-- Discussion containing changed information from previous version are highlighted. --
880
FXUS66 KLOX 170639
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
1139 PM PDT Sun Jun 16 2024

.SYNOPSIS...16/222 PM.

Temperatures will cool off by a few degrees in most areas this
upcoming week, following the warm to hot conditions from this
weekend. Strong northwest to north winds will impact the Central
Coast through interior sections of Santa Barbara County to the
Antelope Valley through Monday night. The strongest winds are
expected to affect the Interstate-5 corridor of northwest Los
Angeles County and the Ventura County mountains, where critical
fire-weather conditions are also expected. In addition, the winds
may shift to a northeasterly direction Monday night into Tuesday,
spreading across the Los Angeles County mountains, the Santa
Monicas, and adjacent eastern Ventura County.

&&

.SHORT TERM (TDY-TUE)...
-- Changed Discussion --
16/844 PM.

***UPDATE***

Forecast is tracking well this evening. Already seeing tightening
pressure gradient to our north in response to the unseasonably
strong descending region of a jet to push into the region over the
next several hours. The latest high resolution guidance shows an
uptick of 10-20 mph in wind gusts within the Ventura mountains and
northwest Los Angeles County mountains (where a High Wind Warning
and incidentally the Red Flag Warning remain in effect),
continuing strong overnight and gradually weakening early Monday.
That will support the well advertised gusts of 50-70 mph,
strongest along the ridgetops. Other Wind Advisories look well
placed with the eastern Santa Ynez Ranged added. Some areas near
the coast may experience a lull in wind overnight.

A strong eddy is likely tonight (Santa Barbara to San Diego is
nearly -3 mb which is very rare) and already seeing signs of that
with low clouds already pushing into Long Beach CA from the south,
3-5 hours early then we often see eddy forced low clouds. Low
cloud forecast tonight is quite tricky as the surging low clouds
with the eddy battles against intensifying northerly flow aloft.
The San Fernando Valley, Inland Oxnard plain, and southeast Santa
Barbara coast having a 10-20 percent chance of low clouds or fog
by day break.

Heat and smoke from the Post Fire in NW Los Angeles County
continued to be noted on satellite, with the smoke now extending
well south and east of the fire, encompassing much of Los Angeles
County. Haze, smoke, and reduced air quality may become more
common across this region in particular overnight. In
collaboration with Los Angeles and Ventura Counties, Air Quality
Alerts have been issued for areas that may be most impacted.

***From Previous Discussion***

Significant deepening of a Pacific Northwest upper low will
sharpen midlevel height gradients and intensify deep-layer wind
fields within the base of the amplifying trough extending over
southern California. This will send significant upper support
southward across the forecast area tonight, causing an
unseasonably-anomalous strong low-level mass response over the
local area. Corresponding northwest to north winds will increase
this evening into tonight over interior sections. Gusts will
increase to 60-70 mph in 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.

Similar wind speeds are expected to occur through at least Monday
night, and High Wind Warnings and Wind Advisories have been
extended in time through Monday night. In addition, the southward
mass flux in the low levels, in response to the strengthening
upper support, is expected to form a strong coastal/barrier
northerly jet just offshore. The latest data is showing an
increasing signal for cross-stream speed shear across the jet to
interact with coastline curvature in the Southern California Bight
to promote the development of a strong Catalina Eddy from Monday
into Tuesday. The circulation around this eddy is expected to
drive a Santa Ana wind-type response, causing a wind shift to the
northeast Monday night into Tuesday. And with with nocturnal
drainage flow enhancements, north to northeast winds could remain
quite strong Monday night through Tuesday. There is a 60% chance
for wind headlines to be extended through Tuesday and/or spread
across the Los Angeles County mountains and Santa Monicas
including adjacent parts of Ventura County.

A Red Flag Warning is in effect 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 in
effect until 3 PM PDT Monday, where critical fire-weather
conditions are expected. Elsewhere, elevated to briefly critical
fire-weather conditions are expected across the interior and
southern Santa Barbara County. 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 County and eastern Ventura County 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.

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 over this weekend. In addition,
surface pressure gradients at the larger scale will be gradually
turning increasingly 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. This
will result in additional cooling for the coasts and coastal
valleys. Temperatures by Tuesday and Wednesday are expected to
have cooled to within a few degrees of normal, generally in the
70s except upper 60s at the beaches and in the 80s and 90s over
some of the interior valleys and foothills.

