Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000
FXUS66 KLOX 300405
AFDLOX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
905 PM PDT MON AUG 29 2016

.SYNOPSIS...

Breezy winds will occur tonight for the south coast and the Santa
Barbara mountains. The skies will be mostly clear into Wednesday
with above normal temperatures as high pressure aloft lingers,
then a low pressure system should arrive Thursday with a deep
marine layer and a cooling trend through early next week.

&&

.UPDATE...

The latest water vapor imagery shows a upper-level ridge of high
pressure near 23N and 126W, or about 900 miles south-southwest of
Los Angeles with the ridge axis over the area this evening.
With the ridge axis overhead and weak offshore flow developing in
some areas tonight, another warm day looks on tap for the region.
There is a chance that northern San Luis Obispo County could be
cooler than forecast. Much will depend upon how quickly pressure
gradients trend more strongly ahead of a trough of low pressure
near 37N and 131W, or about 750 miles northwest of Los Angeles.
Minimal marine layer stratus coverage is expected tonight. Patchy
marine layer coverage could occur for the Central Coast late
tonight and early Tuesday morning, otherwise clear skies will be
prevalent.

Sundowner winds have developed as advertised. KSBA-KSMX surface
pressure gradients have tightened to -4.3 mb and should top out
near -4.6 mb later this evening. A Wind Advisory remains in
effect for gusty winds across Southern Santa Barbara County and a
Red Flag Warning for gusty winds and low relative humidities. The
Sundowner winds are showing some of the effects. Las Flores Canyon
is 87 degrees currently with a northwest wind around 35 mph, while
the Santa Barbara Airport is 66 degrees with a 5 mph from the
southeast.

&&

.PREV DISCUSSION...

SHORT TERM...August will end on a cooling trend as the broad
trough sets up over the west coast on Wednesday. Unlike last week,
this one is driven by a weak 60kt jet and doesn`t look to provide
much lift or moisture as is passes so we`re not expecting a
cumulus buildup over the mountains. The marine layer cloud deck
will thicken slightly and the onshore trends will be weakly
stronger. There will be some cooling.

Thursday will continue under the trough and temperatures will
continue to fall a few degrees. Below normal temperatures may be
experienced along the coasts and seasonal conditions more inland.

LONG TERM...Both the GFS and the EC numerical models agree that
the upper trough will persist through the extended period and will
strengthen a little each day.

Friday and the weekend look to be fairly cloudy along the coasts
and coastal valleys as the trough increases to the point where it
will lift the marine layer deep into the valleys. Expecting night
through morning low clouds and fog extending all the way into the
Santa Clarita valley. Cooler still on Saturday due to lower hgts
and then little change for Sunday.

On Monday the GFS develops the 500mb-level trough into a cutoff
low pressure system to our southwest and slightly higher heights
over our immediate area...which would raise temperatures a little
and affect the wind patterns. The EC does so by Tuesday. Not
putting too much faith in anything that far out but raised the
afternoon temperatures a degree or two for those days.

&&

.AVIATION...30/0025Z.

AT 23Z, the marine layer depth at KLAX was around 500 feet deep.
The top of the inversion was near 2600 feet with a temperature of
32 degrees Celsius.

Low confidence in the current forecast. VFR conditions are
expected throughout the period, except for a chance of LIFR to IFR
conditions at Central Coast and Los Angeles County coastal
terminals between 08Z and 16Z.

KLAX...VFR conditions are expected throughout the period, except
for a 30 percent chance of IFR conditions between 10Z and 16Z.

KBUR...High confidence in VFR conditions throughout the period.

&&

.MARINE...29/800 PM.

A Gale Warning for zones 670 and 673 remains in effect through
Tuesday night. Gusts to 35 knots are expected to become more
widespread through midnight, then increasing to 35 to 40 knots
into Tuesday. A Gale Warning for zone 676 remains in effect
beginning late Tuesday afternoon and continuing through Tuesday
night. Small Craft Advisories remain in effect for zones 645 and
western portions of 650 through late tonight, with gusts to 25
knots and rough short period seas. Another round of Small Craft
Advisories are expected for these areas Tuesday afternoon through
Tuesday night.

Patchy dense fog will be possible across the northern waters
tonight through Tuesday morning..including the nearshore waters
north of Point Sal. There is a 20% chance of patchy dense fog near
Long Beach Tuesday morning.

&&

.FIRE WEATHER...29/215 PM.

For southern Santa Barbara county (the Santa Ynez range and south
coast of Santa Barbara county), gusty sundowner winds are expected
this afternoon/evening and again Tuesday afternoon/evening. With
good north-south pressure gradients and decent upper level support
wind gusts to around 40 MPH are expected through and below passes
and canyons. With the marine inversion expected to remain very
low (below 1000 feet), relative humidity is expected to fall into
the teens, and possibly single digits, late this afternoon/evening
and again late Tuesday afternoon/evening with poor overnight
recoveries. With this combination of gusty winds and low relative
humidity, an extended period of critical fire weather conditions
is expected across southern Santa Barbara county, especially
during the afternoon and evening hours, and a Red Flag Warning
remains in effect through Wednesday morning.

Elsewhere across the area, hot and dry conditions are expected
to continue through Wednesday. Afternoon temperatures will show
a slow cooling trend, but remain well above normal. So with
relative humidity expected to drop into the teens each afternoon,
elevated fire weather conditions can be expected across interior
sections. The warm temperatures near the surface will cause
steepening lapse rates that will enable deep vertical mixing
layers through Wednesday when mixing layer heights are forecast
to range between 12,000 and 15,000 feet. For existing fires or
new ignitions over interior areas, plume dominated fire behavior
will be possible.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory in effect until 3 AM PDT Tuesday For zones
      39-52. (See LAXNPWLOX).
     Red Flag Warning in effect until 10 AM PDT Wednesday For
      zones 239-252. (See LAXRFWLOX).
PZ...Small Craft Advisory in effect until 3 AM PDT Wednesday For
      zones 645-650. (See LAXMWWLOX).
     Gale Warning in effect until 3 AM PDT Wednesday For zones
      670-673. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 PM PDT Tuesday For
      zone 676. (See LAXMWWLOX).
     Gale Warning in effect from 3 PM Tuesday to 3 AM PDT
      Wednesday For zone 676. (See LAXMWWLOX).

&&

$$

PUBLIC...Hall/JLD
FIRE WEATHER...RAT
AVIATION...Hall
MARINE...Smith
SYNOPSIS...Seto/Hall

weather.gov/losangeles



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