Scientific Forecaster Discussion
Southwest California area forecast discussion
National Weather Service Los Angeles/Oxnard California
1005 am PST Wednesday Nov 25 2015
..updated aviation discussion...
A cold low pressure system will bring below normal temperatures and
locally breezy winds to the region today. Partly cloudy skies and
below normal temperatures are expected to continue through Friday.
There is a slight chance for showers Saturday and again on Tuesday
associated with a couple of upper level lows expected to pass to the
Short term (today-fri)...overall the forecast is in good shape for
today. Generally dry northwest flow will continue throughout today
with local Wind Advisory gusts possible in the normally favorable
areas. Currently have a low end Wind Advisory in effect to account
for this. Latest satellite imagery shows generally clear skies over
land with some clouds across the mountains and scattered cumulus
over the water. Cannot completely rule out isolated snow showers
through this afternoon...mainly across the north facing slopes of
the northern Ventura mountains. However any snow showers that do
form will be brief with no accumulations expected. Temperatures on
track for this afternoon. Will consider upgrading the freeze watch
currently in effect across some interior areas to a freeze warning
for late tonight into early tomorrow morning.
***From previous discussion***
The upper low will spin over Nevada on Thursday and Friday. The flow
around the backside of this low is almost all over land and this
will not allow any rain to develop. Skies will be partly cloudy at
worst, maximum temperatures will remain 8 to 10 degree below normal and will
change little from day to day.
Long term (sat-tue)... the extended forecast is simply a mess. A
very large scale Rex block sets up (upper low nestled below and
along the axis of a ridge) the ridge extends from deep in the east
pack all the way to Minnesota and the upper low covers California
Utah and Nevada. Honestly this type of weather pattern really
perplexes the computer forecast models. This is a text book example of
this as all the models disagree with each other on how the Rex block
will evolve and have little run to run consistency. To illustrate
this point the Monday forecast low for Paso Robles by the ec is 28
degrees while the GFS gives a value of 49 degrees. The GFS is much
wetter than the Bone dry ec. Cant ignore the wetter GFS and have
some low probability of precipitation in for Saturday night/Sunday morning and Monday
night/Tuesday but overall confidence in the extend forecast is as close to
zero as one can get.
At 1700z...there was no marine layer at klax.
Moderate to high confidence in 18z tafs...scattered VFR ceilings will
continue to clear during the period...except for fog in the Salinas
valley Thursday morning. Gusty west to northwest winds are expected
across the area through late this evening. 30% chance surface winds
will diminish at ksba in the evening with low level wind shear developing.
Klax and kbur...VFR conds expected through the period with 20%
chance of scattered high MVFR ceilings. Gusty west to northwest winds
may create moderate turbulence in the area through this evening.
High confidence continues in forecast of widespread Small Craft
Advisory winds and steep seas through late tonight. Brief and
localized gale force winds are possible...especially off the central
coast...and in the vicinity of the islands. Seas could remain above
Small Craft Advisory levels across the outer waters through late Thursday morning.
freeze watch (see laxnpwlox).
Coastal Flood Advisory (see laxcfwlox).
Beach hazards statement (see laxcwflox).
Wind Advisory (see laxnpwlox).
Small Craft Advisory (see laxmwwlox).