NWS Los Angeles, CA wrote its last area forecast discussion before the first event at Feb 13, 1:43 PM PST, 7 minutes earlier.
Area forecast discussion, Feb 13, 1:43 PM PST, 7 minutes before
Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
143 PM PST Sat Feb 13 2021
.SYNOPSIS...13/140 PM.
Strong to damaging northwest to north winds can be expected over
much of the region this afternoon, with winds continuing in many
areas through Sunday before slowly diminishing. Moist northerly
flow may bring rain or snow showers to the northern slopes of the
Los Angeles and Ventura County mountains through Sunday morning.
It should be dry late Sunday through next Saturday with gusty
winds at times. Temperatures will mostly be below normal through
Wednesday, then turn slightly above normal.
&&
.SHORT TERM (TDY-TUE)...13/136 PM.
A shield of mostly thin hi level clouds was moving into the
forecast area from the NW early this afternoon with filtered
sunshine across the region. However there were also areas of
stratocu over portions of SLO/SBA Counties and into some mtn
areas. Little change can be expected thru sunset, and in fact
north slope cloudiness will likely increase with a slight chance
of rain or snow showers expected thanks to increasing upslope
flow. Temperatures across the region this afternoon will be a few
degrees below normal for many areas. Highs for much of the coast
and vlys should be in the 60s today, altho should be around 70 for
parts of the SBA County S coast.
There were some gusty NW to N winds noted early this afternoon,
with the strongest winds in the mtns and along part of the SBA
County S coast, where gusts in the 35 to 45 mph range was noted.
Gusty W to N winds will spread to many parts of the forecast area
especially from mid to late this afternoon as a mostly dry cold
front moves thru the area and increases the northerly gradients
along with increasing 850 mb winds to 45-50 kt. The strongest
winds are expected in the mtns and Antelope vly where damaging
wind gusts to 65 mph or more will be possible, and High Wind
Warnings are in effect for these areas. Otherwise, Wind Advisories
are in effect for many other parts of the forecast area, with
strong and gusty W to NW winds expected for much of the coast and
vlys, transitioning to a more northerly wind event this evening
for the L.A./VTU County vlys, L.A. County coast and Santa Monica
mtns.
A broad upper level trof was over the Great Basin this afternoon.
An upper level low will develop at the base of the trof over AZ
tonight before the system moves E thru Sun. For swrn CA, a strong
NW flow aloft can be expected thru Sun. The broad upper level trof
will slowly move E Sun night and Mon, allowing for H5 heights to
increase over swrn CA, reaching to around 572-574 dm on Mon.
Another broad upper level trof will move into the Great Basin Mon
night and Tue, with lowering H5 heights again over swrn CA, down
to around 559-564 dm Tue afternoon. A strong NW flow aloft will
move in once again for Mon night and Tue.
By early this evening, all the ingredients will be in place for a
significant widespread northwesterly to northerly wind event.
There will be a deep layer of strong northwest to northerly flow
through the atmosphere, good cold air advection, and widespread
subsidence due to the location of a powerful 140 knot northerly
jet just to the east of the forecast area. This subsidence will
help force stronger winds aloft into lower elevations, producing
widespread gusty winds, with continued damaging winds in the mtns
and Antelope Vly. It will also increase the possibility for
mountain wave development which can bring damaging winds (usually
for a short period of time such as a couple of hours) to places
that do not often get them, such as portions of the San Gabriel
Valley from La Canada east to Altadena, Sierra Madre and Glendora,
portions of the VTU County Valleys near Lake Casitas, and the Los
Angeles Basin, especially from the Hollywood Hills westward thru
the entire westside (including LAX) out to Malibu.
Gusty winds will begin to diminish this evening on the Central
Coast and in coastal sections of Ventura County, but not until
late tonight or Sunday in most other areas. Wind advisory level
winds will likely continue in the mtns of L.A. and VTU Counties
and the western valleys of L.A. County thru Sun night. For the
most up-to-date info on the High Wind Warnings and Wind
Advisories across the area, please see the latest Non-
Precipitation Weather Message (LAXNPWLOX).
Skies will generally be mostly clear tonight and Sun. The
exception will be on northern slopes of the mountains, especially
the VTU County mountains and the mountains of northwestern L.A.
County, where moist upslope northerly flow will keep skies cloudy,
and may bring periods of showers to the area. Some locations
could possibly receive up to one quarter of an inch of precip
tonight and early Sunday. With snow levels dropping to between
3500 and 4000 feet late tonight and Sun, this could bring some
accumulating snow and icy conditions to portions of Interstate 5.
However, snow accumulations are expected to be mostly less than an
inch, and only locally 1 to 2 inches. Max temps will likely be up
slightly on Sunday, except down a few degrees in the mtns and
Antelope Valley.
