Scientific Forecaster Discussion
Southwest California area forecast discussion
National Weather Service Los Angeles/Oxnard California
315 am PST Thursday Dec 5 2013
Chilly temperatures will bring frost and freezes to several areas
through Friday morning. Another fast moving cold front is expected
to bring rain and mountain snow to the central coast and spread
southward late Friday night into Saturday. Another round of hard
freezes may follow the front Sunday and Monday mornings. Expect a
gradual warming trend by middle week.
Short term (today-sat)...latest satellite imagery indicated mostly
clear skies across the forecast area except for pesky stratocu
lingering across portions of la County this morning....mainly across
the mountains and Antelope Valley. The main story over the next
couple days will be the continued sub-freezing conditions over much
of the interior areas and central coast as well as freezing or near
freezing conditions across most other locations...with the exception
of the la County basin and San Gabriel valley.
At this time most areas under freeze warnings are verifying nicely.
However...the Antelope Valley has actually warmed a few degrees from
a few hours ago thanks to the stratocu deck that developed. This
cloud deck will help prevent maximum radiational cooling. As of 2
am...low temperatures have been between 24-32 degrees. By the looks of
it...this stratocu deck thats around 6000 feet high should stick
around into the morning hours.
The upper trough axis continued to hang over Orange/San Diego
counties this morning. Therefore the best cyclonic flow remains to
the south which is why partly to mostly cloudy skies are persisting
over San Diego and Orange counties. Skies should remain mostly sunny
over most of the forecast area today...with maybe a few flat
stratocu lingering over the San Gabriel Mountains or even the la
County valleys. Maximum temperatures will be a degree or two cooler across most
areas today as the Canadian air mass continues to filter in across
For Friday...another upper level disturbance will begin to drop
south into northern California from Washington state. There will be
increasing clouds ahead of the approaching trough. High temperatures will
be similar to Thursday with a degree or two of warming. Freeze
warnings will continue to be in effect for late tonight into Friday
morning for the same areas as this morning. Not expecting clouds
across the Antelope Valley tonight...so expect low temperatures to make it
down to the teens. Will be issuing another round of frost advisories
for the same areas as well valid for early Friday morning.
Both the GFS and NAM-WRF have slowed down the approach of a cold
front that will initially affect the central coast late Friday night
into Saturday morning. The latest models show a better organized
band of rain moving through the entire forecast area. Rain should
begin for areas S of Point Conception early Saturday morning...with
the bulk of rain and snow pushing into Ventura and la counties by
late Saturday morning through the afternoon hours. This will be a
fast moving system and areas north of Point Conception should be mostly
dry by Saturday evening...with some showers lingering over la County
through the overnight hours. Snow levels will start around 4000 to
4500 feet as the warm sector moves across the area...but as the front
pushes to the southeast...much colder air behind the front will help to
lower snow levels to 3000 feet...locally down to 2500 feet by late
Saturday afternoon. Rain and snow will linger over la County
Saturday night into early Sunday morning. There will be gusty
westerly winds ahead of the front early Saturday morning affecting
the Antelope Valley and adjacent mountains...then turning northwest
to north by late Saturday afternoon. This could make for hazardous
driving conditions across the I-5 corridor as well as Highway 14 due
to the snow and blowing snow expected at the lower levels.
Long term (sun-wed)...in the wake of the exiting cold front...temperatures
will become quite cold once again on Sunday and another round of
hard freezes will be likely Sunday and Monday mornings. Since
interior areas will have already experienced at least two hard
freezes this week...the only areas that will likely need warnings or
advisories will be the coast and coastal valleys. High pressure will
build in from the west Tuesday and Wednesday which will help high temperatures to
rebound to around normal with weak offshore winds through the
period. Not expecting the marine layer stratus to make an appearance
Overall...high confidence in 12z taf package. VFR conds expected all
sites through the period due to cold and dry air mass. There will be
VFR ceilings across la County through at least 18z this morning. No
significant wind issues.
Klax...high confidence in 12z taf. 10 percent chance that NE winds
could reach 10 knots through 16z.
Kbur...high confidence in 12z taf.
freeze warning (see laxnpwlox).
Frost advisory (see laxnpwlox).
Small Craft Advisory (see laxmwwlox).
Marine weather statement (see laxmwslox).