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fxus66 ksgx 070534 
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Area forecast discussion
National Weather Service San Diego California
934 PM PST Fri Dec 6 2019

Synopsis...
a moist, southwest flow aloft will bring periods of light rain
as a weak storm system drops south across the state. Snowfall will
be limited to higher mountain elevations as this is a warm
system. The storm will move east on Monday, with clearing skies
and a warming trend for next week. Further warming is on tap for
next weekend as dry weather persists. At the beaches, a large west
swell will bring high surf this weekend.

&&

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

...

The first wave of light rain, which came earlier than
anticipated, has passed to the east this evening. This was
associated with a shortwave (seen in water vapor imagery) and
moisture advection. Rainfall amounts with that wave of rain were
mostly in the 0.05-0.20 inch range west of the mountains.

There has been a break in the rain mid evening, but additional
showers are developing and moving into Orange, far western
Riverside and San Bernardino counties. These will continue to
expand southeast overnight. This weekend will feature extensive
cloudiness with periods of rain, mostly on the light side but some
moderate rain will occur as well. The heaviest amounts will occur
along the coastal mountain slopes. This will be a warm storm
system with snow limited to higher mountain elevation locations
(snow levels 9,000-10,000 feet lowering to 6,500-7,000 feet by
Sunday night).

..update (issued at .205 PM PST Fri Dec 6 2019)..

Quick update to increase probability of precipitation through this evening. Doppler radar
shows a shield of rain entering Orange County extending south off
the San Diego County coast. This area is moving northeast at
about 35 mph. The radar bark is worse than the bite. Aircraft
sounding data shows a dry layer in the lower levels, so some of
the rain falling is evaporating. Upstream gauges over San Clemente
Island show Max rain over the past hour of 0.07". So this will be
a light rain but most coast and valley locales do look to get wet
late this afternoon through this evening. As such, increased probability of precipitation
substantially to account for this expectation. Rainfall of
trace-0.10 inches is expected through this evening west of the
mountains and along the coastal mountain slopes.

..previous discussion (issued at 1223 PM PST Fri Dec 6 2019)...

Satellite imagery at midday showed a thicker blanket of high clouds
spreading NE across the area. In addition, the radar indicated some
precipitation moving NE over the coastal waters. Some of this could
make it into Orange and San Bernardino diego counties by late
afternoon. The sfc pressure gradients from the deserts were still
weak to moderate offshore, supporting NE winds below the passes with
local gusts 25-35 miles per hour. Still, the sea breeze was evident into the
western valley areas.

A storm system centered 500 miles west of Cape Mendocino today, will
drift east through Saturday, and then drop south through Monday as a
strong ridge builds off the coast. Weak disturbances off the Pacific
ahead of it will gather up some Pacific moisture, sparking some
occasional light precip that will favor the coastal slopes. Upslope
is generally weak though, so no heavy amounts are likely with no
good atmospheric lift to squeeze it out. Snow levels will be quite
high initially, above 8k feet through Saturday, then fall to around 7k
feet by late Sunday.

The final trough axis passes through socal on Monday morning, so
some light, scattered showers may continue into early Monday for San
Diego County especially. Overall precip amounts of 1/4-1/2 inch are
expected west of the mts, and 0.5 to 1.5 inches on the coastal
slopes and higher terrain. For the deserts, less than one-quarter
inch total. Several inches of snow are possible in the San
Bernardino mts by Mon morning above 7500 feet.

A highly amplified ridge develops early next week along the West
Coast and keeps socal protected from activity in the westerlies
through next week. Even though the ridge flattens, it strengthens
further next weekend along 30n latitude. This will likley bring well
above average temps to socal by next weekend, along with continued
fair and dry weather.

&&

Aviation...
070530z...coasts/valleys...sct-bkn cigs 2000-4000 ft mean sea level and vis 2-4
sm in areas of -ra through Sat. Low clouds will obscure terrain
above 3000 ft mean sea level at times.

Deserts...chance of -ra Sat. Cigs around 5000 ft mean sea level and vis 3-5sm
possible in any areas of rain.

&&

Marine...
scattered rain showers through Sunday. Combined seas of 6 to 9 ft
are expected Saturday afternoon through Sunday evening.

&&

Beaches...
a high surf advisory remains in effect for long-period northwest
swells of 14 to 18 seconds at the coasts of Southern California. The
swells will start to build on Saturday, peaking Sunday morning, and
subsiding by Monday morning. Surf of 6-9 ft is expected in San Diego
County and 4-7 ft surf is expected on beaches prone to west-northwest swells in
Orange County.

&&

Sgx watches/warnings/advisories...
California...high surf advisory from 4 am Saturday to 4 am PST Monday for
Orange County coastal areas-San Diego County coastal areas.

Pz...none.
&&

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