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611
FXUS66 KLOX 172140
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
240 PM PDT Mon Jun 17 2024

.SYNOPSIS...
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17/240 PM.

Strong northwest to north winds will impact the Central Coast
through interior sections of Santa Barbara County to the Antelope
Valley through this evening. Later tonight, a surge of northeasterly
winds will spread across the Los Angeles County mountains and
adjacent eastern Ventura County, and potentially through the Santa
Monica Mountains. Critical fire-weather conditions are expected
across the Interstate-5 corridor of northwest Los Angeles County
and the Ventura County mountains, as well as the western San
Gabriels, through tomorrow. Temperatures will be generally within
a few degrees of normal readings this week, before temperatures
across the interior warms considerably this upcoming weekend.
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&&

.SHORT TERM (TDY-THU)...
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17/240 PM.

Satellite loops indicate a deep cyclone crossing the northern
Rockies, with unseasonably high-amplitude troughing extending
southward into Southern California. A shortwave impulse advancing
through the base of the trough will glance the region tonight,
reinforcing ample upper support for strong winds. The passage of
the impulse will also facilitate a wind shift from the northwest
and north to the northeast overnight tonight over the higher
terrain of LA and Ventura Counties, before a drier air mass
overspreads the interior on Tuesday.

Wind gusts are expected to increase to around 60 mph once again
across High Wind Warning areas (Ventura County mountains eastward
to the western Antelope Valley Foothills including the
Interstate-5 corridor of northwest Los Angeles County, as well as
the southwest Santa Barbara County mountains and coast).
Surrounding Wind Advisories are in effect for many areas from the
Antelope Valley westward to the Central Coast, where gusts of
35-55 mph are expected. Winds will gradually taper off during the
day Tuesday.

Of note, the southward mass flux in the low levels, in response
to the strengthening upper support, is expected to continue
fostering the formation of a strong coastal/barrier northerly jet
just offshore. As has been evidenced in longer-range visible
satellite imagery, the interaction of cross-stream speed shear
across the jet, with coastline curvature in the Southern
California Bight, will continue supporting the development of a
strong Catalina Eddy. The circulation around this eddy is expected
to drive a Santa Ana wind-type response, which is also a major
factor supporting the wind-shift to the northeast overnight
tonight into early Tuesday morning. And with nocturnal drainage
flow enhancements, the northeasterly wind surge will remain quite
strong late tonight into Tuesday, with gusts upwards of 45-55 mph
through Tuesday morning, tapering off during the day Tuesday.

Moreover, the re-orienting surface pressure gradient will support
the eastward spread of strong northeast wind gusts across the
western San Gabriel Mountains, where a Wind Advisory has been
issued for the northeast winds late tonight into Tuesday. The
southern extent of the northeasterly wind surge remains in
question, owing to the deepening marine layer being transported
northward within the eastern semicircle of the Catalina Eddy.
There is a 40% chance for wind headlines to be extended farther
toward the coast across the Los Angeles County mountains and Santa
Monicas including adjacent parts of Ventura County in later
forecasts -- if the reinforcing marine layer were to be less
widespread and/or deep. However, greater than 50-50 odds are
present for the marine layer to extend well inland from the coast,
causing the southern extent of the northeast wind surge to remain
confined to the western San Gabriels.

Low relative humidity will be combining with the strong winds to
continue prolonging critical fire-weather conditions. A Red Flag
Warning is in effect for the Interstate-5 corridor in northwest
Los Angeles County and the Ventura County mountains until 6 PM PDT
Tuesday. In addition, a Red Flag Warning is in effect for the
western San Gabriel Mountains and Highway 14 corridor from
Midnight tonight to 6 PM PDT Tuesday. Additional information is
available in the Fire Weather section below, as well as the Fire
Weather Planning Forecast. Also, smoke from the Post Fire complex
will affect a large portion of LA and Ventura Counties and will
bring air-quality impacts to many areas. Please reference the Air
Quality Alert Message for additional information.

By Tuesday night and into Wednesday, the midlevel height gradient
is expected to weaken while broad upper troughing persists across
the region. Correspondingly, low level winds across the region are
forecast to begin a weakening trend, and present indications are
that wind headlines will be unlikely after Tuesday in most areas.
However, Sundowner winds over southern Santa Barbara County could
necessitate additional Wind Advisories (40-60% chance)

With the reinforced upper troughing persisting over the region
through mid-week, temperatures are not expected to be as warm
across the region as they were this past weekend. In addition,
surface pressure gradients at the larger scale will be gradually
turning more onshore through early to mid week. This will favor
deepening of the marine layer with increasing coverage of marine
stratus and fog, and perhaps night/morning drizzle, aided by
persistence of eddies just off shore. This will result in
additional cooling for the coasts and coastal valleys.
Temperatures through Thursday are generally expected to be within
a few degrees of normal, mostly in the 70s except upper 60s at the
beaches and in the 80s and 90s over interior valleys and
foothills.

.LONG TERM (FRI-MON)...17/240 PM.

