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FXUS66 KLOX 220640
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Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
1140 PM PDT Sat Jul 21 2018

.SYNOPSIS...21/630 PM.

Record breaking heat is possible during the early to middle part
of next week in response to a strong ridge of high pressure
building over the Desert Southwest.

&&

.SHORT TERM (SAT-TUE)...21/931 PM.

The latest satellite imagery shows an upper-level ridge of high
pressure centered over the Texas Panhandle this evening. The ridge
center will push west into Arizona through Tuesday. 500 mb heights
and 1000-500 mb thickness values climb across Southern California
through Tuesday. A warming trend will develop as subsiding air
aloft presses down on top of the marine layer and thins it.
Onshore flow across the area will weaken some through the period.
A few very minor tweaks were made to temperatures in the latest
update, but overall, temperatures looks to be in good shape.

Remnant monsoonal moisture lingering over the area on Sunday could
bring an isolated shower or thunderstorm to the mountain areas on
Sunday afternoon and evening. PoPs were increased for this period
but moisture looks more limited relative today.

Gusty Sundowner winds could develop as soon as Sunday evening
across southern Santa Barbara County. NAM-WRF solutions suggest
surface pressure gradients between KSBA and KSMX tightening to
near -4 mb as early as Sunday evening. An advisory is possible for
Sunday afternoon and night, becoming likely for Monday afternoon
and night, and Tuesday afternoon and night. Advisory level winds
are also possible through the Interstate 5 Corridor each night
through morning starting Monday night. Hot and dry conditions
developing will bring elevated fire weather concerns the next
several days. Critical fire weather conditions are possible for
areas with Sundowner winds. A Fire Weather Watch is in effect
from late Tuesday afternoon through Thursday morning.

***From Previous Discussion***

.LONG TERM (WED-SAT)...21/200 PM.

Potential for record breaking heat continues into the long term
with excessive heat watches/warnings continuing through Thursday
(again see NPWLOX for the latest). The aforementioned ridge of
high pressure is expected to gradually break down while shifting
nearly overhead through Thursday before shifting northeast into
the interior. This will support continued hot conditions for
interior areas through Thursday before gradual cooling commences
heading into next weekend. Closer to the surface, gusty and
possibly advisory level Sundowner winds may continue for western
portions of the SBA South Coast into Wednesday or Thursday evening
with breezy but sub- advisory winds also possibly continuing in
the LA and VTA mountains near the I-5 corridor. Once these winds
relax, models are indicating the development of a moderate eddy
circulation by Thursday or Friday which could bring significant
cooling and moistening of the lower atmosphere to the coastal
plain, especially south of Point Conception. It may also mark the
return of more widespread night to morning low clouds to these
areas.

If the ridge of high pressure does reposition near the Great Basin
in Nevada, it would open the door for a potential return of
monsoonal moisture to the region.

&&

.AVIATION...22/0639Z.

At 0545Z at KLAX, the marine layer was 1000 feet deep at KLAX.
The top of the inversion was around 2400 feet with a temperature
near 25 degrees Celsius.

Good confidence in KSMX and KSBP as well as inland TAFs.

Low confidence in coastal TAFs KSBA and southward. Stratus clouds
will develop haphazardly. Cig basses will vary from 008 to 012 and
may dip into LIFR values at KSBA, KOXR and KCMA. VFR transition
Sunday morning could be anywhere from +/- 90 minutes from time of
fcst. Good confidence in TAFs after 18Z.

KLAX...Moderate confidence in TAF. There is a 30 percent chc of
OVC008 conds through 15Z. VFR conds could arrive as late 1830Z.
Good confidence in no east wind component over 4 kt.

KBUR...High confidence in CAVU TAF.

&&

.MARINE...21/926 PM.

