Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 241521
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
821 AM PDT Sat Jun 24 2017

.SYNOPSIS...
High pressure aloft will continue the hot weather far inland this
weekend, while a marine layer and onshore flow keep coastal and
western valley areas mild, with periods of nocturnal low clouds and
fog. The clouds may linger along the coastal strip through the
afternoon. High pressure aloft will weaken and move to the south
next week as a pair of low pressure systems move inland to the north
through Wednesday. This will deepen the marine layer and drop high
temperatures to average or below for late June. Strong rip currents
and higher than normal tides will prevail into this evening.

&&

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

Satellite imagery this morning showed an extensive marine stratus
sheet offshore, extending inland over the western valleys of San
Diego County. Farther to the north, the lower clouds were obscured
by high clouds drifting NW. The 12Z Miramar sounding had a 16+
degree C inversion based near 1350 FT MSL and peaking at 3700 FT AGL
at 31.5 degrees C. The inversion had lowered some 500 FT from
yesterday, but was nearly saturated below 1800 FT. Dew point
depressions were low from 20K-25K FT, corresponding to the higher
clouds that were prevalent early in the morning. Surface pressure
gradients to our local deserts were 4-7 MBS onshore. Peak wind gust
reports have been in the 30-35 MPH range early this morning near the
passes, otherwise mostly below 25 MPH.

Based on the sounding this morning, June may live up to it`s
reputation today. The thick low-level saturated layer my be
difficult to clear over large areas of the coastal strip and inland
for several miles. If the clouds prevail...it will keep temperatures
today below values observed yesterday, and slightly below forecast
in these areas. Meanwhile, farther inland above the marine
inversion, afternoon temps will likely be a few degrees higher, due
to the lower inversion. Otherwise, no changes to the forecast this
morning.

From previous discussion...


.SHORT TERM (Today through Monday)...
High pressure aloft centered over southern Arizona and northwest
Mexico will bring slow warming for inland areas into Sunday. High
temperatures for inland areas are expected to peak on Sunday...
around 3 to 5 degrees cooler than the peak of the heat this past
Tuesday and Wednesday. This will still push hottest high
temperatures in the lower deserts to around 118...near 112 in the
upper deserts...and near 106 in the corridor from Lake Elsinore to
Hemet in the Inland Empire. High pressure aloft is expected to
begin weakening on Monday with a few degrees of cooling for inland
areas.

Water vapor imagery shows a cyclonic circulation early this
morning over the eastern Pacific...somewhat to the west of Point
Conception. This is drawing mid level moisture toward the
northwest...mostly across the coastal waters of Southern
California into adjacent portions of Southern California. This
moisture is quite elevated...mostly centered around 500 mb. There
is also some weak elevated instability off the coast...mostly
centered near and to the west of the offshore islands. There have
been a few lightning strikes overnight with this band of
moisture...mostly around 60 miles off the coast of northern Baja.
The mid level moisture and clouds should gradually decrease from
south to north during the afternoon.

The marine layer remains near 1500 feet deep early this morning
with widespread stratus over the coastal waters extending into
inland orange County and the far western valleys in San Diego
County. The marine layer may become a little shallower the next
two nights with the stratus not extending quite as far inland.
Afternoon clearing may continue to be slow or limited at
times at the beaches...mainly for portions of the San Diego
County coast.

&&

.LONG TERM (Tuesday through Friday)...
Slow cooling will continue for Tuesday and Wednesday followed by
minor day to day fluctuations into next weekend with high
temperatures for inland areas returning to near average for
Wednesday into next weekend. The local workstation WRF nest of the
GFS shows a weak eddy at times for Wednesday through Friday. This
is expected to bring slow deepening of the marine layer with night
and morning coastal low clouds and fog extending into portions of
the inland valleys.

&&

.AVIATION...
241512Z...Stratus 15-20 sm inland, with bases 600-1000 ft msl, tops
1700-2000 ft msl and areas of vis 2-5 sm, will likely clear to
within 3 sm of the coast through 1900 UTC. Very strong marine layer
inversion of 16 deg C this morning. 1900-25/0000 UTC, primarily P6SM
vis and SCT-FEW clouds AOA 15000 ft msl, except within 3 sm of the
coast where BKN-OVC clouds 1000-2000 ft msl are likely to linger.
This could result in KSAN and KCRQ struggling to clear again today.
25/0000-1500 UTC, stratus re-developing and moving inland 10-15 sm,
with bases around 300-700 ft msl, tops around 1200-1700 ft msl,
areas of vis 2-5 sm, and local vis down to around 1/4-1/2 sm along
higher coastal terrain/inland mesas. Confidence in cig heights/vis
is moderate.

Mountains/Deserts...SCT-BKN clouds AOA 15000 ft msl becoming FEW-SCT
after 25/0000 UTC. P6SM vis continuing through Sunday morning.

&&

.MARINE...
A weak wave with with instability aloft will lift north off the
coast of Southern California this morning, bringing a slight chance
of thunderstorms to the outer coastal waters through late morning.
Cloud-to-water lightning will be the main hazard. Little to no
precipitation is expected with any storms that do occur. The
thunderstorm threat will dissipate by early afternoon.

Northwest wind gusts over the outer waters may reach 20-25 kt during
the afternoons and evenings Sunday through Tuesday, potentially
resulting in conditions hazardous to small craft.

&&

.BEACHES...
High tides will reach 7+ ft again this evening. Tides this high may
result in minor tidal overflow at low lying beaches. The Beach
Hazards Statement continues through 11 PM this evening. High tide
will fall below 7 feet Sunday, lowering the tidal overflow threat.


&&

.SKYWARN...
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Excessive Heat Warning until 9 PM PDT Monday for Coachella
     Valley-San Diego County Deserts-San Gorgonio Pass Near
     Banning.

     Heat Advisory from 10 AM to 9 PM PDT Sunday for Riverside County
     Mountains-San Bernardino County Mountains-San Bernardino
     and Riverside County Valleys-The Inland Empire-San Diego
     County Mountains-Santa Ana Mountains and Foothills.

     Excessive Heat Warning until 9 PM PDT Sunday for Apple and
     Lucerne Valleys.

     Beach Hazards Statement through this evening for Orange County
     Coastal Areas-San Diego County Coastal Areas.

PZ...NONE.

&&

$$

PUBLIC...JAD/17
AVIATION/MARINE/BEACHES...Harrison


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