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403
FXUS66 KLOX 181038
AFDLOX

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

.SYNOPSIS...
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18/226 AM.

Increasing temperatures today, in part due to gusty northeasterly
winds this morning for portions of Los Angeles County mountains
and foothills. Critical fire-weather conditions are expected
through today for northwest Los Angeles County and the Ventura
County mountains. Slightly below normal temperatures Wednesday and
Thursday, followed by a warming trend away from the coast through
the weekend.
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&&

.SHORT TERM (TDY-THU)...
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18/330 AM.

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.
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&&

.AVIATION...18/0636Z.

At 0515Z at KLAX, the marine layer was 1600 feet deep. The top of
the inversion was at 2000 ft with a temperature of 16 deg C.

Good confidence in TAFs for KSBP, KSBP, KPMD, KWJF and KPRB. At
KPMD and KWJF, brief restrictions due to BLDU or FU is possible.

Moderate confidence in TAFs for KSMO, KLAX and KLGB. There is a 30
percent chc of rapid clear before 13Z.

Moderate Confidence in TAFs for KCMA and KSBA with a 25 percent
chc of IFR cigs 12Z-17Z.

Low confidence in TAFs for KBUR, KVNY and KOXR with a 40 percent
chc of IFR cigs through 16Z.

VFR or MVFR FU or HZ is possible from KSBA and south.

Weak to moderate LLWS is possible through 18Z at KBUR and KSBA.

KLAX...Moderate confidence in TAF. There is a 30 percent chc of
clearing before 13Z. Low cloud returns Tuesday evening may be as
late as 08Z. There is a 10 percent chance of an east wind
component of 8 kts between 10-16Z.

KBUR...Low confidence in TAF. There is a 40 percent chc of BKN008
conds 10Z-16Z. Lgt LLWS is possible through 18Z. There is a 20
percent chc of 01015KT winds from 13Z to 18Z.

&&

.MARINE...
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18/213 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.
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&&

.BEACHES...17/121 PM.

High surf is no longer expected for the Ventura County beaches.
However, elevated surf conditions and dangerous rip currents will
still continue for some west and northwest facing beaches of
southwest California through this evening.

&&

.FIRE WEATHER...17/240 PM.

The Red Flag Warning for gusty northwest to north winds and low
relative humidity for the Interstate-5 corridor in northwest Los
Angeles County and the Ventura County mountains is now in effect
until 6 PM PDT Tuesday, and includes an expected wind shift to
the northeasterly direction between midnight and 6 AM PDT Tuesday.
In these areas -- after northwest to north winds reached the
45-60 mph range last night, with isolated locales to around 65
mph, northwest to north winds will continue gusting to 35 to 55
mph for the rest of today, increasing up to 60 mph tonight.
Between Midnight tonight and 6 AM PDT Tuesday, winds will shift to
the north to northeast and gust 40 to 60 mph and then gradually
decrease to 25 to 45 mph on Tuesday. With some increase in
midlevel moisture, minimum afternoon relative humidity values
today will be slightly elevated compared to yesterday -- generally
ranging 20-35 percent, today, and locally as low as 15 percent in
downslope-flow favored areas. Only poor to moderate overnight
recovery to around 25 to 45 percent is expected tonight. Late
tonight into Tuesday, relative humidity will quickly fall as very
dry air overspreads the region behind a passing midlevel impulse,
reaching the single digit readings during the day Tuesday.

In addition, the Red Flag Warning has been extended in areal
coverage to include the western San Gabriel Mountains and Highway
14 corridor from Midnight tonight to 6 PM PDT Tuesday, where gusty
northeast winds and relative humidity falling to the single digit
readings are expected. In these areas -- after occasionally gusty
northwest to north winds through this evening, winds will shift
to the northeast after midnight with speeds of 20 to 30 mph and
gusts to 45 mph, locally 55 mph. Relative humidity is expected to
be 20-45 percent tonight falling to 5 to 10 percent Tuesday.

While live fuel moisture readings are still quite high, ample
fuel loading of dead fuels has likely contributed to extreme fire
behavior with the Post Fire complex, and increasingly favorable
meteorological conditions may foster further growth and
intensification of this fire complex or any other fires developing
in the Red Flag Warning areas. After 6 PM PDT Tuesday, decreasing
winds and relative humidity recovery Tuesday night will decrease
the critical fire-weather risk.

Elsewhere across the region, the wind shift to the northeast
tonight into early Tuesday morning will come with the passage of
the impulse, and also with the continued consolidation and
deepening of a Catalina Eddy. The same Catalina Eddy driving this
Santa Ana wind-type pattern will also draw a thickening marine
layer northward across the coasts and coastal valleys including
much of the LA Basin. This marine layer will greatly temper
relative humidity reductions at the lower elevations, possibly
extending as far as the Santa Monica and Santa Susana Mountains
and especially the nearby foothills, and the Santa Clarita Valley.
As a result, there is a lot of uncertainty regarding how far the
northeasterly wind surge will extend off the San Gabriels and the
Ventura County Mountains. Nevertheless, the potential will exist
for this wind surge and accompanying deep mixing with very low
relative humidity to bring critical fire-weather conditions much
farther toward the coast, in a Santa Ana wind-type pattern. Areas
south of the western San Gabriels and Ventura County Mountains
toward the coast will be closely monitored for possible expansions
of Red Flag Warnings (30% chance of further extension), and
elevated to brief critical conditions will be a definitive
possibility in these areas (60-80% chance).

Elsewhere across the region, the combination of gusty winds, warm
temperatures, and low relative humidity will continue to bring
elevated fire-weather conditions across the Santa Barbara County
interior mountains today and Tuesday.

Areawide on Wednesday, weakening winds will be lessening the
fire-weather risk while dry conditions persist across the
interior.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
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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).
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&&

$$

PUBLIC...Schoenfeld/Rorke
AVIATION...Rorke
MARINE...Sirard/Rorke
BEACHES...Sirard
FIRE...Cohen/Gomberg
SYNOPSIS...Cohen/RS

weather.gov/losangeles

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