Scientific Forecaster Discussion
Southwest California area forecast discussion
National Weather Service Los Angeles/Oxnard California
1245 PM PDT Thursday Jul 31 2014
an upper level high...east of the region...will keep temperatures
above normal through the weekend. Night and morning low clouds are
expected along most coasts through the period. A slight chance of
thunderstorms are possible in the mountains and deserts on
Sunday...due to some monsoonal moisture.
Short term (today-sun)...a strong high pressure area aloft
continues to bring warmer than normal temperatures to the area. Temperatures today
have been very similar to Wed, mostly within a couple degrees. Some
small cumulus developing over the mountains today but minimal vertical
development so far and not expected them to develop into
thunderstorms. Expecting another round of sub-advisory level
northerly winds in the sba area this evening.
Not too much change in the pattern through Sat. Gradient trends are
Pretty Flat and models suggest just a very slight cooling trend
going into the weekend as the high weakens a tad. Soundings this
morning showed a stronger marine inversion and we could see a
slightly greater coverage of overnight low clouds by the weekend
south of pt Conception. Otherwise, not much change with highs still
a few degrees above seasonal norms.
Sat night into Sunday the forecast gets a little tricky, especially
for the eastern third of our forecast area. The models continue to
indicate a significant increase in monsoon moisture across
southeastern California, with la County being on the far western
extent of that moisture. A trough moving into northern California will
provide an opposing force to the moisture advection from the
southeast, but whether it will be enough to keep it east of the
County line is still very much in question. Certainly the slight
chance of thunderstorms for sun looks reasonable given how close the
moisture is. If the northern California trough ends up being weaker and the monsoon
moisture axis pushes farther west we could be looking at a more
significant tstorm outbreak across la County (and possibly Ventura
county) with the possibility of heavy rain and even flooding. The
latter would also lead to an increase in cloud cover across the
eastern third of the area and likely cooler temperatures than currently
forecast. Will continue to monitor, but at present the models seem
to be favoring areas farther east and south of la County for the
bulk of the activity.
Long term (mon-thu)...if Sunday ends up being active then it's
likely that Monday will have some thunderstorms over the mountains and
deserts, though moisture is definitely on the decrease by that time.
Keeping it dry for now. Otherwise, not much change in
heights/thicknesses through Wednesday with a weak trough lingering just off
the coast. By Thursday the trough is expected to push inland leading to a
few degrees of cooling most areas.
Moderate confidence in 18z tafs with the reduced confidence due to
the uncertainty regarding the marine layer location... intensity...
and duration. A ninety percent chance of the marine layer
returning to the central coast including dense fog at ksmx... eighty
percent that it returns to Oxnard... and with an eddy developing
there is a sixty percent chance of IFR conditions at klax and klgb
overnight and early tomorrow morning. Conditions should clear by
17z in locations other than ksmx. Otherwise and elsewhere VFR
conditions will prevail.
Klax...moderate confidence in 18z taf. A sixty percent chance of
IFR ceilings 09z-17z... otherwise VFR conditions will prevail
throughout the forecast period.
Kbur...moderate to high confidence in 18z taf. A ten percent chance
of MVFR conditions 13z-16z... otherwise VFR conditions will prevail
throughout the forecast period.
Marine...31/900 am PDT
Moderate confidence in continuance of small craft conditions across
the southern outer waters (pzz673-676) through late tonight.
Otherwise and elsewhere... conditions to remain below Small Craft
Advisory levels through the forecast period.
Small Craft Advisory (see laxmwwlox).