Scientific Forecaster Discussion
Southwest California area forecast discussion
National Weather Service Los Angeles/Oxnard California
740 PM PST Friday Nov 27 2015
The upper level low over the Great Basin will support continued cold
weather through the weekend. A warming trend is expected through middle-
week as the upper level low exits to the east and an upper level
high builds in overhead. Showers are possible late next week as a
second upper level low passes to the north.
Short term (tonight-mon)...update
Afternoon forecast looks to be in good shape. Not anticipating any
changes to the short term forecast. Latest infrared and fog product
imagery indicated mostly clear skies...except some a lingering
clouds across the Los Angeles...Ventura and Santa Barbara
mountains. There could be a few light showers or snow flurries
above4500-5000 feet tonight in these areas tonight. As mentioned in
the earlier discussion...the main issue over the next couple of days
will be the cold overnight temperatures. Hard freeze warnings are in
effect for the interior valleys of slo County and the Cuyama
Valley...while freeze warnings are in effect for the Santa Ynez and
Ojai valleys. A frost advisory was issued for the central coast.
Also went ahead and issued a frost advisory for the San Fernando
Valley...but it is really only for the far western portions
including Westlake Village...Agoura Hills...Calabasas...and Woodland
Hills where low temperatures could reach near freezing levels.
For Saturday...southern cal will continue to be on the western
peripheral of a positively tilted upper low. However another
shortwave on the western side of the parent low will begin to rotate
towards the south. Models do show some showers well off the coast
with this feature...but should not affect the forecast area. There
will be a few degrees of warming across most areas during the
afternoon...but nights will continue to be quite chilly. High temperatures
for Saturday will remain 4 to 8 degrees cooler than
normal...especially across inland areas. Highs will remain in the
middle 60s for most coast and valley locations...and lower 50s across
the interior slo/sba valleys and the Antelope Valley.
For Saturday night...there are freeze watches out for the same areas
that are affected tonight. The one fly in the ointment will be the
upper disturbance moving around the southern fringe of the upper low
over the coastal waters towards the l.A. Coast. This disturbance
will weaken as it fills in across the southern most part of socal
tomorrow night. Some clouds are likely to develop across the
forecast area...especially S of Point Conception Saturday evening
which could keep low temperatures just above freezing for a few
areas. The ec is the only model at this time that slides a little
moisture just across the l.A /Orange County coastal areas. Most of
the shower activity remaining offshore as it weakens. The surface
gradient continues to hold some weak offshore flow over the
area...therefore will not be adding slight chance probability of precipitation for immediate
coast for la/vtu/sba counties at this time. However...will let middle
shift take a closer look as the 00z GFS and Euro come in.
***From previous discussion***
For sun-Mon...daytime highs will gradually rise through early next
week as the main upper-low moves east and height/thickness values
slowly rise. Surface high pressure building into the Great Basin
will also produce weak offshore flow near the surface...which will
help warm areas west of the mountains. Daytime highs will generally
return to near normal by Monday...with coastal and valley areas
south of Point Conception in the middle 60s to around 70...and areas on
the central coast in the low to middle 60s.
Similar overnight temperatures are expected Sunday night. Freeze
and hard freeze Sunday night could even be a couple degrees colder
as the main upper-low pulls east and the airmass continues to dry
Daytime highs will gradually rise through early next week as the
main upper-low moves east and height/thickness values slowly rise.
Surface high pressure building into the Great Basin will also
produce weak offshore flow near the surface...which will help warm
areas west of the mountains. Daytime highs will generally return to
near normal by Monday...with coastal and valley areas south of Point
Conception in the middle 60s to around 70...and areas on the central
coast in the low to middle 60s.
Long term (tue-fri)...
The gradual warming trend will likely continue through middle-week as
weak offshore flow continues. Models are in good agreement that an
upper-level ridge will develop Tuesday into Wednesday...which will
add to the warming. By middle-week temperatures will likely be 5-10
degrees above normal. So middle to upper 70s for coastal and valley
areas south of pt Conception...and around 70 on the central coast.
Models are in good synoptic agreement that a broad trough will move
through the area Thursday through Friday...which will bring a
cooling trend and possibly some rain. At this point it doesn't look
to be a major rain maker though. Current forecast just has a slight
chance for areas north of pt Conception.
At 2330z...there was no marine layer inversion at klax.
High confidence in 00z tafs with VFR conditions are expected through
the 24-hour period. Locally breezy offshore winds will affect the
area through early Saturday.
Klax and kbur...high confidence in VFR conditions through the
period. 20 percent chance of weak low level wind shear at kbur between 12z-18z.
Light winds are expected through the weekend into Monday. South-southeast
swell from Hurricane Sandra will build into the waters on Saturday.
A larger long period northwest swell will begin to move into the
waters Sunday night into Monday...peaking Tuesday around 10 feet at
hard freeze warning (see laxnpwlox).
Hard freeze watch (see laxnpwlox).
Freeze warning (see laxnpwlox).
Freeze watch (see laxnpwlox).
Frost advisory (see laxnpwlox).