Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Southwest California area forecast discussion 
National Weather Service Los Angeles/Oxnard California
730 PM PST Friday Dec 26 2014

Synopsis...

High pressure building into the Great Basin will produce gusty
northeast winds for parts of the area through Saturday. Wind
sheltered areas will remain chilly at night through the weekend. A
large low pressure system may bring unsettled weather to the region
for the early and middle part of next week...along with more below
normal temperatures.

&&

Short term (today-mon)...update...

Not much to add to earlier discussion over the short term. Made a
few minor changes to high temperatures as this infusion of colder air
across the High Desert will not only help to drive the Santa Ana
winds once again late tonight into Saturday morning...but high temperatures
should be a tad cooler as well by a degree or two to around 59-60
for the la/vtu County valleys and lower 60s for the coast.

Earlier today...gusty north to northeast winds continued across the
usual wind prone passes and canyons as well as West Los Angeles.
High temperatures were mostly in the lower 60s along coastal areas while
inland areas were in the middle 50s to around 60. The Antelope Valley
saw highs in the upper 40s. Very brisk.

Latest 00z NAM-WRF is in and continued to show a strong Wind
Advisory event for the wind prone areas of la/vtu counties overnight
and into Saturday morning with wind gusts between 40 and 55 miles per hour for
most affected areas. There will be local gusts over 60 miles per hour as well
in a few elevated locations...including the Malibu Hills. With
another punch of cold air moving into the region..there will be
enough subsidence to bring gusty offshore winds to Catalina and The
Channel islands. Mariners should beware if taking anchor in east
facing harbors such as Avalon and Two Harbors overnight through Sat
morning.

Hard freeze warnings are in effect for the Ojai Valley and the
interior areas of slo County and Cuyama Valley in sba County. Temperatures
lowering to below 28 degrees for a few hours will occur. A freeze
warning is in effect for the Santa Ynez Valley and portions of the
sba central coast...especially around the Lompoc area where lows
will get down to around 29 degrees for a few hours early Sat
morning. And finally...a frost advisory has been issued for the slo
central coast. As mentioned previously...the Antelope Valley will
experience sub freezing conditions...but since they already had two
hard freezes earlier in late November...no freeze products will be
issued any longer through the winter months.

The earlier day forecaster did a nice job explaining the
scenarios possible during the long term period with the expected
cold upper low retrograding towards Southern California. Latest Middle
Range models have not come in with 00z runs yet. Still a few
question Marks with this next dynamic system.

***From previous discussion***

Satellite imagery showing Crystal clear skies this afternoon due to
offshore flow and subsidence on the backside of an upper-level
trough to our east. Surface high pressure building into the Great
Basin continues to result in NE winds for the parts of Ventura and
la County that are prone to Santa anas. Lax-dag strengthened to
-2.7mb early this morning...which has resulted in some marginal Wind
Advisory conditions in la and Ventura County through this afternoon.
The NAM has lax-dag strengthening to at least -5mb by tomorrow
morning...so the wind advisories will be extended through tomorrow
afternoon...although there will be a lull in the NE winds this
evening. NE winds should be a bit stronger tomorrow...so the Ventura
County coast will also added to the wind advisories.

With dewpoints continuing to fall overnight...many wind sheltered
areas will be just as cold or a couple degrees colder than last
night. The interior valleys of slo and sba County will once again
have a hard freeze warning. Additionally...the interior valleys of
Ventura County have been upgraded from a freeze warning to a hard
freeze warning for tonight...with the Ojai Valley being of
particular concern. The Santa Ynez Valley will once again have a
freeze warning. A freeze warning for the sba central coast was also
added for the Lompoc area...as well as any colder outlying areas. A
frost advisory was also added for the slo central coast.

Northwest flow aloft will persist through Monday with a long-wave ridge to
our west and a long-wave trough to our east. The surface high over
the Great Basin will weaken Saturday night into Sunday...which will
bring an end to the wind advisories for the NE winds in Ventura and
la counties. By Monday afternoon...surface pressure gradients will
start to turn offshore as a large upper-low starts to develop over
the northern rockies. As a result Sunday and Monday could be a
degree or to cooler...but really not much change overall. Maximum temperatures
for the coastal and valley areas will remain in the low-middle
60s...which is slightly below normal. Could also start to notice
some high clouds moving into the area on Sunday.

Long term (tue-fri)...

The forecast in the long-term remains fairly uncertain. No changes
were made to the forecast. In general...the models are in good
agreement that a strong 500mb low will develop somewhere near
Southern California between Tuesday and Wednesday...however there are some differences
in the placement and track of the upper-low. Basically there are
three possibilities. One...the upper-low develops off the coast and
gives socal the chance for some significant rain. Two...the
upper-low develop directly overhead...bringing a mix of showers
initially...followed by gusty winds as the upper-low moves east.
Three...the upper-low develops just to the east of the
area...setting up a powerful Santa Ana event. For what its
Worth...the 12z GFS, ECMWF, and Gem favor outcome two or three. The
GFS ensembles also seem to think the first outcome is less likely.
For now...forecast calls for a slight chance of rain for most of the
area Tuesday-Wednesday night. No matter which outcome
verifies...temperatures should be below normal much of next week.
Conditions should improve by Thursday and Friday as the upper-low
moves east.

&&

Aviation...27/0020z...

At 0015z...there was no inversion at klax.

VFR conds expected through the next 24 hours. Areas of gusty NE
winds will affect l.A. And vtu counties from later this evening
through Saturday morning. VFR conds expected everywhere.

Klax...high confidence in the 00z taf. VFR conds will continue
through 24-hour period. There is a 20-30 percent chance of northeasterly
winds reaching 8 to 10 knots Sat morning between 11z and 15z.

Kbur...moderate to high confidence in the 00z taf. VFR conds will
continue through the 24-pd. There is a 30 percent chance gusty
northeast winds could surface a few hours after 03z this evening.

&&

Marine...26/900 am PST...
for the outer waters...northwest to north winds were near Small Craft Advisory
levels...and will diminish by afternoon. Seas at or above 10 feet
will subside below 10 feet during the afternoon.

Across the inner waters...moderate confidence in Small Craft Advisory conds through
early afternoon due to winds from Oxnard to Point Mugu and out to
anacapa and Santa Cruz Island...near shore from Point Mugu to Santa
Monica...and through portions of the San Pedro Channel.

Small Craft Advisory conds will probably affect there areas again Sat morning.

&&

Lox watches/warnings/advisories...
hard freeze warning (see laxnpwlox).
Freeze warning (see laxnpwlox).
Frost advisory (see laxnpwlox).
Wind Advisory (see laxnpwlox).
Small Craft Advisory (see laxmwwlox).
High rip current risk (see laxsrflox).

&&

$$

Public...Kaplan/sukup
aviation/marine...Kaplan

Www.Weather.Gov/losangeles

National Weather Service Glossary of Abbreviations