866
FXUS66 KLOX 190410
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
910 PM PDT Thu Jul 18 2024

.SYNOPSIS...18/909 PM.

A significant heatwave will impact Southern California Friday
into next week. A large portion of the mountains, foothills, and
valleys away from the coast will experience dangerously hot
conditions, and very warm temperatures may extend toward the
coast. Gusty Sundowner winds will affect portions of southern
Santa Barbara County through Saturday night. Monsoonal moisture
will potentially bring thunderstorms to the interior mountains and
valleys each afternoon into next week.

&&

.SHORT TERM (THU-SUN)...18/205 PM.

Synoptically, there is a 558 dam Low in the Gulf of Alaska area
that will drop periodic troughs along the west coast, but not as
far south as SoCal. There is a strong (597 dam) upper level High
over the four-corners area which will weaken to about 594 dam and
begin a slow transit westward until it is centered roughly over
central California by Sunday - where it will remain and build to
~598-600 dam by next Wednesday. Next Thursday should bring a big
pattern shift as a trough finally drops down the coast as far as
SoCal.

There has been some cloud buildup near Wrightwood this afternoon
and one gauge picked up some measurable rain, but so far it looks
like the larger convective cells and lightning threat is staying
well to our east. The ridge of high pressure will continue to
bring in moisture from the south, increasing PWATs to 1.0-1.5
inches, which will bring a less than 20 percent chance of
thunderstorms and monsoonal rain showers to the Los Angeles County
interior mountains and deserts (thanks to orographic lifting)
each day in the short term, especially during the afternoon and
early evening hours.

Temperatures are currently 5-7 degrees above this time yesterday
(except along the immediate coast) as we enter another extended
round of dangerously hot weather. While not quite as hot as the
last heat wave, temperatures will increase several degrees each
day.

The Western Santa Ynez Range and Southwestern Santa Barbara Coast
will see gusty NW Sundowner winds this evening thanks to a -2 mb
SBA to SMX pressure gradient tonight which will be very similar to
last night which brought gusts of 40 mph to locally 45 mph.

Beginning Friday, there are Excessive Heat Warnings and Heat
Advisories for a majority of the mountains, valleys, and far
interior areas which will last through at least the weekend. The
immediate coastal areas (esp south of Point Conception) may see
limited change each day as a shallow marine layer each day will
remain present. Friday night`s SBA to SMX pressure gradient will
strengthen to around -3 mb so wind advisories may be needed for
for wind gusts of 45 to 50 mph winds.

On Saturday a weak low pressure system to our west will move over
Santa Barbara and San Luis Obispo County, which may result in a
slight cooling across the Central Coast. Saturday also brings the
highest chances for thunderstorms over the weekend as the
moisture keeps building in. However, the chances are still too
small to be added into the official forecast at this time.
Saturday night`s SBA to SMX pressure gradient will increase again,
potentially to -4.4, so wind advisories may be needed again for
wind gusts of 45 to 50 mph winds.

By Sunday, temperatures should climb to 105 to 112 degrees across
the lower mountains and far interior areas (including the
Antelope Valley), 95 to 105 across the warmest coastal valleys,
while areas closest to the coast will range in the upper 60s to
high 70s degrees. These temperatures will increase to 5 to 15
degrees above normal as you move away from the coast.

.LONG TERM (MON-THU)...18/211 PM.

The long-duration dangerously hot conditions will continue
through at least Wednesday, at least for the interior mountains
and far interior areas. Temperatures will remain fairly similar
day-to-day Monday through Wednesday as not much will change
synoptically. Nights will remain very warm across the far
interior, with forecast lows to be in the 70s to 80s, resulting in
little overnight relief and potentially worsen heat impacts. On
Thursday a trough should drop down the west coast and
temperatures should drop for the later portion of the week.

The potential for daily monsoonal thunderstorms and locally heavy
showers continues into mid-week. While the moisture continues to
increase and expand across the area early next week, confidence
remains low this far out and PoPs remain below 15% for now. If
thunderstorms were to form, they will likely form over the higher
terrain and interior valleys of Los Angeles and Ventura Counties
and possibly extend into Santa Barbara County by early next week.

