Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 201647
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
947 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 this afternoon...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...

...Update...

A warmer day is set for today with plentiful sunshine through just
a few clouds from Orange County to the San Bernardinos as high
pressure aloft re-gains control. No changes are needed to the
forecast this morning. See previous discussion below for further
forecast details.

...Previous Discussion (Issued at 301 AM PDT Fri Apr 20 2018)...

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...
201630Z...Coast/Valleys...FEW-SCT low clouds with bases mostly abv
3000 ft MSL through this afternoon. Patchy low clouds return to the
coastal areas after 02Z Sat, increasing in coverage after 07Z with
bases around 1000 ft MSL. Confidence in impacts at coastal TAF sites
is low.

&&

.MARINE...
No hazardous marine weather is expected 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...Gregoria (Update)/17 (Prev Discussion)
AVIATION/MARINE...PG



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