443
FXUS66 KLOX 181757 AAA
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
1057 AM PDT Tue Jun 18 2024

updated aviation discussion

.SYNOPSIS...18/1022 AM.

A brief warm-up with dry weather will occur today outside of the
marine influence, but near normal temperatures will continue
across the coastal areas. Slightly below normal temperatures
Wednesday and Thursday, followed by a warming trend away from the
coast through the weekend.

&&

.SHORT TERM (TDY-THU)...18/1016 AM.

A fairly complex pattern exists this morning across the area as
a battle is being waged across the area between onshore and
offshore flow. An eddy circulation remains intact just south of
Catalina Island currently. A pretty good extent of low clouds
pushed into the Los Angeles County coast and valleys this
morning, despite onshore pressure gradients weakening
substantially. The marine layer depth remained wedged in across
the area, continuing to resist the offshore push. Outside of the
marine influence, marginally gusty offshore winds remain at this
time across the Los Angeles County mountains. The wind advisory
will likely be allowed to expire at 11 am this morning.

A drier air mass will push down into the foothills, mountains,
and higher valleys today as the offshore push filter down into
these area. Consequently, warmer conditions are expected across
these locations as the offshore influence weighs more heavily into
the forecast today. Thus, warmer, drier, and marginally windy
conditions will continue to develop less than ideal fire weather
conditions across the foothills, mountains, and higher valleys
through at least tonight.

Very minor changes are expected over the next 24 to 36 hours.
500 mb heights and 1000-500 mb thickness values do not change
much overhead. The latest NAM-BUFR and local 3-km WRF time height
sections suggest the marine layer depth thinning slightly down to
about 1800 feet deep at KLAX from 2600 feet deep currently. As a
result, clouds should be a little less extensive tonight and into
Wednesday morning.

Northerly winds occurring the last several nights across southern
Santa Barbara County and through Interstate 5 Corridor will become
confined to southern Santa Barbara County this afternoon and
evening, but marginally gusty winds will likely continue through
tonight through Interstate 5 Corridor. A wind advisory will remain
in effect for this afternoon and tonight across southern Santa
Barbara County.

***From Previous Discussion***

The region will continue to be under a deep broad trough, with
heights likely to creep upwards very slowly through Thursday.
Overall minimal change to the upper level pattern through the
short term period.

A brief pulse in the broad trough will allow for a short-lived
period of enough cold air advection over the interior to develop
cooler temperatures inland compared to at the coasts. This
temperature difference is quite unseasonable and is reflected in
the pressure gradients. While the LAX to DAG pressure gradient is
currently slightly onshore at 2.1 mb, by around 5 AM today it is
expected to flip to offshore from the northeast by about 1 mb. The
offshore gradient will yield advisory level gusts across the
western San Gabriel Mountains and adjacent areas, including the
I-5 Cooridor and the Post Fire region. Wind gusts of 30-45 mph
will be common, with up to around 50 mph for the highest peaks of
the western San Gabriel Mountains. NE flow may extend southward to
the Santa Monica mountains, and warm the coastal valleys north of
the mountains. Winds are likely to fall below advisory level by
late morning, and Wnd Advisories are in effect for the I-5
Cooridor, the Western San Gabriel Mountains, the western Antelope
Valley Foothills, and the Santa Clarita Valley through 11 AM
today.

The currently northwesterly winds will shift to the northeast
early this morning and will also continue to support critical
fire weather conditions through today (see FIRE WEATHER
discussion). The Post Fire burn areas is likely to see a downward
trend in winds, however the NW winds will shift to to from the NE
in alignment with the San Gabriel Mountains. Smoke from the fire
will continue to affect Los Angeles and Ventura Counties today.
Please reference the Air Quality Alert Message for additional
information.

Sundowner NW winds across southern Santa Barbara County are
expected redevelop this afternoon into late tonight again for the
entire Santa Ynez Range and the western portion of the south
coast. Wind gusts of 35 to 45 mph will be common, peaking over
the higher elevation. Wind Advisories will go into effect for the
aforementioned locations starting at 3 PM today and last until
late tonight. Sundowner winds will likely return Wednesay and
Thursday evening as well, however there is only around a 30%
chance of Wind Advisories being needed, as the N-S surface
pressure gradients are expected to trend downward.

