Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 06/26/19

Area Forecast Discussion

National Weather Service Los Angeles/Oxnard CA

 815 PM PDT Tue Jun 25 2019

.SYNOPSIS...25/1204 PM.

Night and morning low clouds will cover the coasts and valleys
through the end of the week. Interior areas will be mostly sunny.
Breezy conditions will develop in the mountains and deserts today
through Thursday. Daily maximum temperatures will be cool through
Friday.

&&

.SHORT TERM (TUE-FRI)...25/814 PM.

***UPDATE***

Latest forecast is in good shape with no updates expected. It was
another typical June Gloom type day across the forecast area west
of the mountains. The combination of a broad upper trough over
California and a moderately strong onshore flow at the surface
with LAX-DAG gradient peaking just under +9 MB this afternoon
allowed The marine layer to reach around 3000-3500 ft today. The
inversion above the marine layer was quite strong, and therefore
made it tough for the stratus to scour out today, especially
across coastal areas. High temps were around 6-10 degrees cooler
than normal for most areas today.

There was some drizzle and even some measurable light rain that
occurred early this morning across portions of the Santa Barbara
South Coast and adjacent foothills, as well as coast and valleys
of Ventura County. Up to a 0.08" fell across the foothills of the
Santa Ynez Range with mostly 0.02" across Ventura County coastal
areas. There were a few reports of patchy drizzle across portions
of L.A. County as well with no measurable rainfall. There is a
chance for additional patchy drizzle early Wednesday morning
across the same locations.

With the LAX-DAG onshore gradient continuing to be over +8 MB this
evening, local gusty SW winds 30 mph with gusts to 45 mph will
continue around the Lake Palmdale area and adjacent foothills
through this evening. Otherwise most areas in the Antelope Valley
will experience gusts around 20 to 30 mph this evening.

This persistent weather pattern will continue through the next
few days. Although there will continue to be a lingering upper
trough overhead, thickness and heights will increase slightly
Thu/Fri which should cause the marine layer to shallow up
slightly both days which would allow for a few degrees of warming
along some inland areas, but low clouds still expected to be
stubborn to scour out along coastal areas.

***From Previous Discussion***

Overall, 12Z models in good synoptic agreement through the
short-term period. At upper levels, low develops off the Pacific
Northwest tonight/Wednesday then moves slowly inland on Thursday
and Friday. Near the surface, onshore flow peaks in strength today
then weakens Wednesday through Friday (with some weak
northwesterly flow developing).

Forecast-wise, the blandness of June continues. Main issues will
continue to be the extent of the marine layer stratus and
temperatures. Currently, AMDAR soundings indicate marine
inversion around 3000 feet with limited clearing across the
coasts and coastal valleys. With strong onshore gradients, stratus
will push once again into the coastal slopes by Wednesday morning
with the possibility of some patchy drizzle. For Thursday and
Friday, the inversion should become more shallow and stratus less
extensive with rising H5 heights and offshore gradient trends.
Additionally, the weakening onshore gradients will allow for much
better clearing each afternoon from Wednesday through Friday.
Otherwise, skies should be mostly clear through the period.

As for temperatures, coasts and coastal valleys will exhibit a
gradual warming trend through Friday with temperatures at or a
couple degrees above normal by Friday. For inland areas, there
will actually be some slight cooling Wednesday/Thursday with some
slight warming on Friday.

As for winds, the gusty onshore (southwesterly) winds across the
mountains and deserts will gradually diminish through the period,
remaining below advisory levels. Will have to watch the
development of some northerly winds Wednesday night through
Friday, especially during the evening hours. There could be some
low-end advisory level Sundowner Wednesday evening and Thursday
evening across the western half of the Santa Ynez range.

.LONG TERM (SAT-TUE)...25/202 PM.

For the extended, models start to diverge in their respective
solutions. The GFS gradually builds an upper level ridge (from
the southwest) over the area while the ECMWF maintains a trough
(and cyclonic flow) over the area. The GFS would be a warmer and
less cloudy scenario then the ECMWF.

Given the time of year and looking at ensembles, will continue to
veer the extended forecast towards the warmer GFS solution. So,
generally weak onshore gradients will continue through the period
with some northerly gradients during the evening and overnight
hours. So, there will continue to be some locally gusty northerly
winds during the evening and overnight hours in the usual spots
(Santa Ynez Range and I-5 Corridor). The marine inversion will be
shallower through the period with less extensive stratus coverage
during the night and morning hours. Other than the limited
stratus, skies should remain mostly clear. Temperatures will
continue to exhibit a warming trend with Monday likely the warmest
days for most areas.

&&

.AVIATION...26/0034Z.

At 2332Z at KLAX, the marine layer was 3000 feet deep. The top of
the inversion was around 4000 feet with a temperature near 18
degrees Celsius.

N of Point Conception...Expect a persistent stratus pattern once
again this evening. CIGs are expected to be redevelop to IFR
category +/- 1 hours from 00Z TAF. There is a 30% chance that IFR
cigs will not jump up to MVFR after 15-16z Wed and scour out
within an hour of TAFs. Lower confidence for IFR Cigs to develop
at KPRB. There is a 40% chance for VFR Conds 11z-16z.

S of Point Conception...Expect a persistent stratus pattern.
Moderate confidence for IFR CIGs becoming MVFR anytime late this
eve or after midnight. There is a 30% chance CIGs will remain IFR
overnight through 16z before rising to MVFR. There is a 30%
chance for CIGs to scour out along L.A. Coast after 21z Wed.
Otherwise, expect Valley TAF sites to scour out +/- 1 hour from
)00Z TAF.

KLAX...Moderate confidence in the 00z forecast. There is a 30
percent chance of VFR conditions after 21z tomorrow afternoon.

KBUR...Moderate confidence in the 00z forecast. There is a 30
percent chance of MVFR Cigs through 23z tomorrow.

&&

.MARINE...25/1218 PM.

For the Outer Waters, an SCA remains in effect for PZZ670 for
this afternoon through Thursday night. Good confidence that the
entire outer waters will need a SCA by Wednesday evening. Small
craft advisory winds should continue Thursday through Saturday,
with a 40 percent chance of gales between Thursday afternoon and
Friday night.

For the Inner Waters north of Point Sal, winds and seas will
likely remain below SCA levels through early Wednesday, then there
is a 50 percent chance of SCA level winds each afternoon and
evening between Wednesday and Saturday.

For the Inner Waters south of Point Conception, winds and seas
will likely remain below SCA levels through early Wednesday, then
a 40 percent chance of SCA level winds across the western half of
the Santa Barbara Channel Wednesday late afternoon and evening,
then a 50% chance each afternoon and evening between Thursday and
Saturday for the same western portion of the Santa Barbara Channel.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory in effect until 3 AM PDT Friday for zone
      670. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (FRI-TUE).

No significant hazards expected.

&&

$$

PUBLIC...Kaplan/Thompson
AVIATION...Kaplan
MARINE...Sweet
SYNOPSIS...Phillips/Arnold

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