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Area forecast discussion
National Weather Service San Diego California
431 am PST Sat Jan 20 2018

Synopsis...
a low pressure system moving from Southern California into Arizona
will bring much cooler and breezy conditions today. Scattered
showers...with snow showers in the mountains...will continue into
this morning...then end from the northwest in the afternoon.
There will be slow warming for Sunday...with greater warming for
Monday through Wednesday with high pressure aloft. Weak offshore
lower level flow will bring locally gusty northeast winds near the
coastal foothills at times. For next Thursday...another fast
moving low pressure system moving inland through California will
bring cool and windy conditions with a chance of mostly light
showers. Then dry with a warming trend for Friday through next
weekend as high pressure aloft strengthens near the West Coast.
High surf with strong rip currents will continue at the beaches
today.

&&

Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
counties...

A cold low pressure system is centered near Point Conception early
this morning. It will move into Arizona by late afternoon..and
into the central and southern rockies Sunday. Radar and surface
reports show scattered showers continuing early this morning with
the greatest coverage from the valleys into the mountains. Snow
levels have lowered to 3000 to 3500 feet. The coldest air at mid
levels will move across the area this with briefly more intense
showers possible.

Scattered showers will continue into this morning...then decrease
from the northwest during the late morning and afternoon. Isolated
stronger showers with brief heavy downpours are possible through
this morning. The snow level will be near 3000 to 3500 feet early
this morning...then rise to near 4000 feet during the afternoon.
The greatest additional precipitation totals will be across the
inland valleys into the mountains with one to locally two tenths
of an inch in these areas and a few hundredths of an inch or less
elsewhere. In the mountains...local additional snowfall of one to
two inches above 3500 feet is possible through this morning.

Strong and gusty west winds have continued overnight in the
mountains with strongest gusts near Mountain Ridge tops onto the
desert slopes of the mountains with the strongest gust overnight
of 63 mph at Volcan mountain in the San Diego County mountains.
During the late morning through the afternoon...the stronger winds
in the mountains will expand into portions of the deserts...and
stronger winds across the coastal waters will spread inland across
coastal and valley areas of San Diego County and portions of
southern Orange County with strongest winds near the coast.

As the storm exits to the east tonight...a cold dry atmosphere
will remain and with radiational cooling...temperatures in lower
portions of the inland Empire will fall into the upper 20s to mid
30s late tonight into early Sunday morning with areas of frost.
Patchy frost is also possible in some for the inland valleys in
San Diego County with some patchy radiational fog in some coastal
and valley areas as well. Frost should be patchier for late
Sunday night into early Monday morning.

High temperatures will be coolest today...then warm slightly on
Sunday. Greater warming is expected for Monday through Wednesday
as high pressure aloft strengthens near the California coast and
surface high pressure over the Great Basin brings weak offshore
lower level flow with locally gusty northeast winds near the
coastal foothills and below passes and canyons at times.

For next Thursday...another fast moving low pressure system
moving inland through California will bring cool and windy
conditions with a chance of mostly light showers. There remain some
slight timing and intensity differences among the global
models...but the main impacts are expected for late Wednesday
night through Thursday. Then dry with a warming trend for Friday
through next weekend as high pressure aloft strengthens near the
West Coast.

&&

Aviation...
200930z...coast/valleys...sct-bkn clouds with variable bases at or below
6000 feet mean sea level through mid afternoon. Isolated rain showers may lower
briefly lower visible to 3-5sm through midday, otherwise p6sm. Clouds
becoming scattered 20z-23z with VFR conditions and unrestricted visible
through the evening.

Mountains/deserts...mts partially obscured most of the day in clouds
with scattered pcpn, mainly San Diego County. Westerly winds 25 to
35 kts with gusts 45 kts into the evening creating mod-stg up/down
drafts over and east of the mts.

&&

Marine...
northwest winds of 20-30 kts with gusts to 35 kts over the coastal
waters this morning...decreasing to 20 kts with gusts 25 kts late
this evening. Large wind waves on top of an elevated swell, will
create combined seas of 10-15 ft at times. Refer to the Gale Warning
in effect for additional detail. Conditions will be hazardous for
small craft through this evening.



&&

Beaches...
a building fresh swell from a local wind fetch will augment the
large west-northwest swell in place over the coastal waters this
morning, to drive some of the biggest surf of this event. Occasional
sets of 12 to 15 feet are possible for west-facing beaches in
southern San Diego County this morning. Elsewhere along the socal
coast...5 to 10 foot surf will continue into this evening before
subsiding later tonight. Strong rip currents will accompany the high
surf, resulting in dangerous swimming conditions. Please refer to
the high surf advisory for additional details.

&&

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

&&

Sgx watches/warnings/advisories...
California...Winter Weather Advisory until 10 am PST this morning for
Riverside County mountains-San Diego County mountains.

Wind Advisory from 10 am this morning to 6 PM PST this evening
for apple and Lucerne valleys-Coachella Valley-Riverside
County mountains-San Bernardino County mountains-San Diego
County coastal areas-San Diego County deserts-San Diego
County mountains-San Diego County valleys-San Gorgonio Pass
near Banning.

Winter Weather Advisory until 6 am PST early this morning for
San Bernardino County mountains.

Frost advisory from 2 am to 8 am PST Sunday for San Bernardino
and Riverside County valleys-the inland Empire.

High surf advisory until 8 PM PST this evening for Orange County
coastal areas-San Diego County coastal areas.

Pz...Gale Warning until 10 PM PST this evening for coastal waters
from San Mateo Point to the Mexican border and out to 30 nm-
waters from San Mateo Point to the Mexican border extending
30 to 60 nm out including San Clemente Island.

&&

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