Area Forecast Discussion
Issued by NWS Los Angeles, CA
FXUS66 KLOX 290603
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
1100 PM PDT SAT MAY 28 2016
Updated Aviation Discussion
The cut-off low pressure system currently overhead will once
again support the slight chance for afternoon thunderstorms
across the mountains and pushing into the Antelope Valley on
Sunday. High pressure aloft will build into the area by the
middle of next week, supporting much warmer conditions that
will likely persist into next weekend.
A weak upper low just to the west of Point Conception was in a
good position to rotate a weak lobe of PVA into SBA county this
afternoon. The lift from the PVA interacted with weak instability
over the interior sections to spawn about a half dozen TSTMs. The
TSTMs were short lived pulse storms that likely produced brief
heavy downpours and perhaps some small hail.
The marine layer was slow to clear today and there was no clearing
across the south facing beaches of LA and VTA counties as well as
the central coast. The Marine layer stratus deck will slowly
reform overnight and by dawn low clouds will again cover the
coastal and vly areas.
Moderate onshore flow and the late clearing kept max temps several
degrees blo normal across the coasts and vlys but 574 DM hgts and
plenty of sunshine allowed the interior to warm to near normal
Forecast is in good shape and no updates are planned. The big
question mark is tomorrow afternoon`s convection. The upper low
will sit right atop of the area. This will mean better instability
but less in the way of low level dynamics. Given the very steep
sun angle think that there will be enough differential heating to
kick of some storms.
The weak upper level low will drift se across the forecast area
tomorrow morning, then into sern CA for Sun afternoon. An e-w
oriented upper level trof will linger over srn ca Sun night and
Mon, while at the same time upper level ridging builds into
central and nrn CA. The upper ridge will expand into swrn ca Mon
night and Tue.
The marine layer pattern will continue over the next few days, with
the inversion forecast to gradually strengthen and lower each day,
most pronounced Mon night and Tue as the upper ridge builds in and
boundary layer temps warm up. Extensive night and morning low clouds
and fog can be expected to affect the coast and adjacent vlys
tonight thru Tue morning, altho the inland extent of the low clouds
will diminish considerably Mon night due to the shrinking marine
inversion. There will be the possibility of afternoon cu buildups in
the mtns Sun thru Mon, but for Sun there should continue to be
enough moisture and instability for the formation of isolated
showers or thunderstorms in far sern SLO County, Cuyama Vly, the
mtns of SBA/VTU/L.A. Counties and in the Antelope Vly. Any
thunderstorms that develop could drift s into the adjacent vlys over
VTU/L.A. Counties as well by late Sun afternoon or early evening.
The 12Z NAM does indicate the best chance of thunderstorms Sun
afternoon to be over eastern San Gabriel Mtns, but even so a slight
chance of showers and thunderstorms is in the forecast for all of
the above mentioned areas. Otherwise, mostly clear skies are
expected over the forecast area for the most part Sun thru Tue. A
typical onshore flow pattern is expected each afternoon and evening,
with locally gusty sw to nw winds for the foothills, mtns and
Temps for Sun are forecast to be generally 3 to 6 deg below normal
for the cst and adjacent vlys, while inland vlys, mtns and deserts
will be near normal to slightly above seasonal norms. For Mon, temps
will warm a few degrees, especially in the interior areas, mtns and
deserts, where highs should be 4 to 10 deg above normal. For the
coastal plain, Santa Ynez Vly, and vlys of VTU/L.A. Counties, highs
on Mon will be 2 to 6 deg below normal overall. It`ll be warmer
still for Tue with many areas away from the coastal plain warming to
4 to 12 deg above normal. Highs in the warmest vlys on Tue should
reach the upper 80s to mid 90s.
The EC and GFS are in decent agreement Wed and Thu with upper
ridging over the area. For Fri and Sat, the EC keeps the fcst area
on the w side of a large upper ridge, while the GFS brings a broad
upper trof to the CA cst Fri, then upper troffiness moves over the
area thru Sat while a weak upper low swings into nrn Baja from the e
Pac. Either solution will keep dry and warm conditions over swrn CA
thru the extended period. Night and morning marine layer clouds will
continue to affect mainly coastal areas Wed, then be confined to the
L.A. County coast Thu thru Sat. Otherwise, mostly clear skies will
prevail across the region Wed thru Sat. There will continue to be
typical onshore flow afternoon and evening hours, with locally gusty
sw to nw winds in the foothills, mtns and deserts.
Temps will warm to about 5 to 12 deg above normal for many areas
away from the coastal plain Wed thru Fri, with slight cooling
expected on Sat. The warmest days should be Thu and Fri, with highs
in the warmest vlys and foothills reaching the upper 80s to mid 90s,
except mid to upper 90s in the Antelope Vly.
At 0535Z at KLAX the marine layer was 1500 feet deep. The inversion
top was at 2600 feet with a temp of 17 degrees C.
Good confidence in TAFs. Cat changes and clearing times may be off
by +/- 1 hour. There will be isolated TSTMs over the mtns aft 22Z.
KLAX...Good confidence in TAF. There is a 20 percent chc of VFR
conds aft 21Z.
KBUR...Good confidence in TAF. IFR/MVFR transitions and clearing
could occur +/- 1 hour from fcst time.
28/900 PM PDT
Sub small craft advisory level short period waves currently across
portions of the outer waters will gradually diminish overnight.
Small craft conditions for winds or seas are not currently
expected through at least Thursday. The northwest swell currently
across the coastal waters is expected to gradually diminish
through the middle of next week. A long period south swell is
expected to reach the coastal waters by Tuesday, peaking
Wednesday, before gradually diminishing.