Scientific Forecaster Discussion
Southwest California area forecast discussion
National Weather Service Los Angeles/Oxnard California
1130 am PDT Monday Jul 6 2015
..new aviation/marine discussions...
Upper level low pressure off the coast will maintain strong onshore
flow through the middle of the week...with extensive night through
morning low clouds and patchy fog. Below normal temperatures are
expected for the entire region by middle week. Warming is likely by
Update...visible satellite imagery shows that the low stratus and
fog made its way into all of the coastal zones and most of the
valley locations this morning...even to the south slopes of the la
and Ventura County mountains. It is beginning to clear out
some...especially around Santa Clarita and in northern slo County.
Temperatures are much like yesterday at this time...and they will be
so again tomorrow at this time in this steady pattern. Another
windy afternoon and evening in the Antelope Valley and southwest
Santa Barbara County...but not expecting advisory strength.
*** From previous discussion ***
Three very similar June like days on tap today through Wednesday.
Synoptically there is a weak upper low just of the coast and a very
weak ridge over AZ/NV. At the surface moderate to strong onshore flow
will continue from a very large east Pacific surface high to a persistence
thermal low near Yuma. The upper low will keep a fairly deep marine
layer in place. This will allow the marine layer stratus to reach
deep into the valleys. Clearing will be slower than normal and almost
all the beaches will stay cloudy all day.
The only exception will be the sba South Coast. Weak sundowners each
evening will keep the night time stratus away tonight and Tuesday
The deeper than normal marine layer and the stronger than normal
onshore flow will keep maximum temperatures 4 to 6 degrees below normal in most
places. The mountains and the deserts will also cool a little each
day as the upper low slowly moves to the east lower heights as it does.
Long term (thu-sun)...Thursday is the most interesting day of the
next 7. The upper low opens up and moves over slo and sba counties.
The lift with this low will drive low clouds all the way to the
coastal slopes. There might be enough lift for drizzle. Right now
there does not look like there is enough moisture for mountain
convection just afternoon and evening build ups. Its still early and
this could change and will have to monitor for potential moisture
All models agree that the Friday through Sunday period will be
dominated by a West Coast trough and a Four Corners high. Right now
dry SW flow is forecast for our area and any monsoon action will be
confined to eastern sbd/riv counties.
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 afternoon
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).