Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000
FXUS66 KLOX 251813
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
1013 AM PST Mon Jan 25 2021

.SYNOPSIS...25/1004 AM.

A cold storm system with low snow levels and very gusty west to
northwest winds will impact the region through this evening, with
dangerous driving and boating conditions and many mountain road
delays. Drier conditions are forecast for Tuesday, then a much
wetter storm system will stall over the region Wednesday and
Thursday, mainly Santa Barbara and northward, then move
through area later Thursday and Friday. There is a potential for
several inches of rain with flooding.

&&

.SHORT TERM (TDY-THU)...25/945 AM.

***UPDATE***

The organized widespread rain from last night has turned to
showers focused over the Central Coast and coastal waters, as well
as snow showers over the northern mountain slopes and interior
valleys. The snow will be the main precipitation impact for today,
with snow levels hovering around 2500 feet and many mountain roads
(included Interstate 5) facing many hours of delays or hard
closures. Upped the chances of snow up there today and tonight, as
the moderate to strong northwest flow will keep the moisture in
places. Cannot rule out a snow flurry on the Central Coast tonight
as well, especially in the hills. Winds will be the largest
impact today. Widespread Wind Advisories are place through this
evening, and while some of the valleys will probably not hit
criteria, it will be windy so will keep them in play. Besides the
mountains, where Winter Storm Warnings are in play to cover the
wind and snow together, the coastal areas will see the strongest
winds. Gusts into the 50 mph range are not of the question, which
are more than capable of breaking tree branches and poorly rooted
trees, as well as create a few power outages. Thunderstorms remain
possible with such cold air aloft, but trimmed removed the
chances over the mountains and interior valleys as the threat is
mainly closer to the coast. Will look into what to do with the
Freeze Watches currently out, which are challenging due to the
wind and moisture in the air.

***From Previous Discussion***

Showers will taper off overnight with temperatures cooling off
across wind protected areas. A Freeze Watch is in effect for the
wind protected areas in Santa Clarita and Ventura County
Valleys early Tuesday as lows will lower to around 30 degrees.

There will be a brief respite from the rain before the next more
potent system approaches the area Tuesday night and Wednesday.
12Z models from both the GFS and EC continue to hang the
atmospheric river up towards SLO County Tuesday night and
Wednesday. Rain will overspread SLO and SBA counties Tuesday
night and Wednesday with the potential for heavy rainfall
Wednesday and Wednesday evening. The subtropical tap will continue
to stall over the SLO/SBA Counties through Wednesday night.

Through Wednesday evening, SLO and SBA counties are expected to
receive between 2 and 4 inches of rainfall with amounts dropping
down to 0.10-0.25 inches across LA county. Strong southerly flow
ahead of the system will allow for snow levels to increase to
around 5000 feet on Wednesday. Additionally, these southerly winds
could exceed 60 MPH in some areas across SLO and SBA counties and
will need to be watched closely.

.LONG TERM (FRI-MON)...25/333 AM.

For the extended period, both the GFS and EC are now in pretty
good agreement with large scale features as well as the placement
of the heaviest rainfall in association with the atmospheric
river. As mentioned in the short term discussion, the front will
continue to hang across SLO and SBA Counties through Thursday
morning. So, moderate to heavy rainfall will continue across SLO
and SBA counties with lesser rainfall across Ventura and LA
counties. By Thursday late afternoon and evening, the front will
begin to sag southward with heavier precipitation developing over
Ventura and LA counties Thursday night/Friday morning with the
rain tapering off by Friday evening. Overall, this will be a
significant rain and snow event, especially across SLO/SBA
Counties.Rainfall totals from Tuesday night through Friday
evening are expected to range from 4-8 inches across SLO/SBA
counties to 1.50-4 inches across Ventura and LA counties.
Southerly flow ahead of the system will keep snow levels around
5000-5500 feet on Thursday and Friday. So, higher mountain
elevations can expect some significant snowfall accumulations (1-2
feet potentially) if not a little more at the highest elevations.
Additionally, the southerly winds associated with this system
look to be pretty strong. So, widespread advisory level winds are
likely in many areas with the potential for warning level winds.

There will be a myriad of hazards across the area Tuesday night
through Friday. Rainfall amounts and intensities could produce
debris flow problems in and around recent burn areas. Dangerous
winter weather conditions are likely in the mountains. The
combination of gusty southerly winds and a rain-soaked ground
could result in some down trees or tree limbs. Overall, this is a
very significant weather event on tap for our area.

On Saturday and Sunday, there is the potential for a weak storm
to impact the area, mainly north of Point Conception. Rainfall
amounts look to be light. However, enough of a precipitation
threat to warrant chance or slight chance POPs for SLO and SBA
Counties.

