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000 
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

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