.LONG TERM (WED-SAT)...16/223 PM.

The axis of broad mid and upper troughing will shift slightly
offshore for Thursday and 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 next weekend. In
addition, as midlevel heights rise next 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.
-- End Changed Discussion --

&&

.AVIATION...
-- Changed Discussion --
17/0638Z.

At 06Z at KLAX, the marine layer was 1600 feet deep. The top of
the inversion was at 4000 ft with a temperature of 19 deg C.

Moderate confidence in KPMD KWJF and KPRB, due to uncertainty in
gusty winds and the potential for FU from distant fires.

Low to moderate confidence in other TAFs, especially KSBA and
south including KLAX. Low clouds and fog in coastal sections
of L.A. County will likely spread into of the San Gabriel and San
Fernando Valleys by or shortly after midnight, then probably into
coastal and valley areas of Ventura County overnight. There is
even a chance that clouds will push into the south coast of SBA
County very late tonight. Low clouds will likely form in southern
portions of the Central Coast and push into KSMX late tonight.

Conds will be mostly low MVFR to high IFR, except possibly LIFR
to VLIFR in the foothills and from Ventura County northward.
Expect skies to clear by mid to late morning, except early in the
afternoon near the coast of Ventura and L.A. Counties.

There could also be some reduced vsbys from FU at L.A. County
airports overnight and Mon morning.

Gusty W to NW will affect the Antelope Valley through the period.
Blowing dust and sand will locally reduce visibilities to one half
mile or less at times thru Mon evening. Strong and gusty NW winds
will affect the mountains and portions of southern SBA County
thru the period, with gusty NW winds on the Central Coast Mon
afternoon and evening.

Weak to moderate LLWS is possible through 15Z, focused near KSBA,
KBUR, and KVNY. There will be mdt to locally strong uddf at times
near the mountains.

KLAX...Low to moderate confidence in the 06Z TAF. There is a 20%
chance that cigs will scatter out as early as 16Z Mon. There is a
20-30% chance that cigs will linger thru 21Z or 22Z. There is a
20% chance that cigs will not arrive until at least 08Z tomorrow
evening. There is a 30% chance of an east wind component of 8-10
kt between 09Z and 16Z Mon.

KBUR...Low to moderate confidence in the 06Z TAF. There is a 20-30%
chance of IFR/LIFR cigs/vsbys between 09z and 14Z Mon. There is a
30% chance of reduced vsbys from FU from the Post Fire from
09Z-16Z. There is a 20% chance that cigs will linger until 18Z.
-- End Changed Discussion --

&&

.MARINE...16/1256 PM.

For the Outer Waters, high confidence in current forecast. Winds
are expected to remain at Gale force levels through Monday. So,
GALE WARNINGS will remain in place during this time (with a 20%
chance of Storm force winds through tonight). Seas will peak in
the 11 to 14 foot range through Monday. For Tuesday through
Friday night, winds will subside, but remain at Small Craft
Advisory (SCA) levels while seas drop below 10 feet.

For the Inner Waters north of Point Sal, moderate to high
confidence in current forecast. There is a 60-80% chance of Gale
force winds this afternoon through tonight and a GALE WARNING
remains in effect. Seas will peak between 10 to 13 foot through
tonight. For Monday through Wednesday, there is a 60-80% chance of
SCA level winds, mainly afternoons and evenings. For Thursday
through Friday night, winds and seas should remain below SCA
levels.

For the Inner Waters south of Point Conception, moderate to high
confidence in current forecast. For the western Santa Barbara
Channel, high confidence in Gale Force Winds this afternoon
through tonight and a GALE WARNING remains in effect. The winds
will be strongest from mid channel and westward. For Monday
through Wednesday, there will be a 60-80% chance of SCA level
winds across the western half of the Santa Barbara Channel, mainly
afternoons and evenings. Otherwise and elsewhere over the inner
waters south of Point Conception, winds and seas should remain
below SCA levels through Friday night.

Across much of the coastal waters, steep and dangerous seas can
be expected into mid week.

&&

.BEACHES...16/1258 PM.

Short-period wind waves, due to gale force winds over the nearby
coastal waters, will generate significant surf conditions along
the local beaches through Monday, mainly on west and northwest
facing beaches. High surf of 4 to 7 feet will impact the beaches
of Ventura county. For the beaches along the Central Coast as well
as Los Angeles county, elevated surf conditions will continue
through Monday. Along with the surf conditions, dangerous rip
currents can be expected into early this week.

