979
FXUS66 KLOX 281733
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
1033 AM PDT Fri Jun 28 2024

.SYNOPSIS...27/1153 PM.

Slight cooling is expected into Friday as high pressure aloft
weakens. Gusty northwest winds will affect southwestern Santa
Barbara County and the Interstate 5 Corridor tonight. Warmer
weather is expected over the weekend as high pressure returns, and
above normal temperatures will continue through next week.

&&

.SHORT TERM (TDY-SUN)...28/1033 AM.

***UPDATE***

Confidence continues to increase in a dangerous heatwave
affecting Southern California next week, and an Excessive Heat
Watch has been issued for interior areas across portions of
Southern California. The forecast has been updated to account for
the issuance of the Excessive Heat Watch. Otherwise, no changes
have been made to the ongoing forecast.

***From Previous Discussion***

An onshore flow pattern remains in place across the area early
this morning. Slight cooling will continue into today as the tail
end of upper-level trough of low pressure moving through the
northern Intermountain Region will brush the area and slightly
increase onshore flow. Night through morning low clouds and fog,
which have struggled to form over the last several nights and
mornings, are becoming more entrenched along the Central Coast of
California this morning, while an eddy circulation near Santa
Catalina Island still struggles to form stratus clouds around it.
The increase in northwest flow over the offshore coastal waters
and parallel to the southern California coastline should permit
the eddy circulation to become a little more vigorous. With the
shallow marine layer depth along the Central Coast, there is a
high-to-likely (40-60 percent) chance of dense fog developing
along the Central Coast this morning. A dense fog advisory might
be needed for the Central Coast later this morning.

500 mb heights start to climb across the region over the weekend
as an upper-level ridge of high pressure over north Texas this
morning strengthens and expands westward. A warming trend is
forecast for Saturday and Sunday across the region, most
pronounced away from the coast. Onshore flow will weaken some, but
still remain intact into early next week. A persistent marine
layer depth will keep at least patchy low cloud coverage for some
coastal areas, but the marine layer depth will be forced to thin
some. A warming trend is well reflected in the forecast, but with
950 mb temperatures to reaching around 35 degrees Celsius across
the warmest areas, dangerously hot conditions are not forecast at
this time. Temperatures will warm to about 5 to 10 degrees above
normal for this time of year, though. Closer to the coast,
temperatures will remain around normal for this time of year with
a continued marine influence continuing and keeping the sea breeze
cooling the land mass during the afternoon hours.

.LONG TERM (MON-THU)...28/406 AM.

The strong upper-level ridge will pull away farther to the east
for early next week and allow for a piece of an upper-level
trough of low pressure over the Gulf of Alaska to brush the area
and increase onshore flow. A little better onshore push should
occur into the valleys and foothill area and bring some cooling
for Monday. Low cloud coverage should increase some and possibly
extend a little farther inland as the marine layer depth deepens
some.

By late week, the story for the weather pattern will change as a
strong high pressure system over the Central Pacific Ocean this
morning will build into the West Coast. A hot air mass will
develop over the region as 500 mb heights potentially reach 600
decameters over the northern California where the ridge center
could end up being anchored. Looking at the latest ensemble
forecast members, there is a moderate-to-high chance of widespread
dangerously hot weather developing across the region for the
latter half of next week. EPS ensemble means suggest high
temperatures means climbing through next Saturday. NBM values
remain in the forecast for high temperatures for late next week,
but as the ridge builds east into Nevada, a southeast flow aloft
could develop and open the door for monsoonal moisture to sneak
in. This could create some more cloudiness and keeps overnight low
temperatures warmer than normal across the region. Minimum
temperatures break away from NBM values toward the latter part of
the forecast period away from the coast. In addition, the marine
layer induced low cloud pattern could become very patchy in
nature or even non-existent as the middle level clouds and warmer
temperatures will mess with low cloud formation.

The increase in subtropical moisture could also develop more
typical afternoon and evening showers and thunderstorms with a
monsoonal flow pattern. EPS ensemble members suggest precipitable
water means climbing close to 1.00 at KLAX. A very slight (10
percent) chance of showers and thunderstorms has been added to the
forecast for the mountains and desert on Thursday and Friday,
breaking away from WPC and NBM values for late week.

&&

.AVIATION...28/1653Z.

At 16Z at KLAX, the marine layer was 2200 feet deep. The top of
the inversion was at 4500 feet with a temperature of 22 Celsius.

Moderate confidence in all sites becoming VFR today by 19Z. High
confidence in VFR conditions through Saturday at KWJF KPMD. There
is a chance of ceilings at KPRB (20%) KSBA (50%) KBUR (60%) KVNY
(40%) tonight into Saturday. All other sites, high confidence in
ceilings. Moderate confidence in any ceilings tonight being in
similar categories as last night (persistence).

KLAX...Moderate confidence in VFR conditions through at least 04Z.
Moderate confidence on MVFR ceilings occurring tonight. Low
confidence on timing with ceilings starting as early 06Z and as
late 14Z. High confidence in any southeast winds staying under 06
knots.

KBUR...High confidence in VFR conditions through at least 04Z.
There is a 60% of BKN008-012 ceilings forming tonight as early as
08Z and as last as 14Z. High confidence in seasonal winds.

&&

.MARINE...28/931 AM.

The moderate threat of dense fog (visibilities one mile or less)
continuing through the afternoon and returning tonight along the
Central Coast. Moderate confidence that visibilities will be up
everywhere else.

Moderate confidence the Small Craft Advisories (SCA) winds and/or
steep seas will continue through most of tonight from the Central
Coast to San Miguel Island. This will be a low-end event however,
and conditions may stay just under criteria, but it will still be
unpleasant out there. Elsewhere, high confidence in fairly benign
conditions through at least Saturday. High confidence in northwest
winds increasing once again later Saturday Night and lasting
through Monday Night. There is a moderate threat for Gales for the
offshore waters from the Central Coast to Point Conception Sunday
through Monday. There is also a low but present threat of these
winds pushing deep enough into the Santa Barbara Channel to need a
Small Craft Advisory. There is a potential for winds to be
stronger than the most recent event. As a result of these winds,
choppy seas should be expected everywhere.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Excessive Heat Watch in effect from Tuesday morning through
      late Friday night for zones
      38-88-343>345-353-376>379-381>383. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 3 AM PDT Saturday for
      zones 670-673-676. (See LAXMWWLOX).

&&

$$

PUBLIC...Cohen/Hall
AVIATION...Kittell
MARINE...RK
SYNOPSIS...jld/Smith

weather.gov/losangeles

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