Scientific Forecaster Discussion
Southwest California area forecast discussion
National Weather Service Los Angeles/Oxnard California
115 PM PST Monday Nov 30 2015
Temperatures will warm to above normal by middle-week as high pressure
builds aloft and offshore flow continues. A trough of low pressure
will bring cooling and a chance of rain Thursday through Friday
morning...mainly north of Point Conception. Warm and dry weather
will likely return for the weekend as a ridge of high pressure moves
into place and offshore flow redevelops.
Short term (today-wed)...skies were mostly clear this afternoon
except for some high clouds continuing to stream across Los Angeles
and Ventura counties early this afternoon. Temperatures were
trending warmer a degree or two for coast and valleys...while some
mountain locations experiencing up to 10 degrees of warming over the
past 24 hours. Today's highs should reach the middle to upper 60s
forecast and coastal valleys...with highs only in the middle 560s
across the Antelope Valley and most interior valleys.
To the north...a decaying cold front was moving through Monterey
County. By the time the front reaches slo County later this
afternoon it should just bring increased cloud cover for areas north of
Point Conception through this evening. Latest radar showed most of
the shower activity across the Bay area and a few false echoes near
Cambria. Possibly chaff.
Behind the upper trough and frontal passage...high pressure aloft
will build in over southern and central California tonight into
Tuesday. There should be enough light offshore winds across the
central coast tonight to keep most areas above frost thresholds.
There will be a few wind protected areas that could see temperatures
lower to just above freezing. Also...expect one more night of around
freezing conds for the Ojai area late tonight into Tuesday morning.
A freeze warning will be issued with the afternoon zone package.
Also...frost advisory for the southwestern wind protected portion of
the San Fernando Valley including Woodland Hills...Calabasas and
portions of Agoura Hills and Westlake Village.
There will continue to be light offshore winds affecting the usual
wind prone areas of Los Angeles and Ventura counties tonight through
Tuesday evening. Lax-dag surface gradients are expected to remain
offshore this afternoon and then down to -3.5 mb early Tuesday
morning. This will continue to cause light offshore winds to occur
and additional warming across coast and coastal valleys on Tuesday
to more normal readings for this time of year. By Tuesday night into
Wednesday...a cold punch behind an exiting cold front moves into the
Great Basin. In turn...stronger surface high pressure to around 1032
mb builds into northern Nevada. This stronger pressure gradient and
cooler air advection into the High Desert will bolster up Santa Ana
winds a bit. At this time it looks like it will be just below Wind
Advisory thresholds for Wednesday morning...but winds will be more
widespread and should push all the way to the coast. Expect high
temperatures to reach the middle 70s across most coast and coastal valleys in
la/vtu counties. With cooler temperatures expected across the interior
areas...which is typical with this type of offshore pattern.
Long term (thu-sun)...the positive tilted ridge axis that will be
over socal into Idaho will be short lived as a rather strong upper
low begins to dig south as it strengthens. The trough axis becomes
negatively tilted as it approaches the northern half of California.
A strong surface low associated with the trough will develop just
off the coast of nocal by Thursday afternoon. Expect gusty southerly
winds ahead of the approaching trough for areas north of Point
Conception...especially across the coastal waters and slo County. At
this time...best chance of precipitation will occur for areas north of
Point Conception...with a slight chance of showers across the sba
South Coast and adjacent valleys and northern mountain slopes going into
Friday. Snow levels will begin quite high...over 7500 feet...but as
the trough moves through...snow levels should lower to around 5000
feet affecting the northern slopes of the Ventura and western la County
mountains with some light snow fall accumulations.
Best cooling on Thursday will occur for areas north of Point Conception
and all coastal areas as onshore flow kicks in ahead of the trough.
Widespread cooling will continue into Friday as the trough and
associated cold front moves quickly through the region. Another
ridge axis from socal into the Great Basin will develop behind the
exiting trough for Sat and Sunday. Sundowner winds are possible on
Friday with a return of Santa Ana winds by Saturday morning and once
again Sunday morning. Expect some warming across the la/vtu coast
and coastal valleys with offshore winds...but highs should remain in
the lower to middle 70s. Another upper trough could bring some showers
to areas north of Point Conception by Monday.
At 1756z...there was no marine layer inversion at klax.
High confidence in 18z tafs with VFR conditions expected through the
Klax and kbur...high confidence in ceiling and visibility unlimited tafs.
Locally gusty east winds continue in the Santa Barbara Channel with
local gusts to 20 knots near Santa Cruz Island. These winds are
expected to gradually decrease through the day. Otherwise...light
winds are expected through middle week. A large long period northwest
swell will begin to move into the waters tonight into
Monday...peaking Tuesday around 10 feet at 15 seconds.
freeze warning (see laxnpwlox).
Frost advisory (see laxnpwlox).
High surf advisory (see laxcfwlox).