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742
FXUS66 KSGX 270317
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
817 PM PDT Wed Jul 26 2017

.SYNOPSIS...
High pressure across New Mexico and Arizona will expand westward
bringing slow warming and drying of monsoonal moisture through
Friday. The marine layer and weak onshore flow will keep areas
near the coast cooler with areas of night and morning low clouds
and fog extending into the far western valleys. For Saturday
through early next week...the high pressure will move slowly
northward with east to southeast flow aloft developing across
Southern California. This will bring cooling to a little below
average with a return of monsoonal moisture bringing a chance of
thunderstorms...mainly during the afternoon and early
evening...and mostly in the mountains and deserts.

&&

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

...Update...

Convection lessened today with a few tstorms over the Riverside
County mountains with a total of 11 lightning strikes. The
convection has since dissipated and a tranquil night is expected.
Dry air has continued to move into Southern California. The
evening San Diego sounding registered PW at only 1.13", down from
1.63" this morning. The drier air will be in place on Thursday
with no showers or tstorms forecast. No significant changes to the
forecast were made this evening. See previous discussion below for
further forecast details.

...Previous Discussion (Issued at 235 PM PDT Wed Jul 26 2017)...


Isolated showers and thunderstorms will continue this afternoon
with a marginal convective environment and low probability of
strong cells and flash flooding. This activity will diminish this
evening with the loss of daytime heating.

With a drier flow becoming established we expect Thursday through
Saturday to be dry. In addition the large area of upper level high
pressure will retrograde over the SW and reach California this
weekend. Temperatures will spike but relative humidity will be
lower in most areas.

Diurnally driven convection returns to the forecast beginning
Sunday and continuing through mid next week as return flow sets
up. A series of weak easterly waves should help increase
thunderstorm chances over the mountains and deserts Sunday or
Monday, Tuesday and Wednesday. It`s not looking like much of the
tropical moisture from the pair of hurricanes will be working up
into SoCal at this time.

&&

.AVIATION...
270212Z...Coasts/Valleys...Stratus will continue to develop and move
15-20 sm inland through 1500 UTC, with bases around 1300-1800 ft
msl, tops around 2000-2500 ft msl and local vis 3-5 sm. Forecast
marine layer inversion strength of 7 deg C at 1200 UTC. 1500-2000
UTC, stratus likely clearing to the coast, with P6SM and mostly SKC
then prevailing through Thursday afternoon except for possibly some
SCT-BKN clouds 1500-2500 ft msl lingering within 3 sm of the coast.
For areas beyond 20 sm from the coast, P6SM and mostly SKC will
prevail this evening through Thursday afternoon.

Mountains/Deserts...P6SM vis and mostly SKC through Thursday
afternoon.

&&

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

&&

.BEACHES...
Latest runs of the Wave Watch 3 are only showing the upcoming swell
generated by Hurricane Hilary only peaking at around 5 ft/13-15
seconds from 180-190 degrees late Saturday through late Monday.
However, at the same time, a longer period south swell (also from
180 degrees) will reach around 2-3 ft/18-19 seconds. These two
swells will likely combine to bring high surf of 5-7 FT with sets to
8 or 9 FT along south facing beaches of Orange county and Northern
San Diego county. A Beach Hazards Statement has been issued due to
the potential for high surf. The forecast surf heights could change
depending on the track and strength of Hilary, which is still
somewhat uncertain. The swells will also create strong rip and
longshore currents, resulting in dangerous swimming conditions.


&&

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


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement from Friday morning through late Monday
     night for Orange County Coastal Areas-San Diego County
     Coastal Areas.

PZ...NONE.
&&

$$

PUBLIC...Gregoria (Update)/Brotherton (Prev Discussion)
AVIATION/MARINE...Harrison