Scientific Forecaster Discussion
Southwest California area forecast discussion
National Weather Service Los Angeles/Oxnard California
200 PM PST Wednesday Jan 28 2015
A weak low pressure system will move southeast of the area Thursday
and Friday...bringing clouds to the area along with the potential
for some light showers to Los Angeles County. By Saturday and Sunday
dry offshore flow will develop...with the dry conditions continuing
into the middle of next week.
Short term (today-sat)...
overall...12z models in good synoptic agreement through the period.
At upper levels...trough will approach the area tonight/Thursday
then develop into a weak low southeast of the district on Friday and
Saturday. Near the surface...weak offshore flow will prevail through
Friday...then may increase a bit on Saturday thanks to northeasterly
flow develop aloft.
Forecast-wise...immediate short term (tonight/Thursday morning)
looks to be quiet as varying amounts of middle/high level clouds drift
overhead. There also will be the chance for some patchy dense fog to
develop in the Salinas valley (depending on the extent of the
overnight cloud cover). A general partly/mostly cloudy wording
should do the trick.
For the balance of Thursday and through Friday night...focus turns
to the trough/upper low. At this time...still looks like the best
threat of any precipitation will remain south and east of the district.
However the possibility of some showers over eastern Los Angeles
County cannot be ruled out. So...will keep idea of slight chance
probability of precipitation for the Antelope Valley/san Gabriels Thursday afternoon/night
with the slight shower threat spreading into the Los Angeles coasts
and valleys on Friday/Friday evening. Any precipitation that falls across
Los Angeles County should be rather light...and cause no significant
hydrologic issues. Snow levels will remain rather high (7000+ feet)
so only anticipate some minor snow accumulations at the highest
elevations. By Saturday...the upper low will move eastward...and any
shower threat for Los Angeles County should end.
As for winds...there will likely be some locally gusty northeast
winds tonight/Thursday morning...and to a lesser extent Thursday
night/Friday. Do not anticipate anything approaching widespread
advisory levels. By late Friday night/Saturday...the upper support
increases as northeast flow develops aloft. So...northeast winds
will likely be a bit stronger/more widespread on Saturday...and
there will be the potential for low end advisory conditions.
As for temperatures...Thursday should be another nice day with highs
in the lower to middle 70s for most coastal/valley areas...and 60s
across interior sections. Friday will be a few degrees cooler at the
trough/low impact the area...then a rebound on Saturday with
stronger offshore flow.
Long term (sun-wed)...
for the extended...12z models continue to exhibit good synoptic
agreement. At upper levels...ridge will continue to nose in from the
eastern Pacific on Sunday...and remain over the area through
mid-week. Near the surface...varying amounts of offshore flow will
prevail with the strongest offshore flow likely on Sunday...then a
more diurnal flow pattern Monday through Wednesday.
Forecast-wise...the extended should be dry due to the ridge overhead
and offshore flow. Afternoon highs will peak on Sunday then exhibit
a very gradual cooling trend Monday/Tuesday...then possibly rebound
on Wednesday. Overall...most areas should remain a few degrees above
There is a very shallow surface based inversion up to 800 feet and
18 degrees c.
Aside from extensive high cloudiness above 15 kft...interior valleys
like the Salinas and Antelope are still dealing with some trapped
residual moisture and patchy dense fog. The Salinas valley should
have a better than even chance of another round of dense fog while
Palmdale should remain clear. There is better consensus on the
forecast for the coastal sections. The central coast is expected to
have small patches of fog that are reflected in scattered low clouds
in the coastal tafs north of Point Conception. For the coastal tafs
south of Point Conception...there is good confidence in the absence
of low clouds due to persistent high cloud cover and weak offshore
Klax...good confidence in the 18z taf. There is a 30 percent chance
of MVFR or IFR ceilings due to patchy marine clouds.
Kbur...good confidence in the 18z taf. High confidence in VFR
conditions through Thursday.
No significant marine issues through Thursday morning. There will be
a 50 percent chance that a Small Craft Advisory might be needed
across the outer waters...mainly western portion for Thursday
afternoon through Saturday morning.