The offshore flow across the region will lead to an increase in
temperatures today. As the LAX to DAG gradient is expected to
return to onshore Wednesday, temperatures will cool to a few
degrees below normal through Thursday, mostly in the 70s except
upper 60s at the beaches and in the 80s and 90s over interior
valleys and foothills. In addition, strong northerly flow over the
coastal waters is expected to continue, fueled by upper level
support and N-S pressure gradients. The nearshore gradient,
however, points from south to north and this will turn the winds
towards and up the coast forming a persistent Catalina Eddy that
will bring marine influence and morning low clouds and fog along
the southern coasts.

.LONG TERM (FRI-MON)...18/337 AM.

On Friday the trough is likely to break down. The GFS and ECMWF
both agree that the upper level heights will increase rapidly
though Saturday as a strong ridge builds in. Heights of 590-592
dam are expected Sunday and Monday, and strong onshore pressure
gradients are likely into early next week.

This upper level pattern supports a very shallow marine layer
that is likely to cling to the beaches all day. However once out
of the marine layer, inland areas will see very warm to hot
conditions around 10 degrees above normal. The Antelope Valley is
likely to see highs ranging from 100-105 Friday through the
weekend, with interior valleys in the mid 90s. At this time, there
is around a 10-30% chance of heat-related headlines for the
upcoming weekend into early next week.

&&

.AVIATION...18/1756Z.

At 1715Z at KLAX, the marine layer was 2600 feet deep. The top of
the inversion was at 4500 ft with a temperature of 21 deg C.

Good confidence in TAFs for KPRB, KSBP, KSMX, KPMD and KWJF with
VFR conds expected thru the fcst period.

Moderate confidence in TAFs for KSBA, KOXR, KCMA, KSMO, KLAX,
KLGB, KBUR, KVNY. Any low clouds with MVFR conds at the start of
the TAF period should clear to VFR by 20Z. Low clouds and MVFR
conds are then possible at some point tonight into Wed morning.
The timing of the dissipation and onset of low clouds could be off
+/- and hour or two.

KLAX...Moderate confidence in TAF. There is a 30 percent chc of
clearing delayed until 20Z. Low cloud returns this evening may be
as early as 06Z or as late as 08Z. The low clouds should clear to
VFR by 20Z Wed. Any east wind component should be less than 6
knots.

KBUR...Moderate confidence in TAF. There is a 30 percent chc of
clearing delayed until 20Z. Low cloud should return this evening
by 08Z then persist thru 18Z Wed. The timing of the dissipation
and onset of low clouds could be off +/- and hour or two.

&&

.MARINE...18/820 AM.

For the Outer Waters, high confidence in current forecast. Small
Craft Advisory (SCA) Winds are expected through at least Wednesday
night and perhaps as late as Friday. Conditions are expected to be
below SCA levels Friday night through Saturday night.

For the Inner Waters north of Point Sal, high confidence in
current forecast. SCA level winds will persist through at least
Wednesday and probably through Thursday night. The winds will be
strongest during the afternoons and evenings. For Friday through
Saturday night, winds and seas should remain below SCA levels.

For the Santa Barbara Channel, moderate confidence in current
forecast. Winds will mostly be below SCA levels, but during the
afternoons and evenings through Friday there will be local SCA
level gusts across the western third of the channel. There is a 30
percent chance that the gusts will be widespread enough to warrant
a SCA.

South of the SBA Channel, there is a 30% chance for SCA winds
Thursday evening. Otherwise, winds and seas will generally be
below SCA levels.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory now in effect until 11 AM PDT this morning for
      zones 88-378-379-381. (See LAXNPWLOX).
     Wind Advisory in effect until 11 AM PDT this morning for zone
      88. (See LAXNPWLOX).
     Wind Advisory in effect from 3 PM this afternoon to 3 AM PDT
      Wednesday for zones 349-351-352. (See LAXNPWLOX).
     Red Flag Warning in effect until 6 PM PDT this evening for
      zones 376>379. (See LAXRFWLOX).
PZ...Small Craft Advisory in effect until 3 AM PDT Thursday for
      zones 645-670-673-676. (See LAXMWWLOX).

&&

$$

PUBLIC...Hall/Schoenfeld/Rorke
AVIATION...Sirard
MARINE...Sirard/Rorke
SYNOPSIS...Hall

weather.gov/losangeles

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