NW to N flow pattern will continue across the region Sun night
thru Tue, and could be at Advisory levels at times in the wind-
prone areas, or even approach High Wind Warning levels in the
mtns later Mon night into Tue. There will likely be plenty of mid
and high clouds across the forecast area Mon and Mon night, so
skies will likely be mostly cloudy. Clearing skies can then be
expected on Tue. At this point, it appears as though any rain from
a weak disturbance will remain north of the region late Mon and
Mon night. Max temps will change little thru Tue, although should
turn slightly warmer in the mountains and the Antelope Valley Mon
then cool some for Tue.
.LONG TERM (WED-SAT)...13/137 PM.
The GFS and EC are in good agreement for the extended period. A
large upper level ridge over the E Pac will gradually move E Wed
and Thu, with rising H5 heights over the forecast area, and by Thu
should be around 578-580 dm. The upper level ridge will weaken
and flatten out for Fri, with flat upper level ridging for the
most part over the area thru Sat.
Dry weather will prevail Wed thru Sat, with mostly clear skies
into Fri, then some clouds should move in for partly cloudy skies
overall Fri night into Sat. There will be northerly offshore flow
at times into mid-week, then turn offshore to the E Wed night into
Thu. Another round of gusty N winds will be possible Fri night
into Sat as well. High temps across the region will turn warmer
Wed and Thu, with the warmest day Fri when many coast and vly
areas should top out in the lower to mid 70s. It should then turn
slightly cooler for Sat.
&&
.AVIATION...13/1910Z.
At 1723Z, The marine layer was around 2400 feet deep. There was a
marine inversion, with the top of the inversion around 5300 feet
at 8 degrees Celsius.
The confidence level will increase to moderate early this
afternoon and remain fairly high through the remainder of the
forecast period. A tricky morning with a brief marine layer encounter
will yield to VFR conditions this afternoon, but complicated by
gusty winds, low level wind shear in many locations and turbulence
near higher terrain. Strong gusty winds will surface in many
locations and northerly cross winds are a possibility at KLAX
tonight.
KLAX...Mostly VFR conditions are expected through the period.
Northerly cross winds greater than 10 knots are likely after 02Z
Sunday. There is a 40 percent chance of northerly cross winds
greater than 20 knots. Periods of wind shear and turbulence are
possible this evening.
KBUR...VFR conditions are expected through the period. Periods of
wind shear and turbulence are possible this evening into the
overnight hours.
&&
.MARINE...13/142 PM.
Across the outer waters... High confidence with GALE WARNING
winds continuing through late Sunday night for the two southern
zones (PZZ673-676). The northern zone will experience Small Craft
Advisory (SCA) gusts through this afternoon, before reaching GALE
level winds with the other two zones and continue through late
Sunday night as well. Otherwise, good confidence for at least SCA
thresholds continuing through next Tuesday, although GALE WARNING
level winds could resurface Monday and Tuesday afternoons. There
is a 30 percent chance of Gale Force winds Monday afternoon in the
southern outer waters and a 50 percent chance of Gale Force winds
for the entire outer waters on Tuesday. Winds may be weaker
during the morning and early afternoon hours. A relatively large
swell will bring seas over 10 feet this weekend and continue into
early next week. The combination of swells over 10 feet and short
wave periods due to very gusty conditions will bring steep seas
over the next several days.
Across the nearshore waters of the Central Coast... SCA conditions
will continue through Wednesday with a 30-40% chance for Gale
force level winds this afternoon and evening. Winds may be weaker
during the morning and early afternoon hours.
Across the inner waters south of Point Conception...Conditions
will be at least at SCA level through Tuesday with Gale force
level winds continuing through late tonight. Gusts to 40 knots is
likely at times.
&&
.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory in effect until 9 PM PST this evening for zones
34>36-40. (See LAXNPWLOX).
Wind Advisory in effect until noon PST Sunday for zones
39-41. (See LAXNPWLOX).
Wind Advisory in effect until 3 AM PST Sunday for zones
44-45-87. (See LAXNPWLOX).
Wind Advisory in effect from 9 PM this evening to noon PST
Sunday for zone 46. (See LAXNPWLOX).
High Wind Warning in effect until noon PST Sunday for zones
52>54. (See LAXNPWLOX).
High Wind Warning in effect until 3 AM PST Sunday for zone
59. (See LAXNPWLOX).
Wind Advisory in effect until 3 AM PST Monday for zones
88-547. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 9 PM PST Sunday for zone
645. (See LAXMWWLOX).
Gale Warning in effect until 3 AM PST Sunday for zones
650-655. (See LAXMWWLOX).
Small Craft Advisory in effect until 3 PM PST this afternoon
for zone 670. (See LAXMWWLOX).
Gale Warning in effect until 9 PM PST Sunday for zone 670.
(See LAXMWWLOX).
Gale Warning in effect until 3 AM PST Monday for zones
673-676. (See LAXMWWLOX).
&&
.HAZARD POTENTIAL OUTLOOK (TUE-SAT).
Gusty northwest to north winds will affect the region at times
Monday night through Wednesday.
&&
PUBLIC...Sirard
AVIATION...Sweet/CK
MARINE...Sweet
SYNOPSIS...Sirard
weather.gov/losangeles