Scientific Forecaster Discussion
Southwest California area forecast discussion
National Weather Service Los Angeles/Oxnard California
1021 am PST Thursday Dec 18 2014
A weak storm system will be moving out of the area this
morning.There will be isolated showers...mainly near the foothills
today. On Friday...yet another weak system will brush the
area...but any chances of light rain should remain confined to
northern sections and northern slopes of the mountains down to
Ventura County. For Saturday through the first half of next
week...high pressure will build over the area...bringing dry
conditions and a warming trend.
Short term (today-sat)...a weak shortwave has moved through the
forecast area overnight with minimal rainfall amounts. Areas north of
Point Conception received the most...but mostly under 0.15"
elsewhere...rainfall amounts were a tenth of an inch or less. There
were a few widely scattered showers left over this morning...but as
the day moves forward with some weak ridging expected...skies should
remain partly to mostly cloudy with an isolate shower possible near
the foothills. The morning sounding at Vandenberg AFB indicated a
fairly deep moisture layer. NAM-WRF cross sections do show lingering
low level moisture to stick around across much of the forecast area
through tonight ahead of the next weak system. For tonight...patchy
dense fog could be an issue due to the recent rainfall...especially
across the Salinas River Valley. Although there will likely be
partly cloudy skies tonight...with some clearing and relatively
light winds expected overnight...radiational fog could develop in
low lying valley locations or in agricultural areas across the coast
late tonight into early Friday.
Overall...the forecast looks to be in good shape this morning. There
will be a quick moving system that should bring some light showers
to areas north of Point Conception late Friday afternoon and
evening...and possibly affect the northern slopes of the sba/vtu
County mountains by Friday night. Northwest flow will prevail at 850 mb over
Ventura/la counties with this next system over the region...which
will not be conducive for any showers to reach coast and valley
locations. There will be clouds banking up against the northern
slopes of vtu answer western la mountains...so there will be a slight chance
for a few light showers to occur Friday night as mentioned earlier.
A few snow flurries will occur above 6000 feet Friday night.
***From previous discussion***
For tonight/Friday...models indicate another weak system will
flatten the ridge...and generate the possibility of some light
showers Friday/Friday evening across San Luis Obispo and Santa
Barbara counties. So...for these areas...a slight chance of showers
will continue...with only very light amounts anticipated. Would not
be surprised to see some sprinkles/light showers work their way down
to Ventura/Los Angeles counties...but not enough to warrant any
mentionable precipitation chances at this time.
On Saturday...upper ridge will once again begin to build in from the
southwest...ending the threat of any precipitation for the area.
As for temperatures...a gradual warming trend is expected through
the short term...with most areas around seasonal normals by
Long term (sun-wed)...
for the extended...models are in good synoptic agreement and rather
benign weather can be expected. Main feature will be the upper ridge
building in from the southwest...which will peak in strength on
Monday then gradually weaken Tuesday/Wednesday. Near the surface
some offshore flow will develop...northerly Saturday night/Sunday
then turning more northeasterly Monday/Tuesday.
With this pattern...dry conditions are expected through the period.
Temperatures will show a nice warming trend through Tuesday...then
cool slightly on Wednesday. In fact by Tuesday...most coastal/valley
areas should in the 70s to lower 80s. With the northerly gradients
Saturday night/Sunday morning...there may be some decently gusty
northerly winds across the Santa Ynez range (possibly reaching low
end advisory criteria). Otherwise...any offshore winds the first
half of next week are expected to remain light.
Middle/upper level trough upstream will shift over the area. Upper
level strong northwest winds will become moderate west by 19/04z
while middle level moderate north winds become light west by 19/11z
then moderate west-southwest after 19/20z. Decreasing moisture after
18/23z then increasing moisture after 19/19z. Freezing level was
approximately 8kft this morning and will differ by plus 4kft after
19/04z and change little thereafter.
Marine layer at lax at 1725z is none.
Klax...chance ceilings 050 with -shra at times through 18/20z. Otherwise
broken 080 between 18/20-18/24z. Scattered 020 between 19/00-19/21z.
Kbur...chance ceilings 050 with -shra at times through 18/20z. Otherwise
broken 080 between 18/20-18/24z. Scattered 020 after 19/00.
Virtually certain - 95-100%
very likely - 80-95%
likely - 60-80%
chance - 30-60%
very unlikely - 20% or less
Small craft for hazardous seas northwest of the northern Channel
Islands to Point Piedras Blancas excluding the inner waters north of
Point Sal will likely end this afternoon. Hazardous seas will
likely return Friday night as seas generated from a distant storm on
Tuesday from 290-300 degrees relative to Los Angeles County coast
build. The conditions will likely persist through Sunday. There is a
chance small craft conditions for north wind will exist in the
vicinity of The Channel islands Saturday night and persist through
Small Craft Advisory (see laxmwwlox).
Beach hazards statement (see laxcfwlox).