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Southwest California area forecast discussion 
National Weather Service Los Angeles/Oxnard California
830 PM PDT Friday Jul 25 2014

high pressure will remain anchored over the Desert Southwest through
the middle of next week resulting in continued seasonal to above
normal temperatures. High clouds will stream through the area with a
slight possibility of a thunderstorm over the san Gabriels mainly
Sunday afternoon. Overnight low clouds and fog are expected along
most coastal areas.


Short term (tonight-mon)...
Southern California will remain on the western periphery of a large
upper level high pressure system that will remain anchored over the
deserts southwest and Texas through the weekend. Some middle level subtropical
moisture has moved into Southern California today rotating around the
periphery of the high pressure system. Thunderstorm activity remained
to our south and east across san diego's forecast area...but
considerable amount of middle and high level clouds streamed into Los
Angeles and Ventura counties. The influx of middle and high level clouds
combined with increasing onshore flow to bring cooling to much of the
forecast area today. In fact...some of the valley areas saw over 10 degrees
of cooling from yesterday's scorcher. However...the Antelope Valley and
a few mountain locations were still able to reach triple digits

Similar temperatures expected through the weekend...with a continuation
of gusty onshore winds in the mountains and deserts. Strongest winds
will remain focused across the foothills of the Antelope Valley...where
gusts up to 45 miles per hour can be expected. In evening update...have increased
middle level cloud coverage a bit for overnight into latest
00z NAM continues to pump in a good amount of middle level moisture for
areas south of Point Conception. In fact...precipitable water values increase
to 1.2 to 1.4 inches for la/Ventura counties on Saturday afternoon.
However...model sounding showing most of this moisture above the 700 mb
level...and too much middle level cloudiness could inhibit formation of
deeper convection. Models soundings did show some weak cape and instability
for the local mountains on Saturday afternoon. In addition...00z NAM
indciated a weak vorticity maximum rotating into Ventura County on Saturday
which will have to be closely monitored. So most likely will see
some afternoon cloud buildups...however cannot totally rule out an
isolated storm. In evening update...have included some very minor
thunderstorm probability of precipitation of around 10 percent for local mountains on Saturday

*** From previous discussion ***

The one hiccup in the persistence forecast may be Sunday afternoon
and evening in the la and vtu County mountains and the Antelope
Valley. Some indications of some convective activity these areas
Sunday afternoon. Convective parameters not overly impressive other
than models indicating a possible short wave that rotates around the
south side of the high then rotates around and brushes our area on
Sunday. This will come into better focus with new model runs but
have kept the going forecast of a slight chance of thunder over the
eastern san Gabriels for now.

Long term (tue-fri)...the upper level high over the western U.S.
Persists through the long term. The one change is that it pumps up
into southwest Canada as opposed to the east-west elongated high
that it's been as of late. The European model (ecmwf) puts the high axis a little
further west...the result being around a 585 dm thickness over socal
on wedn afternoon versus the 579 dm thickness forecast by the GFS. This
would result in warmer temperatures midweek. Discounting the European model (ecmwf) for now
in part since the operational GFS is in line with the GFS ensembles.
So going with the GFS...not much change in sensible surface weather
from day to day. Temperatures just above average valleys and desert
and at or just below average coastal areas. Onshore gradients will
change little each day so expect some overnight low clouds and fog
along the coasts...but at this time with not much inland extent. We
appear to be right on the western edge of any monsoonal flow so
difficult to tell at this point when we may get enough moisture this
far west for any convective activity. At this time have not included
any mention of it during this period.


marine layer clouds expected to be more widespread tonight across the
coastal plain as onshore flow strengthens and marine layer depth
increases. Latest acars data showing marine layer depth around 1000
feet across the la basin late this afternoon...but is expected to
deepen to between 1500 and 1800 feet by Saturday morning. In 00z taf
package...have moved up timing of IFR/low MVFR ceilings across many of
the coastal taf locations...and kept ceilings lingering to 18z-19z
time frame on Saturday. There is a 20 percent chance that IFR ceilings
could reach kbur and kvny by early Saturday morning. Also a 20 percent
chance of ceilings lingering into the afternoon hours across coastal taf

Klax...moderate confidence in the 00z taf. Low MVFR ceilings expected
to return overnight into Saturday morning...but there is a 20 percent
chance of ceilings lowering into IFR category briefly. There is also
a 20 percent chance of MVFR ceilings lingering into the afternoon hours
on Saturday.

Kbur...mostly VFR conditions through period...with exception of some
MVFR visibilities in haze early Saturday morning. There is a 20 percent
chance of brief IFR ceilings on Saturday morning.


Marine...25/900 PM.

There is a slight chance of shower and thunderstorm development across
southern coastal waters by Sunday. significant
weather is expected at this time.


Lox watches/warnings/advisories...




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