Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 131055
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
255 AM PST Thu Dec 13 2018

.SYNOPSIS...
Warmer west of the mountains today with gusty Santa Ana winds near
and below the coastal slopes of the mountains and below passes and
canyons. Onshore flow will bring cooling for coastal and valley
areas on Friday with more mid and high clouds moving across the
area. A little warmer for most areas for the weekend with weaker
onshore flow. On Monday, a low pressure system will move inland
through California bringing small chances for mostly light
precipitation. For Tuesday and Wednesday, high pressure aloft will
strengthen along the West Coast and combined with gusty Santa Ana
winds will bring a warming trend.

&&

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

There will be high pressure aloft along the West Coast today with
surface high pressure over the Great Basin. Satellite imagery
shows a few patches of stratus early this morning, mostly over the
coastal waters, with a few high clouds as well. The surface high
pressure over the Great Basin will bring periods of gusty east to
northeast winds near the coastal slopes of the mountains and below
passes and canyons. The mountains and deserts may be slightly
cooler today than on Wednesday with several degrees of warming
west of the mountains with greatest warming for inland coastal
areas into the western valleys.

For Friday, a trough of low pressure moving inland to the north
will bring a return of onshore flow which will spread cooling into
coastal and valley areas. That trough of low pressure will also
draw mid and high level subtropical moisture northward across the
area with more clouds on Friday into Friday night. Onshore flow
will be weaker for the weekend with slightly warmer high
temperatures for most areas.

For Monday, the range of model solutions for a trough of low
pressure moving inland across California has not changed much from
the past two days with the solutions ranging from a less
amplified trough of low pressure moving inland faster to a little
slower moving low pressure system that briefly closes off near the
California coast as it moves inland. The faster solutions would
be mostly dry while the slower moving more closed solutions would
bring more widespread precipitation and would more effectively
tap a subtropical moisture plume directed into southern California
ahead of the low pressure system. The current forecast remains
with an intermediate solution that would have a weakening front
moving across southern California with some light precipitation
possible for portions of southwest California.

For Tuesday and Wednesday, high pressure aloft will strengthen
along the West Coast with surface high pressure over the Great
Basin. This will bring a warming trend with periods of gusty
northeast to east winds near and below the coastal slopes of the
mountains and below passes and canyons.

&&

.AVIATION...
131000Z...A patch or two of low clouds and ground fog in the valleys
through 13Z, otherwise mostly clear today and tonight. Localized NE-
E surface wind gusts of 25-35 kt are expected mainly in foothills
and below passes through 21Z today, gradually weakening thereafter.

&&

.MARINE...
No hazardous marine weather is expected through Sunday. A large WNW
swell arriving Monday is forecast to generate combined seas of 10-12
feet, but its very long period will mean hazardous conditions are
not likely.

&&

.BEACHES...
A large long-period swell from the west-northwest is currently
projected to arrive Monday and continue through Tuesday. This would
be capable of producing surf of 6-12 feet, highest in southern San
Diego County. Stay tuned in coming days to any hazard products as
the swell approaches.

&&

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

&&

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

$$

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



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