Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 201001
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
301 AM PDT Fri Apr 20 2018

.SYNOPSIS...
A low pressure system over the southwestern states will move east
with high pressure aloft and weaker onshore flow for Southern
California through early next week. High temperatures for inland
areas will warm to near average today...and to 5 to 10 degrees
above average for Saturday through Monday. The marine layer and
weak onshore flow will keep coastal temperatures near average with
areas of night and morning low clouds and fog. For Tuesday
through Friday...a low pressure system over the eastern Pacific
will move slowly towards the West Coast. This will bring slowly
increasing onshore flow and slow deepening of the marine layer
with night and morning low clouds and fog extending into portions
of the valleys. Slow cooling will spread into the valleys with
periods of gusty southwest to west winds in the mountains and
deserts.

&&

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

The low pressure system that moved through Southern California
Thursday is now centered across Arizona and Utah and continuing to
move to the east. Onshore lower level flow and northwest flow
aloft are continuing to weaken across Southern California early
this morning. Strongest gusts at Whitewater in the northern
Coachella Valley below the San Gorgonio Pass are still around 50
mph...but gusts elsewhere across the mountains and deserts of San
Diego and Riverside Counties are mostly less than 40 mph and
continuing to subside.

Aircraft soundings late Thursday evening showed the main
subsidence inversion aloft around 600 mb with multiple weaker
inversions below that. Satellite imagery shows patchy stratus
across the coastal waters into Orange County...and in a few inland
valley locations near the coastal mountain slopes. Higher
resolution models show some increase in coverage this morning past
sunrise across the inner coastal waters and adjacent coastal areas
of Orange and San Diego Counties with patchier coverage farther
inland to the lower coastal mountain slopes.

High temperatures will warm today...returning to near average. For
Saturday through Monday...high pressure aloft and weaker onshore
flow will bring additional warming with high temperatures for
inland areas 5 to 10 degrees above average. For coastal
areas...weak onshore flow and the marine layer will keep high
temperatures near average with areas of night and morning low
clouds and fog.

For Tuesday through Friday...a low pressure system over the
eastern Pacific will move slowly towards the West Coast with
slowly strengthening onshore flow. Slow cooling will spread into
the valleys as the marine layer slowly deepens with night and
morning coastal low clouds and fog extending into portions of the
valleys. The stronger onshore flow will bring periods of gusty
southwest to west winds in the mountains and deserts.

&&

.AVIATION...
200900Z...Coast/Valleys...Scattered to locally broken clouds will
continue through 16Z this morning. Bases will be around 1500-2500
feet msl. Local terrain obscuration on coastal slopes. Mostly clear
skies thereafter until patchy low clouds develop near the coast
overnight after 08Z with lower bases around 1000 feet msl.

&&

.MARINE...
No hazardous marine weather is forecast through Tuesday.

&&

.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...MM



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