Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 251047

346 AM PDT THU AUG 25 2016


High pressure aloft will keep mostly clear skies and near
normal temperatures over the region today, followed by cooler
temperatures into the weekend as a weak upper level trough of low
pressure moves in. High pressure will build back into the area
Sunday and into early next week for above normal temperatures in
many areas.



The latest water vapor imagery indicates an upper-level ridge of
high pressure near 25N and 125W, or about 700 miles southwest of
Los Angeles, and an upper-level trough of low pressure digging
into the Snake River Valley in Idaho. Closer to the surface,
onshore flow is strengthening this morning and should continue to
increase through Friday as the trough of low pressure flattens the
ridge. A cooling trend should be expected through Friday with a
deepening marine layer depth. A marine layer depth near 1200 feet
this morning should deepen to around 1500 feet later this morning
and could deepen to near 2000 feet by Friday morning. With warm
ocean temperatures over the Southern California Bight, stratus
formation continues to struggle this morning south of Point
Conception. With this in mind, confidence in stratus forecast
south of Point Conception is lower relative to areas north of
Point Conception.

High pressure aloft will start to rebound over the weekend and a
warming trend will take shape. The marine layer will likely thin
some on Saturday, then thin substantially for early next week as
weakening onshore flow develops and the subsidence aloft clamps
down on the marine layer.


With high pressure building back in aloft and less onshore flow, a
warming trend will continue into early next week. The warmest day
of the week looks to be on Monday when the ridge axis moves over
the area. Daytime high temperatures could reach the century mark
in the warmest valley areas and the Antelope Valley.

A trough of low pressure near 40N and 140W early this morning will
wobble around its general vicinity through early next week as the
ridge of high pressure blocks its path. A developing low pressure
system in the Gulf of Alaska will likely phase with the trough,
break down the ridge, and push it out of the way on Tuesday. A
cooling trend looks on tap for latter half of next week along
with a deepening marine layer and stronger onshore flow.



At 0945Z...the marine layer was 1100 feet deep at KLAX. The top
of the inversion was near 4200 feet with a temperature near 24
degrees Celsius.

North of Point Conception...High confidence in LIFR conditions
persisting through 16z. 30% chance that KSMX/KSBP could see VLIFR
conds between 10z-14z. Moderate to high confidence for a similar
time for LIFR to IFR conds to develop tonight into Friday morning.
There is a 30% chance that KPRB will remain VFR.

South of Point Conception...Moderate confidence in IFR conditions
to affect portions of the LA/VTU/SBA coastal terminals. 20%
chance that LAX could stay VFR through 16z. Low confidence with
timing of IFR to low MVFR cigs across coastal areas tonight into
Friday. 10% chance that IFR conds will affect KBUR and KVNY after
13z this morning. Better chance to 50% for IFR cigs to reach
KBUR/KVNY early Friday morning after 10z.

KLAX...Low confidence with timing and moderate confidence with IFR
to low MVFR conditions after 10Z this morning. Otherwise, VFR
conditions will persist. Low clouds should scour out within an
hour of 12z Taf time. Continued low confidence with timing of
stratus to return. Better chance that MIFR-MVFR cigs occur a few
hours earlier. But 30% chance that cigs could be delayed a few
hours from 12z tafs.

KBUR...High confidence in VFR conditions this morning. Low
confidence that IFR cigs developing after 10z Fri morning.


.MARINE...25/230 AM.

Not expecting any SCA level winds or gusts through at least Sat
morning. 40% chance that SCA will be needed for the outer waters
S of Point Sal. to west of San Nicolas Island. There will be
higher confidence for a SCA across the outer waters S of Point Sal
by Sunday afternoon...then affecting all the outer waters by
Monday afternoon. Isolated Gales possible around Pt. Conception by
Monday Evening.



24/745 PM.

Weak high pressure aloft will be the primary influence on our
fire weather conditions for another night before a low pressure
trough begins to develop over the state Thursday to bring cooler
temperatures. In the meantime, the current weather pattern will
support another night of weak to moderate Sundowner conditions
across the Santa Barbara South coast, primarily west of Goleta and
the adjacent hills of the Santa Ynez Range. As of 7 pm, the SBA-
SMX gradient was -3.5 mb, similar to last evening. Peak wind
gusts so far this evening have been 42 mph at Refugio and 30 mph
at San Marcos Pass. The upper ridgetops near the new Bar Fire
(which grew to around 20 acres) will continue to see these gusty
north winds through much of the night, with the potential for some
gusty winds to surface to near the coast. For the Rey fire,
lighter north winds will likely impact the ridgetops
tonight...maintaining poor humidity recoveries at the upper
elevations. This northerly flow will continue to push any smoke
and ash from the Rey Fire southward over Santa Barbara and
Montecito tonight. In addition, there will continue to be smoke
impacts across western portions of Ventura county.

As the low pressure develops over the state, expect some relief in
temperatures and humidity Thursday and Friday. This weather
pattern will eliminate any Sundowner chances, while producing
stronger onshore winds for locally gusty west and southwest winds
both Thursday and Friday through areas such as the Highways 14 and
138 corridors. High pressure begins to rebuild over the state this
weekend and will peak early next week. This pattern will result in
a return to above normal temperatures for all but the immediate
coastal area and a broad extent of minimum relative humidities
less than 20 percent.





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