Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 211106
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
406 AM PDT Sun May 21 2017

.SYNOPSIS...
Through Tuesday...weak onshore flow will bring a slow cooling
trend for coastal and western valley areas...while strengthening
high pressure aloft will continue slow warming farther inland
through Tuesday. Patchy low clouds and fog near the coast early
this morning will increase in coverage and spread a little farther
inland each night. Slightly cooler on Wednesday as high pressure
aloft begins to weaken. For Thursday and Friday...a low pressure
system over the interior western states will bring stronger
onshore flow with cooling to below average high temperatures...
significant deepening of the marine layer...and periods of strong
gusty southwest to west winds in the mountains and deserts.
Warming for inland areas next weekend...while the marine layer
keeps coastal temperatures near average.

&&

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

.SHORT TERM (Today through Tuesday)...
Satellite imagery shows a few patches of stratus developing just
off the coast with greater coverage beyond the offshore islands.
Higher resolution models show some increase in stratus coverage
just off the coast past sunrise with the stratus extending locally
inland near the coast. Aircraft soundings Saturday evening showed
a very shallow and strong marine inversion for Orange and Los
Angeles County coastal areas with the marine layer a little deeper
for southern San Diego County with the inversion base around 1000
feet. Any stratus near the Orange County coast early this morning
could be in the form of dense fog with that a little less likely
along the central and southern San Diego County coast.

Weak onshore flow has returned for coastal areas. Slow deepening
of the marine layer the next few days will result in greater
stratus coverage each night with the stratus spreading a little
farther inland each night. The stratus is expected to spread a
little farther inland into coastal areas tonight into Monday
morning...and into portions of the western valleys Monday night
into Tuesday morning. Cooling near the coast today...will spread
slowly inland into portions of the valleys for Monday and Tuesday.

Farther inland...strengthening high pressure aloft along the
California coast will bring continued slow warming into Tuesday
with high temperatures for Tuesday for inland areas 10 to locally
15 degrees above average. High temperatures in portions of the
lower deserts on Tuesday could be around 110...close to meeting
excessive heat warning criteria for portions of the Coachella
valley.

&&

.LONG TERM (Wednesday through Saturday)...
Slow cooling is expected for all areas on Wednesday as high
pressure aloft begins to weaken. Continued slow deepening of the
marine layer will allow coastal low clouds and fog to spread a
little farther inland into the western valleys on Tuesday night
into Wednesday morning.

For Thursday and Friday...low pressure over the interior western
states will bring stronger onshore flow with significant
deepening of the marine layer for Thursday into Friday. Coastal
low clouds are expected to spread into the far inland valleys on
Thursday morning...and onto the coastal mountain slopes on Friday
morning. Greater cooling is expected for Thursday into Friday with
Friday high temperatures for inland areas around 10 degrees below
average.

For next weekend...high pressure aloft will return near the West
Coast with a warming trend for inland areas. The marine layer will
keep coastal high temperatures near average with the marine layer
becoming shallower through the weekend with night and morning
coastal low clouds and fog not extending as far inland.

&&

.AVIATION...
210900Z...Patchy fog along the immediate coast may develop 12-15Z,
but unlikely to reach any of the coastal airports. Dense fog is more
likely to develop along the coast and up to 5-10 inland after
22/06Z. CIGS below 500 ft MSL and VIS 1SM or less possible at KSAN,
KCRQ, and KSNA. Otherwise clear with unrestricted vis through Monday
morning.

&&

.MARINE...
There is a small chance of patchy dense fog developing over the
coastal waters this morning. Dense fog will be more likely tonight
into Monday morning and again Monday night into Tuesday morning. No
hazardous marine weather is expected Tuesday afternoon through
Thursday.

&&

.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...SS


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