000
FXUS66 KLOX 240415
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
915 PM PDT Thu Mar 23 2023

.SYNOPSIS...23/834 PM.

Some rain and snow showers are expected on the north mountain
slopes tonight through Friday morning. Otherwise, dry and cool
conditions are expected through Monday. Strong and gusty northwest
to north winds are expected for the mountains tonight and into
the weekend. Another storm is possible for next Tuesday and
Wednesday with more rain and mountain snow.

&&

.SHORT TERM (THU-SUN)...23/911 PM.

***UPDATE***

Today was a cool and breezy day. The coasts saw quite a bit of
sunshine but the vlys remained cloudy all day (although the clouds
are now dissipating with the lack of daytime heating). Max temps
across the csts and vlys were only in the mid 50s to the lower
60s or 10 to 15 degrees blo normal.

The atmosphere was slightly unstable today and this resulted in a
few showers over the LA county Vlys. Elsewhere the NW flow is
creating clouds and showers on the north slopes of the mtns near
the Kern County line. Snow levels will drop through the night and
snow will likely fall on the Grapevine. Northerly winds will also
increase as the N to S sfc offshore gradients increase by 2 to 3
mb. Advisory level wind gusts will develop across the mtns by
midnight. These advisory level winds will then persist through
Saturday night. The winds when combined with 1 to 3 inches of snow
that will will lead to winter weather conditions and a winter
weather advisory is in effect through tomorrow morning.

Winds will be stronger tomorrow and the wind advisories may be
needed in a few of the vlys and the SBA south coast.

The current forecast is in good shape and no updates are planned.

***From Previous Discussion***

The weather system that came through Wednesday has mostly moved on
but there is still plenty of low level moisture around with
increasing northwest flow. Not much instability but enough in the
lower levels to generate some light showers, mostly over the
mountains but in these patterns it`s not unusual for stray showers
to spill over into the coastal valleys. Any showers are expected
to be on the light side with minimal, if any impacts in most
areas. The main exception there may be the Grapevine where models
continue to indicate at least a 60% chance of accumulating snow,
especially after midnight tonight when snow levels really start to
drop. Currently they are between 5000 and 6000 feet, but overnight
they are expected to fall to around 4000 feet and by Friday
morning as low as 3000 feet.

Winds are the other main weather story. West winds are increasing
along the coast this afternoon, then this evening and overnight
coastal winds will decrease and north to northwest mountain winds
will pick up to at least advisory levels. Strong northwest flow
is expected to remain in place at least through Saturday morning,
possibly spilling into the valleys and even some of the coastal
areas, including west LA, though probably below advisory levels
there. Friday afternoon and evening additional parts of southern
Santa Barbara County may need to be added to the wind advisory.

Otherwise, dry weather expected through the weekend with slightly
warmer temperatures.

.LONG TERM (MON-THU)...23/209 PM.

One additional dry day (mostly) Monday before the next system
arrives Tuesday. Northwest SLO County could see some light rain
developing as early as later Monday but for most of the rest of
the area this looks like a Tue/Wed storm, though given the
bouncing around of the upper low still not entirely confident on
the timing and this is reflected in the still sub-likely pops in
the forecast, particularly southern areas. Still seems like
mid day Tuesday into early Wednesday is the sweet spot for timing.
And still a fair amount of disagreement on amounts as well with
the ECMWF EPS mean qpf amount at least twice and as much as three
times the GEFS mean. The GEFS PW`s are .2-.4" lower than the EPS.
Also, the deterministic GFS shows a very fast moving initial
frontal passage Tuesday (with limited southerly flow) followed by
mostly west to northwest flow, neither of which are conducive to
a high qpf output system. The ECMWF is slower overall and while
still not super high PW content, the slower speed and colder air
could help generate higher rain rates and a longer duration of
precip overall. The Wednesday portion of the storm has the
potential for having similar weather and impacts as what happened
at the back end of the most recent storm here, meaning frequent
showers, possibly convective, and low snow levels.

Showers could linger into Thursday in some areas, though most
areas should start a drying trend that is expected to last through
the following weekend.

&&

.AVIATION...24/0018Z.

At 2305Z at KLAX, there was no marine layer nor any inversions.

Good confidence in Cig/Vis fcsts. Moderate confidence in wind
fcsts where transitions could be off by +/- 2 hours.

KLAX...Good confidence in Cig/Vis fcst. There is a 20 percent chc
35015kt 10Z-16Z and a near 0 percent chc of any east wind
component.

KBUR...Good confidence in Cig/Vis fcst. There is a 20 percent chc
33012KT conds 10Z-16Z.

&&

.MARINE...23/833 PM.

At issuance time, NW winds are at or near Small Craft Advisory
(SCA) level for all waters. Over the outer waters, moderate to
high confidence that GALE force gusts will develop later tonight,
west and southwest of Point Conception. In addition, there is a
30-40 percent chance that GALES will move into the western Santa
Barbara Channel for a few hours tonight, then easing after
midnight. There is high confidence that moderate to strong winds
will persist through late Saturday night.

Winds and seas are currently expected to drop below SCA for all
waters sometime on Sunday. However for the Inner Waters winds and
seas may drop briefly below SCA level for periods of a few hours,
mainly during the late night to early morning hours.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory in effect until 6 AM PDT Sunday for zones
352-353-376>379-381. (See LAXNPWLOX).
Winter Weather Advisory in effect until 11 AM PDT Friday for
zones 377-378. (See LAXWSWLOX).
PZ...Small Craft Advisory in effect until 3 AM PDT Friday for
zones 645-655. (See LAXMWWLOX).
Small Craft Advisory in effect until 3 AM PDT Sunday for
zones 650-670. (See LAXMWWLOX).
Gale Watch in effect through late Saturday night for zones
673-676. (See LAXMWWLOX).

&&

$$

PUBLIC...MW/Rorke
AVIATION...Rorke
MARINE...Smith
SYNOPSIS...MW/Smith

weather.gov/losangeles

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