Scientific Forecaster Discussion
Southwest California area forecast discussion
National Weather Service Los Angeles/Oxnard California
856 am PDT Friday Sep 4 2015
Moderate onshore flow will weaken over the Labor Day
weekend...leading to The Retreat of morning clouds to some coastal
locations Sunday through next Friday. An upper level high building
into the region next week will be responsible for a gradual warming
trend with above normal temperatures away from the coast by Thursday.
Short term (today-sun)...latest amdar soundings out of lax indicate
marine inversion based around 4500 feet while Vandenberg shows depth
around 2500 feet. With such a deep inversion...a broken to overcast
stratus deck has pushed into the coastal slopes. By early this
afternoon...stratus should dissipate and a sunny/mostly sunny
afternoon is expected for all. Due to deep inversion...slightly
stronger onshore flow and cooler boundary layer...today will be a
bit cooler than Thursday.
Quick look at initial 12z model data indicates forecast thinking in
the short term is still on track. Upper trough will linger over
California through Saturday with a deep marine layer remaining in
place. However with some increase in 500 mb heights and weaker onshore
gradeints...stratus tonight should be a bit less widespread with
less inland penetration. Temperatures on Saturday should be a bit
warmer...but still below normal for early September
For Saturday night/Sunday...still looks like a weak offshore flow
will develop. Not a lot of upper level support...so any northeast
winds should remain somewhat localized and below advisory levels.
However...the offshore flow should be enough to greatly limit the
stratus...confining stratus to southern Los Angeles County. Also the
offshore flow will allow for a noticable jump in temperatures with
locales away from the coast climbing into the middle 80s to lower 90s.
Long term (mon-thu)...for Monday-Tuesday a very weak upper trough will
reach into Southern California and push back the upper ridge
briefly. There will be a return of low clouds and patchy fog across
coastal and a few coastal valleys with continued gradual warming
inland. By Wednesday and Thursday...the upper ridge builds back once
again and strengthens. This will allow for more significant warming
with high temperatures a tad above normal for inland areas.
Aviation...at 1030z...then marine layer at klax was about 3500 feet
deep. The top of the inversion was around 5000 feet with a
temperature of 17c.
Widespread MVFR to VFR ceilings in all coastal and valley areas S of pt
Conception...with clouds to the coastal slopes. IFR conds were
occurring in the foothills and on coastal slopes. On the central
coast and in the Santa Ynez Valley...conds were mostly MVFR. Expect
skies to clear in most areas by late morning. Expect similar conds
tonight/Sat morning...maybe the marine layer will be more shallow.
Small Craft Advisory conditions for northwest winds will very likely
persist from Piedras Blancas to San Nicolas Island including the 0-
10 nm from piedras to Point Sal through early Saturday morning.
There is a chance the Small Craft Advisory conditions will continue through Sunday
morning. A 20 second period or greater south swell is expected to
build through the weekend to 3 to 4 feet and then persist through
early next week. The long period swells will likely generate extra
surging and currents which may be hazardous to anchored boats.
Beaches...beachgoers should be aware of potentially hazardous surf
along exposed south and southwest facing shores this weekend through
next week Tuesday. An increasing risk of rip currents is expected
starting Friday afternoon as the long period swell begins to
arrive...and it is expected that a high rip current risk will be
issued Sunday through Tuesday.
Small Craft Advisory (see laxmwwlox).
Beach hazards statement (see laxcfwlox).