Acton Weather

000
FXUS66 KLOX 081313
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
513 AM PST Mon Mar 8 2021

.SYNOPSIS...08/404 AM.

Strengthening onshore flow will bring a cooling trend through
mid week with a deep moist layer in place across much of the
forecast area today. A cold storm system will likely bring rain
and low elevation snow and gusty winds to the region late Tuesday
through Thursday. A modest warming trend is expected late this
week through the weekend as a ridge of high pressure build in.
High temperatures will remain below normal for this time of year.

&&

.SHORT TERM (TDY-WED)...08/511 AM.

Very deep marine layer around 5500 feet deep across the region
early this morning. Skies were cloudy in most areas, except for
portions of the far interior SLO and SBA Counties, the eastern
Antelope Valley and the highest mountain elevations. Increasingly
cyclonic and moist low level flow has caused some patchy drizzle
and a few rain gauges have even reported some light measurable
rain. Have slight chance pops in the forecast for much of L.A.
and VTU Counties for this morning, especially for the foothills.
with patchy drizzle possible just about everywhere else.

The clearing pattern will probably be haphazard today, but with a
marine layer this deep, a reverse clearing pattern is favored,
with better clearing in coastal areas, and a tendency for clouds
to linger in the valleys. Since there is enough moisture, some
stratocu may develop even if clearing occurs, especially in the
valleys and foothills. Will keep skies mostly cloudy in those area
and partly cloudy elsewhere. Max temps will be down a couple of
more degrees in most areas today, and will be several degrees
below normal. Gusty southwest to west winds will likely reach
advisory levels in the Antelope Valley and through the I-14
Corridor this afternoon and evening, and a Wind Advisory has been
issued. Gusty northwest to north winds may get close to advisory
levels across the Santa Ynez Range and adjacent south coast of SBA
County tonight, but at this point, feel winds will stay just
below advisory levels.

An upper low will drop to a position about 400 miles west of
Eureka by late Tue morning. Between stratus development and
increasing mid/high clouds, expect skies to become mostly cloudy
across the region tonight and remain so on Tue, though there could
be a bit of sun Tue morning across southern and eastern sections.
There is a slight chance of rain on the immediate Central Coast
by late Tue morning, with the chance of rain possibly spreading as
far south as the city of Santa Barbara by late afternoon. Max
temps will drop another couple of degrees Tue, and will be 6-12
degrees below normal in most areas. Gusty west winds will likely
reach advisory levels again in the Antelope Valley Tue.

The upper low will move eastward to a position just off the coast
of northern California late Tue night, then move slowly southward
to just west of San Francisco Wed afternoon. A trough will extend
southward from this low with a decent west-southwest jet aimed at
the forecast area Late Tue night, then shifting south during Wed.
A deep layer of southwesterly flow through the atmosphere will
transport plenty of moisture from the Pacific into the region
Tue night and Wed. Rain will become likely across all but
southern and eastern L.A. County by late Tue night, where there
will be a chance of rain, then rain is expected across the region
Wed. Though precipitable water values still do not look very
high, there will decent dynamics due to good height falls and the
placement of the jet. In addition, favorable southwesterly flow
should provide some orographic enhancement of the precip on and
below southwest facing mountain slopes. Expect periods of rain,
possibly heavy at times late Tue night up north, and Wed across
most of the region. With the very cold air aloft, there will also
be the threat of some thunderstorms north of Pt. Conception late
Tue night and Wed, and across L.A. and VTU Counties by Wed
afternoon. Any thunderstorms could produce briefly higher rainfall
rates and possibly small hail.

As the low tracks southward across the region Wed night, steady
precipitation will turn to showers, but the slight chance of tstms
should continue, especially across southern sections.

Snow levels will be rather low for much of this event, dropping to
around or below 4000 feet by Wed morning, then possibly down to
3000 feet or even lower Wed night and early Thu. This could bring
accumulating snow and dangerous driving conditions to higher
elevations of Interstate 5 and possibly Highway 14. A WINTER STORM
WATCH remains in effect for the mountains of SBA, VTU and L.A.
Counties excluding the Santa Monicas. Some snow is possible in the
foothills around the Antelope and Cuyama Valleys. Needless to
say, it will be very cool across the region Wed, with temps 10 to
18 degrees below normal in most areas.

Rainfall totals are generally expected to average one half to one
inch, except locally 1.5 inches or possibly higher in the
foothills and mountains below the snow level. In the mountains
above 4500 feet, snow accumulations of 6 to 12 inches are
expected, with local totals over 15 inches possible.

It should be noted that the 00Z and the 06Z runs do not look as
unstable or as wet for the region as did previous runs, so if that
trend continues, precip totals may have to be scaled back. For
now, have kept the forecast very similar to previous ones, since
the basic pattern has changed little.

.LONG TERM (THU-SUN)...08/512 AM.

