Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Southwest California area forecast discussion 
National Weather Service Los Angeles/Oxnard California
340 am PDT Monday Oct 20 2014

Synopsis...

A trough of low pressure will bring cooler weather through Tuesday.
There will be some locally gusty northwest winds late tonight
through Tuesday night following the passage of this system. A
warming trend will begin on Wednesday as weak offshore flow
develops...with above normal temperatures expected later this week.
Cooler weather likely returns next weekend with the next low
pressure system.

&&

Short term (today-wed)...
marine layer is 1800 deep. The capping inversion has strengthen over
the last 12 hours. Gradients are onshore and trending onshore. A
weak surface front and its parent trough are approaching the area from the
west. All of this should add up to a decent stratus event. Currently
however this has only happened across the central coast. South of
Point Conception the clouds are much more disorganized. Over the
past however there are signs that the low clouds are finally
blossoming and expect most coastal and valley locations will see plenty
of low clouds by sunrise. The marine layer is too thin to support
drizzle and removed that from the central coast forecast. Skies will
turn partly this afternoon as the remnants of the front wash out
overhead. Heights will fall through the day and the onshore flow will
increase so it will be a cooler day.

High pressure builds into the Central Valley tonight and cooler air
moves in behind the front. There will be a low end north wind event
with the sba South Coast...the I-5 corridor and the Lake Casitas
region all seeing some gusty north winds. There will be a few
advisory level gusts but for the most part this event will fall just
below advisory criteria. North of Point Conception the cool air
behind the front will wipe out the inversion and thus no low clouds
for the central coast. The north winds will keep most of the area
south of Point Conception cloud free but the Long Beach area should
be far enough away from the winds to allow for some low clouds there.

A sunny and breezy day Tuesday as the trough passes over the region.
The interior regions will cool due to lower heights but the morning
offshore flow will allow for some warming across the coasts and
valleys. The central coast will have some decent northeast winds which
will be good enough to create some maximum temperatures in the upper 70s and
lower 80s. It will be a breezy day in the mountains and the Antelope
Valley as well.

More north winds on tap Tuesday night. Still looks just below
advisory criteria. The only change is that the sba sundowner winds
will be a little more focused on Montecito rather than Gaviota.

The barest of ridges probability of precipitation up on Wednesday. The offshore flow should
keep the region low cloud free. Maximum temperatures will bump up everywhere
save for the central coast which will see temperatures similar to tuesdays
readings.

Long term (thu-sun)...
extended models are now in better agreement and all indicate that the
ridging will continue and will peak Thursday. By Friday the ridge
will be slowly pushed to the east in the face of a large upper trough
approaching from the west. The trough will pass over the region during
the weekend and then by Monday a Little Ridge will pop up and move
into the area.

Temperatures will peak Thursday and then cool slightly Friday before
cooling fairly sharply over the weekend. Maximum temperatures will rebound to
seasonal normals on Monday.

The low clouds will most likely stay away Thursday and Friday and there will
likely be pretty good night through morning low clouds across the
coasts and valleys Sat night through Monday morning. Friday night and
Saturday morning is the question mark. Right now it looks like it
will be a mostly clear morning...but for sure not a slam dunk.

&&

Aviation...

20/06z...

Marine layer depth at klax at 0515z... 1800 feet with a weak
inversion in place. Inversion top is at 4100 feet with a temperature
of 20 degrees c.

Overall...low to moderate confidence in the 06z tafs due to
uncertainty with the marine layer location... timing... and
intensity. The inversion on the klax sounding remains weak and the
inversion on the kvbg sounding is not much stronger. These are
better conditions for a marine intrusion at coastal and adjacent
inland sites than they were last night but still a concern for
developing and keeping low ceilings in the tafs. A bit more development
has already occurred along the coast so will go with it again
tonight but there is a Forty Five percent chance that the ceilings would
lift by daybreak at any given location/S. Another chance at a
marine intrusion again the following night. Otherwise and
elsewhere... VFR conditions will prevail.

Klax...low to moderate confidence in the 06z taf due to uncertainty
with the marine layer timing and intensity. The inversion on the
klax sounding remains weak and the inversion on the kvbg sounding is
not much stronger. These are better conditions for a marine
intrusion than they were last night but still a concern for
developing and keeping low ceilings in the taf. A bit more development
has already occurred along the coast in general so will go with it
again tonight but there is a Forty Five percent chance that the ceilings
would lift by daybreak. Another chance at a marine intrusion again
the following night. Otherwise... VFR conditions will prevail.

Kbur...low to moderate confidence in the 06z taf due to uncertainty
with the marine layer timing and intensity. The inversion on the
klax sounding remains weak and the inversion on the kvbg sounding is
not much stronger. These are better conditions for a marine
intrusion than they were last night but still a concern for
developing and keeping low ceilings in the taf. A bit more development
has already occurred along the coast in general so will go with it
again tonight but there is a Forty Five percent chance that any ceilings
that develop would lift by daybreak. Another chance at a marine
intrusion again the following night. Otherwise... VFR conditions
will prevail.

&&

Marine...19/800 PM...

Widespread Small Craft Advisory winds expected by Monday evening
across the outer waters...with a chance of gale force winds. As a
result...a gale watch has been posted for the outer waters. There is
a chance that the gales will persist through late Tuesday
night...with the strongest winds likely from Point Sal to San
Clemente Island. Swells within 285-300 degrees relative to the Los
Angeles County coast will build Monday night through Tuesday then
gradually subside Tuesday night through Wednesday. The locally
generated seas and distant arriving swells will combine and create
hazardous seas Monday through Wednesday.

&&

Lox watches/warnings/advisories...
high surf advisory (see laxcfwlox).
High rip current risk (see laxsrflox).
Gale watch (see laxmwwlox).

&&

$$

Public...rorke
aviation/marine...kj
synopsis...sukup

Www.Weather.Gov/losangeles

National Weather Service Glossary of Abbreviations