Scientific Forecaster Discussion
Southwest California area forecast discussion
National Weather Service Los Angeles/Oxnard California
145 PM PDT Monday Jul 6 2015
Strong onshore flow through the middle of the week will keep night
through morning low clouds and patchy fog along the coast. Below
normal temperatures are expected for the entire region by middle week
and they will remain low into the weekend.
Short term (today-thu)...afternoon temperatures will be quite
similar to yesterday as most of the coast any valley areas remain
under the strong influence of the marine layer and strong onshore
flow...the exception may be in the mountain areas which are running
a degree or so cooler. Coastal stratus is still present from la
County through Santa Barbara.
The wind is beginning to blow in the Antelope Valley with two
reports of 25 miles per hour gusts so far. Expecting offshore evening winds in
western Santa Barbara County to help keep the stratus off of the sba
County South Coast tonight.
Tuesday and Wednesday will be very similar to today while cooling a
degree or so each day. The deep marine layer and onshore flow will
drive the forecast for the coasts and coastal valleys. Synoptically
there is an upper low about 450 miles west of San Francisco and a
weak ridge over AZ/NV. The low will slowly move east and be over
Monterey by middle-morning Wednesday. Monterey and Hanford have
introduced precipitation possibilities for their areas on Wednesday...but
not seeing enough forcing or moisture for our area at this time.
As the low passes to our north on Thursday it could bring enough
lift to raise the low clouds up the coastal slopes and force some
drizzle. Later in the day a 100 miles per hour jet streak will pass directly
over our area and there are mechanics for lift which introduce the
possibility of some afternoon storms...not seeing very much moisture
at this time...but enough to introduce a slight chance of afternoon
convection into the forecast... primarily over the Ventura County
Long term (fri-mon)...
There will be an upper trough to our southwest even after the low
passes by and it will keep the onshore push going with continued
coastal stratus through the weekend. The European and GFS models
begin to diverge in the long term. The GFS solution is for a return
to the offshore low and SW/NE elongated Four Corners high that could
start moving monsoon moisture back to the area by late Monday. The
European spins an upper low from the Gulf of Alaska down to the
California/or border and has the ridge oriented more north/south which keeps
the monsoon moisture to our east. Favoring the GFS at this time as
it has been the better model so far this Summer.
At 1745z the marine inversion at klax was based at 2500 feet. The
top of the inversion was at 4000 feet with a temperature of 21
A deep marine layer is in place and a slow clearing trend points to
the possibility that some coastal sections will not clear out today.
The 18z tafs continued a pessimistic forecast for the coastal
sections with some taf sites not clearing this afternoon. This
situation will be monitored closely as it is difficult to be sure
which coastal sites might not clear out during the entire afternoon.
For tonight...there is good confidence in the return of a deep
marine layer with clouds causing MVFR conditions in the coastal
sections and IFR to MVFR ceilings in the valley sites. Finally...
the Antelope Valley sites will again see gusty southwest
Klax...good confidence in the 18z taf. There is a 30 percent chance
of afternoon clearing today. There is a 30 percent chance of clouds
returning plus or minus two hours from the forecasted time.
Kbur...good confidence in the 18z taf. There is a 30 percent chance
of the clouds returning plus or minus two hours from the forecasted
Northwest winds will increase across the outer waters today. Decided that
gusts to 25 knots would be just widespread and frequent enough to
warrant winds at Small Craft Advisory levels for the southern two-thirds of the outer
coastal waters this afternoon through tonight. There is an even
better chance of Small Craft Advisory level winds across the southern two-thirds of the
outer waters late Tuesday afternoon into Tuesday night.
Small Craft Advisory (see laxmwwlox).