Scientific Forecaster Discussion
Southwest California area forecast discussion
National Weather Service Los Angeles/Oxnard California
342 PM PST sun Dec 28 2014
Updated aviation section
High pressure over the region will keep a dry weather pattern in
place through Tuesday. A brisk and cold weather pattern will move
into the area as a trough of low pressure originating from Canada
drops into the region for middle-to-late next week. This will bring a
chance of showers to the area as well as low elevation snow for the
mountains and Antelope Valley.
Short term (today-wed)...weak high pressure will maintain quiet
weather across the area through early Tuesday with mostly clear
skies. Chilly overnight temperatures with light offshore flow and will go
with another frost advisory tonight for temperatures near to just above
freezing for the valleys and central coast.
A very cold storm dropping out Canada today will continue to move
south and reach Southern California late Tuesday night. Due to its
terrestrial trajectory it's pretty starved of moisture but not
entirely. It will pick up a little moisture as the westerly flow
around the south end of the low moves over water and this will bring
the southeastern portion of the forecast area, mainly southern la
County its best chance of precipitation either late Tuesday afternoon or
evening. Other areas will have a shot at some isolated showers but
very light amounts. As the low continues to drop south and east
Tuesday night the low level flow will quickly shift to northeast. As
this happens concern will shift to the la/Ventura mountains and the
Antelope Valley as snow levels drop to 2000 feet or lower and
northeast winds generate orographic lift. Models indicate the best
lift will be across the eastern half of the av and san gab mtns,
basically from Highway 14 east. Although amounts may struggle to
reach true warning level criteria due to the limited moisture, given
the impacts on Holiday travel over Interstate 5 and through the
Mojave Desert it was felt that a Winter Storm Watch was justified.
Coast and valley shower chances will diminish Wednesday morning with
the downslope flow while precipitation across the interior is expected to
taper off Wednesday afternoon as the low moves farther east and
south of the area. Rainfall amounts to the Lee of the mountains expected
to be under a quarter inch. For the mountains and av a quarter to half
inch liquid equivalent, translating to around 3" of snow for the av
floor and the Grapevine and as much as a foot for the north slopes
of the eastern san gab mountains
Long term (thu-sun)...a cold start to 2015 expected with lows in
the valleys, including the Pasadena area in the lower 30s and
possibly as low as the middle to upper 20s in the colder wind protected
areas such as Ojai and the western sfv. Otherwise dry and mostly
clear skies through next weekend with a very slow warming trend. By
Sunday highs should be back to near normal levels.
At 2342z...there was no marine inversion at klax.
VFR conditions are expected throughout the period...except for a
slight chance of LIFR conditions at coastal terminals between 11z
Klax...VFR conditions are expected throughout the period except for
a 10 percent chance of vlifr conditions between 10z 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.
28/200 PM PST.
As high pressure remains off the north California and low pressure
develops over the S California coast...expect some localized Small Craft Advisory
gusts across the outer waters. Otherwise...as the pressure gradient
strengthens...expect increasing northwest winds over the outer waters
through Monday with Small Craft Advisory likely needed by 2 PM. The winds will
continue through Tuesday with gusts to 30 knots likely and gusts to 35
knots possible by Tuesday evening. At the same time...increasing northwest to
west winds will push into the western portion of the near-shore
waters. A Small Craft Advisory will likely be needed for the western portion of the
southern inner waters. Less confidence that winds will increase to
Small Craft Advisory level over pzz645. Swell will remain small but wind seas will
grow as the moderate to locally strong winds continue...building to
near 10 feet over the outer waters by Tuesday.
Winter Storm Watch (see laxwswlox).
Frost advisory (see laxnpwlox).