Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 220307
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
807 PM PDT Sat Apr 21 2018

.UPDATE...
At 8 PM, water vapor satellite showed a weak upper-level low
spinning to our south and helping to stream high clouds across the
region. The clouds will likely disrupt the development of much,
if any, low clouds overnight along the coast. A few areas may see
patches of stratus, but most coastal valleys should be free of
low clouds and fog. This was the only change to the forecast
update this evening. Previous forecast remains on track.

&&

.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...

.PREV DISCUSSION...
Sunday-Monday will feature similar weather conditions under high
pressure aloft dominating the weather. This will lead to dry
weather and warm temps with plenty of sunshine. Nighttime and
morning low clouds will move onshore the coast and into the inland
valleys.

For the middle part of next week, global models show a trough
cutting off and meandering off the California coast. Dry weather
will continue with some slight cooling west of the mountains, but
the deserts will see little changes in temps. Winds will increase
from the mountain tops to the deserts as southwest flow increases.

The big uncertainty lies on where the cut off low will go through
late next week and global models are at odds in a big way. The
latest GFS takes it over SoCal (with rain chances and cooler
temps) while the EC takes it inland over far northern CA and
Oregon with a ridge building locally (dry and warmer). Given such
high uncertainties, no changes were made to the extended
forecast.

&&

.AVIATION...
220300Z...Coast...SCT-locally BKN low clouds could form late tonight
within 5 miles of the coast, with most likely time of any cig
between 11Z and 16Z Sunday. Confidence is low that any cigs will
reach any airports, but there is a small chance KSAN could have a
cig. Cloud bases will most likely be between 300 and 700 ft MSL.
There is a chance of fog, with vis less than 3 miles, near the
coast, with a small chance of vis around 1/4 mile. Otherwise, BKN
clouds at/above 25000 ft MSL tonight will become SCT by Sunday
afternoon.

Valleys/Mountains/Deserts...BKN clouds at/above 25000 ft MSL will
become SCT by Sunday afternoon. Vis will be unrestricted through
Sunday.

&&

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

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...NONE.
&&

$$

UPDATE...JJT
PUBLIC...Gregoria
AVIATION/MARINE...Maxwell



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