Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000
FXUS66 KLOX 280327
AFDLOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
827 PM PDT FRI MAY 27 2016

.SYNOPSIS...
Weak low pressure will linger over the area keeping temperatures
a little below normal through Sunday. There is a slight chance of
thunderstorms across mountains and some interior valleys on
Saturday afternoon and evening. Next week, high pressure will
build in causing a gradual warming trend across inland areas
while the coastal temperatures will remain steady.

&&

.SHORT TERM...(TONIGHT-MON)

Weak upper level trough developing across Southwest California
tonight, will become a cutoff low pressure system centered near
SLO county by tomorrow afternoon. This low pressure system
combined with strengthening onshore flow and a developing eddy
circulation will likely generate widespread low clouds and fog
across most coastal/valley areas tonight into Saturday morning.
Current satellite imagery showing low clouds beginning to fill in
across the Central Coast and LA basin this evening.

The main short term weather concern will be convective potential
for portions of our interior sections on Saturday
afternoon/evening. Earlier this afternoon, some cloud buildups
developed across the local mountains. As the weak closed low
pressure system approaches the forecast area on Saturday
afternoon, there will be some weak cyclonic flow aloft along with
increasing instability. While the 500 mb temperatures only fall to
around -14 to -15 degrees celsius with this system, this is
sufficient cold air aloft for this time of year (with strong May
sunshine) to bring a convective threat. There is some discrepancy
between NAM and GFS models on how the moisture will be displaced
with this system, but either way feel that there will be enough
moisture to go with convective parameters (Lifted Index values
between -3 and -5 along with CAPE values in excess of 1000 j/kg)
to warrant a slight chance of tstms across the mountains on
Saturday afternoon/evening (mainly SBA and Ventura counties).
Could also see some storms drift into the Cuyama Valley and
southeast portion of SLO County, so have included these areas in
thunderstorm threat for evening update.

The latest 00z NAM model has slowed down the eastward progression
slightly for the cutoff low pressure system on Sunday, holding
onto some fairly unstable conditions across interior portions of
LA/Ventura counties. As a result, later shifts may need to
consider adding slight chance of tstms for LA/Ventura county
mountains and Antelope Valley for Sunday afternoon/evening.

*** From previous discussion ***

Temps are forecast to change little for Sat thru Sun. Highs will be
generally 3 to 6 deg below normal for the cst and adjacent vlys,
while inland vlys, mtns and deserts will be near normal to slightly
above seasonal norms. For mon, temps will warm a few degrees,
especially in the interior areas, mtns and deserts, where highs
should be 4 to 10 deg above normal. For the coastal plain, Santa
Ynez Vly, and vlys of VTU/L.A. Counties, highs on Mon will be 2 to 6
deg below normal overall. The warmest day will be on Mon, with highs
expected to reach the 80s to around 90 in the warmest vlys and
foothills, except lower 90s in the Antelope Vly.


.LONG TERM...(TUE-FRI)

The EC and GFS are in fairly good agreement Tue thru Wed with upper
level ridging moving into CA. The models diverge for Thu and Fri,
with the EC bringing a broad upper level trof into the e Pac by Thu
then moves the trof inland over CA on Fri. The GFS, however, keeps
the upper ridge over srn CA Thu and Fri, with 500 mb heights
increasing to 590 dm by Fri. Over the past few model runs, the GFS
and EC have been flip-flopping on the idea of a persistent upper
ridge vs. a broad upper trof in the vicinity of the fcst area for
later next week. For now, will lean toward the GFS solution as the
Canadian mdl lends credence to this solution as it is also
indicating the upper ridge will linger.

It looks like dry weather with increasingly warm conditions will
affect the areas mid to late next week. Marine layer clouds and fog
should continue to affect coastal areas s of Pt Conception Tue thru
Thu, alto the extent of the low clouds will diminish each night as
boundary layer temps increase and the marine layer shrinks. By Thu
night into Fri morning, the marine inversion should be sufficiently
squashed to prevent low clouds from affecting even the beaches. Some
low clouds and fog are expected along the Central Coast Mon night
and Tue morning, but then offshore flow night and morning hours in
this area will prevent the low clouds from moving in Wed thru Fri.
Otherwise, mostly clear skies will prevail across the region Tue
thru Fri.

It looks like temps will warm several more degrees for Tue with
highs about 4 to 10 deg above normal away from the coastal plain. By
Thu, highs will warm further to about 5 to 12 deg above normal for
many areas away from the immediate coast, with similar temps
expected on Fri. The warmest day overall in the extended period
should be Thu with highs reaching the upper 70s to lower 80s for the
inland coastal plain, the 80s to low 90s in the vlys and foothills,
and mid 90s to near 100 in the Antelope Vly.

&&

.AVIATION...28/0100Z.

At 0000Z the marine layer at LAX was 1200 feet with an inversion
to 3600 feet with a temp of 18 degrees C.

Low to moderate confidence in TAFs at coastal TAF sites including
KBUR and KVNY mainly due to the timing of ifr to mvfr cigs through
the period. Timing of low cigs may be off by +/- 3 hours with a 20
percent chance of ifr cigs for several hours for coastal TAF sites
from KSBA to KLGB. There is a 30 percent chance of no afternoon to
evening clearing of MVFR cigs at KLAX KLGB and KOXR. At KBUR and
KVNY, there is a 30 percent chance of IFR cigs mainly between 9
and 14Z with a 20 percent chance that vfr conds prevail. There is
a 20 percent chance of lifr cigs/vsbys at KSMX and KSBP mainly
between 10 and 14Z. There is a 20 percent chance of low ifr to
lifr cigs at KPRB from 10 to 16Z.

KLAX...There is a 30 percent chance that low cigs do not occur
between now and 04Z/28. A second push of low cigs is expected between
04 and 10Z and last through at least 20Z with a 30 percent chance
of MVFR cigs continuing through 06Z/29.

KBUR....There is a 30 percent chance of IFR cigs mainly between 9
and 14Z. There is also a 20 percent chance that vfr conds
prevail.


&&

.MARINE...27/800 PM.
Small craft wind conditions continuing for portions of the outer
waters this evening, but winds are expected to drop off later
tonight. A Catalina eddy is expected to develop each night over
the bight through Tuesday and northwest winds are expected
elsewhere and fill in the bight each afternoon. A complex storm
system over the Southern Ocean last Monday with a fetch oriented
190-210 degrees from Ventura generated swells that will arrive
Monday and build through Tuesday. The swells will remain below
small craft advisory for hazardous sea conditions but there will
be extra surging and currents along exposed south facing shores.


&&

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

&&

$$

PUBLIC...Gomberg
AVIATION...Munroe/Gomberg
MARINE...Gomberg
SYNOPSIS...Gomberg

weather.gov/losangeles


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