Moderate-to-high confidence in the current forecast. West to
northwest winds will increase across the coastal waters through
Monday evening. There is a 80 percent chance of Small Craft
Advisory level winds developing between Sunday afternoon and
evening, then continuing through at least Tuesday across the
southern two outer waters zones (PZZ673/PZZ676). There is a 30
percent chance of Gales on Monday night. Winds will continue to
increase with advisory level winds likely across the northern
outer waters on Monday afternoon and evening.

For the nearshore waters north of Point Conception, Small Craft
Advisory conditions are not expected through Monday morning, then
Small Craft Advisory conditions will become likely, mainly during
the afternoon and evening Monday through Thursday.

For the inner waters south of Point Conception, there is a 60
percent chance of advisory level winds across the Santa Barbara
Channel each afternoon and night through Wednesday. There is a 30
percent chance of similar conditions across the inner water
portion south of Point Mugu.

A long-period south swell from the Southern Hemisphere is expected
to move into the waters early next week.

&&

.BEACHES...21/930 PM.

A long-period southerly swell originating from near New Zealand
will move north out of the Southern Hemisphere through Wednesday.
Strong rip currents and elevated-to-high surf conditions are
likely at Southern California beaches between Monday and
Wednesday.

&&

.FIRE WEATHER...21/336 PM.

Some residual monsoonal moisture with instability will bring isolated
thunderstorm activity to the mountains of Los Angeles and Ventura
counties and Antelope Valley through early evening. A strong upper level high
pressure system building over Southwest California will bring a long
duration heat wave Sunday through at least Friday, peaking in
strength from Monday through Thursday. High temperatures between 100
and 110 degrees will be common in the valleys, lower mountains, and
deserts during the peak, with humidities likely falling to between
10 and 20 percent by Tuesday. Several nights of gusty sundowner
winds are expected across southern Santa Barbara county from
Sunday night through Wednesday night when gusts between 30 and 45
mph will be common across western portions, with isolated gusts as
high as 50 mph near Gaviota and Refugio hills. These persistent
gusty Sundowner winds will add to the fire weather threat across
southern Santa Barbara county, with conditions potentially
reaching critical levels by late Tuesday when humidities fall
between 10 and 20 percent and temperatures potentially climb to
around 100 degrees. The projected SBA-SMX gradient for Sunday
night is -4.6 mb, and could reach or exceed -5 mb on Monday night,
Tuesday night, and Wednesday night. A Fire Weather Watch has been
issued for the Santa Barbara south coast and mountains. Breezy
northwest to north conditions are also expected across the
Interstate 5 corridor in the los Angeles county mountains.

The long duration of hot and dry conditions coupled with dry fuels
will bring an increased risk of large vertical plume growth across
interior sections next week, especially in the foothills and
mountains. Widespread elevated fire weather conditions will occur
next week across Southwest California due to the long duration heat
wave. Very warm overnight low temperatures and poor humidity recoveries
in the foothills and mountains will add to the fire weather threat
in those areas.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Excessive Heat Watch in effect from Tuesday morning through
Thursday evening for zones 34>38-51. (See LAXNPWLOX).
Excessive Heat Warning in effect from 10 AM Monday to 8 PM
PDT Thursday for zones 39>41-44>46-52>54-59-88-547. (See LAXNPWLOX).
High Surf Advisory in effect from 8 AM to 9 PM PDT Monday for
zones 40-41-87. (See LAXCFWLOX).
Fire Weather Watch in effect from Tuesday afternoon through
Thursday morning for zones 239-252. (See LAXRFWLOX).
PZ...Small Craft Advisory in effect from 3 PM Sunday to 3 AM PDT
Monday for zones 650-673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (TUE-SAT).

An extended heat wave is expected Monday through at least
Thursday of next week, especially for inland areas. Widespread
elevated fire weather conditions are expected to develop during
this time. Elevated to high surf is likely Monday through
Wednesday, focused across south facing beaches.

&&

$$

PUBLIC...Hall/Munroe
AVIATION...Rorke
MARINE...Hall
BEACHES...Hall
FIRE...Gomberg
SYNOPSIS...Munroe

weather.gov/losangeles
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