The axis of broad mid and upper troughing will shift slightly
offshore for Friday, as small-scale impulses pivoting through the
surrounding cyclonic flow reposition its primary axis. This will
favor continued deepening of the marine layer, with abundant night
and morning marine stratus and fog over the coasts and coastal
valleys. As a subtropical ridge builds westward from the south-
central CONUS for late in the week into next weekend, larger-scale
onshore pressure gradients will substantially strengthen. This
will reinforce low clouds and fog at the coast while supporting
stronger heating over the interior.

With the midlevel ridging, high temperatures are forecast to
reach the 90s to around 100 degrees over many interior valleys,
and upwards of 105 degrees in the Antelope Valley for the upcoming
weekend. In addition, as midlevel heights rise during the upcoming
weekend, more substantial diurnal clearing may occur over inland
areas away from the coast owing to increasingly shallow marine-
layer depths. This could expand the areal coverage of very warm to
hot temperatures closer toward the coast next weekend. There
appears to be a 10-30% chance for heat-related headlines to be
issued for the upcoming weekend into early next week.
-- End Changed Discussion --

&&

.AVIATION...17/1803Z.

At 17Z at KLAX, the marine layer was 2500 feet deep. The top of
the inversion was at 5400 ft with a temperature of 18 deg C.

Overall, moderate to high confidence in the 18Z TAF package. For
most sites, VFR conds are anticipated through the period. However
for KSMO, KLAX, and KLGB, cig restrictions to MVFR will be
possible until around 20Z today for KSMO and KLGB, then sometime
between 05Z-18Z tonight and Tue for all three airfields. However,
there is also a 20% chance of MVFR cigs developing tonight at
KBUR. The timing of the onset and any dissipation of the low
clouds may be off +/- an hour or two.

Gusty W to NW winds are expected this afternoon into this evening
for KSBP, KSMX, KPMD and KWJF, strongest in the deserts where
gusts over 40 knots are possible along with a 20% chance of
restricted vsbys due to blowing dust.

KLAX...Moderate to hi confidence in the 18Z TAF. VFR conds will
prevail into this evening. For tonight, moderate to hi confidence
in return of MVFR cigs between about 06Z and 20Z. The timing of
the onset and dissipation of the low clouds may be off +/- an
hour or two. An east wind component tonight up to 6 knots is
expected from about 06Z-17Z.

KBUR...Moderate to high confidence in the 18Z TAF. VFR conds are
expected thru the TAF period, except for a 20% chance of MVFR cigs
developing tonight aft about 07Z and linger into early Tue
morning.

&&

.MARINE...
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17/121 PM.

For the Outer Waters, high confidence in current forecast. Winds
are expected to remain at Gale force levels into late tonight. For
Tuesday through Friday, winds will subside, but remain at Small
Craft Advisory (SCA) levels. Seas drop below 10 feet on Tuesday.
Conds are then expected to below SCA levels Friday night through
Saturday night.

For the Inner Waters north of Point Sal, moderate to high
confidence in current forecast. SCA level winds will persist
through Thursday night, strongest afternoons and evenings. For
Friday through Saturday night, winds and seas should remain below
SCA levels.

For the Inner Waters south of Point Conception, moderate to high
confidence in current forecast. Gale Force winds are likely for
the western Santa Barbara Channel through this evening. For Tuesday
through Thursday, there will be a 60% chance of SCA level winds
across the western half of the Santa Barbara Channel during the
afternoons and evenings. South of the SBA Channel, there is a
50-70% chance of SCA level winds for the western and northern
portions this afternoon into evening. Otherwise and elsewhere
through Saturday night, SCA conditions are not expected.
-- End Changed Discussion --

&&

.BEACHES...
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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.
-- End Changed Discussion --

&&

.FIRE WEATHER...
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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.
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&&

.LOX WATCHES/WARNINGS/ADVISORIES...
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CA...Wind Advisory remains in effect until 3 AM PDT Tuesday for
      zones 88-340-341-346-347-352-353-356-383. (See LAXNPWLOX).
     High Wind Warning remains in effect until 3 AM PDT Tuesday
      for zones 349-351-376>378-381. (See LAXNPWLOX).
     Wind Advisory remains in effect from midnight tonight to 6 PM
      PDT Tuesday for zone 379. (See LAXNPWLOX).
     Red Flag Warning in effect until 6 PM PDT Tuesday for zones
      376>378. (See LAXRFWLOX).
     Red Flag Warning in effect from midnight tonight to 6 PM PDT
      Tuesday for zone 379. (See LAXRFWLOX).
PZ...Small Craft Advisory in effect until 3 AM PDT Thursday for
      zone 645. (See LAXMWWLOX).
     Gale Warning in effect until 3 AM PDT Tuesday for zones
      650-670-673-676. (See LAXMWWLOX).
     Small Craft Advisory in effect until 9 PM PDT this evening
      for zone 655. (See LAXMWWLOX).
-- End Changed Discussion --

&&

$$

PUBLIC...Cohen
AVIATION...Sirard
MARINE...Sirard
BEACHES...Sirard
FIRE...Cohen/Gomberg
SYNOPSIS...Cohen

weather.gov/losangeles

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