Scientific Forecaster Discussion
Southwest California area forecast discussion
National Weather Service Los Angeles/Oxnard California
1034 am PST Sat Dec 20 2014
Synopsis...a weak frontal system will bring isolated showers to
northern sections and the northern slopes through tonight. Gusty
northwest to north winds will affect parts of the region tonight
through Sunday night...then locally gusty northeast winds will
affect Ventura and Los Angeles counties Monday through Tuesday.
Building high pressure will bring a warming trend through midweek
before slightly cooler conditions arrive by Christmas day.
Short term (rest of today-mon)...plenty of moisture continues to
stream across California this morning in advance of the building
eastpac ridge. Very isolated and light showers are moving across
parts of slo County...paso measuring .01 in the last couple of hours
and a trace at Santa Maria. Went ahead and updated the forecast to
extend the slight chance probability of precipitation for mainly northern slo County into
the afternoon based on general 12z model concensus and statistical
guidance. Again...amounts will be very light...likely under a tenth
at most...and isolated at that. Also kicked up the sky cover across
southern sections given latest satellite imagery showing plenty of
middle and high cloudiness streaming across and to continue for today
into tonight. Temperatures have generally warmed at least several degrees
over readings at this time yesterday despite the continued cloud
cover...but thanks to the high pressure now building into the area
and increasing thickness. High pressure will continue to build into
the area as we switch to a drier north and northeast wind regime for
a while. Sunday will warm further as well as additional warming on
Monday when we fully go offshore. Current sky cover forecast for
Sunday may be too optimistic with so much high level moisture still
forecast to be streaming across. Should at least see clearer skies
by evening time.
Will take a close look this afternoon at the possibility of a Wind
Advisory for the I-5 corridor and possibly westward to the Santa
Ynez range for tonight. 12z models indicating borderline advisory
level north winds these areas tonight...but a better chance of
stronger winds tomorrow night...also possibly reaching down to the
sba South Coast.
***From previous discussion***
Long term (tue-fri)...a strong upper ridge over the region and
continued offshore flow should make for a rather warm day on Tuesday...with
plenty of sunshine...and daytime temperatures well above normal...likely
reaching or exceeding 80 degrees in the warmer locations in the valleys
and interior coastal plain. Locally gusty NE winds are expected over
l.A. And vtu counties. The upper high will begin to break down
on Wednesday...and offshore flow is expected to weaken. Still... expect
another fairly warm day...especially in the valleys. The ridge will
continue to break down on Thursday...with either zonal flow or a weak
trough across the region on Friday depending upon which model is
believed. The ec would suggest a slight chance of showers on Thursday. No
matter what...a cooling trend will occur...with temperatures down to
slightly below normal levels by the end of the week.
Middle/upper level ridge of high pressure centered west of the area
will shift east. Upper level moderate to strong northwest winds will
become strong north and middle level moderate northwest winds become
moderate north by 21/03z over the area. Relatively moist middle/upper
levels through 21/06z. Freezing level was approximately 9kft this
morning and will differ by plus 4kft Sunday morning.
Marine layer at lax at 1730z is none.
Klax...current sky/visibility conditions through 21/03z likely then
decreasing upper level clouds.
Kbur...current sky/visibility conditions through 21/03z likely then
decreasing upper level clouds.
Virtually certain - 95-100%
very likely - 80-95%
likely - 60-80%
chance - 30-60%
very unlikely - 20% or less
Small craft for hazardous seas and wind conditions from the outer
waters north of San Clemente Island to Point Conception and over the
entire area north of Point Conception will likely persist through
Sunday. The swells today were generated from a distant storm on
Tuesday from 290-300 degrees relative to Ventura County coast. The
distant swells will likely peak today but locally generated seas
will build tonight through Sunday and combined seas will remain
hazardous and greater than 10 feet through late Sunday. North and
northwest winds will likely increase tonight with local gusts in the
vicinity of the northern channel and there is a chance gales will
exist Sunday night and persist through Monday morning.
Surf will peak today along the central coast...with breakers 15
to 20 feet along exposed northwest facing shores. The water level is
expected to be around minus 1 foot at low tide this afternoon and
the impacts will be strong rip currents and minor beach erosion
through the afternoon. The surf will likely range 8 to 11 feet
tonight through Sunday and the water level is expected to be over 6
feet Sunday morning and some minor coastal flooding of low lying
areas is expected then.
An 18 second swell will continue to move through the bight from
290-300 degrees. The swell direction is not favored for widespread
high surf but high surf is expected in areas from Ventura to Point
Mugu and in the Santa Monica South Bay at times especially around
the time of high tides. Frequent and strong rip currents will likely
occur in the vicinity of the high surf.
coastal Flood Advisory (see laxcfwlox).
Small Craft Advisory (see laxmwwlox).
High surf advisory (see laxcfwlox).
High rip current risk (see laxsrflox).
Marine weather statement (see laxmwslox).
Gale watch (see laxmwwlox).