Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 211035
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
335 AM PDT Sat Apr 21 2018

.SYNOPSIS...
High pressure aloft and weak onshore flow will bring warmer
weather through Monday with a gradual return of night and morning
coastal low clouds and fog. For Tuesday through Friday...a low
pressure system off the West Coast will begin to move towards the
Pacific Northwest late in the week. This will slowly strengthen
onshore flow across southern California and bring slow deepening
of the marine layer. Areas of night and morning coastal low clouds
and fog will spread into portions of the valleys with a cooling
trend spreading into the valleys.

&&

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

.SHORT TERM (Today through Monday)...
Weak upper level low pressure over the eastern Pacific off the
Baja coast beyond 120W will move towards the east and inland
across northern Baja tonight and spread some high clouds into
Southern California into Sunday.

The marine inversion was still quite weak Friday evening with
satellite imagery showing stratus coverage still quite patchy over
the coastal waters and adjacent coastal areass. High pressure
aloft will strengthen some for late Sunday into Monday which
should help strengthen the marine inversion. This should bring
increasing coverage of night and morning coastal low clouds and
fog.

Surface high pressure over the Great Basin will bring locally
gusty north winds this morning near the coastal slopes of the San
Bernardino County mountains. For coastal and valley areas...high
temperatures will be warmer today with similar high temperatures
for Sunday. This will push high temperatures into the 80s in the
valleys and portions of inland Orange County. There may be slight
cooling on Monday for some coastal and valley locations. Areas
farther inland will warm for today and Sunday with little change
for Monday.

&&

.LONG TERM (Tuesday through Friday)...
A trough of low pressure over the eastern Pacific along 140W will
close off off the California coast between 130W and 140W...then
begin to move slowly towards the northeast on Thursday...to a
position off the coast of Oregon and northern California on
Friday...with a blend of the ECMWF and GFS preferred.

For Southern California...high pressure aloft will weaken and
onshore flow will strengthen. The marine layer will deepen with
areas of night and morning low clouds and patchy fog spreading
farther into the valleys. A cooling trend will spread into the
valleys.

&&

.AVIATION...
210905Z...Low clouds slow to develop this morning. There is a small
chance of CIGS 700-1100 ft MSL along the San Diego County coast and
up to 5 mi inland 11-16Z, but confidence in timing and occurrence at
the coastal airports is low. Low clouds and fog possible along the
coast and up to 5 miles inland again this evening into Sunday
morning, with the potential for CIGS below 700 ft MSL and areas of
vis 3 SM or less, but confidence is low with this as well. Otherwise
a few high clouds and unrestricted vis through Sunday morning.

&&

.MARINE...
No hazardous marine weather is expected through Wednesday.

&&

.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...17
AVIATION/MARINE...SS



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