High Wind in California, March 23 to 24, 2021

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
955 PM PDT Tue Mar 23 2021

.SYNOPSIS...23/148 PM.

A moderate Santa Ana Wind event will develop this evening through
mid day Wednesday with strongest gusts across the Los Angeles
County Mountains and across the wind prone valley passes and
canyons. High temperatures will peak on Wednesday for coast and
valleys, then significant cooling expected by Thursday with more
clouds and a chance of light showers. A significant warming trend
is expected over the weekend under clear skies and mostly light
winds.

&&

.SHORT TERM (TUE-FRI)...23/756 PM.

***UPDATE***

North wrap around flow from a an upper low over AZ brought a few
showers to eastern LA county this afternoon. Otherwise, skies were
mostly sunny this afternoon but max temps cool (esp inland) as the
north flow brought in plenty of cool air. Aside from a smattering
lower 70s in the LA vlys most non mtns max temps today were in the
60s.

Winds were the big deal today with mtn gusts in the 45 to 50 mph
range and many vlys seeing 35 to 40 mph gusts. The coasts were
also breezier than normal.

Everything is on track for a quick switch to the decent Santa Ana
event as the upper flow switches to the NE and strong sfc high
pressure builds into NV. Warning level wind gusts to 60 mph will
likely develop in the LA mtns. While Advisory level gusts between
35 and 50 mph develops in the the VTA and Santa Monica mtns and
the vlys of LA VTA counties save for the San Gabriel Vly. As
mentioned in the afternoon discussion the Santa Ana will be short
lived as a rapid switch to onshore flow will occur late Wednesday
morning.

Forecast is in good shape and no update is planned.

***From Previous Discussion***

Increasing northeast flow expected tonight following the passage
of an upper low into Arizona. High pressure quickly building
behind it across the Great Basin and this will set the stage for a
Santa Ana wind event tonight into Wednesday. This one is not
exactly a typical Santa Ana event as there is more of a northerly
component to the winds aloft, meaning not quite as much wind in
Ventura County and the Santa Lucias but still quite strong across
parts of LA County, especially in the mountains where a high wind
warning is in effect from tonight into Wednesday. At most just
wind advisories elsewhere in LA County and eastern Ventura County.
Current northwest/north winds will shift to northeast by this
evening and peak later tonight and early Wednesday with rapidly
lowering humidities.

With the next inside slider quickly following on the heels of
this one offshore flow will reverse quickly Wednesday and by mid
to late afternoon all areas will be experiencing a strong onshore
push. Thus, high temps, which are expected to be into the 70s in
many areas, will likely occur pretty early in the day, especially
near the coast where that onshore flow will be advecting very
cold air from the ocean surface where SST's are only in the low to
mid 50s.

Wednesday night into Thursday there will be a rapid development
and deepening of the marine layer with the marine layer depth
going from basically zero to 4000' or higher in a matter of hours.
By Thursday morning most lower elevation areas, including the
coastal mountain slopes, will be under a deep marine layer with
possibly some drizzle or light showers, especially southeastern LA
County. Clearing will be slow and likely taking on a reverse
clearing pattern where the coastal areas clear sooner than inland
areas. Temps will drop a good 10 degrees from Wednesday and
possibly as much as 15-20 degrees in the valleys where highs will
struggle to reach 60.

Still a deep marine layer Thursday night and Friday with plenty of
clouds but northerly flow developing Friday along with a weakening
inversion should help scour out the clouds and lead to much more
sunshine than Thursday and warmer temps.

.LONG TERM (SAT-TUE)...23/147 PM.

There are some differences in the model solutions for the weekend
but the vast majority of the ensembles support a fairly
significant warming trend in all areas as a strong high pressure
ridge moves over the West Coast. Highs in the low 80s are possible
by Sunday for the valleys and inland coastal zones.

Some cooling Monday as the ridge temporarily buckles and allows
the next inside slider to drop into the Great Basin. Onshore flow
will increase and temps will shed about 5 degrees from their
Sunday levels, possibly more if the onshore flow increases as much
as what the models are suggesting. Additional cooling expected
Tuesday with possibly some marine layer clouds returning.

&&

.AVIATION...24/0055Z.

At 0000Z at KLAX, There was no marine layer nor a sfc based
inversion.

Very good confidence that all sites will have VFR conds through
the period.

Fair confidence in wind forecast. Wind transitions could be off by
as much as two hours. Wind speed could be up to 7 kt stronger than
fcst.

There will be areas of LLWS, mdt UDDFs and lgt-ocnl mdt turbc
over and near to the hier trrn through 18Z.

KLAX...Good confidence in VFR conds. Lower confidence in wind
fcst. There is a 30% chance of northerly cross wind gusts to 25
kts through 10Z. Lgt LLWS is possible.

KBUR...Good confidence in VFR conds. Lower confidence in wind
fcst. Lower confidence in wind fcst. There is a 30% chance of
northerly wind gusts to 35 knots through 14Z. Lgt LLWS and lgt
ocnl mdt turbc sfc-140 through 18Z.

&&

.MARINE...23/954 PM.

Across the outer waters, moderate confidence in current Small
Craft Advisory (SCA) for winds and seas. Winds will likely drop
below SCA levels earlier Wednesday, however seas should remain at
or near SCA levels. By Wednesday afternoon, SCA level winds
return but confidence is lower for which zones will experience
SCA level winds. Higher confidence for Thursday with more widespread
SCA level winds. Seas will be near or above SCA levels late
tonight through Thursday.

Across the inner waters north of Pt
Sal, SCA level winds and seas will continue thru tonight, then
conds will drop below SCA levels. There is a 30% chance of SCA
level winds Wed afternoon/evening. SCA level winds and seas are
likely Thu afternoon/evening. SCA conds are not expected late Thu
night through Sat.

In the SBA Channel, moderate confidence in current SCA. Winds may
drop below SCA levels at times tonight for much of the region,
however, stronger gusty NE winds are expected south of Oxnard
after midnight. Another brief break in SCA level winds is expected
before SCA level W winds develop during the afternoon thru late
evening hours Wed. Lower confidence in the ending time of the SCA
winds, but at this time they are expected through Thursday night.

In the southern inner waters, good confidence in current SCA for
the N-NE winds developing from Pt. Mugu to Santa Monica after
midnight into Wed morning. The SCA has been extended to cover the
westerly winds Wednesday afternoon, however a break in these gusty
winds is likely as they shift from easterly back to west. The next
chance for SCA level winds will come Thursday afternoon to
Thursday night. SCA conditions are not expected late Thu night
thru Sat.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory in effect until noon PDT Wednesday for zones
      41-44>46-53-88-547. (See LAXNPWLOX).
     High Wind Warning in effect until noon PDT Wednesday for zone
      54. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 3 AM PDT Wednesday for
      zone 645. (See LAXMWWLOX).
     Small Craft Advisory in effect until 9 PM PDT Wednesday for
      zones 650-655. (See LAXMWWLOX).
     Small Craft Advisory in effect until 10 AM PDT Thursday for
      zones 670-673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (FRI-TUE).

No significant hazards expected.

&&

PUBLIC...MW/Rorke
AVIATION...Rorke
MARINE...Phillips/Sweet
SYNOPSIS...MW

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