&&

.AVIATION...18/2312Z.

At 23Z at KLAX, the marine layer was 1100 feet deep. The top of
the inversion was at 3900 feet with a temperature of 29 Celsius.

High confidence in CAVU TAFs for KPRB, KBUR, KVNY.

High confidence in TAFs at KPMD and KWJF. There is a 5-10% chance
for thunderstorms this afternoon.

Low confidence in KSBP, KSMX, KSBA, KOXR, and KCMA. 40% chance for
minimum flight categories to be off by one category. Flight category
changes may be off by +/- 3 hours from current forecasts.

Moderate confidence in KSMO, KLAX, and KLGB. 20% chance of
minimum flight categories to be off by one category. Flight
category changes may vary by +/- 3 hours from current forecasts.

KLAX...Moderate confidence in TAF. There is a 20% chance for cigs
below 005 between 10Z and 15Z. High confidence in cigs
dissipating by 18Z. Flight category changes may be off +/- 3
hours. No east wind component expected.

KBUR...High confidence in CAVU TAF.

&&

.MARINE...18/908 PM.

For the outer waters, Small Craft Advisory (SCA) northwest winds
are ongoing and are expected to continue through this weekend.
There is a 70% chance of low end Gale Force winds to impact the
outer waters this weekend. A Gale watch is in effect from
Saturday afternoon through Sunday night. Winds will likely taper
off Monday, but there is a 50% chance of SCA winds Monday through
early next week. Steep seas will also impact the outer waters
beginning Friday through at least Monday.

For the inner waters north of Pt. Sal, northwest winds are
expected to reach SCA levels starting Friday afternoon and
continuing into Sunday night. The strongest winds are expected
during the later afternoon and evening hours each day. There is a
30% chance that SCA winds don`t occur Friday, but they are much
more likely Saturday and Sunday (70%). Steep and hazardous seas
are expected Friday afternoon into the weekend.

For the inner waters south of Pt. Conception, NW to west winds
are expected to remain below SCA levels in the Santa Barbara
Channel overnight. Winds will increase for Friday afternoon
through this weekend in the Santa Barbara Channel. A SCA is in
effect starting tomorrow at 2 PM and lasting through Sunday night,
primarily impacting the western portion. There is a 30% chance
that winds will remain below SCA level in the Santa Barbara
Channel Friday afternoon/evening. SCA winds are far more likely
Saturday and Sunday (60%).

In the furthest southern inner waters, there is a 30% chance for
SCA northwest winds to occur over the waters off of the Los
Angeles and Orange County coasts Saturday and Sunday. The highest
chances are during the afternoon and evening hours across the San
Pedro Channel, and west of Catalina Island.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Excessive Heat Warning remains in effect from 10 AM Friday to
      10 PM PDT Wednesday for zones
      38-88-344-345-351>353-371-372-376>383. (See LAXNPWLOX).
     Heat Advisory remains in effect from 10 AM Friday to 10 AM
      PDT Sunday for zones 342-343-369-370-374-375. (See LAXNPWLOX).
     Excessive Heat Watch remains in effect from Sunday morning
      through Wednesday evening for zones 342-343-369-370-374-375. (See LAXNPWLOX).
     Heat Advisory remains in effect from 10 AM Friday to 9 PM PDT
      Saturday for zones 373-548. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect from 2 PM Friday to 11 PM PDT
      Sunday for zones 645-650. (See LAXMWWLOX).
     Small Craft Advisory in effect until 2 PM PDT Saturday for
      zones 670-673-676. (See LAXMWWLOX).
     Gale Watch in effect from Saturday afternoon through Sunday
      evening for zones 670-673-676. (See LAXMWWLOX).

&&

$$

PUBLIC...Lund/jld
AVIATION...Lewis
MARINE...Lewis
SYNOPSIS...Smith

weather.gov/losangeles

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