Heat Advisory 8, NWS Los Angeles, CA

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
858 AM PDT Fri Aug 13 2021

.SYNOPSIS...13/853 AM.

High pressure aloft will build over the region through this
weekend with an associated warming trend. Excessive heat is
expected to begin Saturday in the Antelope Valley and interior
portions of San Luis Obispo County, and into the Los Angeles
County mountains and Santa Clarita by Sunday.

&&

.SHORT TERM (TDY-SUN)...13/850 AM.

***UPDATE***

As mentioned previously, there was not an eddy formation along the
south coast this morning and the decreased cloud cover should help
keep things a bit warmer along the coast. The weekend heat looks
like it could also now include the Santa Clarita Valley and LA
County mountains so they may be added to the excessive heat watch
for Sunday. The afternoon gusty conditions the LA County mountains
and Antelope Valley will be stronger than yesterday but remain
under advisory strength.

***From Previous Discussion***

A 595 dam upper high centered over the Great Salt Lake covers the
entire west coast. 592 dam hgts are over most of the state. The
onshore trends forecast ydy have arrived but the eddy did not spin
up and as a result there are much less low clouds south of Pt
Conception than anticipated. The onshore push the to the east is
still forecast to increase to about 8 mb this afternoon and this
will likely keep a few beaches (esp Central Coast and west facing
coast of VTA county) cloudy through the day. The strong onshore
flow will again bring gusty winds to the LA mtns and the western
portion of the Antelope Vly. These winds will combine with warm
temperatures and low humidities to produce an elevated fire wx
threat. Max temps are forecast to be cooler today across the
csts/vlys south of Pt Conception due to an increase in onshore
flow. Not entirely convinced of this cooling or at least the
magnitude of the cooling since there are hardly any marine clouds
but all very recent short term ensemble guidance is onboard the
cooling idea. The remnants of Hurricane Kevin are making their
way up the coast and there could be enough eastward travel to make
the Central Coast's skies partly cloudy.

There will be strong onshore flow to the north and the east
tonight and this should provide enough oomph to bring low clouds
to most of the coastal areas. The marine layer will remain shallow
enough to preclude any stratus from reaching the vlys save for the
Santa Ynez.

The upper high shifts to the west and into NV on Saturday. Hgts
over the state will increase to about 594 dam. The marine layer
and the strong onshore flow will actually cool the coasts and
lower vlys while the interior warms by 1 to 3 degrees. This will
push the max temps across the interior (excluding the higher
elevations) up into the upper 90s to 104 with 106 degree readings
possible in the Antelope Vly. There is an excessive heat watch in
effect for these areas - these temps are on the edge between heat
advisory and heat warning criteria and the day shift will decide
after looking at the 12Z guidance. Max temps across the coasts
and lower vlys will be a few degrees blo normal but the far
interior will be about 8 degrees above normal.

There will be a very strong marine inversion in place Saturday
night. Locations near the inversion top, likely around 1200 ft,
will have very warm overnight lows possibly in the 80s.

Sunday still on track to be the warmest day of the next 7. The
upper high will shift further west and its central hgt will rise
to 598 dam pushing the hgts over Srn Ca up to 596 dam. On top of
the rising hgts there will also be offshore trends both from the
north and east. The weaker onshore flow will delay the sea breeze
and allow cst/vly warming. Between the hgt rises and weaker sea
breeze max temps will rise 3 to 6 degrees across the area.
Excessive heat warning conditions look likely for the interior
with advisory level heat in the Santa Clarita and Portions of the
San Fernando Vlys.

.LONG TERM (MON-THU)...13/313 AM.

The upper high will weaken a little on Monday but not enough to
cool the interior much. It is likely that heat advisories/warnings
will again be needed for portions of the interior. The onshore
flow will increase some and this should bring some cooling to the
csts/vlys but perhaps not enough to preclude another heat advisory
for the Santa Clarita vly.

Better cooling on tap for Tuesday as a trof moves out of the Pac
NW and into nrn CA. Hgts fall to 590 dam. There will also be a
little more onshore flow. Look for 4 to 8 degrees of cooling
across the interior and 1 to 3 degrees of cooling for the
csts/vlys.

Broad troffing will be over the state on Wednesday as the pos
tilted upper low moves into Idaho. There will not be much change
in the weather for SoCal with low clouds and fog over the near
shore areas during the night through morning hours and couple more
degrees of cooling in the afternoon. Most max temps will end up a
few degrees blo normal.

2 to 3 degrees of warming is forecast for an unremarkable weather
day next Thursday as the upper low pulls away and hgts increase
slightly.

&&

.AVIATION...13/1115Z.

At 0629Z at KLAX, the marine layer was 600 feet deep. The top of
the inversion was around 2400 feet with a temperature of 25 C.

High confidence in valley and desert 12Z TAFs and moderate
confidence for coastal TAFs north of Pt Conception with IFR CIGs.
There is a 40% chance that CIGs will lower to LIFR between 12z-
15z. IFR expected for coastal sites south of Point Conception but
low confidence in timing, with a 30-40% chance for each site to
remain VFR. Good confidence for persistent stratus deck once again
for coastal TAF sites N of Point Conception.

KLAX...Low to moderate confidence in 12Z TAF. There is a 30-40%
chance of IFR CIGs this morning. Better confidence for earlier
IFR/low MVFR CIGs after 08z tonight. No significant east wind
component is expected.

KBUR...High confidence in 12Z TAF.

&&

.MARINE...13/824 AM.

Except for local gusts to 25 kt across the northern outer waters
(PZZ670) both this evening and Saturday evening, there is good
confidence that seas will remain below Small Craft Advisory (SCA)
thresholds until late Sunday afternoon or evening when there is a
70% chance that SCA level gusts become more widespread across the
entire outer waters. There is a 40-50% chance for Gale force
winds Sunday evening through Monday for the outer waters north and
west of Point Conception.

South to southeast swells 2 to 4 feet with 11-13 second periods
are expected through early next week from Hurricane Linda.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Excessive Heat Watch in effect from Saturday morning through
      Monday evening for zones 37-38-51-59. (See LAXNPWLOX).
PZ...NONE.

&&

.HAZARD POTENTIAL OUTLOOK (SUN-THU).

Hot conditions in the San Luis Obispo interior and Antelope Valley
will peak on Sunday and continue into Monday. The Los Angeles
County mountains and Santa Clarita will likely also be quite hot
on Sunday.

&&

PUBLIC...Rorke/jld
AVIATION...Kaplan
MARINE...MW/Kaplan
SYNOPSIS...jld

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