Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000
FXUS66 KLOX 260346
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
846 PM PDT Wed Apr 25 2018

.SYNOPSIS...25/507 PM.

A trough of low pressure will approach the West Coast through
Friday before settling over the region through early next week.
This will result in a gradual cooling trend with increasing night
to morning low clouds through Friday. It will be breezy at times
in the evening to overnight hours and near normal temperatures
will continue through the weekend.

&&

.SHORT TERM (WED-SAT)...25/845 PM.

***UPDATE***

The marine inversion early this evening ranged from around 900 ft
deep at LAX to near 1800 ft deep at VBG. Patchy marine layer
clouds and fog were noted along the Central Coast and VTU County
coast this evening which are expected to expand overnight along
the coast and into the adjacent vlys. Otherwise, mostly clear
skies will prevail thru the night. Locally gusty SW winds were
noted in the Antelope Vly this evening, strongest in the
foothills, which should diminish overnight.

***From Previous Discussion***

Southwest flow aloft and increasing onshore flow are the themes
for the next few days as a large low pressure trough dominates
across the eastern Pacific Ocean. This pattern will result in a
deeper marine layer through Saturday with locally gusty southwest
winds through the highway 14 corridor of the San Gabriels and into
the Antelope Valley. Pressure gradients increase 2-3 mb over today
and reach a peak of 9.5 mb between LAX-DAG on Thursday afternoon.
WRF high-res model data also shows sustained winds over 25kts so
would expect a wind advisory will be needed for the AV for the
afternoon and evening time frame.

There will be weak north winds for the western canyons of the
south Santa Barbara coast this evening. This may be just enough to
kick stratus southward off the coast by Thursday morning, and
models support this idea. Elsewhere, the low clouds and patchy fog
May Gray pattern will persist overnight and through the morning
hours through Saturday. Temperatures will remain rather cool near
the beaches and normal for inland valleys and mountains. Stronger
onshore flow tomorrow will result in gusty west winds for the
central coast in the afternoon. Then, we will see Sundowner season
get fully underway both Thursday and Friday evenings as north
winds kick in for passes and canyons west of Santa Barbara.
Advisory level winds look likely to occur with the SBA-SMX
pressure gradient peaking between 4-5mb late Friday and again late
Saturday.

.LONG TERM (SUN-WED)...25/1228 PM.

Confidence in the longer term forecast is moderate. The eastern
Pacific low pressure trough moves inland across northern
California and Oregon over the weekend, then carves a trough
throughout the Great Basin early next week. This brings a more
northerly wind pattern into southwest California with periods of
gusty north-northwest winds across the region. Depending on the
location of the trough and/or low pressure systems we could see
some light showers in the mountains early in the week, but this
scenario is an outlier and chances will remain under 15 percent.
The ECMWF and to a lesser degree on the GFS, high pressure will
build into the west coast by mid-week with temperatures rebounding
on Wednesday with the start of a warming trend and weak offshore
flow for the later part of the week.

&&

.AVIATION...26/0006Z.

At 2314Z at KLAX, the marine layer was near 800 feet deep. The
top of the inversion was near 1700 feet with a temperature around
19 C.

Moderate confidence overall in the 00Z TAFs. A marine layer pattern
with low clouds and LIFR/IFR/MVFR cigs is expected for the coast and
adjacent vly airfields tonight and Thu morning. Low clouds are
forecast to develop between 03Z at KOXR to 11Z at KVNY, then clear
to VFR between late Thu morning to early Thu afternoon, with the
latest clearing expected at KLAX and KOXR around 21Z Thu afternoon.
The timing of the onset and clearing of the low clouds could be off
+/- an hour or two, and there is also a 20%-30% chance the low
clouds may persist most of the day at KOXR, KSMO and KLAX.

A brief period of low clouds with MVFR cigs should affect KPRB from
about 14Z-18Z Thu morning as well, but the low clouds could move in
1 to 2 hours sooner, and there is a 20%-30% chance of IFR cigs.

For KWJF and KPMD, hi confidence in the 00Z TAFs with VFR conditions
thought Thu afternoon. Gusty SW winds can also be expected by late
Thu afternoon.

KLAX...Moderate confidence overall in the 00Z TAF. Low clouds with
MVFR cigs are expected from about 05Z-21Z tonight and Thu, with VFR
conditions for the rest of the afternoon and early evening before
MVFR cigs develop again around 03Z Thu evening. The timing of the
onset and clearing of the low clouds could be off +/- an hour or
two, and there is also a 20%-30% chance the low clouds may persist
most of the day at the airfield.

KBUR...Moderate confidence overall in the 00Z TAF. Low clouds with
MVFR cigs are expected from about 10Z-1630Z tonight and Thu morning,
with VFR conditions for the rest of the time. The timing of the
onset and clearing of the low clouds could be off +/- an hour or two.

&&

.MARINE...25/748 PM.

High confidence in winds and seas remaining below Small Craft
Advisory levels across the waters through Thursday morning. Winds
will likely increase across the outer waters Thursday afternoon
through much of the following week. A Gale Watch has been issued
for the two southern outer water zones starting Friday afternoon
and continuing through early Monday afternoon. There is a 50%
chance GALE force winds will continue across the same area into
early next week. NW winds will continue to be gusty across the
northern outer waters zone but should remain below GALE levels.
Expect building short period seas during this time as well that
will translate into the inner waters.

Inner Waters for areas S of Point Conception...Waters should be
mostly quiet through Friday morning, then strong SCA level gusts
and a 40% chance that GALE force winds could affect the western
portion of the eastern SBA Channel Friday afternoon and evening.
Gusty NW winds will become more widespread across the entire inner
waters Saturday. 70% chance for SCA winds and 30% chance for GALE
force winds western portion of SBA Channel in the afternoon. There
will be a 40% chance for SCA across the inner waters from Point
Sal north on Friday, and 70% chance for Saturday. Winds should
taper off a bit Sunday for all inner water locations with a 30%
chance for a SCA.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Gale Watch in effect from Friday afternoon through late
      Sunday night for zones 673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (SAT-WED).

There will be potential gale force winds mainly for the outer
coastal waters during the outlook period.

&&

$$

PUBLIC...Boldt/Sirard
AVIATION...Sirard
MARINE...Kaplan/Gomberg
SYNOPSIS...RM/B

weather.gov/losangeles



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