Scientific Forecaster Discussion
Southwest California area forecast discussion
National Weather Service Los Angeles/Oxnard California
155 PM PST Wednesday Nov 25 2015
Synopsis... 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 late Saturday
into Sunday and again on Tuesday associated with a couple of upper
level lows expected to pass to the north.
Short term (today-sat)... overall the forecast is in good shape for
today. Generally dry northwest flow will continue throughout
today...however have cancelled the Wind Advisory over the mountains
as wind gusts will mostly remain below advisory levels. Latest
satellite imagery shows generally clear skies over land with some
clouds across the mountains and scattered cumulus over the water.
The cooling trend has continued today behind the cold front with
temperatures generally 5-10 degrees below this time yesterday at
lower elevations and 10-20 degrees below this time yesterday for the
mountains which matches up nicely with today's forecasted highs.
Continued clearing with the cold air mass aloft tonight is expected
to support sub-freezing conditions for some interior areas...have
updated the freeze watch to a freeze warning through early tomorrow
morning across parts of interior slo County including Paso Robles as
well as the Ojai Valley.
Expect similar conditions Thursday and Friday as guidance continues
to show a nearly stationary upper level low across the Great
Basin...allowing for only a gradual moderation in temperatures.
Slight offshore trends are expected to support a couple degrees of
warming to the west of the mountains on Friday. There will be some
gusty winds along the South Coast of sba County but at this point it
looks to stay below Wind Advisory criteria as the offshore pressure
gradient remains weak...even though there is decent upper level
Saturday some energy cuts under the Rex block...eventually merging
with the nearby persistent trough. Models are having a difficult
time resolving the exact timing of the merge which drastically
impacts the strength and location of the feature...the GFS
consisently absorbing the short wave earlier than the Euro. At this
point have clouds working their way in during the day with slight
probability of precipitation in for Saturday night to the north of Point Conception to
reflect the uncertainty. The timing on any precipitation could easily be
off by +/-12 hours.
Long term (sun-wed)... below average confidence continues into the
long range forecast. While the 12z runs of the GFS and Euro are in
relatively good agreement aloft...the surface reflection and
precipitation chances in particular are weak and inconsistent run to
run. The persistent trough across the Great Basin finally begins to
lift out of the region by early next weak. Weak ridging is expected
to occur as the trough exits the region. This will result in a
modest warming trend through Tuesday. However...the GFS and Euro
bring a weak short wave into the region from the northwest along the
northeast portion of the ridge...with light precipitation mainly north of
Point Conception exhibited in the GFS. The Euro keeps low levels dry
and hence keeps precipitation out of the picture. Have continued
slight probability of precipitation north of Point Conception as a result. Wednesday
operational solutions of the GFS and Euro continue to diverge...the
GFS brings broad zonal flow into northern California. While the Euro
develops a ridge across the southwest in advance of a trough
approaching the US Pacific northwest. Have leaned towards the GFS as
it as been consistent in the long range as shown by 500 heights with
the moderate trends tools...resulting in similar looking temperatures for
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.
Marine...25/ 900 am...
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.
coastal Flood Advisory (see laxcfwlox).
Freeze warning (see laxnpwlox).
Small Craft Advisory (see laxmwwlox).