Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 241800 AAA
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
1100 AM PDT Thu May 24 2018

updated aviation discussion

.SYNOPSIS...24/808 AM.

A trough currently over the Pacific will be moving into central
California this weekend. Mostly cloudy skies are expected through
early Saturday in most areas, but partly cloudy over the valleys.
A chance of showers in the northern parts of the CWA tonight and
Friday. Night to morning low clouds and drizzle elsewhere. Expect
cool temperatures through Saturday when the warming rend begins.

&&

.SHORT TERM (TDY-SAT)...24/911 AM.

Marine layer up to between 4000 and 5000` with a few reports of
some drizzle around, mainly south of Pt Conception. Another day of
slow clearing today, likely slower than yesterday, with temps 3-6
degrees below normal on average. Further deepening tonight as an
upper low approaches from the west so expect more in the way of
drizzle and light rain, especially foothills and other upslope
areas.

***From previous discussion***

A sharpening upper trough in the eastern Pacific will evolve into
an upper low about 400 nm west of Pt Conception later this
morning. This low will drift eastward, and be centered about 100
nm west of Monterey by late tonight, while taking on somewhat of a
negative tilt as it does so. Some upper level diffluence and
decent low and mid level lift should be sufficient to produce at
least isolated shower activity north of Pt Conception late
tonight and Fri. Elsewhere, deep moisture and strongly cyclonic
flow will likely allow for patchy drizzle late tonight/Fri morning
from the coastal slopes west and south. Have left pops out of the
forecast for now, but a case could certainly be made for some
slight chance pops, especially in the foothills of L.A. County.
Skies will likely remain mostly cloudy west of the mountains again
on Fri. Max temps will change little on Fri, except there will be
several degrees of cooling in the mountains and Antelope Valley.
Gusty winds in the mtns and Antelope Valley may get close to
advisory levels Fri afternoon and evening.

The upper low will move across Central CA Fri night and early Sat
Saturday, with a trough extending southward into the forecast
area. Expect the marine layer to remain very deep, but a weakening
inversion could make for a more ragged cloud field. Still, there
should be a fair amount of night through morning clouds in coastal
and valley areas. There could still be some patchy drizzle in
coastal and valley areas of L.A. and VTU Counties. Developing N-S
gradients Fri night should bring some gusty winds to the Santa
Ynez Range and adjacent south coast of SBA County Fri night, which
could keep skies clear there, or at least delay clouds until morning.

Expect better clearing on Sat as the trough axis moves east of the
region in the afternoon. North to south offshore gradients will
continue to sharpen, and there should be gusty northwest to north
winds across southern SBA County and the I-5 corridor late Sat
into Sat night. Max temps will likely be up a few degrees in most
areas on Sat, but should still be below normal, except possibly
across the south coast of SBA County due to downsloping northerly
flow.

.LONG TERM (SUN-WED)...24/421 AM.

The upper low will move eastward into northern Utah on Sunday,
then will move very little thru Mon. Height rises and weakening
onshore flow should allow for a warming trend Sun and Mon, with
somewhat of a decrease in coverage and inland extent of the night
thru morning low clouds and fog. By Mon and Tue, max temps should
be near or a bit above normal, especially across the interior.
However, latest models keep some weak troughing across the region,
with a very weak upper low forming just west of the area by Tue.
This may have the affect of keeping max temps down a bit, but
heights will be fairly high. A more significant trough will
approach the Pacific Wed, bringing cooling to the region.

&&

.AVIATION...24/1759Z.

At 1741Z, the marine inversion at KLAX was around 3900 ft deep. The
top of the inversion was around 5800 feet with a temperature of 11
deg C.

Moderate confidence overall in the 18Z TAFs. Low clouds with MVFR
conditions will persist into this afternoon for most coast and vly
airfields before improving to VFR mid to late afternoon into the
early evening. Low clouds with mostly MVFR conditions can be
expected to redevelop at the coastal and vly airfields this evening
to later tonight then persist thru late Fri morning. There is
uncertainty in the timing of the improvement to VFR this afternoon
and development of MVFR cigs tonight which could be off +/- two or
more hours.

For KWJF and KPMD, there is hi confidence in VFR TAFs thru Fri
morning. Gusty SW winds will affect these airfields this afternoon
and evening as well, with some gusty winds expected to linger at
times overnight into Fri morning.

KLAX...Moderate confidence overall in the 18Z TAF. Low clouds with
MVFR cigs can be expected thru early this afternoon then improve to
VFR into early this evening. The cigs should then lower to MVFR aft
about 02Z then persist thru Fri morning before improving to VFR aft
about 18Z Fri. There is uncertainty in the timing of the improvement
to VFR this afternoon and development of MVFR cigs tonight which
could be off +/- two or more hours.

KBUR...Moderate confidence overall in the 18Z TAF. Low clouds with
MVFR conditions can be expected through about 00Z with cigs
improving to VFR thru the evening. Low clouds with MVFR cigs should
redevelop around 08Z then persist thru Fri morning. There is a 30%-
40% chance the low clouds may not improve to VFR this afternoon and
early evening. There is also uncertainty in the timing of the
improvement to VFR late this afternoon and development of MVFR cigs
tonight which could be off +/- two or more hours.

&&

.MARINE...24/857 AM.

For the Outer Waters, high confidence in the current forecast.
Winds and seas will remain below Small Craft Advisory levels
through at least Friday. There is a 60 percent chance of Small
Craft Advisory level northwest winds across the southern portion
of the Outer Waters from Point Conception to San Nicolas Island
from Friday night through Sunday. Confidence is somewhat lower
for advisory level gusts for the northern portion of the Outer
Waters from Saturday afternoon through Sunday.

For the Inner Waters, generally high confidence in the current
forecast. For the waters north of Point Sal, winds and seas will
remain below SCA levels through Monday, except for a 40 percent
chance of SCA level winds Saturday night.

For the waters south of Point Conception, winds and seas will
remain below SCA levels through Friday. For Friday night through
Sunday, there is a 60 percent chance of SCA level winds at times,
especially across western sections of PZZ650.

A long period southerly swell will continue to move through the
coastal waters through early Friday. Locally rough conditions may
occur at local harbor entrances, especially those with southerly
exposure.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement in effect until 7 PM PDT this evening
      for zones 40-41-87. (See LAXCFWLOX).
PZ...NONE.

&&

.HAZARD POTENTIAL OUTLOOK (SAT-WED).

Advisory level Sundowner winds are possible for western portions
of the SB south coast this weekend.

&&

$$

PUBLIC...MW/DB
AVIATION...Sirard
MARINE...Kaplan/Sirard
SYNOPSIS...Delerme

weather.gov/losangeles



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