248
FXUS66 KLOX 231045
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
345 AM PDT Sun Jun 23 2024

.SYNOPSIS...23/227 AM.

Dangerously hot weather will continue away from the coast as high
pressure aloft remain in place across much of the southern United
States. There will be a gradual cooling trend over many locations
during the upcoming week, except for the Antelope Valley where
conditions will stay very hot into mid- week. There is a slight
chance of a few thunderstorms this afternoon through Monday.

&&

.SHORT TERM (TDY-TUE)...23/344 AM.

The heatwave is in full swing, with the region underneath the
westernmost portion of a large high pressure system centered over
the Desert Southwest. Very little change is expected in the
overall pattern over the next few days. Temperatures will be very
similar today compared to yesterday. However expect a couple
degrees of warming along the coasts, as a result of the warming
airmass and slightly lower onshore pressure gradient

The marine layer is currently very shallow and capped by a strong
temperature inversion. Dense fog is occuring this morning up and
down the nearshore area, and may return tomorrow and Tuesday
morning as well. A Dense Fog Advisory is in effect for all coasts
until 900 AM today. The low clouds and fog will keep most beaches
much cooler than even nearby coastal plains and valleys.

Excessive Heat Warnings are in effect through today for the
interior Santa Barbara mountains through the Antelope Valley and
western San Gabriel Mountains, where high temperatures today are
expected to reach 95-105 degrees (locally to around 108 in the
Antelope Valley), producing major HeatRisk. For the Antelope
Valley and eastern Antelope Valley Foothills, these conditions are
expected to be prolonged into the upcoming week, and the
Excessive Heat Warning extends through Thursday. For the rest of
the region, except the coasts, conditions will be very warm today
and hazardous for sensitive groups. Heat Advisory is in effect
through today for much of the region (again except for the coasts).
High temperatures for areas under the Heat Advisory will be
between 90-100 degrees, locally up to 104 degrees for the warmest
areas (including Woodland Hills).

At this time, satellite imagery indicates that mid-level moisture
from Tropical Cyclone Alberto has reached the waters off the
coast of San Diego and is approaching San Diego County from the
southeast. Higher moisture will raise humidities, which will
cause an increase in apparent temperatures and minimize radiative
cooling overnight. These factors will add to the HeatRisk for
tomorrow especially. Monday and Tuesday, temperatures across the
region will trend downwards by a few degrees each day. This is
caused by slightly increased onshore flow, and higher overall
mositure in the atmosphere dampening daytime heating.

The influx of mid-level moisture will increase the convective
potential across the region. However, the atmospheric conditions
are rather stable, with little vorticity or upward momentum. For
thunderstorms to develop, it would require either very strong
daytime heating at the surface or a disturbance in the atmosphere.
At this time, there is a small (< 20 percent) chance of showers
or thunderstorms this afternoon through tonight. Because the
moisture and instability is elevated well above the surface, the
main hazards if a storm were to form will be will be cloud-to-
ground lightning strikes and gusty wind. Rainfall will be fairly
limited, as the air near the surface will remain dry. Heavy
rainfall or small hail is unlikely, with the best chances across
the mountains. Dry lightning strikes with minimal rainfall will
have the potential for new fire ignitions. Please see Fire Weather
Planning Forecast discussion for more details on the elevated
fire weather concerns across the interior through early next week.

Gusty southwesterly winds are expected over the Interstate-5
corridor and the Antelope Valley and foothills each afternoon and
evening. Wind gusts between 25 to 35 mph will be common, and wind
advisories are not anticipated.

.LONG TERM (WED-SAT)...23/344 AM.

There is very good agreement between the GFS and ECMWF that a
trough passing through the Pacific Northwest will weaken the
persistent high pressure aloft for much of the extended period.
Strong onshore flow is expected to persist as well. The marine
layer will deepen and temperatures will trend downwards each day
through Friday. Highs will be within a few degrees of normal
Thursday through Saturday. Morning low clouds and fog along the
coasts and coastal plains/valleys, as well as drizzle, will be
possible each morning, the the marine layer lifts with falling
heights.

Next weekend, there is moderate-to-high confidence that hieghts
will start to build again, after the trough to the north exits to
the east. There is the potential for the next heat event to
surpass the current ongoing event. 500 mb heights have a chance to
reach as high as 595 dam early next week.

Conditions are very likely to remain dry in the long term.
However there is a slim (< 5 percent) chance of residual monsoonal
moisture reaching the region by the middle of next week, which
would increase the risk for mountain shower or thunderstorms.

&&

.AVIATION...23/1038Z.

At 0815Z at KLAX, the marine layer was 600 feet deep. The top of
the inversion was at 1700 ft with a temperature of 28 deg C.

Very good confidence in valley TAFs, KLGB and desert TAFS.

Moderate confidence in TAFs for KSMX and KSBP with a 25 percent
chc of LIFR conds through 16Z.

Moderate confidence remainder of coastal TAFS. Dissipation timing
could be off by 2 hours. Vis at KSBA, KOXR and KCMA will likely
vary frequently between 1/4SM and 3/4SM through 16Z. There is a 30
percent chc of VIS less than a mile at KLAX and KSMO.

There is a 10-15 percent chance of SHRA or TSRA this afternoon
and evening.

KLAX...Moderate confidence in TAF. 2SM BR BKN004 conds could last
as late as 18Z. There is a 30 percent chc of 1/2SM FG conds
through 16Z. There is a 25 percent chc BKN005 conds arriving as
early as 00Z. There is a 15 percent chance of SHRA or TSRA
20Z-06Z. Good confidence that any east wind component will be
under 5kt.

KBUR...High confidence in TAF. There is a 15 percent chance of
SHRA or TSRA 20Z-06Z.

&&

.MARINE...23/242 AM.

High confidence in the winds and sea forecast. Low confidence in
the expected weather and possible gusty winds associated with any
thunderstorm activity.

For waters southwest through northwest of the Channel Islands and
along the Central Coast, winds and seas will remain below Small
Craft Advisory (SCA) levels through at least early Wednesday.
There is a 40-60 percent chance of SCA level winds developing
between Wednesday and Friday morning.

Inside the southern California bight, winds and seas will remain
below Small Craft Advisory (SCA) levels through at least early
Wednesday. There is a 20-40 percent chance of SCA level winds
developing between Wednesday afternoon and evening, and again
Thursday afternoon and evening.

In addition, there is a slight chance of thunderstorms over the
waters this afternoon and evening, as remnant moisture aloft from
Tropical Cyclone Alberto advances into the region. Areas of dense
fog will likely continue at times through early next week. Please
see the Marine Weather Statement (LAXMWSLOX) for information of
the thunderstorm potential, as well as the potential for dense
fog.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory remains in effect until 8 PM PDT this evening
      for zones 38-88-342>345-352-356>358-368>375-380-548. (See LAXNPWLOX).
     Dense Fog Advisory in effect until 9 AM PDT this morning for
      zones 340-346-349-350-354-355-362-366. (See LAXNPWLOX).
     Excessive Heat Warning remains in effect until 8 PM PDT this
      evening for zones 353-376>379-381. (See LAXNPWLOX).
     Excessive Heat Warning remains in effect until 8 PM PDT
      Thursday for zones 382-383. (See LAXNPWLOX).
PZ...NONE.

&&

$$

PUBLIC...Schoenfeld/Rorke
AVIATION...Rorke
MARINE...Hall/ASR
SYNOPSIS...Hall/RS

weather.gov/losangeles

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