Gale Warning 32, NWS Los Angeles, CA

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
211 PM PST Sun Nov 24 2019

.SYNOPSIS...24/108 PM.

Conditions will be warm and dry today with locally gusty wind.
Winds will be stronger and more widespread beginning Monday
afternoon ahead of a storm that will bring periods of rain and
mountain snow Tuesday night through Saturday and possibly Sunday.
There is a slight chance of thunderstorms Wednesday through Friday.

&&

.SHORT TERM (TDY-WED)...24/153 PM.

Gradients trending onshore now as surface pressures fall across
the interior ahead of the next Pac NW trough. After a warm weekend
most areas are slated to drop several degrees Monday. One likely
exception is srn SB County where downslope winds will offset most
of that cooling. Monday afternoon into early Tuesday morning a
strong north to northwest flow will develop as the trough drops
through the Great Basin. Winds between 850-700mb will range from
40-60kt and combined with a 100kt upper level jet and decent
subsidence warning level winds are likely to develop across the
mountains, especially SB County and the I5 corridor area. Portions
of the Antelope Valley may also experience warning level winds,
especially the western end and foothills and many other areas
are likely to get winds near advisory levels including the srn SB
County south coast, Santa Clarita Valley, and parts of the San
Fernando Valley and Santa Monica Mountains.

Models have backed off slightly with the northeast gradients for
Tuesday morning and afternoon but still some gusty sub-advisory
level winds expected across the LA/Ventura Valleys and portions of
the coast. Similar temps most areas except cooling north of Pt
Conception as the next storm approaches and clouds increase.

Starting to get a little more details on the mid week storm as we
enter into the time window of some of our higher resolution
models, including the NAM and local WRF. Both of those are showing
a fairly robust initial frontal passage Tuesday night into
Wednesday with 1" PW's and a 3-6 hour period of moderate to strong
upslope flow. The GFS and ECMWF have been showing very little
upslope component with the system and thus much lower rainfall
amounts early in the event, however the higher res models are
showing 2-3 times the amounts of the GFS/EC for Tue night and Wed.
For this forecast have trended the rainfall amounts closer to the
higher amounts early on in the event, generally .5-1"
coast/valleys and 1-2" in the mountains. These amounts equate to
roughly 75% of the total precipitation from this entire event,
though for northern areas it's more like 90%.

There is a quick shot of instability with the frontal passage so
an isolated rumble of thunder is possible Tue night and Wed,
though chances are somewhat better later Wednesday into Thursday
with the colder air aloft.

Snow levels will actually rise as the front approaches to around
6000-7000' but can't rule out some light snow at lower elevations
as the precip begins and before the warmer air moves in ahead of
the front. Snow levels will fall rapidly Wednesday and Wednesday
night behind the front and there could be some accumulating snow
over the Grapevine as early as Wednesday afternoon and evening
during what typically is a high travel period ahead of
Thanksgiving. Better chances for impactful snowfall over the
Grapevine Wednesday night into Thursday.

Primary impact for this system likely will be with the winter
weather issues in the mountains and travel as rainfall rates in
general won't likely pose a flash flood threat. However, the rates
in thunderstorms may be high enough to trigger some minor mud and
debris flows and will have a better handle on this possibility as
we get closer to the event.

.LONG TERM (THU-SUN)...24/210 PM.

Following the frontal passage Wednesday we'll generally be in a
showery period with highly variable rainfall amounts and even sky
conditions. There is a second impulse that is expected to rotate
around the base of the trough on Thanksgiving day though models
are taking most of this energy south into Orange and San Diego
Counties. This will generate a secondary increase in precipitation
mainly across LA County, though again the cold air aloft with
500mb temps ranging from -30C to -32C and ample moisture below
700mb will spawn numerous showers elsewhere and possibly some
isolated thunderstorms. Snow levels will be very low, mostly
around 3000', though as low as 2000' in convection. Rain amounts
Thursday will vary from as low as a quarter inch to as much as
1.5", and generally speaking the higher amounts in eastern LA
County.

Snow totals in the mountains will range from 6-12", though as
much as 2 feet in the eastern San Gabriels. The Grapevine should
receive 3-6". Should see up to a few inches in the Antelope
Valley foothills and possibly a dusting down to the valley floor.

Activity expected to wind down quickly Friday as the trough lifts
out. Can't rule out an isolated shower or two, especially over
higher terrain but minimal amounts.