The upper low will track to the east of the region Thu, but the
GFS shows a second weak center developing across near Catalina
Island. There will certainly be enough moisture and instability
across the region to keep a slight chance or chance of showers in
the forecast. The big question is how plentiful will those showers
be. At this point, it appears the best chance of showers will be
across L.A. and eastern VTU Counties. In addition, lifted index
values indicate increasing instability on Thu, so a slight chance
of thunderstorms may actually have to be added to the forecast for
at least L.A. County. Expect dry weather Fri through Sun with
some warming, more so if the EC if correct since it shows higher
heights across the region. Overall though, expect temps to
generally remain below normal through the weekend.

&&

.AVIATION...08/1235Z.

At 12Z, the marine layer depth was around 5500 feet deep around
KLAX. The top of the marine inversion was around 6300 feet with a
temperature of around 8 degrees Celsius.

Moderate confidence with 12z TAFs in respect to MVFR/VFR TAFs
through this afternoon. There is a 40% chance for -DZ or light
rain through 18z at all TAF sites S of Point Conception except
for desert TAF sites KPMD,KWJF. Stronger W winds gusting to 40 kt across
desert TAF sites between 20z-05z. No LLWS issues expected.

South of Point Conception, ceilings at or below 5500 feet are likely
for coastal and valley terminals through 20z. MVFR conditions
expected through at least 20z. There is a slight chance of IFR
conditions in drizzle through 18z.

North of Point Conception, MVFR conditions will continue through
18z. There is a 30% chance that MVFR CIGs will continue through
20z.

KLAX...Ceilings at or below 5500 feet will continue through 20z
There is a 30 percent chance of a later clearing as late as 22Z.
There is a 10 percent chance of IFR conditions in drizzle.

KBUR...Ceilings at or below 5500 feet will continue through
18-19z. There is a 40 percent chance of a later clearing as late
as 22Z. There is a 20 percent chance of IFR conditions in
drizzle.

&&

.MARINE...08/206 AM.

A moderately strong storm will move through the coastal waters
Tuesday through Thursday bringing a chance of rain and slight
chance for thunderstorms.

For the Outer Waters... Small Craft Advisory (SCA) thresholds will
remain in effect through late tonight, but will likely continue
through much of the week due to hazardous seas with swells
persisting between 9 and 11 feet through at least Thursday evening.
There will also be periods of gusty SCA level winds as well.
Strongest winds will occur for areas South and west of Point
Conception through Tuesday night then becoming more widespread
across the entire outer waters after that. There is a 60% chance
for gusty NW winds to continue through Friday.

For the Inner Waters north of Point Sal... SCA level winds and
seas will continue through late tonight with a brief lull in
winds in the morning hours. Seas will diminish early on Tuesday
but then increase to SCA level again by Tuesday night and continue
through Wednesday. Winds will remain below SCA level Tuesday and
Wednesday and both winds and seas will be below SCA level Thursday
and Friday.

For the Inner Waters south of Point Conception... SCA is in effect
for gusty W to NW winds from noon today through 3 AM Tue morning.
Winds will diminish late each night. Expect two more afternoon and
evenings of SCA level winds for the entire inner waters Tue and
Wed as well.  Otherwise, conditions will remain below SCA levels.

&&

.BEACHES...08/224 AM.

A strong storm across the Gulf of Alaska will cause a NW swell 10
to 11 feet to develop across the coastal waters adjacent to the
Central Coast late this afternoon. This swell will persist through
much of the week. This will translate into surf across northwest
and west facing beaches between 8 and 12 feet along with dangerous
rip currents late this afternoon and continue through at least
next Thursday afternoon. There will be peak periods where local
sets to 14 feet will occur tonight and again on Wednesday and
Thursday.

Some of the swell energy will filter into the SoCal Bight mainly
into the inner Santa Barbara Channel towards the Ventura Coast
where elevated surf 3 to 6 feet is expected tonight through
Wednesday. There is a chance that higher surf 6 to 8 feet could
affect the Ventura County Coast by Wednesday evening. If this is
the case, a High Surf Advisory will likely need to be issued at
that time through at least Thursday evening.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory in effect from 3 PM this afternoon to 9 PM
      PST Thursday for zones 34-35. (See LAXCFWLOX).
     Winter Storm Watch in effect from Tuesday evening through
      Thursday evening for zones 52>54. (See LAXWSWLOX).
     Wind Advisory in effect from noon today to 9 PM PST this
      evening for zone 59. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 3 AM PST Tuesday for
      zones 645-670-673-676. (See LAXMWWLOX).
     Small Craft Advisory in effect from noon today to 3 AM PST
      Tuesday for zones 650-655. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (WED-SUN).

High surf and dangerous rip currents are likely through the
middle of the week. Gusty west to northwest winds will create
driving and boating hazards at times through Wednesday. A winter
storm will bring rain and snow to the area Wednesday and Thursday.

&&

$$

PUBLIC...DB
AVIATION...Kaplan
MARINE...CK
BEACHES...CK
SYNOPSIS...DB

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