-- Discussion containing changed information from previous version are highlighted. --
933
FXUS66 KLOX 210650
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
1150 PM PDT Thu Jun 20 2024

.SYNOPSIS...20/134 PM.

Temperatures will trend upwards each day into the weekend, as
high pressure builds aloft. Above normal temperatures expected
Friday into early next week, especially for areas away from the
coasts. Dangerously hot conditions are possible this weekend,
especially for the mountain areas and Antelope Valley. There is a
slight change of rain showers Saturday through Tuesday.

&&

.SHORT TERM (THU-SUN)...
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20/1003 PM.

Clouds are slower to move into areas south of Point Conception
this evening but the low cloud field is well entrenched along the
Central Coast. Clouds are making a decent push into the Central
Coast and Santa Ynez Valley. The latest update encapsulates cloud
cover a little better, expanding clouds into the Santa Ynez
Valley and scaling back coverage along the Ventura County coast.
The timing along the Los Angeles County coast was delayed a bit,
but there is a 30 percent chance of no low cloud coverage for Los
Angeles County coastal areas.

With less low cloud coverage and high pressure aloft building in
much quicker, temperatures were warmed a bit more for Friday, most
significantly across the valley areas and into the mountains. 950
mb temperatures respond jumping by about 3-7 degrees across the
area on Friday, closer to where the thermal trough sets up across
the inland areas. 950 mb temperatures approach 33 degrees Celsius
at KPRB, a value indicative of 100 degree temperatures for
daytime highs. A warming trend will continue through Saturday,
potentially reaching dangerously hot levels across the Interior
valleys, such as the Antelope Valley, and into the mountains.

A marginal wind advisory was added for southwestern Santa Barbara
County through late tonight as surface pressure gradients
tightened a little more than advertised. KSBA-KSMX surface
pressure gradients have tightened to -4.1 mb currently, 0.7
mb tighter than this time last night. Wind gusts to between 45
and 50 mph have been observed along the Southwestern Coast and the
western Santa Ynez Range.

No further updates are planned at this time.

***From Previous Discussion***

Onshore flow remains in place across the area early this evening
as weak troughing aloft sits over the state. Low clouds and fog
hug the coast near Point Conception and poising to make a return
back into the Central Coast this evening. The latest AMDAR
soundings from KLAX indicate the marine layer depth to be around
1000 feet deep currently, which agrees well with NAM BUFR time
height sections. With the depth of the marine layer near 1000 feet
deep across the area, there is a chance that low clouds could be
a little more extensive and make their way back into Santa Ynez
Valley very late. South of Point Conception, clouds at best should
remain confined to coast and possibly the San Gabriel Valley.

The marine layer depth should thin over the coming days and
onshore flow will weaken as a strong ridge of high pressure aloft
over the eastern States expands across the Sun Belt and re-centers
into West Texas by late Sunday night. NAM BUFR time height
sections and deterministic model pressure gradients suggest the
marine intrusion and onshore flow remaining intact, but it will be
much thinner and weaker respectively. NAM and GFS BUFR time
height sections suggest the marine layer depth thinning closer to
near 500 feet deep. By the weekend, any low clouds (if at all)
will be confined to the immediate coastal areas and patchy in
nature. There is a moderate chance that the marine layer
cloudiness could become non-existent over the weekend. With less
onshore flow and the thinner marine layer depth, the air mass will
heat up. EPS ensemble members suggest a warming trend turning
more significant over the coming days as a hot air mass will
expand into the region. Above normal temperatures will likely
persist into early next week. Heat headlines have been issued with
an excessive heat watch in effect for areas outside of the marine
influence. There is a high-to-likely chance of dangerously hot
conditions developing across the interior portions of the area. On
the periphery of the marine layer, a heat advisory is in effect
across many valley and interior coastal areas, which will see hot
temperatures causing heat impacts for those sensitive to the heat.

