today, a transition
day, from offshore flow to onshore. A shortwave will amplify into
a low pressure trough that cuts off and moves from around Reno,
to Las Vegas and down into Phoenix by Wednesday. Models have been
consistent in depicting a robust coastal eddy to develop tonight
and continue into early Wednesday in response to this low. This
will cool and humidify areas west of the mountains today and
Tuesday, and should generate some patchy low clouds and fog.
There`s a small chance some true fog will develop Tuesday morning
near the coast, but with the rapidly building eddy, any low
visibilities would be short-lived at most. The patchy low clouds
would spread farther inland Tuesday night into early Wednesday.
Just ready to get flushed out of the coastal basin as offshore
winds strengthen Wednesday. The upper low contributes some upper
support to the surface gradients, aligning offshore Wednesday.
Strongest gusts appear Wednesday through and below the Cajon Pass
area into the Riverside area. Top gusts could reach 40-50 mph in
those foothills. As the upper low moves east Thursday, it takes
much of the upper support with it, leaving offshore winds
primarily driven by the surface pressure gradient. They`ll be
weaker than on Wednesday, but that pressure gradient will maintain
night and morning offshore winds mainly in foothills and adjacent
valleys at least into the weekend. Occasional high clouds will
drift across the sky this week for some pretty sunrises and
sunsets. High temperatures will continue a few degrees above
normal. High pressure aloft really amplifies for Friday and
Saturday, when high temps could get 5-15 degrees above normal. Dry
and calm air will allow nights to stay cool, near normal, for
most areas. Of course, nights will be warmer where breezes
persist. When will it rain? A very fuzzy picture says probably
some time next week. The range of ensemble outcomes includes rain
as early as next Monday, or not at all.

&&

.AVIATION...
111605Z...SCT-BKN clouds at/above 20000 feet MSL with unrestricted
VIS through this evening.

&&

.MARINE...
No marine weather hazards are expected through Friday.

&&

.FIRE WEATHER...
Provided we get enough sun and mixing, we do expect temperatures to
revisit the 70s this afternoon, and that will drive minimum RH
values back into the 10-15% range. Winds will be mostly light and
variable today, with a weak sea breeze returning along the coast and
into the western valleys. A more robust RH recovery comes Tuesday,
as a coastal eddy develops and drives marine air well inland. There
will be some cooling as well. Northerly, moderate offshore flow
develops on Wednesday, and could be gusty along the south slopes and
foothill areas of the San Bernardino Mountains, into the Inland
Empire. Flow will turn more northeasterly and weaken after
Wednesday, but still scour out the marine layer. This weak Santa Ana
pattern will maintain minimum RH values of 15-25% each day, and well
above average daytime temperatures, especially west of the
mountains. Winds may get locally gusty at times in the usual Santa
Ana wind-prone areas on Thursday, but the pattern suggests winds
will remain weak through the coming weekend.

&&

.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...10/MM
FIRE WEATHER...10
AVIATION/MARINE...APR