Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 161103
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
303 AM PST Tue Jan 16 2018

.SYNOPSIS...
Weak onshore flow will spread cooling inland today with slight
warming for Wednesday and slight cooling on Thursday. There will
be some patchy night and morning low clouds and locally dense fog
for coastal areas into Thursday along with some continuing high
clouds. For Friday through early Saturday...a low pressure system
will move inland through California bringing cooling...strong
gusty west winds in the mountains...deserts...and portions of the
coastal waters...and a chance of mostly light precipitation along
with lower snow levels. There will be slow warming for Saturday
with a little greater warming for Sunday and Monday. High surf at
the beaches is expected to peak today and tonight...then begin
subsiding Wednesday.

&&

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

.SHORT TERM (Today through Thursday)...
A low pressure system moving inland through British Columbia and
the Pacific Northwest has flattened the upper ridging over
Southern California and strengthened the weak onshore lower level
flow slightly. Satellite imagery shows the continuing flow of
some high clouds across the area with enough breaks to enhance
sunrises and sunsets...but not inhibit daytime heating much. There
was some slight deepening of the marine layer Monday
evening...but as high pressure aloft rebuilds across Southern
California tonight and Wednesday...the marine inversion will
strengthen and lower a little.

Satellite imagery also shows patchy stratus across the coastal
waters into coastal areas early this morning. Fog could briefly
be dense this morning with any of the patches of stratus. For
tonight into Thursday...flow across the coastal waters into
coastal areas will be weakly onshore and weakly offshore farther
inland. Patchy to areas of night and morning coastal low clouds
and fog should not extend too far inland into coastal areas and
could be in the form of locally dense fog.

High temperatures will be slightly cooler today...warm around 5
degrees for valleys and inland coastal areas on Wednesday...then
cool for valley and inland coastal areas around 5 degrees on
Thursday.

&&

.LONG TERM (Friday through Monday)...
A Pacific low pressure system will move inland through California
on Friday and through Arizona Saturday. This will bring stronger
onshore flow for Southern California. High temperatures for the
valleys...mountains...and upper deserts will be 15 to 20 degrees
cooler on Friday with coastal and lower desert areas around 5
degrees cooler. There will be slight warming for coastal and
valley areas on Saturday with slight cooling farther inland. There
will be a little greater warming for Sunday and Monday.

The stronger onshore flow for Friday will bring strong gusty west
winds for the mountains...deserts...and coastal waters into
coastal areas for Friday into Friday night. That low pressure
system moving inland through California on Friday will also bring
a chance of mostly light precipitation for late Thursday night
through early Saturday. The bulk of any precipitation is expected
for Friday morning through Friday evening. Rainfall could range
from less than one tenth inch near the coast to one tenth to one
quarter inch in the mountains with locally greater amounts. Snow
levels will lower to 5000 to 5500 feet for Friday afternoon and
evening...and around 3500 feet for late Friday night into early
Saturday. A few inches of snowfall is possible above 4000 to 4500
feet...with isolated totals to around 4 inches above 6000 feet.

The global models are in better agreement for Sunday and Monday in
showing a dry west northwest flow pattern across Southern
California. However...the model to model and run to run
consistency for late in the weekend into next week across the
eastern Pacific into California has not been all that great. There
remains the potential for one of the low pressure systems
traversing the Pacific to amplify near the West Coast and bring
more precipitation to Southern California.

&&

.AVIATION...
161000Z...Coast...Variable and intermittent low clouds and patchy
fog through 14Z. When/where cigs occur, bases would vary between 200-
1000 feet msl. Vis 3-5sm, except locally 1sm. Similar patchy low
cloud and fog conditions after 06Z tonight. Otherwise, VFR
conditions with broken high clouds today, turning scattered late
afternoon and tonight.

&&

.MARINE...
Patchy fog with visibility of 1NM this morning. Combined seas of 7-
11 feet with a long period in the outer waters south of San Clemente
Island today, gradually decreasing Wednesday. A storm will bring
hazardous winds and seas Friday through Saturday.

&&

.BEACHES...
High surf will peak today and tonight before gradually decreasing
Wednesday. See the High Surf Advisory and the surf forecast for
details. A new swell associated with a Pacific storm will arrive
Friday afternoon and continue through Saturday.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory until 6 AM PST Thursday for Orange County
     Coastal Areas-San Diego County Coastal Areas.

PZ...NONE.

&&

$$

PUBLIC...17
AVIATION/MARINE/BEACHES...MM


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