Area Forecast Discussion
Issued by NWS Los Angeles, CA
FXUS66 KLOX 010311
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
811 PM PDT SAT APR 30 2016
Expect fair to partly cloudy skies on Sunday, with a slight chance
of showers or thunderstorms across the local mountains in the
afternoon and evening hours. Warmer weather is expected early
next week as weak high pressure builds over the region, but
another trough of low pressure could bring showers and cooler
conditions to the area late next week.
A weak vort max moved over eastern L.A. county and while it did
not have enough oomph to produce any thunderstorms it did produce
a batch of showers a few of which made it up and over the San
Gabriels bringing rain to portions of the San Fernando and San
Gabriel valleys. The showers are rapidly diminishing at the moment
and will be gone soon.
The next real problem is the marine layer cloud forecast. Current
forecast calls for an eddy to spin up and to bring clouds to the
coasts and most of the vlys south south of Point Conception. The
00Z run of the NAM continues to support this idea. But...skies are
very clear right now. There are some indications of an eddy (KLGB
has a weak south wind) so the current marine layer fcst is the
best bet...but its not a slam dunk.
Mdls also hinting at a slow to no clearing day for the csts
tomorrow but feel that is over done since the eddy is not
forecast to last into the afternoon.
The instability will be a little better tomorrow with CAPE values
of 500-750 J/kg, but the upper low will be further east. Depending
on what happens in the next couple of hours, the slight chance of
showers and thunderstorms may be removed from the forecast for
this afternoon and evening. We will leave the slight chance of
showers/t-storms in the forecast for tomorrow for the Antelope
Valley and mountains of Los Angeles, Ventura, and Santa Barbara
counties, but would not be surprised if future shifts remove them.
Tonight through Monday the upper low currently near Needles, CA,
will move east and weaken below a longwave ridge. As this happens,
the marine layer will shrink but the inversion will sharpen. As a
result the night/morning low clouds and fog may because more
organized and fill in across the coastal and valley areas. This is
reflected in the current forecast. The Catalina Eddy should help
with the development of the stratus south of Pt. Conception
tonight and Sunday morning, but the Central Coast may remain cloud
free. The boundary layer moisture in the NAM suggests a better
chance for stratus on the Central Coast both Sunday and Monday
With the upper low moving east and high pressure taking over,
there should be slight warming each day through Tuesday.
Temperatures should be slightly above normal by Tuesday, with
temperatures in the 60s at the immediate coast, mid to upper 70s
for inland portions of the coastal plain, and 80s in the valleys.
Other than night/morning stratus and the slight chance of
showers/t-storms for interior areas on Sunday, generally fair
skies are expected for most of the populated areas through
Tuesday, with no wind issues anticipated.
A cooling trend should begin by Wednesday with an upper-level
trough approaching from the northwest. Models are in good synoptic
agreement that a cutoff low will develop over the area Thursday
night through Friday, then slowly drift east on Saturday. There
will be a chance for hit and miss showers in most places late
Wednesday night through Saturday. At this time, it looks like late
Thursday through Friday would be the best chance for any showers.
Thunderstorms are not in the forecast at the moment, but they may
need to be added at a later time, as 500 mb temps are as low as
-25 deg C when the center of the upper low moves overhead.
AT 2300Z at KLAX there was no Marine layer nor was there an
Good confidence in TAFs through 08Z. Lower confidence after 08Z
for coastal and vly TAFs KSBA and southward due to uncertainty in
timing of stratus arrival. Stratus could arrive at any time
between 08Z and 13Z. Lower confidence in clearing fcst as BKN high
MVFR or low VFR cigs could remain late into the afternoon.
KLAX...Good confidence in TAF through 08Z. There is a 30 percent
chc of MVFR cigs 08Z-11Z. There is a 30 percent chc that MVFR cigs
will persist until 23Z.
KBUR...Good confidence in TAF through 09Z. There is a 30 percent
chc of MVFR cigs 09Z-12Z. There is a 30 percent chc that SCT
conds will develop aft 22Z.
The gusty northwest winds have retreated west and will continue
over the outer waters through late tonight...as high pressure
weakens offshore. Nearshore...winds will be mainly light through
tonight. Locally moderate southeast winds 10 to 15 knots are
expected Sunday morning over the San Pedro Channel and Santa
Monica Basin up to around Point Mugu...which will likely create
locally choppy seas for mariners.
Seas over the outer waters will remain near or above 10 feet
through Sunday morning. Otherwise sca conditions are not expected
Sunday afternoon through Wednesday. Northwest winds are expected
to increase Thursday and there is a chance sca conditions will
exist over the entire area Thursday through Friday. A south swell
will continue to build through Sunday and extra currents and
surging as well as hazardous surf are likely along exposed south
facing shores through Monday.
CA...Beach Hazards Statement in effect through Sunday evening For
zones 34-35-40-41-87. (See LAXCFWLOX).
PZ...Small Craft Advisory in effect until 9 PM PDT this evening
For zones 645-650. (See LAXMWWLOX).
Small Craft Advisory in effect until 3 AM PDT Sunday For
zones 670-673-676. (See LAXMWWLOX).