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Forecast Discussion for San Diego, CA

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000
FXUS66 KSGX 050450
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
850 PM PST Sat Dec 4 2021

.SYNOPSIS...
Low clouds likely to spread inland again tonight with areas of
dense fog forming in portions of the inland valleys. Weak
northeasterly winds will develop Sunday in the foothills. The
northeasterly flow will combine with a brief ridge aloft to bring
warmer weather for Sunday and Monday. However, an approaching
trough of low pressure will bring gusty westerly winds late Monday
into Tuesday. A storm from the north could bring rain, wind and
mountain snow to Southern California Thursday through Friday along
with colder conditions.

&&

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

This evening, the marine layer is about 2000 ft deep and low
clouds are beginning to increase in coverage and spread inland.

From previous discussion...
The northeasterly flow aloft and rising heights will help lower
the marine layer depth, though areas of stratus and fog will still
develop tonight. Areas of dense fog could develop in some of the
valleys. This weak offshore flow pattern should mostly bring the
northeast surface winds to the mountains as forcing is too weak to
bring it down to the valley floors except in some of the very far
northern valleys, such as directly below Cajon Pass. Only local
mountain wind gusts above 40 MPH are expected, and much less than
that in the valleys. There should be some warming Sunday, though
the warming should be modest near the coast due to the continuing
marine layer presence. Less northeast mountain flow and somewhat
less stratus will occur Monday morning, but then onshore flow will
develop Monday afternoon and bring westerly winds in the
mountains and deserts, with gusts over 50 MPH possible in some
mountain locations. A trough of low pressure moving inland to the
north will assist with the westerly winds. The marine layer
likely will not get deep enough for drizzle. Moisture aloft
probably will be insufficient as well, though clouds aloft should
increase for a while at least Monday night into Tuesday. Brief
weak offshore flow will likely develop Tuesday, but again mostly
just in the mountains and perhaps the northern part of the Inland
Empire.

The notable event next week will be the broad troughing across the
western US Thu/Fri, and with a couple of shortwaves on the back side
of the trough, we could finally get some meaningful rain fall, the
first since October. Rainfall amounts could exceed 1/2 inch in some
locations, mostly likely in the foothills and west-facing mountain
slopes, though most ensemble members have less than 1/2 inch closer
to the coast. Lowering snow levels that could bring snowfall at
least in the second half of the storm in the mountains. GFS/ECWMF
IVT maps show at least somewhat of an atmospheric river over
California, though likely not a strong one. Fair weather will likely
return the following weekend, though guidance is suggesting a
possible deep trough around Mon/Tue Dec 12/13 which could bring
greater rainfall over SoCal.

&&

.AVIATION...
050440Z...Coast/Valleys...Areas of low clouds with bases 1400-1700
ft MSL and tops to 2200 ft MSL will continue to develop over the
coastal areas and valleys and eventually spread 25-30 mi inland
overnight. Areas of vis 3-5 SM in BR/HZ, locally below 1
SM in the inland valleys. Confidence low for CIGS at KONT, though
vis restrictions likely to continue through about 16Z. Clouds
clearing to the coast 16-18Z with vis becoming unrestricted by 20Z.
Patchy low clouds and fog may redevelop over the coastal waters
Sunday night, but are not expected to reach the coastal airports.

Mountains/Deserts...Mostly clear skies with unrestricted vis
through Sunday evening. North to northeast winds will
increase after 10Z over the RIV/SBD mtns, with gusts 25 to 35
kt. Winds will weaken slightly during the afternoon. Weak
to moderate up/downdrafts and LLWS expected over/southwest of the
mountains.

&&

.MARINE...
No hazardous marine weather conditions are expected through
Wednesday. Gusty west-northwest winds near 20 to 25 kts expected by
Thursday and Friday as a storm moves through.

&&

.BEACHES...
King tides near 7 feet Sunday morning could lead to minor
coastal flooding, mainly for low lying beach parking lots and
boardwalks. Surf will remain relatively small, limiting the flood
threat.

&&

.FIRE WEATHER...
Northeasterly winds will develop tonight over the San Bernardino
County and Riverside County mountains and extend locally into the
foothills and far inland valleys Sunday morning. Decreasing humidity
and increasing temperatures and winds will elevate fire weather
conditions though most of the valley locations should maintain
humidity at/above 20 percent. Local wind gusts could exceed 40 MPH,
but this will mainly be near the mountain crests where temperatures
will be lower and RH values a little higher. Winds will weaken
Sunday night, but onshore flow will develop late Monday with locally
strong winds in the mountains and deserts, accompanied by
increasing humidity. A storm system around Thursday or Friday will
likely bring wetting rains to the region.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Dense Fog Advisory from 11 PM this evening to 9 AM PST Sunday
     for San Bernardino and Riverside County Valleys-The Inland
     Empire-San Diego County Valleys.

PZ...NONE.

&&

$$

PUBLIC/FIRE WEATHER...PG
AVIATION/MARINE...SS

Previous Forecast Discussions may be found at
NWS San Diego, CA (SGX) Office Forecast Discussions.
(Click 'Previous Version' there to view past versions successively.
Some may differ only in time posted.)

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