Scientific Forecaster Discussion
Southwest California area forecast discussion
National Weather Service Los Angeles/Oxnard California
925 PM PDT Monday Jun 1 2015
Night through morning low clouds for the coast and valleys and
breezy conditions across the Antelope Valley will persist through
Thursday...along with seasonal temperatures overall. Low pressure
will bring cooler temperatures to the area along with a slight
chance of afternoon and evening thunderstorms to eastern Los Angeles
County Friday and Saturday. Fair and warmer weather will return to
all areas for Sunday and Monday.
Water vapor imagery indicates increasing southwest flow aloft taking
place between a broad ridge of high pressure near the Hawaiian
islands extending into southwest California...and a trough of low
pressure in the Gulf of Alaska. Influence from southwest flow aloft
and an onshore flow pattern will keep a persistent marine layer in
place through midweek. Klax amdar soundings indicate a marine layer
depth near 1100 feet this evening...which agrees well with the
latest NAM bufr time height sections.
The marine layer should deepen overnight to near 2000 feet as a
remnant eddy circulation regenerates after midnight and lift the
marine layer depth. Confidence in stratus coverage is waning
slightly as a weak northerly surface gradient is in place over the
area. Package leaves patchy coverage in for the Santa Clarita valley
and Santa Barbara South Coast on Tuesday morning...but there is a
chance that skies could be much sunnier as the sun rises on Tuesday.
Stratus could also be difficult to clear along the beaches on
Tuesday afternoon as the ridges influence presses down on top of the
marine layer and strengthens the marine inversion. The next shift
will be briefed accordingly on the possibility of the beaches
remaining socked in with stratus on Tuesday.
The northerly gradient is producing locally gusty northerly winds
across the area. Both Las Flores Canyon and Gaviota observation
sites are breezy to windy at times as the ksba-ksmx surface pressure
gradient has tightened to near -3 mb. Some breezy to locally windy
conditions should also be expected through the Interstate 5 corridor
in the mountains after midnight. No Wind Advisory level winds are
expected at this time.
The marine layer should start to deepen between Tuesday night and
Wednesday as a trough of low pressure over the Gulf of Alaska ejects
out and strengthens as it drops south into the region for late week.
Short term...drab weather next few days with June gloom in effect.
Marine layer to hover in the 2k-3k' range before additional deepening
occurs Thursday with the next trough. So very little change through Thursday
with the usual night/morning clouds...maybe some spotty drizzle...
clearing to near the coast each afternoon. Temperatures near to slightly
Some breezy winds expected near the Grapevine tonight and in the
Antelope Valley everyday this week but mostly below advisory levels.
Long term...still considerable disagreement with the handling of
Andres moisture this weekend. All models agree on a deepening trough
late Thursday into Friday evolving into a semi-cutoff low somewhere in
our vicinity through at least early Monday. At a minimum we'll see a
deep marine layer in place and temperatures at least a few degrees below
normal...and again some possible drizzle at times for coast/valleys.
However...the big question mark centers around Andres moisture and
where it will all go. The GFS appears to be a lone holdout pulling
the moisture well west of the Colorado River and as far north as northern
California. This seems an unlikely scenario and though I favor the
models that keep everything well east the wetter GFS cannot be
ignored. So the forecast through the weekend remains largely unchanged
with probability of precipitation across most of la County. The one change in the GFS today
was the 1 day delay in subtropical moisture from Friday to Sat. But
didn't feel comfortable taking probability of precipitation out with one model run.
By Sunday the GFS shifts the moisture north of our area so precipitation
chances ending Sat for most areas look good at this time.
However...the upper low lingers until at least early Monday so will
have to keep an eye on possible mountain convection Sunday. Temperatures to
remain below normal through early next week.
At 0000z...the marine layer at klax was 1000 feet deep...with the
inversion top near 3250 feet with a temperature of 20 degrees c.
MVFR conditions will likely return through through 11z. There is a
chance of up to a 3 hour delay in arrival. There is a chance of LIFR
to IFR conditions at terminals north of Point Conception between 08z
and 16z. A tightening marine inversion on Tuesday could produce
slightly later clearing times.
Klax...MVFR conditions will spread in through 08z...and persist
through at least 17z...or as late as 20z. VFR conditions should
develop by 20z at the latest.
Kbur...MVFR conditions will spread in between 11z and 16z. There is
a 20 percent chance of IFR conditions between 11z and 15z. VFR
conditions will develop between 15z and 17z.
Locally gusty winds and choppy seas will occur across the western
portions of the nearshore waters through late tonight. Otherwise...
Small Craft Advisory winds will develop across the outer waters
through Tuesday morning...and possibly spread into the nearshore
waters in the afternoon. High confidence exists in the small craft
condition developing for the outer waters. There is a 70 percent
chance of Small Craft Advisory conditions for the northern nearshore
waters...with a 30 percent chance for inner waters in the Southern
Small Craft Advisory (see laxmwwlox).