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Southwest California area forecast discussion...updated 
National Weather Service Los Angeles/Oxnard California
338 PM PST Sat Dec 27 2014

Updated aviation section

Synopsis...

It will remain chilly at night through the weekend with below normal
daytime highs as well. A large low pressure system will bring cold
and unsettled weather to the region Tuesday into early Wednesday
with possible showers and low snow levels. Cold temperatures will
continue through New Years Day but dry weather is expected through
the end of next week.

&&

Short term (today-tue)...mostly quiet the next few days as we
transition from offshore to onshore flow. An advancing ridge from
the west will bring a warmer air mass to the area, but decreasing
winds overnight and still very dry air in place will likely lead to
colder temperatures in places that were windy last night. Will be issuing
frost advisories for most valley areas tonight as well as the
central coast for temperatures near to just above freezing and a freeze
warning for the Ojai Valley. The ridge will be a dirty one with lots
of high clouds spilling over it Sunday. Otherwise continued cool
daytime temperatures with highs mostly in the lower 60s through Monday,
then cooling Tuesday as colder air moves in with the next upper low.

Models in pretty good agreement with this next system, tracking it
mostly over land through interior Oregon and California before
settling in so cal Tuesday night and early Wednesday. Moving over
land it will be starved for moisture, but a very cold air mass will
likely enable light showers to develop just about anywhere, though
most likely over the mountains downsloping winds will likely reduce
chances for measurable rain for most areas except the eastern portion of
la County where there will be some limited upslope flow. Areas south
of la County will stand a better chance of getting measurable precipitation
from this event due to the topography so am leaving probability of precipitation in the
20-30 range for the most part. Despite the cold air aloft with 500 mb
temperatures near -30c across the eastern part of the forecast area it doesn't
look particularly unstable at this time. It's a very cold air mass
from top to bottom and lifted indice's remain above zero for the duration of
the event so will not be adding thunderstorms at this time. Tuesday
night looks like our best chance at precipitation with decent pva, but
again very limited moisture. Snow levels likely down to around 2500'
but minimal accumulations expected. Still could pose some hazards
over the Grapevine as basically any accumulations there cause
problems.

Long term (wed-sat)...the upper low starts to exit the area
Wednesday morning and by 18z most of the action is south and east of
our area. Could still be some wrap around moisture from the north
into the mountains and Antelope Valley but not seeing a whole lot of
dynamics to support anything more than just some isolated showers.
Gusty Santa Ana winds likely for Ventura and la counties as a decent
offshore gradient develops behind the departing upper low.

With clearing skies and mostly light winds new years morning should
be very cold and likely will need freeze warnings for many of the
valleys and central coast and possibly frost advisories for the
la/Ventura coast. Those planning on camping out in Pasadena for the
rose parade should plan accordingly for a very cold night with lows
possibly in the low 30s.

Fairly quiet weather then through next weekend as weak high pressure
builds in for a slow warming trend. Still quite cold overnight
through at least Saturday morning.

&&

Aviation...27/2338z.

At 2315z...there was no marine inversion at klax.

VFR conditions are expected throughout the period...except for a
chance of IFR to MVFR conditions at terminals north of Point
Conception between 11z and 16z.

Klax...VFR conditions are expected throughout the period except for
a 10 percent chance of vlifr conditions between 13z and 16z. Any
east winds will remain less than 5 knots.

Kbur...VFR conditions are expected throughout the period. No wind
issues are expected at this time.

&&

Marine...27/200 PM PST...
offshore winds are subsiding across the near shore waters as the
Great Basin high shifts further east and begins to weaken. Winds
over the waters will turn to the southeast this afternoon and
evening then swing around to the north by Sunday. High pressure will
remain off the northern California coast as a coastal trough of low
pressure develops over the Southern California bight. North winds will
increase to locally moderate speeds by Sunday night over the outer
waters. Monday night into Tuesday winds will increase from the
northwest with gusts to 30 knots expected Tuesday afternoon...with
local gusts to 35 knots possible by Tuesday night. Winds up to Small Craft Advisory
level will push into the western portion of pzz650 and pzz655
Tuesday afternoon and evening. Combined seas 7 to 9 feet are
expected as a small swell combines with increasing wind waves Monday
night through Tuesday night.

&&

Lox watches/warnings/advisories...
freeze warning (see laxnpwlox).
Frost advisory (see laxnpwlox).

&&

$$

Public...mw
aviation...Hall
marine...Smith

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