Scientific Forecaster Discussion
Southwest California area forecast discussion
National Weather Service Los Angeles/Oxnard California
1105 am PDT Friday may 29 2015
..updated aviation discussion...
Above normal temperatures are expected for inland areas through the
weekend as high pressure moves overhead. Temperatures will return to
near normal next week as a moisture starved frontal system
approaches late Sunday...then a broad trough of low pressure
develops. There is a good chance of night through morning low clouds
and fog for coastal areas and some valley areas through next week.
Short term (today-sun)...upper level high pressure system building over Southern
California today through Saturday...with moderate onshore flow continuing near the
surface. Satellite imagery showing a late surge of low clouds and fog into some of
the valley areas this morning but is starting to burn off as of 9 am. Acars sounding
and pilot reports showing marine layer depth ranging between 1500 and 2000 feet this
morning across the la basin. With rising heights and thicknesses...inland areas
will likely nudge upward a couple of degrees today. Warmest locations
in the San Fernando and Santa Clarita valleys should climb to around 90 degrees
today while the Antelope Valley tops out in the middle 90s. Areas closer to
the coast will likely show little change as the steady marine layer influence and
onshore flow continues. Some low clouds may linger across some of the immediate coastal
areas the next couple of afternoon due to strengthening marine inversion. As
indicated in previous discussion...still on track to see shallower marine layer depth
over the weekend. Saturday will likely be the warmest day of the week for many locations
as 950 mb temperatures and thicknesses peak across inland areas.
*** From previous discussion ***
By Sunday...the ridge axis will have been replaced with a broad upper
trough associated with a cutoff low just of the northern California coast.
The marine layer is expected to deepen in advance of the trough...which
will help to cool most areas a few degrees north of Point Conception...while the
valleys of la/vtu counties will be similar or a degree or two
Long term (mon-thu)...both the GFS and European model (ecmwf) are indicating a
persistent upper trough pattern across California through most of
the week. Expect modest widespread cooling through Wednesday...with
more significant cooling on Thursday. The marine layer will deepen
up allowing for stratus to reach the coastal valleys most night
through mornings. Not expecting any precipitation...but there could
be some early morning patchy local drizzle over la/vtu County coast
and valleys...with cooler than normal high temperatures.
At 1700z the marine layer depth at klax was around 2300 feet deep. The
top of the inversion was around 3900 feet with a temperature of 22
Moderate confidence in 18z tafs...with low MVFR conds at most
coastal locations...except IFR at ksba. Expect slow burnoff for
portions of the central coast and near pt Conception southeastward to koxr
this afternoon. Similar low cloud pattern expected tonight into Sat
morning...although at this time not expecting low clouds in the l.A.
Valleys. However...there is a 30% chance that this will occur.
Klax...moderate confidence in 18z taf. Expect haze to linger through
20z as low clouds remain nearby...with a 10% chance MVFR ceilings will
return periodically through 22z. For the overnight period...expect
low MVFR/IFR ceilings. IFR conds could persist longer than forecast.
Kbur...moderate confidence in the 18z taf. VFR conds expected at
least through late this evening. There is a 30% chance that low
clouds will bring IFR conds to the site after 09z.
For the outer waters...moderate confidence that northwest Small Craft Advisory winds
will continue through today. Although winds may diminish somewhat
for a few hours starting late morning...feel that they will increase
in the middle-afternoon and persist through late tonight. Otherwise
winds expected to be generally 10 to 20 knots over the outer waters.
Across the inner waters...fairly high confidence winds will remain
below Small Craft Advisory levels through Monday.
Small Craft Advisory (see laxmwwlox).