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FXUS66 KLOX 202103
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
203 PM PDT Thu Sep 20 2018

.SYNOPSIS...20/200 PM.

The temperatures will be above normal into next week with fair
skies, except for an overnight coastal marine layer. A low may
approach early next week, then a high will follow and linger into
the weekend.

&&

.SHORT TERM (TDY-SUN)...20/155 PM.

Our one day offshore event brought the expected warmup to
LA/Ventura Counties and the Central Coast with SLO up to 90 and
Pismo at 80 for highs. However, gradients are already starting to
reverse and we're seeing southerly winds now increasing over the
coastal waters south of Ventura county which are expected to
spread north overnight and all the way up the Central Coast by
Friday morning. This should also bring the marine layer stratus
all the way north along the coast through SLO county and beyond
with a better inland push as well than this morning, likely making
its way into the SF, SG, and Conejo valleys. The combination of
that and the lack of warming subsidence will bring temps down a
good 10 degrees along the Central Coast and 2-4 degrees in
LA/Ventura counties. Mtns and Antelope Valley will be more under
the influence of the building ridge aloft so temps there will warm
a few degrees.

Models show gradients reversing again Saturday, though not as much
as today and with no real support aloft for low level subsidence
so temps should warm only a couple degrees. Later Sunday a trough
will pass north of the area, though the ECMWF is deeper with it
than the GFS leading to some uncertainty on impacts to
temperatures. Given that the trough passage should be later in the
day or evening going with little change in temps Sat to Sun.
Marine layer stratus again mostly confined to coastal zones but
could sneak into some of the lower valley areas, especially the SG
and Conejo valleys.

&&

MW

.LONG TERM (MON-THU)...20/202 PM.

Models actually pretty similar after the Sunday night trough
passage, showing a ridge returning (faster on the GFS) and hanging
around at least into Friday of next week. With onshore flow still
in place and likely a solid marine layer up and down the coast
will keep temps fairly steady and near normal at the coast but go
with a few degrees of warming for inland areas, especially after
Tuesday. Winds mostly on the light side with standard afternoon
sea breezes each day and no signs of any significant northerly
flow returning. If the weaker GFS forecast gradients late next
week verify temps at the coast could warm up a few degrees more
than currently expected but given how the offshore flow today was
weaker than expected have opted to go with a forecast closer to
persistence.

&&

.AVIATION...20/1812Z.

At 1706Z, at KLAX, the marine layer depth was 1600 feet. The top
of the inversion was 2700 feet with a temperature of 22 degrees
Celsius.

The overall message this morning indicates a return of the marine
clouds to the coast and valleys tonight and Friday morning. There
is only moderate confidence in the 18z TAF package. Timing of the
arrival of marine clouds tonight is one of the main aspects of
uncertainty. IFR to LIFR conditions are expected on the central
coast and in the valleys, with IFR to MVFR conditions expected on
the south coast.

KLAX...Moderate confidence in the 18z TAF. There is a 40% chance
of the marine clouds arriving plus or minus two or more hours
from the forecasted time.

KBUR...Moderate confidence in the 18z TAF. There is a 40% chance
of the marine clouds arriving plus or minus two or more hours
from the forecasted time.

&&

.MARINE...20/128 PM.

For the Outer Waters... Local gusty winds may at times reach 25
kts across the northern outer waters today. Conditions will remain
below Small Craft Advisory (SCA) levels through at least
Saturday. On Sunday and Monday, there is a forty percent chance of
SCA level winds developing across the northern and central outer
waters.

For the Inner Waters... Patchy fog will continue across the inner
waters south of Point Conception through late morning. The fog may
be locally dense in the early morning hours and near shoreline
with little sun exposure. Otherwise winds and sea conditions will
remain below SCA levels through at least Monday.

&&

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

&&

.HAZARD POTENTIAL OUTLOOK (SUN-THU).

No significant hazards expected.

&&

$$

PUBLIC.../MW
AVIATION...Sweet
MARINE...Sweet
SYNOPSIS...STu

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