Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 06/21/20
Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
903 PM PDT Sat Jun 20 2020
Night to morning low clouds and fog will affect the coast and
some of the coastal valleys tonight through next Saturday.
Otherwise skies will be mostly clear through the period except for
some high clouds on Wednesday. Gusty onshore winds will affect
the mountains and deserts during the afternoon and evening hours
through the coming week. Temperatures will be a few degrees below
normal along the coast and near to slightly above normal inland.
.SHORT TERM (SAT-TUE)...20/901 PM.
The latest fog product imagery shows stratus well-entrenched and
stretching into the coastal and valley areas this evening. Stratus
should continue to fill in overnight and into Sunday morning. The
latest AMDAR soundings from KLAX indicate a marine layer depth
near 1650 feet deep, which agrees well with 00Z KVBG RAOB
soundings. The current forecast of a marine layer depth near 1800
feet is reasonable, but the latest NAM-WRF solutions suggest the
marine layer deepening to closer to 2300 feet late this evening
or later tonight, then thinning toward daybreak Sunday.
The marine layer should thin and onshore flow should weaken some
over the into early next week as high pressure aloft builds east
into the California coast through Monday.
The beaches and coastal areas will likely to struggle to clear
again on Sunday afternoon and clouds will likely hug the coast as
the high pressure building in aloft clamps down on the marine
layer. A strong marine inversion will likely inhibit the clouds
from mixing out.
A few tweaks will be made to the forecast to account for an
earlier arrival tonight and slow clearing on Sunday.
***From Previous Discussion***
Upper level ridging will slowly build over the area thru early
next week with H5 heights increasing from about 588 dm today to
around 592 dm by Mon afternoon, with little change expected
The upper level ridging will help to gradually lower the marine
inversion through early next week. The marine layer depth should
be around 1200 to 1800 ft or so tonight into Sun morning, and
about 800 to 1200 ft Sun night into Mon morning, and again Mon
night into Tue morning. The marine layer pattern will continue
west of the mtns with night and morning low clouds and fog for the
coast and vlys, altho the inland intrusion of the low clouds will
decrease thru early next week. In fact, it looks like the low
clouds should be confined mainly to the coastal plain Sun night
into Mon morning, with just some low clouds and fog extending into
the adjacent vlys. A further decrease in inland extent of the low
clouds is expected Mon night into Tue morning as well. The low
clouds should clear to or off the coast each day thru Tue, but
continued strong onshore gradients may result in only partial
afternoon clearing at some of the beaches. Otherwise, mostly clear
skies can be expected across the region through the period.
The NAM forecasts the gradients from LAX-DAG to continue to be
quite strong Sun afternoon at around +9.2 mb, then turn slightly
lower to +8.8 mb Mon afternoon and +8.4 mb Tue afternoon. Breezy
to gusty S to W afternoon and early evening winds will continue
across many areas each day. The strongest winds should be in the
Antelope Vly on Sun, but gusts should remain at sub-advisory
Temps on Sun are forecast to be several degrees below seasonal
norms for the coast and adjacent vlys, and several degrees above
normal for interior areas. On Mon, the coast and vlys should warm
to near normal to a few degrees below normal, while the interior
vlys, mtns and deserts heat up further to about 4-10 deg above
normal. Coastal areas should remain several degrees below normal
on Tue, while the vlys, mtns and deserts warm up further to about
4-12 deg above normal. Highs on Tue in the warmest interior vlys
and Antelope Vly should reach the low 100s.
.LONG TERM (WED-SAT)...20/140 PM.
Upper level ridging will persist into Wed. The EC forecasts
upper level ridging to continue Thu thru Sat, while the GFS brings
a weak upper level trof into the region Thu into Fri with weak
upper ridging moving back in Sat. The EC is the warmer solution
overall but went with a blend of the EC and GFS for the extended
At the surface, good onshore gradients will continue with the
marine layer pattern persisting. Night and morning low clouds and
fog are expected mainly for the coastal plain with only minor
intrusion into the adjacent vlys. Otherwise, mostly clear skies
will continue thru the extended period except some hi clouds
should bring a period of partly cloudy skies to the area Tue night
Temps will continue to be about 4-12 deg above normal on Wed for
the vlys, mtns and deserts, with slightly cooler than normal
conditions for the coast. The coast and vlys should turn slightly
cooler Thu thru Sat to near normal to slightly above normal.
However, the far interior vlys, mtns and deserts should be
slightly above normal overall thru the period.
At 23Z, the marine layer depth was around 1800 feet deep at KLAX.
The top of the inversion was around 3800 feet with a temperature
of 24 degrees Celsius.
North of Point Conception, moderate confidence in the current
forecast. LIFR to IFR conditions will spread into coastal and
coastal valley terminals through 06Z, then likely drop to the
LIFR category between 06Z and 16Z. There is a chance of VLIFR
conditions between 10Z and 14Z. Conditions should improve one
category between 15Z and 17Z. VFR conditions at coastal terminals
should develop about 30 minutes to an hour later than today.
South of Point Conception, moderate confidence in the current
forecast. IFR to MVFR conditions will spread into coastal and
coastal valley terminals through 08Z. There is a chance of
terminals becoming predominately IFR between 10Z and 16Z.
Conditions should improve one category between 16Z and 18Z. VFR
conditions should develop as soon as 18Z, or as late as 22Z. KOXR
and KSBA may not clear at all on Sunday.
KLAX...MVFR conditions will likely continue through at least 19Z.
There is a 30 percent chance of IFR conditions between 10Z and
16Z. Conditions should improve one category between 16Z and 18Z.
VFR conditions should develop as soon as 19Z, or as late as 21Z.
KBUR...MVFR conditions will spread into KBUR between 04Z and 07Z.
There is a 60 percent chance of IFR between 09Z and 16Z.
Conditions should improve one category between 15Z and 17Z. VFR
conditions should develop around 18Z.
Overall, moderate to high confidence in forecast. There is a 60%
chance of Small Craft Advisory (SCA) level conditions over the
outer waters north of Point Sal. Gusty NW winds will then expand
in areal coverage on Sunday, and there is a 60% chance that winds
will exceed SCA level across the outer waters from Point Sal to
San Nicolas Island by Sunday afternoon. Then on Monday, the focus
of the gusty winds will be focused from Point Conception to San
Nicolas Island. For both Sunday and Monday, there is a 30% chance
that SCA level winds will affect the western portion of the Santa
For Tuesday through Thursday, high confidence that winds and seas
will be below SCA criteria.
Night through morning patchy fog will continue across the waters
through next week. North of Point Conception fog may be locally
dense with visibility under one nautical mile.
PZ...Small Craft Advisory in effect until 3 AM PDT Monday for zone
670. (See LAXMWWLOX).
Small Craft Advisory in effect from 3 PM Sunday to 3 AM PDT
Monday for zones 673-676. (See LAXMWWLOX).
.HAZARD POTENTIAL OUTLOOK (TUE-SAT).
No significant hazards expected.