Area Forecast Discussion
Issued by NWS San Diego, CA

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364
FXUS66 KSGX 211656
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
955 AM PDT Mon Aug 21 2017

.MORNING UPDATE...
Minor tweaks were made to the cloud cover early this morning.
Otherwise the coastal stratus field is quickly scattering out even
at the beaches this morning. Should be good eclipse viewing all
areas. Still a slight chance of showers & thunderstorms late this
afternoon over the highest peaks of Riverside and San Bernardino
Counties and in the high desert late this afternoon on the very
western fringe of a mid level monsoonal flow from Northern Sonora.
Please see remainder of the previous discussion below for more
details on the forecast.

&&

.SYNOPSIS...
A weak low pressure system off the Southern California coast will
keep high temperatures a few degrees below average today with
areas of low clouds with patchy fog and drizzle extending into
portions of the inland valleys this morning. Mid level monsoonal
moisture to the east and north will bring some afternoon clouds to
the mountains with a slight chance for thunderstorms for the San
Bernardino County mountains and adjacent deserts this  afternoon.
There will be warming to near average high temperatures for
Tuesday through Friday...with high pressure over the Great Basin
bringing warming to 5 to locally 10 degrees above average for next
weekend.

&&

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

A weak low pressure system will remain off the central and
southern California coast through Tuesday...then slowly weaken
and move inland Wednesday and Thursday with a trough of low
pressure moving inland through the Pacific Northwest and northern
Rockies Thursday. High pressure aloft will develop over Arizona
Friday...then shift northward and be centered over the Great Basin
for Sunday and Monday.

High temperatures will remain a few to around 5 degrees below
average today...warm to near to slightly below average for
Tuesday through Friday...then warm to around 5 degrees above
average for next weekend with some portions of the Inland Empire 5
to 10 degrees above average.

Satellite imagery shows widespread stratus over the coastal waters
extending inland across much of the San Diego County valleys and
spreading into western and southern portions of the Inland
Empire. The stratus is expected to cover much of the valleys by
around sunrise. Some patchy drizzle is possible in coastal areas
this morning. The coastal stratus is expected to clear back
towards the beaches by late morning.

There are also mid clouds spreading northwestward across the
eastern deserts of Southern California with scattered showers over
the far eastern deserts. The greatest influx of mid level moisture
today will remain to the east and north...but may still be
sufficient for some clouds this afternoon for the San Bernardino
County mountains and deserts with a slight chance of
thunderstorms.

For Tuesday through Friday...areas of night and morning coastal
low clouds and patchy fog will extend into portions of the western
valleys with a few afternoon clouds near the mountains at times.

For next weekend...the marine layer will become shallower with low
clouds not extending as far inland. Mid level moisture in
southeast flow aloft could bring some additional afternoon clouds
to the mountains.

&&

.AVIATION...
211521Z...Coast/Valleys...Stratus 20-50 sm inland, with bases 1700-
2500 ft msl, tops around 2500-2800 ft msl, and areas of vis 3-5 sm
in the inland valleys, will continue to clear to the coast through
1900 UTC. Marine layer inversion strength of 7 deg C. 1900-22/0000
UTC, P6SM vis and FEW clouds AOA 10000 ft msl, except for possible
BKN cigs 2000-2800 ft msl within a few miles of the coast. 22/0000-
1500 UTC, stratus will re-develop and move inland 15-20 sm, with
bases around 1200-1700 ft msl, tops around 1800-2200 ft msl, and
areas of vis 3-5 sm along higher coastal terrain/mesas.

Mountains/Deserts...FEW-SCT clouds AOA 10000 ft msl and P6SM vis
through Tuesday morning.

&&

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

&&

.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/JMB
AVIATION/MARINE...Harrison



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