Area Forecast Discussion
Issued by NWS Los Angeles, CA
FXUS66 KLOX 031035
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
335 AM PDT TUE MAY 3 2016
Night through morning low clouds and fog are expected for many
areas west of the mountains through Wednesday, followed by
partial afternoon clearing. A slow moving low pressure system
will bring a chance of showers and thunderstorms Thursday through
Sunday, along with cooler conditions. Temperatures will likely
return to near normal early next week as high pressure returns.
The marine layer is about a 1000 feet deep at the moment. But sfc
gradients are just barely onshore and there is no eddy to speak
of and as a result there are hardly any low clouds. It looks like
this mornings low clouds will be confined to the immediate central
coast and the long beach area. Otherwise skies will be sunny in
the morning and partly cloudy in the afternoon as some high level
cloud advect in ahead of an upper level trof. The sunshine and the
reduced onshore flow will allow all areas to warm a few degrees
from Mondays values.
A wise old long retired forecaster here once said of the marine
layer stratus "just forecast persistence and then you`ll only be
wrong once" Will foolishly go against this advice and once again
forecast a fairly robust marine layer stratus deck tonight on the
basis of the approaching upper level trof which will provide
enough low level lift to create the clouds. The onshore flow is
not really what it should be so may well be another stratus free
start to the day.
On Wednesday the trof cuts off into a closed low and approaches
the coast. clouds and onshore gradients will increase through the
day and hgts will fall. Look for max temps to fall 4 to 8 degrees
from todays readings.
The upper low moves from a point about 60 NM west of KSFO early
Thursday morning to a point 60 miles SW of Point Conception late
Thursday evening and then to the Needles area by afternoon
Friday. There is not much moisture to work with and am not
expecting too much rainfall maybe a quarter inch and more like a
tenth of an inch from hit or miss showers that will occur over the
two day period. The big question mark will be afternoon cloud
cover. If afternoon skies are partly cloudy the high sun angle sfc
heating below the cool upper air aloft will form a very good
convective environment. If skies are more on the overcast side of
things there will be much less in the way of shower activity. The
best chance of TSTMs on Thursday will be over the interior with
some vorticity moving overhead. On Friday the area will switch
over to all of LA and VTA counties as the cold pool aloft moves
directly overhead for maximum instability. snow levels will fall
to about 6000 feet and there could be some local accumulations at
the highest elevations.
Scattered shower activity will persist Saturday across the
interior and especially the mtns as the upper low moves into SE
NV and spins several vort lobes into the area from the NE. In fact
if skies are fairly clear there could be quite a bit of afternoon
The upper low will then pull so far to the east that it will no
longer affect Srn CA and a ridge will begin to nose in from the W.
This will kick off a clearing and warming trend.
At 1020Z, the marine inversion at KLAX was around 1400 feet. The
top of the inversion was 2300 feet with a temperature of 19 degrees
N of Point Conception...
Moderate confidence with 12z tafs. 30% percent chance that cigs
will scour out +/1 2 hours from tafs. low confidence for mvfr
cigs. good confidence that cigs will return back and be a bit
deeper with a better chance of ifr/low mvfr cigs.
S of Point Conception...Low to moderate confidence with areal
coverage and timing of stratus. 30 percent chance for ifr cigs for
klax and 30 percent chance that ifr cigs will not develop at klgb
this morning. Higher confidence for ifr/mvfr cigs across most
coastal sites later tonight. +/- 2 hours from current tafs.
KLAX...low to moderate confidence in 12Z TAF. 30 percent chance
for ifr cigs to develop between 12z-16z this morning. Higher
confidence for ifr/mvfr cigs and vsbys later this evening. +/- 2
hours from 12z taf time.
KBUR...high confidence in 12Z TAF for VFR conditions are
anticipated through the TAF period. There is a 30% chance of IFR
conditions 09Z-17Z Wed.
High confidence for coastal waters remaining below SCA levels
through Friday morning. There is a 60% chance for SCA level winds
from Friday afternoon to late Friday night across the very
western portion of zone PZZ670 from Point Piedras Blancas to Point
There is a 60% chance of patchy dense fog off the Orange County
Coast this morning...with less chance to 40% off the Los Angeles