Area Forecast Discussion
Issued by NWS Los Angeles, CA
FXUS66 KLOX 270432
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
932 PM PDT FRI AUG 26 2016
High pressure aloft will build into the region through early next
week before being replaced by a deepening low pressure aloft by
mid week, possibly lasting into the weekend. This will result in
a brief warm up to start the week before a prolonged cooling trend
with expanding night to morning marine layer clouds takes hold.
Upper level trough and strong onshore flow brought significant cooling
to the region today, with many inland locations running 10 to 15
degrees below normal. A couple notable high temperatures today
included Paso Robles at 76 degrees and Woodland Hills at 84
degrees. Satellite imagery showing low clouds beginning to fill
in across portions of the coast this evening. With a deep marine
layer and strong onshore flow in place, expecting low clouds to
fill in across most coastal/valley locations overnight into
With upper low pressure system moving eastward on Saturday, there
will be rising heights and some northerly flow aloft that will
help to shrink the marine layer. As a result, expecting low
clouds to burn off a bit quicker on Saturday, with the exception
of the immediate coastal areas where low clouds could linger
due to strengthening inversion. Inland areas away from the coast
are generally expected to see 3 to 6 degrees of warming on
Saturday. There is also some mid level easterly flow that imports
some mid level moisture on Saturday afternoon, so looking for
some afternoon cloud buildups over the local mountains.
00z NAM model continues to show a more significant
warming potential for Sunday/Monday as an upper level ridge of
high pressure builds in over the area while onshore gradients
continue to weaken. Warmest valley locations could approach
100 degrees by Sunday, with high confidence of triple digit
readings on Monday. Also of note, will be the potential for
gusty sundowner winds Sunday night and Monday night. SBA-SMX
gradient expected to peak around -4 mb each night. While the
strongest winds will likely be focused across the western portions
of the SBA South coast (Gaviota to Goleta) and adjacent Santa
Ynez mountains, there will be the potential for some north to
northeast winds gusting up to 25 mph across the higher
elevations of the Rey Fire each night.
*** From previous discussion ***
The marine layer pattern with night and morning low clouds and
fog for coastal areas is forecast to continue tonight thru Mon.
However, the marine inversion should lower enough by Sat night to
prevent the low clouds from moving well inland over VTU/L.A.
Counties. The inversion should then lower further to below 1000 ft
Sun night into Mon morning with low clouds confined to the coastal
plain except the SBA County s cst should remain clear due to
northerly canyon winds. In addition, patchy dense fog can be
expected with the low clouds Sun night and Mon morning. Some mid
level moisture should move in during the period as well, with a
few afternoon cu buildups possible in the mtns. Otherwise, mostly
clear skies will continue thru Mon altho a smoke layer may persist
in a few locations at least into the weekend. Weaker onshore
gradients will persist during the afternoon and evening hours,
with local gusty s to w winds at times in the foothills, mtns and
deserts. Some generally weak offshore flow is also expected later
Sun night into Mon morning, mainly over SLO/SBA Counties and in
the foothills and mtns of VTU/L.A. Counties.
Temps are forecast to have a warming trend Sat thru Mon, with highs
a few degrees below normal on Sat, several degrees above normal away
from the coast on Sun, and 4 to 10 deg above normal for many areas
on Mon. By Mon afternoon, the warmest vlys and foothills will reach
the upper 90s to 102.
There is generally good agreement between the GFS and EC in the
medium range, altho some minor differences show up later next week.
The upper ridge will weakened some for Tue as an upper trof passes to
the north. A lingering, broad upper level trof can be expected along
and off the CA coast Wed thru Fri. The GFS is slightly deeper with
the upper trof with lower 500 mb heights over srn CA than the EC for
Thu and Fri, but both models continue a dry sw flow aloft over the
region. The upper trof will promote stronger onshore flow and a
deeper marine inversion by late next week.
The marine layer pattern will become more organized during the
period, with widespread night and morning low clouds and fog
expected for the cst and vlys including the Santa Clarita Vly by the
end of the week. Otherwise, mostly clear skies will prevail across
the region. Temps will continue well above normal away from the
coast on Tue, then drop each day thru Fri. Temps on Fri are expected
to cool to 4 to 8 deg below normal in all areas. The warmest day
will be on Tue with highs in the warmest vlys and foothills reaching
the mid 90s to 102. By Fri, highs in these areas will only be in the
Marine layer at LAX at 1500Z is 1600 feet deep and the inversion
top is at 4000 feet with a temp of 21.0 degrees C.
Strong onshore flow and deep marine layer will bring a high
probability of low clouds filling in across coastal/valley TAF
locations tonight into Saturday morning. Mostly ifr/lifr cigs
for TAF north of Point Conception, and mostly MVFR category
for TAF sites south of Point Conception. There is a 20-30
percent chance of cigs lowering to IFR category for some
locations south of Point Conception.
KLAX...High confidence of mvfr cigs tonight into Saturday morning
but some uncertainty in arrival time of cigs. There is a 20
percent chance of ifr cigs.
KBUR...High confidence of mvfr cigs tonight into Saturday morning
but some uncertainty in arrival time of cigs. There is a 30
percent chance of ifr cigs.
Small craft advisory conditions are not expected through Sunday
morning. But occasional west gusts to 25 knots may occur in the
west portion of Santa Barbara Basin late Saturday afternoon into
the evening. Northwest winds are expected to increase Sunday
afternoon and there is a of chance small craft advisory
conditions from Piedras Blancas to Point Sal 10-60 nm and from
Point Sal to San Nicolas Island. The Northwest winds are expected
to increase Monday afternoon and there is a chance of occasional
gale-force gusts over the outer Coastal Waters.