High Wind in California, May 19 to 20, 2021

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
1004 PM PDT Wed May 19 2021

.SYNOPSIS...19/1002 PM.

A low pressure system over southwest Oregon will drop south into
the region through the end of the week and bring cooler
temperatures. Gusty west to north winds will continue across some
areas through Friday, strongest over Santa Barbara County, the
Interstate 5 corridor, and the Antelope Valley. A warming trend
is expected Monday and Tuesday.

&&

.SHORT TERM (WED-SAT)...19/946 PM.

The latest satellite imagery indicates a deep upper-level low
pressure system over southwest Oregon, while flat ridging remains
in place over southern California. The upper-level trough will
dig south into Owens Valley through Friday morning, then slosh
into southwest California Saturday. A moderately strong northerly
surface pressure gradient across the state will continue to
produce gusty to marginally damaging winds occurring this evening.
A Wind Advisory for southern Santa Barbara County was upgraded to
a High Wind Warning as several sites have reached 40 mph sustained
and Gaviota RAWS station is gusting to 59 mph. With KSBA-KSMX
surface pressure gradients tightening to -5.1 mb earlier, the
warning seems to make sense. Wind advisory headlines remain intact
for the Antelope Valley, the Central Coast, and the Los Angeles
County Mountains.

***From Previous Discussion***

Gradients are a little weaker Thursday night, especially the I5
corridor area but advisory level winds are still likely.

Thursday and Friday afternoons those north winds will shift to
west over the coastal waters and move onshore across the Ventura
and LA County coastal plain resulting in gusty winds that may
reach advisory levels at times. This strong onshore push will lead
to cooler temperatures for coast and valleys the next couple
days. There is very low confidence in the marine layer forecast as
the northwest flow and cold advection is weakening the inversion
and it will be difficult for stratus to reform. But the most
likely area would be southern LA County.

Another very tricky forecast for Saturday as the upper low reaches
its closest point to southern California. Models show a rapidly
deepening marine layer but also still a very weak inversion so sky
cover forecast is again very uncertain. In this scenario it's
possible many areas could start out clear but then develop a
stratocumulus deck through the day as heating and onshore flow
generate lift, especially near the foothills. For now have removed
drizzle from the forecast but can't completely rule it out.
Daytime temperatures expected to drop a couple more degrees most
areas Saturday.

.LONG TERM (SUN-WED)...19/200 PM.

The upper low is expected to exit the area Sunday which will help
temperatures recover back to near normal levels, though a stronger
inversion will also likely allow the marine layer to reform in
some areas. A brief ridge develops Monday with weakening onshore
flow to help temperatures jump back into the 80s for inland areas.
But that will be short lived as a weak trough moves in Tue/Wed for
cooler but near normal temperatures.

&&

.AVIATION...20/0209Z.

At 00Z, the marine layer depth was around 1900 feet deep at KLAX.
The top of the marine inversion was near 3000 feet with a
temperature near 15 degrees Celsius. There was another inversion
up to around 5200 feet.

Low-to-moderate confidence in the current forecast for coastal and
Los Angeles County valley terminals. Otherwise, high confidence in
the current forecast. With exception to the Los Angeles County
coastal terminals where MVFR conditions are likely, there is a
low-to-moderate (20-40 percent) chance of IFR to MVFR conditions
at coastal terminals and Los Angeles Valley terminals. VFR
conditions are expected by 18Z at the latest.

KLAX...MVFR conditions could arrive as soon as 07Z, or as late as
11Z. VFR conditions could develop as soon as 15Z or as late as
18Z. Southeast to east winds between 5 and 9 knots are likely
between 09Z and 16Z.

KBUR...There is a 40 percent chance of MVFR conditions between 10Z
and 15Z.

&&

.MARINE...19/959 PM.

DANGEROUS WINDS AND SEAS ACROSS MUCH OF THE COASTAL WATERS
FOR THE REST OF THIS WEEK.

Across the outer waters, Gale Force winds are expected thru at
least Thursday night. There is a 20-30 percent chance of local
STORM FORCE gusts to 50 kt through Thursday evening. Winds are
expected to decrease to Small Craft Advisory (SCA) levels late
Thursday night and persist through Sunday. However, there is a
30-40 percent chance that Gale Force winds will continue through
Friday evening.

Across the nearshore waters along the Central Coast, seas will
continue across SCA levels due to their heights and short
periods. NW winds at Gale Force will continue this evening, then
diminish some late tonight and Thursday morning. Seas will remain
above SCA levels through at least late Friday night. Gale force
NW winds are expected to redevelop quickly Thursday and continue
through Thursday night. There is a 30 percent chance of Gale
Force NW winds Friday afternoon and evening. SCA level NW winds
are likely during the afternoon and evening hours Sat and Sun.

In the Santa Barbara Channel, Gale Force W-NW winds across far
western portions will continue through late tonight, diminish some
early Thursday morning, then likely increase back to Gale Force by
Thursday afternoon. Elsewhere, SCA W winds will linger through
Thursday night. Dangerous seas will likely remain at or above SCA
levels thru Friday night. SCA level winds are expected across the
SBA Channel again Friday afternoon into Friday night, with a
20-30 percent chance of Gale Force winds across far western
portions. SCA winds are expected during the afternoon and evening
hours Saturday and Sunday, especially in western portions.

For the southern inner waters (PZZ655), SCA conditions will
likely reach SCA levels across much of the zone tonight and
persist through Friday night. SCA level W-NW winds are likely
across most of the zone during the afternoon and evening hours
Thursday and Friday, and mainly across western portions Saturday
afternoon and evening. There is a 40 percent chance of GALE FORCE
winds Thursday afternoon and evening.

The strong winds will result in large short period waves across
the entire coastal waters, with hazardously steep seas. This will
be a dangerous week for inexperienced boaters and those with small
craft to be on the waters off southern California.

&&

.BEACHES...19/1002 PM.

With anticipated strong west winds in the inner coastal waters
through Friday in addition to a steep wind waves and a decent
south swell, there is a pretty good shot of seeing elevated surf
and a high rip of dangerous rip currents on most southwest
California beaches from late this morning through Sat morning.
Refer to the Beach Hazards Statement (LAXCFWLOX) for additional
information.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory in effect until 9 PM PDT Thursday for zones
      34-35-59. (See LAXNPWLOX).
     Beach Hazards Statement in effect through Saturday morning
      for zones 34-35-40-41-87. (See LAXCFWLOX).
     High Wind Warning in effect until 4 AM PDT Thursday for zones
      39-52. (See LAXNPWLOX).
     Wind Advisory in effect from 4 AM Thursday to 6 AM PDT Friday
      for zones 39-52. (See LAXNPWLOX).
     Wind Advisory in effect until 10 AM PDT Thursday for zone 54. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 3 PM PDT Thursday for
      zone 645. (See LAXMWWLOX).
     Gale Watch in effect from Thursday afternoon through Thursday
      evening for zone 645. (See LAXMWWLOX).
     Gale Warning in effect until 9 PM PDT Thursday for zone 650. (See LAXMWWLOX).
     Small Craft Advisory in effect until 5 AM PDT Saturday for
      zone 655. (See LAXMWWLOX).
     Gale Warning in effect until 3 AM PDT Friday for zones
      670-673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (SAT-WED).

No significant hazards expected.

&&

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

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