Right now it's looking dry and slightly warmer most areas next
Saturday with weak/dirty ridging aloft but models are showing a
lot of high clouds passing through the ridge. The next system to
our west gets very close to the Central Coast Saturday night and
Sunday and some ensemble members are showing some light rain so
will go with small rain chances there but dry elsewhere.

&&

.AVIATION...24/1847Z.

At 1800Z, there was no marine layer around KLAX.

High confidence in 18Z TAFS.

KLAX...High confidence in CAVU 18z TAF. There is a 30 percent
chance of east winds near 8 knots Monday morning.

KBUR...High confidence in 18z CAVU TAF.

&&

.MARINE...24/130 PM.

Outer Waters...SCA level gusts are expected by late afternoon
across the entire outer waters through early Monday morning. A
GALE WARNING has been issued valid from 3AM Monday through 3 AM
Tuesday for the entire outer waters. After that, there is good
confidence that SCA level winds and seas will continue for the
remainder of the outer waters through at least midweek.

Inner Waters N of Point Sal...Should remain below SCA levels
through Monday morning. There is a 30% chance for SCA offshore
winds Sunday morning. About a 60% chance of SCA conditions
developing Monday afternoon through Tuesday night.

Inner Waters S of Point Conception...There is a 60% chance for
SCA conditions late Monday and Monday night, mainly the western
portion of the SBA Channel inner waters. Also, there is a 40%
chance for a SCA for gusty North-Northeast winds Monday night
across the Santa Monica Basin. Winds will turn more NE after
midnight.

There will be an increasing NW swell approaching 12-18 feet
from late Monday through Tuesday night affecting the outer
waters.

&&

.BEACHES...24/133 PM.

A High Surf Advisory remains in effect for the central coast for
surf of 8-12 feet through today. After a short period of time
below high surf criteria, the high surf is expected to return by
Monday and continue through Wednesday at 10-15 feet. High surf
conditions will persist into Wednesday.

Furthermore, the area affected by high surf is expected to expand
into areas south of Point Conception, specifically west facing
beaches of Ventura County Monday and Tuesday, possibly Los Angeles
County Tuesday. The surf will range from 4 to 7 feet.

Finally, astronomical high tides will peak near 7 feet early this
week, and combined with high surf will result in the issuance of
a Coastal Flood Advisory for minor tidal overflow during the time
of peak tide, mainly for Los Angeles and Ventura counties. Minor
flooding will be confined to the lowest areas of coastline,
including possibly some exposed beach parking lots.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory in effect until 3 PM PST Wednesday for
      zones 34-35. (See LAXCFWLOX).
     Wind Advisory in effect from noon Monday to 3 AM PST Tuesday
      for zones 39-59. (See LAXNPWLOX).
     Coastal Flood Advisory in effect from 6 AM Monday to 10 AM
      PST Tuesday for zones 40-41. (See LAXCFWLOX).
     High Surf Advisory in effect from 1 PM Monday to 7 AM PST
      Tuesday for zone 40. (See LAXCFWLOX).
     High Wind Warning in effect from noon Monday to 3 AM PST
      Tuesday for zones 52>54. (See LAXNPWLOX).
     Winter Storm Watch in effect from late Tuesday night through
      late Thursday night for zones 52>54. (See LAXWSWLOX).
PZ...Small Craft Advisory in effect until 3 AM PST Monday for zone
      670. (See LAXMWWLOX).
     Gale Watch in effect from late tonight through late Monday
      night for zone 670. (See LAXMWWLOX).
     Small Craft Advisory in effect until 9 AM PST Monday for zone
      673. (See LAXMWWLOX).
     Gale Watch in effect from Monday morning through late Monday
      night for zones 673-676. (See LAXMWWLOX).
     Small Craft Advisory in effect from 9 PM this evening to 9 AM
      PST Monday for zone 676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (WED-SUN).

Wednesday and Thursday with periods of heavy rain, thunderstorms,
and low elevation snow causing major travel disruptions along
with possible mud and debris flows near burn areas. Cold
temperatures are forecast for latter half of next week with
widespread frost or freeze conditions likely across the interior,
possibly extending into some coastal valley locations.

&&

PUBLIC...MW
AVIATION...Sweet/Kaplan
MARINE...Sweet
BEACHES...Sweet
SYNOPSIS...Kj

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