Scientific Forecaster Discussion
Southwest California area forecast discussion
National Weather Service Los Angeles/Oxnard California
910 PM PDT Tuesday Jul 29 2014
Increasing tropical moisture will bring clouds and a small chance of
showers to the area later tonight and Wednesday. By afternoon that
will shift to the mountains and Antelope Valley along with a slight
chance of thunderstorms. Temperatures will remain above normal
through Friday...with some cooling expected this weekend into early
Short term (tonight-fri)...plume of middle and hi level moisture from
remnants of Hernan continued to stream north and northeast into the
forecast area this evening although the focus of the plume appears to
be drifting more northward with time and away from l.A. County. The
affects of remnants of tropical systems over southwestern California can be
difficult to predict...but it appears a few showers cannot be ruled
out over much of the area later tonight into Wednesday morning. Will keep
the 20 percent chance of showers in the forecast...and an isolated
high-base thunderstorm cannot be ruled out...but chance of this
occurring is 10 percent or less. Otherwise...low clouds should move
into the central coast tonight...with varying amounts of middle and hi
level clouds across much of the region.
A persistent upper level ridge of hi pressure can be expected over
Southern California Wednesday through Friday...with a broad but generally weak S to SW flow
aloft. Some middle level moisture will linger over the forecast area
during the period for partly cloudy skies at times. Varying amounts
of marine layer low clouds should affect coastal areas night and
morning hours as well. As far as convection...there should be enough
middle level moisture and instability over the mountains and Antelope Valley to
warrant a slight chance thunderstorms Wednesday afternoon and evening. The
latest WRF suggests an isolated thunderstorm may be possible in
these areas Thursday afternoon and early evening...but with a less than
10 percent chance. Gusty southwest winds should affect the Antelope
Valley each afternoon...with some gusty North Canyon winds along the sba S
coast and mountains in the evening. Temperatures across the region are forecast
to remain several degrees above normal for most areas through Friday...
with low 100s in the warmest valleys each day.
***From previous discussion***
Long term (sat-tue)...la County expected to be near the westward
extent of a plume of moisture streaming north from Mexico over the
weekend. GFS keeps this plume east while the European model (ecmwf) is right along
the la County border. For now am leaving the forecast dry but have
added some clouds to the eastern portion of our County Warning Area and silent probability of precipitation
(<15). A trough moving into northern California over the weekend will begin
a cooling/drying trend that will continue into early next week. Look
for highs drop back to normal levels by Monday, if not sooner,
especially for slo/sba counties.
Aviation...30/0000z...generally hi confidence in the 00z tafs. Low
clouds and IFR/LIFR conditions should affect ksbp and ksmx later
this evening through middle morning Wednesday. MVFR visibilities will be possible at
times later tonight and Wednesday morning for koxr and klax. Otherwise...
VFR conditions can be expected at the airfields through Wednesday. There is
also a 20 percent chance of a thunderstorm in the vicinity of kpmd
and kwjf Wednesday afternoon. Gusty mainly west winds at kpmd and kwjf this
evening will diminish tonight then increase again Wednesday afternoon.
Klax...generally hi confidence in the 00z taf. There is a 50-60
percent chance of MVFR visibilities 14z-18z Wednesday. Otherwise...VFR conditions
can be expected through Wednesday evening.
Kbur...hi confidence in the 00z taf with VFR conditions expected
through Wednesday afternoon.
Marine...29/830 PM PDT
A Small Craft Advisory is in effect through late tonight in zones
673 and 676. Strong winds may also affect the western portion of
zones 650 and 655 as well... and will periodically affect the region
through Friday. Offshore winds will likely affect the waters
immediately surrounding the Santa Barbara coast Thursday night and
early Friday morning.
Small Craft Advisory (see laxmwwlox).