Tornado in California, September 9, 2021

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
154 PM PDT Thu Sep 9 2021

.SYNOPSIS...09/142 PM.

High temperatures will remain above normal through the weekend
due to high pressure aloft. Weak onshore flow and a shallow marine
layer will keep night through morning low clouds mainly confined
to the coast.

&&

.SHORT TERM (TDY-SUN)...09/137 PM.

A couple small and fast moving storms have developed in
southeastern SLO County with some lightning but that's been it for
convection so far. Conditions should remain favorable through the
afternoon so there may be more to come, though as we've seen the
steering winds are pretty fast so storms aren't lingering very
long in any one place. Main impact from these storms will be gusty
winds and lightning.

Going forward not much change in the forecast through the middle
of next week. Highs will remain 5-10 degrees above normal through
Friday with heat advisories then cooling slightly over the
weekend. Could make a case for extending heat advisories into
Saturday but interior areas should see just enough cooling
to lower the heat risk. Western San Fernando Valley areas will be
in the lower 100's through Sunday while most other valley
locations will stay in the 90s. Warm, but not worthy of a heat
advisory given the location and time of year.

Today is likely the last day of any potential thunderstorms as a
drier southwest flow aloft will push moisture and instability out
of the area.

Marine layer stratus will remain a daily forecast conundrum.
Ocean temps are closer to July levels than September so stratus
has a better chance of developing than usual given the pattern.
And where there is stratus there will be dense fog since the
marine layer depth should remain at or below 1000'.

.LONG TERM (MON-THU)...09/151 PM.

Model ensembles continue to strongly favor a cooling trend next
week with highs getting close to normal Monday and 1-3 degrees
below normal Tue-Thu for all except the far interior areas. There
are minor differences in the models that will impact temperatures
by a few degrees either way but the overall cooling theme looks
solid with increasing onshore flow through the period. Overall
minimal weather impacts next week except likely some gusty winds
around the Antelope Valley and low-ish humidities.

&&

.AVIATION...09/1838Z.

At 1726Z, the marine layer at KLAX was 900 ft deep. The top of
the marine inversion was around 2400 ft with a temperature of
30C.

Low to moderate confidence in the 18z TAF forecast. The marine
clouds have cleared from all TAF sites, but are lingering right
along the coast. Guidance suggests that the marine clouds will
linger near the coast for the daytime hours before surging into
the coastal sections again early this evening. IFR to VLIFR
conditions are again likely tonight into early Friday morning.

There is a slight chance of thunderstorms across all mountains,
the Antelope Valley, the interior valleys of SLO County and the
Cuyama Valley this afternoon and evening.

KLAX...Low to moderate confidence in the 18Z TAF. Low clouds were
just off the coast, and the marine clouds are expected to surge
back into the airfield around 03-04z. There is a 30% chance that
cigs will not arrive tonight until after 08Z. Wind issues are not
expected.

KBUR...High confidence in the 18Z TAF with VFR conds thru the pd.

&&

.MARINE...09/134 PM.

Areas of dense fog with visibilities of 1 nm or less are expected
across most of the coastal waters this morning.

Across the outer waters, a SCA has been issued for the northwest
corner of zone 670 for tonight through Friday night. Stronger
winds are expected to slowly spread across the northern two zones
of the outer waters tonight into Friday morning. A SCA has been
issued for zone 673 starting Friday morning through Friday night.
Across the southern outer waters zone, confidence is rather low
beyond Fri, with a 40% chance of SCA conds Fri afternoon thru Sat.
There is a good chance of SCA level winds through Saturday night
at a later time.

Across the inner waters north of Pt. Sal, SCA conds are not
expected thru Fri morning, then are likely during the afternoon
and evening hours Fri, and possible on Sat. There is a 20-30%
chance of SCA conds during the afternoon and evening hours Sun and
Mon.

Across the inner waters south of Pt. Conception bight, conditions
will likely remain below SCA levels through the period.

Short period seas up to 6-8 feet will affect portions of the
outer waters Fri thru Sat night. Several long period swells will
move through the waters this weekend, with the most significant
effect on those in or near the surf zone.

&&

.BEACHES...09/134 PM.

Tropical Storm Olaf was located off the coast of Mexico this
morning, and is forecast to track just south and west of Cabo San
Lucas tonight and early Friday as a hurricane. Latest computer
models keep this storm closer to the coast, at least initially,
then show it weakening rapidly as it moves westward away from the
coast. This would minimize the amount of southerly swell it sends
into our coastal waters. However, other long period southerly
swell is expected to move into the Southern California waters
Saturday morning through early next week. At this time it appears
that strong rip currents and elevated surf are likely. High surf
conditions are possible on south facing beaches very late in the
weekend into early next week.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory in effect until 8 PM PDT Friday for zones
      37-38-51>54. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect from 5 PM this afternoon to 3
      AM PDT Saturday for zone 670. (See LAXMWWLOX).
     Small Craft Advisory in effect from 8 AM Friday to 3 AM PDT
      Saturday for zone 673. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (SUN-THU).

Increasing southerly swells are possible later in the weekend into
next week potentially leading to an increase in coastal hazards,
including high surf and rip currents.

&&

PUBLIC...MW
AVIATION...Sweet/DB
MARINE...Sweet
BEACHES...Sweet
SYNOPSIS...MW

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