Duarte Weather

908
FXUS66 KLOX 291219
AFDLOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
519 AM PDT Thu Jun 29 2017

.SYNOPSIS...
Warmer than normal temperatures will continue across inland areas
with a return of triple digit heat across the Antelope Valley by
Friday. High pressure aloft will give way to a weak upper trough
and a modest cooling trend through the middle of next week.
Expect night through morning low clouds across coast and some
coastal valleys over the next several days.

&&

.SHORT TERM...(TDY-SAT)

Latest fog product imagery indicated widespread stratus across the
Central Coast and Santa Ynez Valley as well as entering the
Salinas River Valley around the Monterey Border. For areas S of
Point Conception, a Catalina Eddy was causing the low clouds to
move north out of Orange County and fill in across the LA County
coast and coastal valleys. The Ventura County Coast and a portion
of the Ventura County Valleys should fill in by sunrise. Low
clouds and patchy fog were also developing across the SBA S.
Coast. Latest AMDAR sounding was showing a significant rise of the
marine layer to around 2000 ft this morning from earlier last
evening. A strong inversion remains in place. The combination of
a deeper marine layer, strong inversion and continued strong
onshore gradient should allow low clouds to linger across coastal
areas into the afternoon and possibly stay cloudy all afternoon at
some beaches. Valleys should clear out by mid morning.

Synoptically, A 592 DM high located 500 NM W of Los Angeles will
expand a bit eastward and cause a slight increase in heights over
the next couple of days. The combination of the deep marine layer
and relatively strong onshore flow across LA/VTU counties today will
keep coast and coastal valleys a few degrees cooler compared to
yesterday. Some warming is expected across most areas N of Point
Conception. Highs will be in the 80s for most valleys, except up
to the lower to mid 90s across the interior areas of SLO County
and the Cuyama Valley. There will be a degree or two of warming
across the Antelope Valley in to the upper 90s. There will be
a modest Sundowner affecting the western portion of the SBA South
Coast and adjacent foothills this afternoon and Friday afternoon.
Gusty SW to W winds continue once again today and Friday across
the Antelope Valley. The gusty onshore winds combined with
continued very warm and dry conditions across the far interior
sections of our forecast area will continue to bring elevated fire
weather concerns...see fire section below for more details. The
onshore flow is expected to weaken some on Friday leading to a
brief, but significant warming trend for interior sections on
Friday. The Antelope Valley is expected to see a return of triple
digit temperatures on Friday as the upper ridge expands and
strengthen over southern California. Valleys should be in the mid
80s to mid 90s. Although the onshore gradient will be weaker
Friday, coastal areas should remain mild with night through
morning low clouds and patchy fog continuing through the short
term period. The marine layer depth should allow for some stratus
to filter into some coastal valleys as well.

By Saturday, a weak upper trough digs in across the west coast
pushing the upper ridge back over the Eastern Pac. There will be
widespread cooling 3-6 degrees across the forecast area. Valley
areas S of Point Conception will be in the 80s to around 91 in
warmest locations, while interior valleys across SLO/SBA counties
will remain in the mid 90s. The Antelope Valley should reach the
upper 90s to around 101. Coastal areas should remain mild with
night through morning low clouds and patchy fog continuing through
the short term period. The marine layer depth should allow for
some stratus to filter into some coastal valleys as well.

.LONG TERM...(SUN-WED)

Both the GFS and EC models continue to show the upper trough
moving through the forecast area Sunday through Tue continuing a
modest cooling trend. Still warmer than normal for this time of
year inland. The marine layer coverage is expected through the
middle of next week. By next Wednesday, the pattern becomes more
typical for this time of year with a persistent upper trough to
the northwest, and a four corners upper high developing. The
location and orientation of the ridge is favorable for monsoon
moisture to flow into southeast California should a moisture
source develop. Models are hinting at a few inverted shortwaves
rotating around the high through the area from the southeast
which could pose a threat for thunderstorm activity later next
week into next weekend. There will be a warming trend beginning
Wednesday, with more significant warming late in the week.

&&

.AVIATION...29/1215Z.

At 1130Z at KLAX...the marine layer was 2000 feet deep. The top
of the inversion was 4000 feet with a temperature of 21 degrees
Celsius.

Low clouds were widespread in all coastal and most valley areas
this morning, with mostly low MVFR conds, except IFR to LIFR
conds across SLO and SBA County coastal areas and the Salinas
Valley.

Expect clearing during mid morning in the valleys, and late
morning to around noon across the coastal plain.

Similar low cloud pattern expected tonight, widespread in coastal
and most valley areas, with generally IFR conds, except low MVFR
conds across coastal sections of L.A. County.

KLAX...Moderate to high confidence in the 12Z TAF. There is a
20% chance that cigs will linger until as late as 22Z. There is a
20% chance that cigs tonight will be in the IFR category.

KBUR...Moderate to high confidence in the 12Z TAF. There is a 20%
chance that cigs will linger until as late as 18Z. There is a 20%
chance that cigs tonight will arrive as early as 06Z.

&&

.MARINE...29/300 AM.

High confidence in at least Small Craft Advisory (SCA) conditions
across the outer coastal waters, at least from San Nicolas Island
northward through Saturday night. Gale Force winds are possible
across the northern two thirds of the outer waters Friday
afternoon through Saturday evening, so a Gale Watch is effect.
There is a slight chance of gale force winds as early as tonight.
The strongest winds for this event will be beyond 20 miles from
shore. There will be lulls each morning within 10 miles from the
coast.

Good confidence in SCA conds across the northern inner waters this
afternoon through late tonight, and each afternoon through night
through Saturday.

Moderate confidence that conds will remain below SCA levels in
the Santa Barbara Channel and the southern inner waters for the
next several days. There is a 20% chance of SCA winds across
western sections of the SBA Channel this evening and Fri evening.

Seas will increase in height through late this week with short
periods dominating. A long period Southwest swell will affect the
southern inner waters in PZZ655...and may be noticeable nearshore.

&&

.FIRE WEATHER...28/800 PM.

Elevated fire danger will continue across the interior valleys,
mountains, and Antelope Valley through at least Friday as gusty
onshore winds combine with very warm and dry conditions. Unusually
strong onshore pressure gradient for late June observed this
afternoon, with LAX-Daggett gradient peaking at +7.9 mb. Similar
strong onshore pressure gradient expected on Thursday. The
strongest onshore winds will likely be focused across the
Antelope Valley, LA county mountains, and Santa Clarita Valley,
where gusts between 25 and 40 mph will be common. In addition,
drier conditions are forecasted for most interior sections
on Thursday, with widespread humidities falling into the teens
across interior sections...except widespread single digit readings
in the Antelope Valley. In fact, there is the potential for
3 to 5 hours of critical fire weather conditions across the
Antelope Valley on Thursday, but not sufficiently long to
warrant a Red Flag Warning.

While onshore winds are not expected to be quite as strong on
Friday, elevated fire weather concerns will continue across
interior sections due to a return of hotter temperatures and
continued very dry conditions.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory in effect from 3 PM this afternoon to 3
      AM PDT Friday for zone 645. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 PM PDT Friday for
      zones 670-673. (See LAXMWWLOX).
     Gale Watch in effect from Friday afternoon through Saturday
      evening for zones 670-673. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PDT Sunday for zone
      676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK...(SAT-WED)
No significant hazards expected.

&&

$$

PUBLIC...Kaplan
AVIATION...DB
MARINE...DB
FIRE...Gomberg
SYNOPSIS...Kaplan

weather.gov/losangeles

NWS LOX Office Area Forecast Discussion