Scientific Forecaster Discussion
Southwest California area forecast discussion
National Weather Service Los Angeles/Oxnard California
937 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)...clear and chilly today and Friday.
Antelope Valley lows were warmer than expected this morning due to
some overnight cloud cover that wasn't anticipated but we shouldn't
have that problem tonight so lows in the teens look reasonable
there. Some other areas had some light offshore breezes this morning
that kept lows from dropping below freezing but offshore gradients
are weaker Friday so we shouldn't have that issue again either.
Not seeing too many changes with the Friday night/Sat system except
some uncertainty with the timing. That's to be expected with a 150kt
jet driving it, though I really do prefer the slightly earlier
timing on the GFS and yesterday's NAM given that strong jet. Will
almost certainly need a Winter Weather Advisory for the mountains
with low snow levels. Snow/water ratios will be much higher than
usual due to the cold air so accumulations will be higher than what
we normally would see with liquid equivalent amounts in the quarter
to half inch range.
***From previous discussion***
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
Middle/upper level trough of low pressure centered east of the area
will continue moving east while a trough over British Columbia
shifts south. Upper level moderate northwest winds will become
moderate west while middle level moderate west winds become light west
after 06/12z over the area. Freezing level was around 4kft this
morning and will differ by plus .4kft Friday morning. Mixed weak
onshore and offshore pressure gradient through 06/02z then weak
offshore between 06/02-06/18z and weak onshore thereafter.
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).
Frost advisory (see laxnpwlox).
Small Craft Advisory (see laxmwwlox).
Marine weather statement (see laxmwslox).