000
FXUS66 KLOX 211038
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
338 AM PDT Sun Oct 21 2018

.SYNOPSIS...21/315 AM.

Weak offshore winds with warm and dry conditions will continue
today yet some cooling as the seabreeze should develop earlier
this afternoon for coastal areas. Temperatures will be cooler
through midweek then turn warmer late in the week. Patchy night
through morning coastal low clouds will develop early this week.
There is a slight chance of showers or thunderstorms in the
Ventura and Los Angeles County mountains this afternoon and early
evening hours.

&&

.SHORT TERM (TDY-TUE)...21/312 AM.

Latest Fog Product Imagery indicated mostly clear skies across the
forecast area this morning. There were patchy low clouds and dense
fog affecting a few coastal areas across San Luis Obispo and Santa
Barbara Counties. San Luis Obispo Airport was reporting dense fog
of a quarter mile or less at 2 AM. There is a slight chance that
the fog will scour out before sunrise as weak offshore flow across
the Central Coast is expected before dawn. At this time, it does
not look like low clouds will develop off the coast of L.A.
County, but don`t be surprised if some patchy low clouds and fog
do occur towards sunrise for a brief period. Overall there will
be cooling between 4 to 10 degrees compared to yesterday, with
best cooling expected along the coast as the seabreeze is expected
to kick in earlier this afternoon. More substantial cooling is
expected along the immediate Central Coast with up to 15 degrees
of cooling possible. The LAX-DAG offshore gradient is expected to
weaken today to a neutral 0.00 MB this afternoon which generally
would keep weak offshore flow continuing across much of the wind
prone areas one more day. Therefore have bumped up high temps a
few degrees from what was in the Sunday forecast although still
cooler compared to Saturday`s highs. More prominent cooling is
expected on Monday as onshore gradients finally strengthen. LAX-
DAG expected to be up to +3 MB Mon afternoon. Not too high, but a
cooler trend nonetheless. Better chance of more widespread low
clouds and fog reaching more coastal areas Monday night into Tue
morning.

Synoptically, A weak cutoff low has developed across much of
California with a deep trough as far south as southern Baja Cal
this morning. At this time, thunderstorms were developing across
southern Nevada as decent diffluent area has developed allowing
good lift for convection. This upper low is expected to fill in by
Monday but continue a deep yet weak trough over the region through
Tuesday. For today, high res models continue to show some
instability across the L.A. and Ventura County Mtns, but not as
impressive as it looked in earlier runs. There will still be
enough mid level moisture to warrant a slight chance of showers or
an isolated thunderstorm this afternoon. At the least there will
be some cumulus buildups over some mountain areas this afternoon.
Best convective parameters will remain to the east. With less of
a chance on Monday for showers over the mountains with the upper
low begins to fill in and weaken over the region.

For Tuesday, the trough axis will begin to push into Nevada and
Arizona with slight increases in H5 heights and boundary layer
temps. This should translate to high temps nudging up every so
slightly, S of Point Conception, and slight cooling for interior
areas to the north. A more significant warming trend will begin
in the second half of the week as high pressure aloft begins to
build in from the Eastern Pac. Expect continued night through
morning low clouds and fog for coastal areas. There could be a
slight chance that some fog could drift into a few coastal valleys
Tue morning.

.LONG TERM (WED-SAT)...21/337 AM.

Both the GFS and ECMWF models are continuing to be in good
agreement with large scale features through Friday with some
inconsistencies by Saturday. Overall, there will be a warming
trend as a relatively strong ridge builds over the Eastern Pacific
by Wednesday. Expecting a few degrees of warming Wednesday across
the board. There should be patchy low clouds and fog across
portions of the coast and possibly coastal valleys, but more
significant warming is expected both Thu and Fri as high pressure
nudges farther east over Southern California. The jet stream will
stay to the north pushing any disturbances across the PAC NW. High
temps will rise significantly as a sharp northerly gradient
develops Thursday morning, then shifting northeast on Friday. The
combination of the building upper ridge aloft and strengthening
offshore flow, Highs will reach the upper 80s and lower 90s across
L.A. and Ventura Coastal areas and into the lower to mid 80s for
the Central Coast due to the weak offshore flow. Not expecting any
low clouds by Thursday through Saturday. Some limited cooling on
Saturday as the offshore gradients weaken and likely shift onshore
in the afternoon. By Saturday the GFS continues the upper ridge
axis over much of California while the EC shifts the ridge axis
east as a weak trough approaches. At this time, feels that some
initial cooling is likely on Saturday. Not anticipating any
strong northerly winds on Thu and Santa Ana winds Fri morning at
this time. But expect relative humidities to lower into teens and
possibly lower Thu-Fri which could heighten fire weather concerns.

&&

.AVIATION...20/2333Z.

At 2330Z at KLAX, there was no inversion or marine layer present.

Hi confidence in the 00Z TAFs with VFR conditions expected at most
of the airfields thru Sun. However, there is a 20% chance of low
clouds and LIFR conditions at KSMX late tonight into Sun morning.
There is also a 40% chance of low clouds and IFR conditions at
KLGB early to mid morning Sunday, and 20% chance reaching KLAX.

KLAX...Hi confidence in the 00Z TAF with VFR conds thru the pd.
There is a 20% chance of low clouds and LIFR conditions at KLAX
early to mid morning Sunday.

KBUR...Hi confidence in the 00Z TAF with VFR conds thru the pd.

&&

.MARINE...21/325 AM.

For the outer waters, low to moderate confidence in the forecast.
There is a 40% chance that a Small Craft Advisory (SCA) will be
needed, especially across the northern two zones during this
afternoon and evening. There is a 40-50% that a SCA will be
needed Mon in all zones. SCA conds are expected in all outer
waters zones Mon night thru Thu.

Across the inner waters N of Point Conception, winds should remain
below SCA levels thru Mon morning. There is a 30%-40% chance of SCA
level NW winds during the afternoon/evening hours Mon/Tue, then
SCA conds are likely during the afternoon/evening hours Wed/Thu.

For the inner waters S of Point Conception, winds should remain
below SCA levels thru Thu, except there is a 20% chance of SCA
level gusts across western portions of the SBA Channel Tue evening.

Patchy dense fog with visibilities one nautical mile or less will
affect the the outer waters and northern inner waters this
morning and again late tonight and Mon morning.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...NONE.

&&

.HAZARD POTENTIAL OUTLOOK (TUE-SAT).

A significant warming trend is possible late next week.

&&

$$

PUBLIC...Kaplan
AVIATION...Gomberg
MARINE...DB
SYNOPSIS...Kaplan

weather.gov/losangeles




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