Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 222024 AAA

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
124 PM PDT Sun Apr 22 2018

updated marine discussion

.SYNOPSIS...22/1242 PM.

There will be overnight and morning coastal low clouds and fog
for several days this coming week otherwise conditions will be
warm and dry. Temperatures will cool a bit Friday and Saturday as
a weak weather system moves across the region.


.SHORT TERM (TDY-WED)...22/1226 PM.

Weak upper level ridge of high pressure combined with a continued
warm air mass bringing another very warm day across interior
sections today, with warmest locations approaching 90 degrees.
Closer to the coast, onshore winds are helping to bring some
cooling. Latest NAM/WRF models still indicating the potential
for low clouds and fog to return to some coastal areas tonight,
possibly reaching the San Gabriel Valley by Monday morning. The
marine layer will be quite shallow, so there is the potential for
patchy dense fog. The increased onshore flow and marine influence
expected to bring some cooling to coastal and valley areas on
Monday, however little change in temperatures across the mountains
and deserts.

A weak upper low will approach the forecast area from the
southwest Monday night into Wednesday which will bring some
higher level clouds at times to the region. There will continue
to be moderate onshore flow and marine influence which will bring
some night/morning low clouds and fog to coastal/valley areas.
High temperatures will continue to slowly trend down into midweek.

.LONG TERM (THU-SUN)...22/1239 PM.

Large upper level low pressure system will be spinning off the
northern California coast by Thursday. Latest 12z GFS model
trending further northward (similar to ECMWF model) with moving
this low pressure system inland Friday night into Saturday.
As a result, keeping Pops below 15 percent in the Friday
night/Saturday time frame seems reasonable for now across our
area, as most of the moisture and energy with this system is
projected to remain well north. Also of note, the latest GFS
ensembles also trending much drier with this system for our
area. The main impact of this system will be gusty west to
northwest winds across the region along with a cooling trend.



At 1710Z at KLAX, the marine inversion was around 400 ft deep. The
top of the inversion was at 2200 ft with a temperature of 21 deg C.

Moderate confidence overall in the 18Z TAFs due to uncertainties
with the timing and extent of low clouds and fog for all coastal
airfields except KSBP later tonight into Mon morning. The
development of the low clouds with LIFR/IFR cigs/vsbys are expected
to range from about 08Z at KSMX and KLGB to around 13Z at KSBA then
persist thru late Mon morning for the most part. The timing of the
onset of the low clouds may be off +/- an hour or two. Otherwise,
VFR conditions can be expected.

At KSBP, MVFR vsbys and scattered low clouds are expected from 12Z-
16Z Mon morning, however there is a 40% chance low clouds and
LIFR/IFR conditions could move into the airfield at that time.
Otherwise, VFR conditions should prevail at the airfield
thru Mon morning.

For KPRB, KBUR, KVNY, KWJF and KPMD, there is hi confidence in the
18Z TAFs with VFR conditions expected thru Mon morning.

KLAX...Moderate confidence overall in the 18Z TAF due to
uncertainties with the timing and extent of low clouds and fog for
later tonight thru Mon morning. The development of the low clouds
with LIFR conditions are expected around 09Z then improve to IFR
around 14Z and to MVFR around 17Z before scattering to VFR around
19Z. The timing of the onset and dissipation of the low clouds may
be off +/- an hour or two. Otherwise, VFR conditions can be expected
thru Mon afternoon.

KBUR...Generally hi confidence in the 18Z TAF with VFR conditions
expected through Mon morning. There is a 20% chance of IFR cigs Mon
morning, however.


.MARINE...22/123 PM.

Generally hi confidence in the current forecast. Gusty NW winds to
Small Craft Advisory (SCA) can be expected over outer water zone
PZZ670 through late tonight. Otherwise, winds and seas are
expected to remain largely below Small Craft Advisory (SCA) levels
tonight through Thursday across the coastal waters. There is a
50%-60% chance of SCA winds developing on Fri for much of the
coastal waters.

A shallow marine inversion may generate some patchy dense fog
later tonight and Monday morning across the coastal waters.


PZ...Small Craft Advisory in effect until 3 AM PDT Monday for zone
      670. (See LAXMWWLOX).



No significant hazards expected.



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