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Area forecast discussion
National Weather Service San Diego California
323 am PST sun Dec 15 2019

Synopsis...
it will be fair and slightly cooler today as onshore flow weakens,
and clouds and isolated light showers diminish this morning. For
tonight through Tuesday, high pressure builds back into the Great
Basin, turning winds offshore. Gusty east to northeast winds are
likley over offshore, wind-prone areas. This will mean lower
humidity, mostly clear, cooler nights, and sunny, warmer days west
of the mountains. Weak offshore flow and high pressure aloft will
continue fair and warmer weather into next weekend. A Pacific storm
system brings a chance for precipiation early next week.

&&

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

Rain gages show light accumulations of rain, mainly long the coastal
slopes of the mts, and radar shows isolated weak returns at 3 am PST
drifting southeast. Over the past 6 hours totals have been mostly under one-
tenth of an inch. The sfc pressure gradients were still trending
onshore (at 2 am 10 mbs ksan to SW nv). Westerly winds were running
30 mph, with peak gusts to 45 to locally 60 miles per hour through the wind-
prone pass and slope areas. Satellite imagery still showed a fair
amount of cloud cover along and west of the mts, but skies were
mostly clear over the coastal waters and expect clearing through the
morning over land as well.

A shortwave trough is dropping through the Great Basin this morning,
supporting sfc pressure falls and strong onshore flow. As the trough
swings east today, the sfc pressure gradient will relax, allowing
winds to slowly weaken. Brief and isolated early morning showers are
in the forecast for San Diego County. But fair skies and cool
conditions will prevail later today, with a cooler night on tap due
to drier air and the lack of clouds.

For Mon/Tue, a strong sfc high builds into the Great Basin, setting
up offshore flow over socal that will last into Wednesday morning.
This will bring fair skies, warmer days and cool nights west of the
mts. Mountain and desert areas will see less warming. East to
northeast winds will be gusty on the coastal mtn slopes and through
the passes. On Wednesday, a Pacific shortwave trough will move onto
the central California coast. Very dry Continental air over socal overwhelms
any precip generation here as the trough weakens and moves onshore.
Models now show precip remaining north of Los Angeles on Wednesday.

For the latter half of the week, a more substantial longwave trough
develops over the eastpac, pumping up a warm ridge over the
southwest. This will bring storied, classic, Mediterranean climate
winter weather to socal into next weekend with fair skies and warmer
days.

By Sunday, the ridge is out of the picture and effects of the large
longwave trough over the eastpac will begin to be felt. Onshore flow
will bring cooling, and clouds will begin to stream in from the SW.
Small probability of precipitation have been added to Sunday, but models show precip more
likely over socal on Monday of next week.

&&

Aviation...
151105z...coast/valleys...sct-bkn clouds with bases 2000-4000 ft and
tops to 5000 ft with scattered showers this morning. Showers will
end and clouds will scatter out from north to south between 15-20z.

Mountains/deserts...west facing mountain slopes will be obscured in
clouds and fog through 15z, with isolated light showers. Ridgetops
and eastern mountain slopes will be mostly clear with unrestricted
vis through tonight. Gusty west winds in the mountains/passes and
over the desert slopes with gusts to 50 kts through this morning,
with strong up/downdrafts and low level wind shear.

&&

Marine...
a long-period west northwest swell of 15-17 seconds will combine
with a 7-9 second swell to produce combined seas of 9 to 12 ft
through today. West northwest winds gusting 25 to 30 knots will
continue through this afternoon. The combination of wind and swells
will produce hazardous boating conditions. A Small Craft Advisory is
in effect for all of the coastal waters through 4 PM today.

&&

Beaches...
a high surf advisory is in effect through 4 PM today for 5-10 ft
surf, highest in San Diego County. The surf will contribute to areas
of minor beach erosion during the 6 ft+ morning high tides.

&&

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

&&

Sgx watches/warnings/advisories...
California...Wind Advisory until 10 am PST Sunday for apple and Lucerne
valleys-Coachella Valley-Riverside County mountains-San
Bernardino County mountains-San Diego County deserts-San
Diego County mountains-San Gorgonio Pass near Banning.

High surf advisory until 4 PM PST Sunday for Orange County
coastal areas-San Diego County coastal areas.

Pz...Small Craft Advisory until 4 PM PST Sunday 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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