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638
FXUS66 KLOX 240413
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
913 PM PDT Sun Jun 23 2024

Updated marine section

.SYNOPSIS...23/852 PM.

Dangerously hot weather will continue away from the coast as high
pressure aloft remain in place across much of the southern United
States. There will be a gradual cooling trend over many locations
during the upcoming week, except for the Antelope Valley where
conditions will stay very hot into mid- week. There is a slight
chance of thunderstorms through Monday.

&&

.SHORT TERM (SUN-WED)...23/851 PM.

Another hot day for areas away from the immediate coast. Many
interior areas climbed to over 100 degrees including Chatsworth
at 104 degrees, Woodland Hills at 103 degrees, and
Lancaster/Palmdale at 102 degrees. Even the interior coastal plain
saw a rise in temperatures today, with Long Beach Airport reaching
95 degrees, downtown LA at 90 degrees, and a new record high for
the date at Camarillo Airport at 89 degrees. The influx of
moisture from former tropical cyclone Alberto added to the heat
discomfort. With daytime heating, the moisture and instability
generate a strong and nearly stationary thunderstorm complex
across the mountains of northeast Ventura County and extreme
northwest LA county (near the Post Fire). This thunderstorm
complex generated numerous lightning strikes and doppler radar
estimated rainfall rates as high as 2 inches per hour at the core
of the storm. This resulted in the issuance of a Flash Flood
Warning and a significant weather advisory for strong wind gusts
and frequent lightning.

While convection ended over the mountains after sundown,
satellite imagery continues to show a surge of mid level clouds
moving towards the coasts of Ventura and Santa Barbara counties.
The influx of mid level moisture and elevated instability will
still bring a 10-15 percent chance of elevated thunderstorms
tonight, mainly Santa Barbara and San Luis Obispo counties. If any
thunderstorms were to develop, the main threats would be isolated
dry lightning strikes with limited rainfall, and gusty downdraft
winds. On Monday, there continues to be residual moisture across
the region. This moisture combined with increased instability will
bring a slight chance of afternoon thunderstorms to the mountains
of Ventura County and eastern San Gabriels, as well as the
eastern Antelope Valley. 00Z NAM model showing better instability
on Monday afternoon, with lifted index values between -3 and -6
for these mountain areas. Taking a look at model soundings for
these areas, the Ventura County mountains have a better moisture
profile with light steering flow, which could bring the threat of
slow moving storms and localized flash flooding. Further east
over the eastern San Gabriels and Antelope Valley, there is less
moisture, with more of an inverted-v structure and DCAPE values
over 1000 J/kg. As a result, the main risks for these areas will
be isolated dry lightning strikes with less rainfall and strong
downdrafts. Another interesting feature to watch will be SLO
county on Monday afternoon, as the models have been showing some
upper level divergence along with the residual mid level
moisture/instability that could bring a 10-15 percent chance of
thunderstorms for SLO county. With the lower levels of the
atmosphere still quite dry, there could also be a threat of
isolated dry lightning strikes with less rainfall.

Another very warm day on tap for Monday, but most areas should see
a few degrees of cooling as onshore flow continues to strengthen.
Heat Warning remains in effect for the Antelope Valley through
Thursday as afternoon high temperatures continue to exceed 100
degrees. The Heat Warnings for the Santa Barbara Interior
mountains and West San Gabriels were downgraded to a heat advisory
for Monday, with temperatures still expected to reach close to 100
degrees at lower elevations. Heat advisories were extended into
Monday for the Santa Clarita Valley, western San Fernando Valley,
Santa Ynez Valley, Cuyama Valley, and interior San Luis Obispo
county. All of these areas will see high temperatures of 92
to 101 degrees, with continued warm overnight lows.

*** From previous discussion ***

A reorientation of the flow aloft to the southwest to west and
departure of mid level moisture should support increased and
breezy onshore winds Monday into Tuesday, supporting the
aforementioned cooling trend most notable for coasts and coastal
valleys. The marine layer may struggle to form clouds for a day or
two for Los Angeles, Ventura, and Southern Santa Barbara
Counties. Where low clouds do form, patchy dense fog will be
possible through at least Monday as the ridge aloft keeps a
shallow marine layer in place.

.LONG TERM (THU-SUN)...23/132 PM.

Only moderate confidence in the extended period as there is a
60-70 percent chance for significant rebound in the heat (as hot
if not hotter for many areas) next weekend. Similar to the ongoing
heat, the marine layer will probably somewhat limit the heat and
related impacts near the coast. Low to moderate heat risk will
continue Thursday through Friday or Saturday, before potentially
increasing to moderate to high levels next weekend. If the higher
heat scenario plays out, there may be a monsoon push into at least
Los Angeles County towards the end of the weekend or into early
next week. Breezy northwest to onshore winds will continue,
potentially nearing advisory levels for southwest Santa Barbara
County in particular late in the week.

&&

.AVIATION...23/2324Z.

At 0000Z at KLAX, the marine layer was 800 feet deep. The top of
the inversion was at 2200 ft with a temperature of 30 deg C.

Low to moderate confidence for all sites in Santa Barbara and San
Luis Obispo Counties. Monsoonal moisture moving over the area
will bring a 10-15 percent chance of a thunderstorm affecting the
airports during the overnight period through 12Z. In addition
there is low confidence in the low cloud forecasts for KSBA, KSMX
and KSBP as the monsoonal flow may disrupt the marine layer,
resulting in no low cloud formation.

Otherwise, moderate confidence in the remainder of the coastal
TAFs, and high confidence for the LA County valley and desert
sites. The timing of low clouds arrival along the coast is low
confidence.  and there is a 30 percent of no cloud cover
overnight.

KLAX...Moderate confidence in the 00Z TAF. The arrival time of low
cigs could differ by +/- 2 hours from TAF time, and there is a 30
percent chance of no low clouds. There is a 10 percent chance of
SHRA or TSRA through 06Z. Good confidence that any east wind
component will be under 5kt.

KBUR...High confidence in the 00Z TAF. There is a 15 percent
chance of SHRA or TSRA through 06Z.

&&

.MARINE...
-- Changed Discussion --
23/912 PM.

High confidence in the winds and sea forecast. Low confidence in
the expected weather and possible gusty winds associated with any
thunderstorm activity.

For waters southwest through northwest of the Channel Islands and
along the Central Coast, winds and seas will remain below Small
Craft Advisory (SCA) levels through at least early Wednesday.
Then, there is a 50-70 percent chance of SCA level winds
developing between Wednesday and late Friday night, highest in the
vicinity of Point Conception south to northwest of San Nicolas
Island.

Inside the southern California bight, winds and seas will remain
below Small Craft Advisory (SCA) levels through at least early
Wednesday. There is a 20-50 percent chance of SCA level winds
developing between Wednesday afternoon and evening, and again
Thursday afternoon and evening. The highest chances will be for
the western portions of the Santa Barbara Channel.

In addition, there is a slight chance of thunderstorms over the
waters through Monday evening as remnant moisture aloft from
post-tropical Cyclone Alberto move over the region. Otherwise, a
shallow marine layer depth will continue areas of dense fog
through Monday morning.
-- End Changed Discussion --

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory now in effect until 8 PM PDT Monday for zones
      38-88-344-345-348-353-372-379. (See LAXNPWLOX).
     Excessive Heat Warning remains in effect until 8 PM PDT
      Thursday for zones 382-383. (See LAXNPWLOX).
PZ...NONE.

&&

$$

PUBLIC...Gomberg/Munroe
AVIATION...Smith
MARINE...Hall
SYNOPSIS...Hall/Gomberg

weather.gov/losangeles

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