Wind Advisory 24, NWS Los Angeles, CA

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
255 AM PST Thu Feb 23 2023

.SYNOPSIS...23/254 AM.

A cold and potentially dangerous winter storm will bring periods
of heavy rain and snow to most of Southwest California Friday into
Saturday. Another round of rain and mountain snow is on tap
sometime early next week.

&&

.SHORT TERM (TDY-SAT)...23/254 AM.

Overnight ensemble guidance showed no reason to deviate
significantly from the previous forecast. Shallow convective
showers will continue through this evening, gradually becoming
more numerous with better orographic enhancement this evening as
flow turns southwest aloft in response to significant height falls
to our West as an elongated positively tilted trough off the West
Coast dives south while wrapping into deep stacked power house of
a low pressure system. Associated warm air advection will enhance
precipitation coverage and intensity from north to south late this
afternoon through tonight.

The storm will track parallel to the coast through Friday night
before wobbling inland across Southern California late Saturday.
The slow moving system will pump moisture off of the Pacific Ocean
carried along a 50 kt low level jet and enhanced locally through
nearly ideal orographics and upper dynamics, coupled with shallow
instability. Isolated thunderstorms will expand from north to
south across the area Friday into early Saturday before gradually
diminishing towards the southeast later Saturday. To add insult to
injury the wobbly nature of this system may lead to the stalling
and even brief retrograding of the heaviest precipitation along
Ventura, LA, or Orange County Friday night or Saturday.

All told, rare rainfall totals of two to five inches will be
common in the coasts and valleys through Saturday night with five
to locally seven inches in the foothills and where the heaviest
band of precipitation may stall. Flooding of small streams and
urban areas will be possible with this amounts and a few main stem
rivers may overflow their banks. Peak rainfall rates will
generally be 0.25 to 0.75 inches per hour, but locally around an
inch in thunderstorms and foothills to lower mountain slopes
(where it is not snowing). These rates are capable of create
shallow mud and debris flows in and below recent burn scars. The
current Flood Watch will remain in place for lower elevations
south of Point Conception.

Snow levels between 1500 and 2500 feet today will increase to
around 4500 feet during the heaviest precipitation Friday through
early Saturday. Light snow accumulations around and above 2000
feet will be possible late morning or early afternoon for much of
the area with no changes in winter products for this period.
Snowfall totals of two to five feet with locally seven feet of
snow is still forecast for the mountains above 5000 feet. Six to
18 inches will likely prevail between 3500 and 4500 feet.

Advisory to warning level southerly winds will overspread the
entire area Friday into Friday night, strongest across the
mountains to deserts. Still expecting wind gusts of 55 to 75 mph
where with the extraordinary snow amounts, so the current Blizzard
Warnings look good. Winds may drop off Saturday, so the Blizzard
Warning may be downgraded early for some areas. Expect whiteout
conditions at times within the Blizzard Warning, mainly above
3500 to 4500 feet in elevation. Significant blowing and drifting
of snow combined with the whiteout conditions will make driving
very difficult to impossible, including for rescue crews. The
incredible amount of snow combined with the strong wind will lead
to extreme avalanche conditions along steeper terrain and at lower
elevations than we typically experience in southern California.
The most significant threat for Avalanches is typically within 24
hours of new snowfall. The heavy snowfall will increase risk of
downed trees and power outages and can cause damage to roofs which
have shallow slopes.

This very cold storm, especially for late February will bring
unusually cold temperatures through Saturday with temperatures
confined to the mid 30s to low 50s (coldest at night) for lower
elevations and 20s and 30s for high elevations, which may be
dangerous those without sufficient access to heating.

.LONG TERM (SUN-WED)...23/254 AM.

A shortwave ridge may provide a brief break in the action Sunday
before action weather returns for the early to middle part of next
week. If skies clear fast enough, a late season frost/freeze could
be in play for some coastal valleys early Sunday morning.
Forecast confidence drops of precipitously during this time frame
but a return to rain and mountain snow is probably. The set up
does not look nearly as volatile as the incoming storm, but still
could be a moderate storm in it's own right. Below normal
temperatures continue through the period, and most residents of
southwest California will still be awaiting their first 60 degree
daytime high temperature since early this week.

