Area Forecast Discussion
Issued by NWS San Diego, CA

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518
FXUS66 KSGX 100515
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
915 PM PST Fri Dec 9 2016

.SYNOPSIS...
A weak trough passing by to the north will bring high clouds, a
deeper marine layer and possible light showers Saturday night and
Sunday. Weak high pressure aloft will bring seasonal weather Monday
and Tuesday. A stronger storm that could bring showers late next
week.

&&

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

.Update - No significant forecast changes...

Yet another tranquil day across SoCal with a more hazy sky today
along with high level cloudiness. Highs today reached into the 60s
to near 70 at most locales, except in the 50s at the higher
elevations. The marine layer cloudiness has moved in and now lies
along the Orange and San Diego coast. This low cloudiness will
spread some 20-25 miles inland overnight along with the potential
of patchy fog over the inland valleys.

For further forecast details beyond tonight, see previous
discussion below.

.Previous Discussion (Issued at 130 PM PST Fri Dec 9 2016)...

Weak impulses in the fast zonal flow over the Pacific will bring
precip to NorCal this weekend, and perhaps a little light rain to
SoCal too. An atmospheric river over the Pacific currently aimed at
north-central CA will shift southward Saturday afternoon with a weak
shortwave. PWATS of 1.40" approach SoCal Saturday night, with most
of this increase in the 700-500 mb layer. This increased moisture
may contribute to scattered light showers in the mountains Saturday
night into Sunday. In the low levels, the marine layer will deepen
to 5000-6000 feet for possible light showers west of the mountains
Saturday night through midday Sunday. Weak PVA and the lack of a
strong lifting mechanism (sfc cold front) will limit the precip
potential with this system. Precip in most areas will be light with
trace amounts to a few hundredths of an inch, with locally higher
amounts of 0.10-0.20". The precipitation will end Sunday afternoon
as drier air moves behind the departing wave. Mild Monday and
Tuesday with scattered to broken high clouds in prevailing zonal
flow aloft.

Long Range...Timing issues abound in the long range guidance next
week as zonal flow transitions into a high amplitude wave pattern
where predictability is lower. Guidance diverges early next week
with the ECMWF maintaining weak ridging over the Southwest, while
the GFS sweeps another trough across CA. Both models project a long
wave trough over the West late next week but with significant
timing, strength and location differences. Best solution today is a
model blend of the GFS and EC ensembles, both of which have
troughing over the Southwest late next week for cooler weather and
a chance of precipiation.

&&

.AVIATION...
100310Z...Coast/Valleys...Areas of low clouds will continue
increasing in coverage overnight, with bases 1000-2000 ft MSL and
tops around 2500 ft MSL. Expect mostly unrestricted vis except after
09Z when areas of vis 3-5 sm will be possible in the valleys. Only
partial clearing is expected after 17Z Sat. Forecast confidence is
moderate.

Mountains/Deserts...BKN clouds AOA 20000 ft msl and unrestricted vis
continuing through Saturday.

&&

.MARINE...
No hazardous marine weather is expected through Wednesday.

&&

.BEACHES...
Morning high tides will reach 6.7-7 feet Monday through Thursday but
surf and swells are expected to be small, so any tidal overflow
threat will likely be minor and very localized.


&&

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

$$

PUBLIC...Gregoria(Update)/Moede
AVIATION/MARINE...PG



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