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Area forecast discussion
National Weather Service San Diego California
921 am PDT Wed Jul 26 2017

Morning update...
coastal clouds are burning off this morning fairly rapidly with
mainly clear skies inland. 12z knkx sounding shows less atmospheric
moisture and elevated instability to work with today. Cannot rule
out a slight chance of showers/thunderstorms for this afternoon over
the highest mountains due to residual moisture there. The limiting
factor will be the environmental winds which are too strong to
support updrafts...so any storms that do occur will be short-lived.
No other changes were made this morning to the forecast.

&&

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...

Short term (today through friday)...

High pressure aloft centered over New Mexico will expand westward
slightly through Friday while a weak trough of low pressure off
the California coast brings drier southwest flow aloft. Mid level
monsoonal moisture will gradually decrease. The combination of
slightly stronger high pressure aloft and decreasing monsoonal
moisture will allow for slow warming through Friday with high
temperatures on Friday near to slightly above average.

Precipitable water values that had increased to more than 2 inches
early Tuesday morning with the Miramar sounding decreased to
around 1.75 inches late Tuesday afternoon. Instability on both
soundings was quite weak with only isolated thunderstorm
development near the mountains in the afternoon. Slow drying of
the mid level moisture will continue...with the atmosphere no
more than weakly unstable at times. Afternoon clouds near the
mountains will continue. Most likely there will be nothing more
than clouds near the mountains this afternoon...but there are
very small chances for an isolated shower or thunderstorm.

The marine layer is around 2200 feet deep early this morning. As
the mid level moisture has decreased...coastal stratus has become
more widespread and extends into the western valleys.

&&

Long term (saturday through tuesday)...
high pressure aloft will shift slowly northward with the flow
aloft becoming southeast to east across Southern California. This
will bring cooling to near average. A return of monsoonal
moisture will bring a chance of thunderstorms...mainly during the
afternoon and early evening...and mostly in the mountains and
deserts.

&&

Aviation...
261545z...coasts/valleys...low clouds with bases 1300-1800 ft mean sea level
beginning to clear at the inland extremities this hour. Expect
clearing inland by 17z, with only partial clearing along the coast
during the afternoon. Low clouds likely to spread inland again after
00z Thu, with similar bases.

Mountains/deserts...a few cu may develop over the mountain ridges
during the afternoon with bases around 8000 ft mean sea level. Otherwise mostly
clear with unrestricted vis through Thursday morning.

&&

Marine...
no hazardous marine weather is expected through Sunday.

&&

Beaches...
a south swell generated by Hurricane Hilary will bring high surf Fri-
Tue, peaking sun-Mon. Current projections are for surf of 5-7 feet
with sets to 10 feet along south facing beaches. A beach hazards
statement has been issued Fri-Tue 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.

&&

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

&&

Sgx watches/warnings/advisories...
California...beach hazards statement from Friday morning through late Monday
night for Orange County coastal areas-San Diego County
coastal areas.

Pz...none.

&&

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