Area Forecast Discussion
Issued by NWS Los Angeles, CA

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606
FXUS66 KLOX 202104
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
204 PM PDT Sun May 20 2018

.SYNOPSIS...20/203 PM.

A trough of low pressure is expected to push into the region
through Monday before shifting eastward. This will support cooler
conditions early in the week with drizzle possible across coasts
and valleys south of Point Conception. There is also a slight
chance of showers or thunderstorms for adjacent interior areas
Monday afternoon and evening. Temperatures will likely rebound
later in the week.

&&

.SHORT TERM (TDY-WED)...20/200 PM.

The marine inversion early this afternoon at LAX was around 3500 ft
deep. Low clouds cleared to or off the Central Coast early this
afternoon, while they remained rather stubborn over the coast and
vlys S of Point Conception thanks to onshore flow and a persistent
eddy. Otherwise, varying amounts of hi clouds were moving into
the forecast area. Little change can be expected for the rest of
the day. Temps this afternoon should be a few degrees below
seasonal norms for the coast and vlys, and near normal overall for
the mtns and deserts. Highs in the vlys and inland coastal areas
should reach the low to mid 70s.

An upper level trof of low pressure is forecast to develop along the
CA coast thru this afternoon, then deepen into an upper level low
pressure system over swrn CA late tonight and Mon with 500 mb
heights around 565 to 566 dm. This system is expected to slowly
drift off to the NE and away from the forecast area Mon night and
Tue with upper level troffiness lingering over srn CA thru the
period. Weak upper level ridging should then move into the region
for Tue night and Wed.

The marine layer will deepen a bit more tonight into Mon morning
with the low clouds extending from the coast to even further into
the coastal slopes. With the upper low nearby and cyclonic flow
aloft, there should be enough added lift for patchy drizzle as well
later tonight and Mon morning for the coast, vlys and coastal slopes
S of Point Conception.

500 mb temps around -16 deg C will accompany the upper level low on
Mon. This plus the strong May sunshine will help to bring decent
instability (LI`s of -3 to -4) to the higher mtns and deserts by
early Mon afternoon. This will support a slight chance of
thunderstorms over these areas Mon afternoon and early evening.
Otherwise, another day of partial clearing to the coast can be
expected especially S of Point Conception.

Marine layer clouds will spread quickly inland Mon night and move up
to the coastal slopes again, but support for any drizzle will be
minimal. The low clouds will likely clear back to the coast N of
Point Conception by early Tue afternoon, with at least partial
clearing in the afternoon elsewhere. Afternoon cu buildups can also
be expected in the mtns Tue afternoon. There should be a slightly
lower marine inversion Tue night, with more low clouds and fog for
the coast to the lower coastal slopes expected into Wed morning.
Better clearing to or off the coast is forecast for Wed afternoon.

Continued marine layer influence and onshore flow will keep temps
down some Mon and Tue, with highs a few degrees below normal for
most areas. Temps should turn slightly warmer and closer to normal
in the mtns and deserts for Wed, while the coast and vlys will
continue to have slightly below normal readings.

.LONG TERM (THU-SUN)...20/200 PM.

The 12Z EC and GFS are now in generally good agreement with the
synoptic features over the ern Pac and wrn U.S. for the extended
period. An upper level low and surface storm system is forecast to
develop about 1000 miles W of the forecast area Wed into early
Thu. This system is expected to meander over the ern Pac while
edging closer to the CA coast Thu thru Fri night before moving
inland over srn CA late Sat and Sat night. Some upper level
ridging out ahead of the upper low can be expected over srn CA Thu
thru Fri, then the region will be on the southern periphery of
the upper low for Sat. Weak and flat upper ridging should move
into the area for Sun.

Dry weather with a persistent marine layer pattern will prevail Thu
thru Sun. There will be varying amounts of night and morning low
clouds and fog for the coast and vlys during the period, otherwise
skies will be mostly clear over the region. Temps will have minor
day-to-day changes thru the period, with highs generally near normal
to slightly below normal. Highs in the warmest vlys and inland
coastal areas should reach the mid 70s to low 80s each day.

&&

.AVIATION...20/1804Z.

At 1723z at KLAX... the inversion was around 3100 feet. The top
of the inversion was 4600 feet with a temperature of 16 degrees
Celsius.

Overall... Moderate confidence in the coastal and adjacent valley
TAFs and high confidence in Antelope Valley TAFs. The reduced
confidence is due to uncertainty in the dissipation and
redevelopment timing. MVFR conditions will be slow to dissipate
today and some locations in Los Angeles County may not clear at
all. MVFR conditions will redevelop prior to midnight at Central
Coast and Los Angeles Basin locations and by a few hours
afterwards at other coastal and coastal adjacent locations.
Otherwise and elsewhere VFR conditions will prevail.

KLAX... Moderate confidence in the current TAF. The reduced
confidence is due to uncertainty in the dissipation and
redevelopment timing. MVFR conditions will be slow to dissipate
today and there is a high likelihood that KLAX will not clear at
all though CIGs become high enough to become VFR conditions. If
VFR conditions break out... MVFR conditions will redevelop prior
to midnight. There will be no east winds greater than eight knots
during the forecast period.

KBUR... Moderate confidence in the current TAF. The reduced
confidence is due to uncertainty in the dissipation and
redevelopment timing. MVFR conditions will be slow to dissipate
today and there is a forty percent chance that KBUR will not clear
at all though CIGs could become higher than 3000 ft and therefore
VFR. If VFR conditions break out... MVFR conditions will
redevelop prior to midnight.

&&

.MARINE...20/133 PM.

For the Outer Waters... Small Craft Advisory (SCA) level winds
and seas will continue through late Monday night. For Tuesday
through Thursday, winds and seas will remain below SCA levels.

For the Inner Waters north of Point Sal... SCA level winds will
return this afternoon and evening and Monday afternoon and evening.
For Tuesday through Thursday, winds and seas will remain below
SCA levels.

For the Inner Waters south of Point Conception... winds and seas
will remain below SCA levels through Thursday although there is a
forty percent chance of SCA level winds across the western half
of the Santa Barbara Channel this afternoon and evening and again
Monday afternoon and evening.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory in effect until 3 AM PDT Tuesday for
      zones 645-670-673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (WED-SUN).

No significant hazards expected.

&&

$$

PUBLIC...Sirard
AVIATION...Kj
MARINE...Kj
SYNOPSIS...Munroe/Sirard

weather.gov/losangeles



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