Scientific Forecaster Discussion
Southwest California area forecast discussion
National Weather Service Los Angeles/Oxnard California
430 am PDT Tuesday Sep 2 2014
..updated aviation discussion...
A weak upper level trough will bring cooler temperatures...onshore
breezes...and overnight low clouds and fog through Thursday. Most
daytime temperatures will be near or below normal. High pressure is
expected to return Friday and Saturday and warm temperatures a few
degrees. Another cooling trend is expected early next week.
Short term (today-thu)...
really dull weather on tap. Today will be the last gasp of the high
pressure system that dominated the Holiday weekend. Heights will start
out at 591 dm this morning but will fall a few dm as the high shifts
east while a Pacific northwest trough begins to move in. 1800 foot marine layer
combined with a weak eddy will bring marine stratus to all coasts
and valleys this morning. Skies should be mostly clear by late morning
however as the eddy is not that strong. There is enough of a onshore
push up north to keep a few of the central coast beaches cloudy. A
good dose of inland cooling today compared to ydy and a few degrees
of cooling across the coasts and valleys. The deeper than normal marine
layer will keep maximum temperatures below normal.
Not much change Wednesday. If you like to look at weather maps you
will notice the upper high has pushed well eastward and that the
western portion of the nation is under the SW flow form a long wave
trough. But this will not affect the weather much. Low clouds for the
coasts and all valleys. Mostly sunny afternoon with maximum temperatures below
normal and in fact a couple degrees cooler than today.
More trofing and lower heights slated for Thursday. More marine clouds.
Still sunny in the afternoon. Thursday will be the coolest day of
the next 7 with maximum temperatures 6 t0 12 degrees below normal.
Long term (fri-mon)...
all extended models agree that the upper high will push slightly
westward and bump up The Heights and smoosh the marine layer some. Look
for a small increase in temperatures and a small decrease in marine layer
Extend models do develop another hurricane near Baja California and move it along a
path similar to Marie (a little further to the north) next Sunday.
GFS and ec then disagree abouts its fate but no matter what happens
it does not look like it will affect so cal weather although it
might affect the surf.
Overall...moderate confidence in 12z taf package. Latest amdar
soundings indicate marine inversion based around 1500 feet...and
stratus/fog has filled into the coastal valleys early this morning.
Through late morning...IFR/MVFR conds will prevail south of Point
Conception...with IFR/LIFR conds across the central coast. Clouds
should dissipate by early afternoon (at the latest) but will return
this evening and overnight.
Klax...moderate confidence in 12z taf. Timing of dissipation of MVFR
conds could be an hour or two later than current 18z forecast. For
tonight...high confidence in stratus return...but low confidence in
Kbur...moderate confidence in 12z taf. High confidence in return of
stratus tonight...but low confidence in timing.
Overall...moderate to high confidence in current forecast. Through
the week...weak to locally moderate west to northwest flow will
continue across the coastal waters. There will likely be some local
gusts reaching small craft levels around Point Conception this
afternoon and evening...but do not expect the gusts to be widespread
enough for any advisories.
A long period south swell (18-20 seconds) originating from the
southern hemisphere will arrive on Thursday night...then peak Friday
through Sunday. Elevated surf and high rip current risk will be
likely across south facing beaches of Los Angeles and Ventura
counties during this time. While the surf heights will not be nearly
as high as we saw with Hurricane Marie...there is a chance that high
surf advisory thresholds of 6 feet or greater will occur across
favored south facing shores.