Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 210300

Area Forecast Discussion
National Weather Service San Diego CA
800 PM PDT Sun Aug 20 2017

Low pressure off the SoCal Coast will keep the weather seasonably
cool for mid-summer, and support considerable marine cloud
development nights and mornings. Temperatures will remain below
average into midweek, with modest warming expected during the latter
half of the week as the low dissolves and the marine layer thins.
There remains a slim chance for a few showers and thunderstorms over
the mountains and high desert on Monday, otherwise fair and dry
weather will prevail. Warmer early next week as high pressure builds
over the West.



Marine clouds were forming inland along the Coast at 8 PM PDT. A few
mid/high clouds were scattered near the mts, but more widespread
farther to the east over the Lower Colorado River Valley and north
through Death Valley. Elsewhere over was clear. The 00Z
Miramar sounding had increasing SSE winds from 25-30KT from about
4000 to 15K FT but still quite dry and stable. There was a 5 degree
C inversion based near 2500 FT MSL. This was about 600 FT higher
than yesterday evening. Surface pressure gradients were holding
around 6-8 MBS onshore KSAN to the local deserts, supporting west
winds of 15-25 MPH with gusts 25-35 MPH in wind prone mts/desert

Precip chances on Monday still look very slim for northern areas of
the CWA, due to dry and stable atmosphere. But models still show a
decent shortwave rotating inland around the low offshore, so will
keep a slight chance in there. No forecast changes.

From previous discussion...

The weak low pres trough continues just off the coast of Southern
California with an unseasonably deep marine layer remaining in
place. Coastal low clouds will develop this evening over the coastal
waters and push inland well into the western valleys overnight. Low
clouds will linger near the coast through late Monday morning,
putting a damper on the eclipse viewing opportunities there, but
away from the coast conditions will be mostly sunny by the time of
partial eclipse in Southern California.

A weak shortwave will swing across SE California Monday afternoon
and could generate a few showers and thunderstorms over our
northern mountains, with marginal mid level moisture there,
mainly affecting San Bernardino and Riverside Counties. Any
convection will quickly die off after dark.

Continued cool with unseasonably troughy pattern along the coast
for much of the new week with temperatures generally settling to
around normal levels.

Some ridging may develop towards the end of the week and into next
weekend, bringing a slight warmup along with a bit of mid level
moisture on a return flow pattern from the SE. No weather was
added to the forecast however during this cycle as the chances are
too low at this time.


210300Z...Coast/Valleys...Low clouds with bases near 2000 ft msl and
tops near 3000 ft msl will continue to push inland through 14Z.
Clouds should reach the coastal foothills, and visibility will be
limited to 3 SM or less near higher terrain. Clearing to the coast
on Monday is anticipated between 17Z and 19Z, with SCT low clouds
lingering along the coast and over the coastal waters throughout the
afternoon. Afternoon sea breezes will be light. Low clouds will
return to coastal area after 01Z on Tuesday with bases between 1500
and 2000 ft msl.

Mountains/Deserts...Mostly clear skies and unrestricted visibility
through Monday.


No hazardous marine weather is expected through Friday.


Minor tidal overflow will be possible this evening due to high tides
near 6.7 ft and elevated surf (3 to 5 ft). Thus a Beach Hazards
Statement remains in effect through midnight.


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


CA...Beach Hazards Statement until midnight PDT tonight for Orange
     County Coastal Areas-San Diego County Coastal Areas.



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