Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 291015

315 AM PDT Thu Jun 29 2017

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.



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.


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.



At 2330z at KLAX...there was 1200 foot marine layer. The inversion
top was 3300 feet with a temperature of 23 degrees Celsius.

At 2355z, satellite imagery showing low clouds and fog returning
to immediate portions of the Central Coast and LA Coast. Eddy
circulation combined with strengthening onshore flow expected
to bring additional deepening of the marine layer overnight across
Ventura and LA counties, with a more expansive coverage of low
clouds and fog into the valleys. A shallower and less expansive
marine layer coverage expected north of Point Conception.
99 percent chance of CIG 006-012 at KSMX KSBP KOXR KCMA KSMO KLAX
KLGB tonight, 70 percent chance at KBUR KVNY, 20 percent chance
at KPRB. Moderate confidence in TAF timing +/- 3 hours.

KLAX...High confidence of IFR/MVFR cigs returing to KLAX this
evening and continuing through Thursday morning.
Catalina Eddy expected overnight into Thursday morning, with SE
winds likely 05-08KT at times after 10Z. 10 percent chance of
exceeding 10 KT.

KBUR...High confidence in VFR conditions through 06Z. 70 percent
chance of CIGS around 006 arriving 08-13Z.


.MARINE...28/800 PM.

High confidence in at least Small Craft Advisory (SCA) conditions
from the Central Coast to San Nicolas Island through Saturday
night. Gale Force winds will be possible as early as Thursday
night, but more likely by Friday afternoon...which should then
continue through Saturday evening. A Gale Watch will be in effect
starting Friday afternoon, but there is a chance a Gale Warning
will be needed earlier. 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.

Moderate confidence in the Santa Barbara Channel staying below
SCA for the next few days. Southeast winds may be locally gusty
each morning in the San Pedro and Santa Barbara Channels...through
at least Saturday.

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.


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).


No significant hazards expected.



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