&&

.AVIATION...25/1405Z.

At 12z at KLAX, there was no marine inversion.

There will be areas of low VFR to high MVFR cigs this morning,
except IFR to VLIFR cigs in the mtns and foothills. Clouds will
decrease by late morning, with just scattered low VFR to high
MVFR cigs expected through early evening, mainly associated with
scattered showers. Skies will be mostly clear tonight. There will
be widespread strong west to northwest winds across the region
through this evening, with areas of moderate to possibly severe
turbulence, and mdt to strong UDDF. Winds will slowly diminish
late this evening through the overnight hours.

KLAX...Moderate to high confidence in the 12Z TAF. Expect VFR
conds through the period. There is a 20% chance of high MVFR/low
VFR cigs through this evening, especially if a shower affects the
airport. Very strong west to northwest winds are likely this
morning through late this evening, with areas of turbulence
likely.

KBUR...Moderate to high confidence in the 12Z TAF. Expect VFR
conds through the period. There is a 20% chance of high MVFR/low
VFR cigs through this evening, especially if a shower affects the
airport. Gusty northwest winds are likely later this morning
through late this evening, with areas of turbulence likely.

&&

.MARINE...25/549 AM.

***Very dangerous wind and sea conditions across the entire
coastal waters through early Tuesday***

Widespread Gale force winds will affect the entire coastal waters
thru Tue. There is a 20-30% chance that winds will drop below
Gale force in some areas during the morning hours Tue, instead of
the afternoon as currently forecast.

There is a 30% percent chance that wind gusts could reach STORM
WARNING levels of 50 knots in some areas through this evening
anywhere in the coastal waters, even near the coast.

Seas will become extremely dangerous due to their size and
steepness. Seas will peak at 15-20 ft across the outer waters and
the inner waters north of Pt. Sal today and tonight and at 10-14
ft across the inner waters south of Pt. Conception, including the
Santa Barbara Channel. Wave periods will generally be less than
10 seconds. This will be a particularly dangerous episode of winds
and seas across the coastal waters.

Winds will diminish Tue afternoon, and should drop below SCA levels
for a while. However, winds will shift to the south and increase
again Tue night, reaching SCA levels across the northern outer
waters and the inner waters north of Pt. Sal, except Gale force
across the far northern outer waters, Gale force southerly winds
are likely across the outer waters and northern inner waters Wed
and Wed night, with SCA level winds Thu into Thu night or Fri. SCA
level SE are likely in the Santa Barbara Channel Wed afternoon
thru Thu night, and there is a 50% chance of SCA level SE winds
across the southern inner waters.

&&

.BEACHES...25/553 AM.

Surf will peak at 14 to 18 feet with local sets to 20 feet
on the Central Coast today and tonight. On west facing beaches
south of Point Conception, surf will peak at 8 to 12 feet with
local sets to 14 feet Today through early Tuesday. Surf will
slowly subside on Tuesday before increasing again Wednesday.

There may be minor coastal flooding today through Tuesday
morning, especially within a few hours of the times of
high tide. There will be strong and dangerous rip currents on all
area beaches through Tuesday. The surf will likely cause some
beach erosion.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory in effect until 10 PM PST Tuesday for
      zones 34-35. (See LAXCFWLOX).
     Wind Advisory in effect until 10 PM PST this evening for
      zones 34>37-39>41-44>46-88-547. (See LAXNPWLOX).
     Winter Weather Advisory in effect until 10 PM PST this
      evening for zone 38. (See LAXWSWLOX).
     High Surf Advisory in effect until 6 PM PST Tuesday for zones
      39>41-87. (See LAXCFWLOX).
     Freeze Watch in effect from late tonight through Tuesday
      morning for zones 44-45-88. (See LAXNPWLOX).
     Winter Storm Warning in effect until 10 PM PST this evening
      for zones 51>54. (See LAXWSWLOX).
     High Wind Warning in effect until 10 PM PST this evening for
      zones 59-549-550. (See LAXNPWLOX).
     Wind Advisory in effect until 3 AM PST Tuesday for zone 87. (See LAXNPWLOX).
PZ...Gale Warning in effect until 3 PM PST Tuesday for zones
      645-650-655-670-673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (THU-MON).

Moderate to heavy rainfall and mountain snow is likely Wednesday
through Friday. Rainfall intensities could result in debris flow
issues for the recent burn areas. Gusty southerly winds could
result in downed limbs, trees and power lines.

&&

$$

PUBLIC...Kaplan/Kittell
AVIATION...DB
MARINE...DB
BEACHES...DB
SYNOPSIS...RK

weather.gov/losangeles


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