&&

.FIRE WEATHER...16/223 PM.

GOES-16 satellite imagery indicates that the ongoing Post Fire
complex in the vicinity of the I-5 corridor in northwest LA
County and adjacent northern Ventura County continues to grow in
size and intensity. Weather conditions will become increasingly
conducive for further growth and intensification of this complex,
especially tonight, and a Red Flag Warning has been issued for the
I-5 corridor in northwest LA County and the Ventura County
Mountains. For these areas, the latest data suggest that northwest
to north winds will gust to 45 to 55 mph today, increase to 60 to
70 mph range tonight, and then gradually decrease to 30 to 50 mph
through the day Monday. Sustained wind speeds will generally be
in the 20 to 40 mph range. These strong winds, with the notable
uptick tonight, will be caused by increasing upper support
overspreading Southern California in the base of a deepening
cyclone centered well north of the area. The upper pattern will
also bring an influx of abundant dry air into the area, and
minimum afternoon relative humidity values are expected to range
from 15 to 25 percent, locally as low as 10 percent in downslope-
flow favored areas -- with only poor to moderate overnight
recovery to around 25 to 40 percent tonight. While live fuel
moisture readings are still quite high, ample fuel loading of
dead fuels is likely contributing to the extreme fire behavior
with the Post Fire complex, and increasingly favorable
meteorological conditions are expected to foster further growth
and intensification of this fire complex or any other fires
developing in the Red Flag Warning area. The Red Flag Warning is
currently set to expire at 3PM PDT Monday, however, conditions
will be re-evaluated for possible extension of the Warning in
subsequent forecasts, given the potential for gusty winds to
continue into Monday night and Tuesday. There is a 40 percent
chance that the Red Flag Warning is extended into Monday night or
Tuesday. There is also the potential for winds to shift to the
northeast Monday night and Tuesday.

Elsewhere across the region, gusty northwest to north winds are
expected to continue through Monday, peaking in intensity tonight
with a secondary peak Sunday night into early Monday. Wind gusts
of 30 to 50 mph will be common at times through the period for the
Central Coast, mountains of Santa Barbara, Ventura and northwest
LA County as well as the Antelope Valley (strongest in the
mountains and deserts). Isolated gusts to 65 mph will be likely in
the strongest periods of wind across western the Santa Ynez Range
and adjacent western Santa Barbara County South Coast, primarily
in the evening and overnight hours in conjunction with Sundowner
wind enhancements and nocturnal drainage processes. Meanwhile, a
warm and dry air mass will remain in place, with widespread 8 to
15 percent humidities across the interior today, and 12 to 20
percent on Monday. Poor overnight recoveries in the foothills are
also expected. The warm and dry air will continue to descend into
some coastal foothills on Sunday, including portions of southern
Santa Barbara County. The combination of gusty winds, warm
temperatures, and low humidities will continue to bring elevated
to brief critical fire weather conditions across southern Santa
Barbara county through Sunday night, and all interior areas
through Monday. There is an increased risk for fast-growing grass
fires over much of the area, that could transition into wildfires
where the fuel beds are most abundant and dry.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement in effect through Monday evening for
      zones 87-340-346-362-366. (See LAXCFWLOX).
     Wind Advisory remains in effect until 3 AM PDT Tuesday for
      zones 88-340-341-346-347-353-356-383. (See LAXNPWLOX).
     High Wind Warning remains in effect until 3 AM PDT Tuesday
      for zones 349-351-376>378-381. (See LAXNPWLOX).
     Wind Advisory in effect until 3 AM PDT Tuesday for zone 352. (See LAXNPWLOX).
     High Surf Advisory in effect until 7 PM PDT Monday for zone
      354. (See LAXCFWLOX).
     Red Flag Warning in effect until 3 PM PDT Monday for zones
      376>378. (See LAXRFWLOX).
PZ...Gale Warning in effect until 3 AM PDT Monday for zone 645. (See LAXMWWLOX).
     Small Craft Advisory in effect until noon PDT Monday for zone
      650. (See LAXMWWLOX).
     Gale Watch in effect from Monday afternoon through late
      Monday night for zone 650. (See LAXMWWLOX).
     Gale Warning in effect until 7 PM PDT Monday for zones
      670-673-676. (See LAXMWWLOX).

&&

$$

PUBLIC...Munroe/Cohen
AVIATION...DB
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