The forecast gets tricky for Sunday as the remnant moisture of
Tropical Storm Alberto makes its way across the Sonoran Desert and
into southern California. EPS ensemble members suggest KLAX
precipitable water value means climbing to 1.50 inches, which
would be about 225 percent of normal for this time of year. The
current forecast indicates slight chance PoPs over the southern
and eastern Los Angeles County, but deterministic solution
maintain southwest flow aloft, which typically keeps a lid on the
atmosphere. Deterministic solutions keep the best moisture and
instability to the south and east of the area. EPS cloud cover
and QPF means look less favorable for any precipitation. In fact,
only a handful solutions advertise QPF values across the region.
Cloud cover will likely bring some cooling during the day, but
overnight low temperatures will remain warm. While the forecast
keep PoPs, the most probable scenario looks to be with very warm
to hot, humid, and uncomfortable weather across the region with
the best chance of any shower activity remaining out of the area.
That being said, PoPs do remain in the forecast, but there is
still plenty of time to iron out the finer details.

.LONG TERM (MON-THU)...20/530 PM.

The region will continue to be under the western portion of
strong high pressure centered over Arizona and New Mexico through
the extended period. With only minor changes in the upper level
pattern, weather conditions will be similar from day to day.
Temperatures will be much cooler at the beaches, with very warm-
to-hot interior temperatures. Monday and Tuesday could also see a
slight chance of showers/thunderstorms.

While high heights will remain though the extended period, the
center of the high pressure will migrate to the west by Wednesday.
This will change the positioning of the anticyclonic flow, and
will stifle the stream of mositure into the region.
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&&

.AVIATION...
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21/0649Z.

At 0515Z at KLAX, the marine layer was 1100 feet deep. The top of
the inversion was at 2300 ft with a temperature of 21 deg C.

Very good confidence in TAFs for KSBA, KOXR, KCMA, KBUR, KVNY,
KPMD and KWJF.

Moderate confidence in TAFs for KPRB, KSBP and KSMX where flight
cat changes could be off by +/- 90 minutes and cigs hgts off by
300 ft.

Low confidence in TAFs for KSMO (40 percent chc of MVFR cigs
12Z-17Z) and KLAX and KLGB (40 percent chc of no cigs).

KLAX...Low confidence in TAF. There is a 40 chance of no cig/vsby
restrictions tonight. No significant east wind component is
expected.

KBUR...High confidence in TAF.
-- End Changed Discussion --

&&

.MARINE...20/931 PM.

For the Outer Waters, high confidence in current forecast. Small
Craft Advisory (SCA) winds are expected through Friday evening.
Thereafter, SCA conditions are not expected through at least
early next week.

For the Inner Waters north of Point Sal, moderate to high
confidence in current forecast. SCA winds will remain possible
through Friday evening, highest chances in the afternoon and
evenings. Thereafter, SCA conditions are not expected through at
least early next week.

For the inner waters south of Point Conception, moderate to high
confidence in current forecast. SCA winds are expected over the
western Santa Barbara Channel through tonight, with a 50% chance
tomorrow afternoon and evening. Otherwise, SCA conditions are not
expected through at least early next week.

In addition, there will be some possibility for a few
thunderstorms to impact the local waters this weekend, as remnant
upper-level moisture from Tropical Cyclone Alberto advances into
the region. Please reference the Marine Weather Statement for
additional information.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory remains in effect from 10 AM Saturday to 8 PM
      PDT Sunday for zones 38-88-343>345-372-373-548. (See LAXNPWLOX).
     Wind Advisory in effect until 4 AM PDT Saturday for zones
      349-351. (See LAXNPWLOX).
     Excessive Heat Watch remains in effect from Saturday morning
      through Sunday evening for zones 353-376>382. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 3 AM PDT Saturday for
      zones 645-670-673-676. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PDT Friday for zone
      650. (See LAXMWWLOX).

&&

$$

PUBLIC...Hall/Schoenfeld/Rorke/jld
AVIATION...Rorke
MARINE...Cohen
SYNOPSIS...jld

weather.gov/losangeles

Experimental Graphical Hazardous Weather Outlook at:
https://www.weather.gov/erh/ghwo?wfo=lox