High Wind in California, March 21, 2021

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
921 PM PDT Sun Mar 21 2021

.SYNOPSIS...21/754 PM.

There will be gusty northerly winds at times through Tuesday,
with moderate Santa Ana winds developing late Tuesday night into
Wednesday. Temperatures will be near to slightly below normal
through the period, except slightly above normal Wednesday with
the offshore winds. Dry conditions will continue through the week.

&&

.SHORT TERM (SUN-WED)...21/918 PM.

The latest satellite imagery shows an upper-level trough of low
pressure over extreme southern California this evening, downstream
of the forecast area, while an upstream ridge of high pressure
was building into northern and central California. A tightening
northerly pressure gradient across the area is bringing gusty
northerly winds to southern Santa Barbara County this evening.
Locally gusty winds could also develop through the Interstate 5
Corridor and into the western portion of the Antelope Valley
tonight and Monday morning. A wind advisory remains in effect for
southern Santa Barbara County through Monday morning.

The marine inversion is pretty disrupted with the trough moving
to the south of the area. Patchy stratus could develop along the
Central Coast tonight and maybe southern Los Angeles County, but
the extent will be very limited. There is a better chance for the
adjacent coastal waters tonight and into Monday morning. With high
pressure aloft building in from the north, the marine layer
depth, around 1100 feet in the KVBG sounding, will likely thin
some overnight. Any low clouds and fog could result in patchy
dense fog tonight and into Monday morning.

Otherwise, a warmer day is on tap for Monday as high pressure
aloft builds in.

***From Previous Discussion***

High pressure over the eastern Pacific will continue to provide a
favorable upper level pattern for troughs passing north and then
east of the area through the middle of the week, commonly known
as inside sliders for southern California. This means a
continuation of gusty northwest to northeast winds in favored
areas. For tonight through Tuesday it will mostly be the northwest
favored areas, including southern SB County, the I5 corridor, and
the Antelope Valley. It's a little less favorable tonight but
still strong enough for a low grade wind advisory for srn SB
County, especially the western end near Gaviota.

Monday night as the next trough approaches we'll see northerly
gradients strengthening again and likely more widespread advisory
level winds in the mountains and Antelope Valley as well as srn SB
County again. Some of those winds will likely surface down into
the LA/Ventura valleys and even parts of the LA Coast Monday
night but probably just below advisory levels.

Also with that northerly push Monday night models are showing
enough low level moisture with it to possibly generate some light
showers across the far interior sections from southeast SLO County
through the Grapevine. At this time it doesn't appear cold enough
for snow on Interstate 5 but there could be some light snow down
to around 5000' early Tuesday.

As that trough moves through Tuesday night and high pressure
settles in over the Great Basin a more traditional Santa Ana wind
event is expected to develop into Wednesday, bringing gusty
northeast winds to much of LA/Ventura Counties. Once again, more
wind advisories are likely but covering more of the populated
areas including the LA/Ventura coastal zones.

Temperatures expected to remain fairly steady through Tuesday
with highs near to slightly below normal and lows a few degrees
below normal in most areas. Then a few degrees of warming
Wednesday with the Santa Ana's.

.LONG TERM (THU-SUN)...21/159 PM.

Following the Santa Anas Wednesday gradients will quickly reverse
and turn onshore Thursday as another inside slider drops out of
Canada and into the Great Basin. Several degrees of cooling
expected with the return to onshore flow, especially coast and
valley areas.

The forecast gets a little trickier Friday as some models are
showing another trough coming down but with a little more westerly
track to it. If this happens we could see a rapid deepening of the
marine layer and possibly even some drizzle across parts of LA
County Friday morning, mainly the eastern and southern sections.
About half of the ensembles are showing at least some trace
amounts of precipitation Friday morning in those areas. Otherwise,
just continued cooler temps.

Dry weather expected next weekend though lower confidence on
temperatures. The ECMWF is favoring a rapid warmup even for
coastal areas, but with a large spread of ensemble solutions.
This is likely due to the uncertainty with the previous trough and
how far west it will move. The deterministic GFS actually
retrogrades it out over the Pacific and keeps it in the vicinity
through early next week so next weekend's forecast still very much
in doubt with regards to temperatures.

&&

.AVIATION...22/0209Z.

At 01Z, there was no marine layer at KLAX.

VFR conditions are expected through the period, except for a
chance of VLIFR to LIFR conditions at KPRB and IFR conditions at
KLGB between 10Z and 17Z. There is a chance of moderate low-level
wind shear and turbulence through 08Z at terminals south of Point
Conception.

KLAX...VFR conditions are expected through the period. North
cross winds greater than 10 knots are very likely (80-90 percent
chance) between 02Z and 08Z. There is a 40 percent chance of north
cross winds greater than 20 knots. There is a 30 percent chance
of moderate low-level wind shear and turbulence through 06Z.

KBUR...VFR conditions are expected through the period. There is a
50 percent chance of moderate low-level wind shear and turbulence
through 06Z.

&&

.MARINE...21/815 PM.

There will be fog dense fog along the Central Coast overnight and
tomorrow morning. Widespread gusty winds and choppy short period
seas will persist throughout the forecast period with the strongest
winds Monday afternoon through Tuesday morning, when they will be
Gale force across the outer waters.

Across the outer waters... Small Craft Advisory (SCA) winds will
continue through Monday morning, increase to Gale force level
Monday afternoon through Tuesday, then diminish to SCA level
through at least Friday. There is a forty percent chance of Gale
force winds this evening. Seas will be SCA level through Thursday.

Across the inner waters north of Pt Sal... Winds will increase to
SCA level this evening and will continue through Tuesday primarily
in the afternoon and evening hours. Winds will likely be SCA
level again on Thursday. Seas will be SCA level Monday through
Tuesday, then again on Thursday.

In the southern inner waters... Northwesterly winds will increase
to SCA level this evening and will continue through Tuesday
primarily in the afternoon and evening hours. On Wednesday,
northeasterly winds will likely increase to SCA level along the
coast from Point Mugu to Santa Monica in the morning through
midday. Conditions will be below SCA level on Thursday and Friday.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory in effect until 9 AM PDT Monday for zones
      39-52. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 3 AM PDT Tuesday for
      zones 645-650-655. (See LAXMWWLOX).
     Small Craft Advisory in effect until 2 PM PDT Monday for
      zones 670-673-676. (See LAXMWWLOX).
     Gale Warning in effect from 2 PM Monday to 9 AM PDT Tuesday
      for zones 670-673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (WED-SUN).

A moderate Santa Ana wind event is likely to impact Los Angeles
and Ventura counties on Wednesday resulting in driving and boating
hazards as well as elevated fire weather concerns.

&&

PUBLIC...Hall/MW
AVIATION...Hall
MARINE...Kj
SYNOPSIS...Kj

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