Scientific Forecaster Discussion
Southwest California area forecast discussion
National Weather Service Los Angeles/Oxnard California
937 am PST Wednesday Dec 4 2013
cold air behind an exiting cold front will bring a hard freeze to
several interior locations each morning through Friday as well as
frost issues for some coast and coastal valleys. Temperatures will
plummet to well below normal levels through the period. A second
system may bring rain and snow showers to the area Friday night into
Short term (today-fri)...cold front has passed leaving behind
chilly temperatures today and lighter winds. Gradients trending strongly
offshore, and while we will have some locally gusty north to
northeast winds this morning, by afternoon winds in most areas
should be less than 15 miles per hour. Main issue through Friday is the cold
overnight lows which will drop well below freezing in many areas.
Freeze warnings are in effect for much of the interior and the
12z models continue to advertise a brief light rain event for most
of the area Friday night into Saturday morning. It's still taking an
inside track but models have been consistent last couple days
showing decent moisture below 10000 feet and a strong 150 knots
northwesterly jet driving the front through at a very fast clip. So
while there is a very good chance of rain across most of the area it
will be short lived and likely totaling a quarter inch or less for
most lower elevation locations. Upslope areas will naturally see two
to three times that amount. For the central coast rain should be
over by sunrise and for the la basin area precipitation should be tapering
off by around noon or before. Probability of precipitation will be raised further with the
***From previous discussion***
Long term (sat-tue)...
at this time both the European and GFS models are indicating some
precipitation pushing over the forecast area late Friday night and
Saturday. This trough will likely take an inside track once again
just brushing so cal. Therefore with little trajectory over the
coastal waters...precipitation should be mostly light in nature. Ahead of
the front in the warm sector...snow levels should be around 4000 to
4500 feet early Saturday...but as the trough pushes through...the snow
level will plummet down to around 2500 feet. The coldest temperatures will
occur when most of the moisture has pushed to the south and east of
the region. With so much cold air in place...the possibility of snow
flurries occurring across some of the interior valleys as well as
the Antelope Valley...Santa Monica Mountains and Santa Clarita
valley will not be out of the question. This area of precipitation will be
a quick hitter and should be out of the area by Saturday night or
early Sunday morning. There will likely be gusty northerly winds as
well with this cold front developing behind the front.
High temperatures will remain quite cold through the extended period as
norhterly flow aloft will persist across the region through Tuesday.
As skies become clear Sunday through Tuesday...low temperatures will continue
to be quite frigid. Not anticipating any low clouds as it will be
tough to start an inversion with such cold temperatures. Expect highs to
remain in the 50s and lower 60s across coast and valleys...with
colder temperatures for other locations.
Middle/upper level trough of low pressure centered over central
California will move south and over the area. Upper level strong
west southwest winds will become moderate northwest while middle level
moderate west winds become moderate northwest over the area after
05/16z. Freezing level was around 4.3kft this morning and will
change little through the period. Mixed weak onshore and offshore
pressure gradient through 05/02z and after 05/21z otherwise weak
Klax...current sky/visibility conditions very likely throughout period.
Chance winds through a layer 005-010 at 09012kt between
Kbur...virtually certain current sky/visibility conditions will persist.
Virtually certain - 95-100%
very likely - 80-95%
likely - 60-80%
chance - 30-60%
very unlikely - 20% or less
freeze warning (see laxnpwlox).
Wind Advisory (see laxnpwlox).
Gale Warning (see laxmwwlox).
Small Craft Advisory (see laxmwwlox).
High rip current risk (see laxsrflox).