Scientific Forecaster Discussion
Southwest California area forecast discussion
National Weather Service Los Angeles/Oxnard California
1050 am PDT Monday Sep 1 2014
..new aviation discussion...
upper level high pressure over the region will move southeastward as
a weak upper trough slowly approaches the West Coast today through
middle week. This will bring a cooling trend to the region through
Wednesday...with daytime temperatures falling to below seasonal
normals. Below normal temperatures will continue Thursday and
Friday...then some warming is expected over the weekend as high
pressure builds back into the area.
Short term (today-wed)...
the upper level ridge that brought US such warm conditions over the
last few days has begun to shift slightly to the east. More
significantly...coastal stratus has returned to all coastal areas. A
fairly strong coastal eddy spinning south of Point Conception
brought a much deeper marine layer (1100-1900ft) with stratus
pushing into the valleys earlier this morning. The center of this
eddy has meandered westward which has pulled the bulk of the clouds
off the coast with easterly flow. While a deeper marine layer and
stratus arrival usually spells a healthy dose of cooling...concerned
that this easterly flow will negate the cooling effects of the
marine layer. Current forecast looks good with just a slight cooling
trend...which is the most probable outcome...but there is a chance
that some coastal and adjacent valley areas dont see much in the way
of cooling. No northwesterly wind concerns today...but breezy
sub-advisory southwest winds should form over the interior sections
by later this afternoon.
***From previous discussion***
The upper high across Southern California will shift southeastward tonight through
Wednesday...and a weak upper trough will slowly approach the West Coast.
Heights and thicknesses will fall each day...as will temperatures at 850 mb
and 950 mb. Expect the marine layer to remain rather deep through
Wednesday...and night through morning low clouds and fog should be
widespread west of the mountains clearing could be rather slow on
Tuesday and more likely on Wednesday...especially across the coastal plain.
Maximum temperatures will be down a few degrees each day...with temperatures several
degrees below normal in most areas by Wednesday. There will be some gusty
winds each afternoon and evening in the mountains and deserts.
Long term (thu-sun)...the upper trough will linger to the west of
the region on Thursday...with the GFS showing a sharper trough than the
ec. Either way...expect temperatures to remain several degrees below
normal...with plenty of low clouds and fog west of the mountains Wednesday
night/Thursday and again Thursday night/Fri. If the ec is correct...slight
rises in heights may bring a couple of degrees of warming on
Friday...but any change in maximum temperatures should be minor. The GFS maintains
a sharper trough along the West Coast on Sat...with the trough axis
moving across the state on Sunday...while the ec shows some height
rises as a weaker trough allows an upper high over the S central
U.S. To build back into the region. If the ec is correct...expect a
few degrees of warming over the weekend...with a reduction in night
through morning low clouds and fog...especially in the valleys.
Marine layer is near 2300 feet deep. Better confidence in an earlier
arrival of low clouds tonight. The marine clouds are expected to
push into the valleys as well due to a persistent eddy.
Klax...good confidence in the 18z tafs. Expecting MVFR conditions
with the marine clouds. There is a 30 percent chance of marine
clouds arriving more than 2 hours off from taf estimate.
Kbur...good confidence in the 18z tafs. Expecting MVFR to IFR
conditions with the marine clouds. There is a 30 percent chance of
marine clouds arriving more than 2 hours off from taf estimate.
Outer waters...good confidence that conditions should remain below
small craft levels through mid-week. There is the possibility of
occasional gusts to 25 knots in the outer waters this afternoon and
Inner waters...good confidence in no Small Craft Advisory conditions