&&

.AVIATION...23/0615Z.

At around 0600Z at KLAX, there was no marine layer nor an
inversion.

Low confidence in TAFs, due to the timing of wind changes and the
showery pattern. CIGs will bounce between VFR and MVFR and
scatter and reform.

KLAX...Moderate confidence in the TAF. CIGS and SHRA will be
variable. Starting at 6z there is a 30-40% change of the easterly
wind component reaching 8 kts.

KBUR...Moderate confidence in the TAF. CIGS and SHRA will be
variable.

&&

.MARINE...22/1032 PM.

Overall, moderate confidence in the current forecast. Winds and
seas will continue on a decreasing trend, however, there is a
50-60% chance that the Small Craft Advisory (SCA) seas will
persist across the outer waters and the inner waters north of
Point Conception up until the next system.

On Thursday night through Friday night another frontal system
will bring S-SW winds into the region, with a 90% chance of Gale
Force gusts in the outer waters north of Point Conception through
Friday afternoon. Starting Friday morning through Friday night,
there is a 80% chance of Gale Force gusts for all of the waters
South of Point Conception. Along the front in the outer waters,
there is a 40% chance of Storm Force level winds gusts.

Steep hazardous seas will increase to 12 to 15 feet over the
outer waters, and to 8 to 12 feet nearshore during these southerly
winds. Winds and seas will likely diminish and subside
respectively below SCA levels by Saturday evening.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Winter Storm Warning in effect until 4 AM PST Friday for
      zones 53-54-353. (See LAXWSWLOX).
     Blizzard Warning in effect from 4 AM Friday to 4 PM PST
      Saturday for zones 53-54-353. (See LAXWSWLOX).
     Flood Watch in effect from late tonight through Saturday
      afternoon for zones 53-349>359. (See LAXFFALOX).
     Flood Watch in effect from Friday morning through Saturday
      afternoon for zones 54-88-362>365-547-548. (See LAXFFALOX).
     Winter Weather Advisory in effect until 10 AM PST Friday for
      zone 59. (See LAXWSWLOX).
     High Wind Warning in effect from 10 AM Friday to 5 AM PST
      Saturday for zone 59. (See LAXNPWLOX).
     Wind Advisory in effect until 3 AM PST early this morning for
      zone 87. (See LAXNPWLOX).
     High Surf Advisory in effect from 10 AM Friday to 8 AM PST
      Saturday for zones 87-354-362-364. (See LAXCFWLOX).
     Wind Advisory in effect from 10 AM Friday to 1 AM PST
      Saturday for zones 88-350-352-354>359-363-547. (See LAXNPWLOX).
     High Surf Advisory in effect until 8 AM PST Saturday for
      zones 340-346. (See LAXCFWLOX).
     Wind Advisory in effect from 4 AM to 4 PM PST Friday for
      zones 340>344-346>349-351. (See LAXNPWLOX).
     Winter Weather Advisory in effect until 1 PM PST this
      afternoon for zones 342-344-351-352. (See LAXWSWLOX).
     Winter Storm Warning in effect until 4 PM PST Saturday for
      zone 345. (See LAXWSWLOX).
     Wind Advisory in effect from 1 PM Friday to 4 AM PST Saturday
      for zones 364-365-548. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 9 PM PST this evening
      for zones 645-670-673-676. (See LAXMWWLOX).
     Gale Watch in effect from this evening through Friday morning
      for zones 645-670. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PST early this
      morning for zones 650-655. (See LAXMWWLOX).
     Gale Watch in effect from late tonight through Friday
      afternoon for zone 650. (See LAXMWWLOX).
     Gale Watch in effect from late tonight through late Friday
      night for zone 655. (See LAXMWWLOX).
     Gale Warning in effect from midnight tonight to 10 AM PST
      Friday for zone 673. (See LAXMWWLOX).
     Gale Warning in effect from 3 AM to 2 PM PST Friday for zone
      676. (See LAXMWWLOX).

&&

PUBLIC...Munroe
AVIATION...Schoenfeld/RM
MARINE...Schoenfeld/KL
SYNOPSIS...Munroe

weather.gov/losangeles

Experimental Graphical Hazardous Weather Outlook at:
https://www.weather.gov/erh/ghwo?wfo=lox