074
FXUS66 KLOX 181140
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
440 AM PDT Thu Jul 18 2024

.SYNOPSIS...18/408 AM.

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 conditions 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 over the weekend and into next week.

&&

.SHORT TERM (TDY-SAT)...18/359 AM.

Another extended round of dangerously hot weather returns as we
approach the end of the week and continuing through much of next
week. While not quite as hot as the last heat wave, temperatures
will increase several degrees each day and by Sunday 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. Therefore, excessive heat warnings and advisories
have been issued for a majority of the mountains, valleys, and far
interior areas Friday through at least the weekend. It is highly
recommended to know the signs of heat illness as anyone is at risk
for it, stay hydrated, and avoid hiking in the mountains over the
weekend if possible.

Weather pattern-wise, an upper level ridge of high pressure is
building over the area (and much of the western states in fact),
in congruence with the Aleutian Low over the NE Pacific
strengthening and reinforcing the ridge. This ridge will cause
an increase in upper level heights across the interior, resulting
in the warming of several degrees each day, along with the slight
decrease in onshore flow warming away from the coasts as well as
the coastal valleys. Direct coasts south of Point Conception may
see limited change each day as a shallow marine layer each day
will remain present near the coasts.

One caveat to the warming across the Central Coast is a weak low
pressure system to the west that will move over Santa Barbara and
San Luis Obispo County through Saturday, which may result in a
slight cooling across the Central Coast through Saturday. Decided
to issue a heat advisory into Sunday morning for this area rather
than an Excessive Heat Warning. Sunday might be another story,
and can be read about in the section below.

The ridge of high pressure will 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, especially during the afternoon and
evening hours. The highest chances for thunderstorms look to be
Saturday as the moisture keeps building in. However, the chances
are still too small to be added into the official forecast at this
time. As for the Central Coast, if the upper low pressure system
is delayed for any reason and the moisture from the south is able
to sneak into the area in time, there may be some concern for
thunderstorms across the Central Coast due to the lift provided by
the pressure system. While this scenario is not likely to happen
for the Central Coast, there is a small enough chance that it is
worth mentioning.

As for winds, each evening into overnight period, the Western
Santa Ynez Range and Southwestern Santa Barbara Coast will see
gusty NW Sundowner winds thanks to a -2 mb SBA to SMX pressure
gradient tonight which will be very similar to the previous night.
While tonight may see gusts of 40 mph to locally 45 mph, Friday
nights gradient will strengthen to around -3 mb, and Saturday
potentially up to -4.4, so wind advisories may be needed for the
subsequent nights for wind gusts of 45 to 50 mph winds.

.LONG TERM (SUN-WED)...18/439 AM.

The extended period of dangerously hot conditions continues
through much of the extended period, if not all of this upcoming
work week - at least for the interior mountains and far interior
areas. Temperatures will remain fairly similar day-to-day through
the week as not much will change synoptically. The main change
will be for the Central Coast on Sunday, mainly the Santa Lucia
Mountains and the San Luis Obispo portion of the Salinas Valley.
The low pressure system going over the northern part of the region
will start to break down Saturday evening and the ridge of high
pressure will build westward and warm the aforementioned areas to
tick the HeatRisk levels up to major, so the Excessive Heat Watch
was pushed back to start Sunday morning. One thing to note
temperature-wise, is that the 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. To close out the temperature talk for this morning, all
of the current heat products may be extended through the rest of
the week as we get closer, due to the little change in conditions
each day.

The potential for monsoonal thunderstorms and locally heavy
showers continue into mid-week, and while the moisture continues
to increase and expand across the area early next week, confidence
remains low this far out and will remain out of the official
forecast for now. If thunderstorms do 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. The conditional potential for strong, erratic
outflow winds causing rapid spread rates of fires, lightning-
induced fire ignitions, and flash flooding from localized intense
rainfall rates will exist with any thunderstorm that decides to
develop.

&&

.AVIATION...18/0557Z.

At 05Z over KLAX, the marine layer was 1200 feet deep. The top of
the inversion was at 3500 feet with a temperature of 28 Celsius.

High confidence in VFR conditions through Thursday at KBUR, KVNY,
KPMD, and KWJF. There is a There is a 5-10% chance of -TSRA at
KPMD KWJF Thursday afternoon.

Low confidence in KSMX, KSBP, KSBA, KOXR, and KCMA. Flight cat
changes may be off +/- 2 hours. VLIFR conditions possible at KSMX
(40%) and KSBP (30%) through 16Z.

Moderate confidence at KPRB, KSMO, KLAX, and KLGB. Flight cat
changes may be off +/- 2 hours. 30% chance of IFR conditions at
KLAX and KSMO through 16Z. 10% chance of IFR conditions at KLGB
through 16Z. There is 10% chance of LIFR conds 12Z-16Z.

KLAX... Moderate confidence in TAF. BKN008 cigs arriving as early
as 09Z possible. Good confidence in cigs dissipating by 18Z at the
latest. No significant east wind component expected.

KBUR...High confidence in TAF.

&&

.MARINE...18/354 AM.

For the outer waters, Small Craft Advisory (SCA) northwest winds
are ongoing and are expected to continue for the remainder of this
week and into this weekend. As a band of northwesterly winds
strengthens this weekend, confidence continues increasing in the
potential for low-end Gale Force wind gusts to occur (60% chance),
and a Gale Watch has been issued from Saturday afternoon through
Sunday night. Winds will taper off early next week, though SCA
winds will likely linger into Monday (70% chance). With the strong
winds, steep and hazardous seas are expected Friday afternoon
into the weekend.

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 afternoon and evening hours each day. Steep and
hazardous seas are expected Friday afternoon into the weekend.

For the inner waters south of Pt. Conception, there is a 10-30%
chance for SCA northwest winds to occur in the Santa Barbara
Channel through Friday morning -- with the highest chances during
the afternoon and evening hours and focused between Santa Cruz
Island and Pt. Conception. Winds will increase further for Friday
afternoon through this weekend across the Santa Barbara Channel,
with more widespread SCA winds expected especially during the
afternoon and evening hours. Farther south across the southern
inner waters, there is a 10-30% chance for SCA northwest winds to
occur over the nearshore waters off of the Los Angeles and Orange
County coasts -- highest chances during the afternoon and evening
hours across the San Pedro Channel, and also west of Catalina
Island. Seas over the coastal waters well offshore will be
building later this week into this weekend and become choppy.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Excessive Heat Warning 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 in effect from 10 AM Friday to 10 AM PDT Sunday
      for zones 342-343-369-370-374-375. (See LAXNPWLOX).
     Excessive Heat Watch now in effect from Sunday morning
      through Wednesday evening for zones 342-343-369-370-374-375. (See LAXNPWLOX).
     Beach Hazards Statement in effect through this evening for
      zones 354-362-366. (See LAXCFWLOX).
     Heat Advisory 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
AVIATION...Lewis/KL
MARINE...Cohen
SYNOPSIS...jld/KL

weather.gov/losangeles

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