Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 240454
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
954 PM PDT Sat Mar 23 2024

.SYNOPSIS...23/914 PM.

A lingering storm system will continue a cold and unsettled
weather pattern into Sunday. Scattered showers with isolated
thunderstorms are possible with snow levels lowering to as low as
3500 feet. West to northwest winds will continue to
strengthen through Sunday evening as a tight northerly pressure
difference develops across the state. Warmer and drier weather is
expected for early week, than another storm system, potentially
heavy rainfall, is possible for next weekend.

&&

.SHORT TERM (SAT-TUE)...23/952 PM.

A broad upper-level trough continues to move over the western
United States this evening. The latest radar imagery indicates
scattered showers with isolated thunderstorms moving over the
area. The cold air mass aloft is starting to dive into the region
this evening. The latest model solutions cool 700 mb temperatures
to near -9 degrees Celsius by Sunday morning, which will lower the
snow level down to 3500 feet. With any convective burst, the snow
level could lower down to 3000 feet. Reports of pea size hail and
graupel having been arriving at the office this evening and it is
not surprising given the cold and unstable air mass in place.

Another piece of the broad upper trough over the southwest Oregon
coast will dig south into the Central Valley through Sunday
afternoon. 500 mb temperatures cool to near -29 degrees Celsius
and will steepen lapse rates during the day. Steeper lapse rate
with the vort max moving over the region with the next piece of
the trough will bring another threat of showers and thunderstorms
on Sunday. Snow levels will nudged lower in the latest update and
some concern is placed for snow levels lowering locally down to
2500 feet with any convective bursts of precipitation. A winter
weather advisory continues to be pondered due to advisory level
winds and any snow.

Gusty northerly winds will continue to develop across the area
through Sunday night as the colder air mass moving in across the
state will tighten the northerly surface pressure gradient.
Wind advisories have been issued and there is some concern that
gusty winds could reach a little farther into the Ventura County
valleys on Sunday evening. Wind advisories for the southern
beaches this evening worked out well but will be let go until
Sunday morning.

A forecast update will be issued shortly.

***From Previous Discussion***

The initial front moved through the area this morning with
rainfall amounts around a half inch on average, though a little
less in LA County. The transition to a showery/convective regime
is in progress, though that won`t fully take effect until Sunday
when the upper low arrives with much colder air aloft. Can`t rule
out an isolated heavy shower or even a storm this afternoon,
though best chance for that would be in SLO County. Moderate
northwest to west flow is developing across the area this
afternoon with winds in the 25-35 mph range along the coast and
over the coastal waters. Those will settle down overnight over the
land but resume Sunday with even stronger gusts and advisories
have been issued for all coastal areas tomorrow afternoon.

Increasing lapse rates and cooling aloft will provide an
increasingly favorable environment for convective activity Sunday
afternoon, especially north of Pt Conception and in LA County.
Can`t rule out a storm elsewhere but downslope flow off the
mountains will be a limiting factor. Locally heavy rain, small
hail, and gusty winds all possible with the storms. For some areas
the rain for this weekend is over but areas north of Pt
Conception, the mountains, and in LA County are most likely to see
at least some additional precip by tomorrow. Lowering snow levels
also expected tonight into Sunday with that cooler air moving in.
Still expecting snow levels to drop to the low 4000s early Sunday
and again Sunday evening with a 30-50 percent chance of light snow
near the Grapevine summit on Interstate 5. Increasing northerly
flow later Sunday will create some gusty winds up to 50 mph in
the mountains and across southern Santa Barbara County. Some of
those northerly winds will filter down into the western LA
valleys and coastal areas Sunday night but likely below advisory
levels.

Dry and warmer weather expected Monday and Tuesday with some
breezy northerly winds at times, especially in the mountains.

.LONG TERM (WED-SAT)...23/225 PM.

Dry and warmer again Wednesday with highs jumping into the low to
mid 70s in the valleys. Then turning cooler Thursday as the first
of two storm systems approaches from the northwest. Can`t rule out
a shower northern areas Thursday though models have scaled back
in recent runs and only about a third of the ensembles have precip
reaching SLO County. At most it would be very light rain.

A second system is expected to dumbbell around the first upper
low later Thursday and drop much farther south Friday through the
following weekend. Deterministic models have the low center as
low as 529dam Friday afternoon just west of the Bay Area. Based on
the latest ensembles precip chances are expected to increase
Friday night with all areas getting either rain or mountain snow
by Saturday and continuing into Sunday and possibly even early
Monday as the upper low is mostly cut off from the westerlies and
very slow moving. If the track and timing remain reasonable stable
this could deliver a significant amount of rain to the area.
Ensemble solutions are currently indicating roughly 1-3 inches of
rain at lower elevations and possibly up to twice that in the
upslope areas. There are a number of solutions that are even
higher than that. And given how cold this system is with
thicknesses down to 540, this could also be a big snow producer
for the mountains.

&&

.AVIATION...24/0222Z.

At 2345Z at KLAX, there was no marine layer nor inversion.

Moderate to low confidence in TAFs due to strong gusty winds,
scattered/isolated showers, and potential (20% chance) for
thunderstorms this evening and again tomorrow. Generally VFR
conditions are expected except MVFR to locally IFR near convective
showers.

KLAX...Moderate confidence in TAF. VFR conditions are expected
to prevail except MVFR to brief IFR conditions in heavier showers.
Best chances for heavier showers/thunderstorms will be from 18-00Z
Sunday. Lower confidence start and end times of stronger gusty
winds.

KBUR...Low to moderate confidence in TAF. Best chances for
heavier showers/thunderstorms will be from 18-00Z Sunday. Lower
confidence start time of stronger gusty winds tomorrow.

&&

.MARINE...23/114 PM.

Dangerous seas are likely this afternoon through Monday,
especially on Sunday when widespread Gales are nearly certain. The
strongest winds will be focused across all the waters south of
Point Sal, with winds dropping below Gale Force at times northward
of Point Sal. There is a 30 percent chance of Gales starting this
evening for the Santa Barbara Channel and the Santa Monica Basin
and 50-70 percent chance for the inner waters south of Point Mugu
with particular focus between Point Mugu and Palos Verdes. As
such, have started the Gale Warning now with the afternoon package
for the inner waters south of Point Mugu. There is a 40 percent
chance that the current Gale Watches will need to be extended
through Monday for the waters south of Santa Barbara. In addition
to the winds, there is a 10 to 20 percent chance of thunderstorms
this evening through Sunday early evening with the potential for
locally gusty winds, brief heavy rainfall and/or hail, and
dangerous cloud to surface lightning. Conditions will improve
Tuesday and Wednesday, but it will still be hazardous to most
small craft due to choppy seas. Winds and seas will increase once
again on Thursday and Friday with widespread Gale Force Winds
possible.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory in effect until 10 PM PDT this evening for
      zones 87-349-350-354-362-366. (See LAXNPWLOX).
     High Surf Advisory in effect from 3 AM Sunday to 9 AM PDT
      Monday for zones 87-340-346-354-362-366. (See LAXCFWLOX).
     Wind Advisory in effect from 11 AM to 6 PM PDT Sunday for
      zones 340-341-346-347-354-355-362-366>368. (See LAXNPWLOX).
     Wind Advisory in effect from 4 PM Sunday to 3 AM PDT Monday
      for zones 349>353-376>379. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 3 AM PDT Sunday for
      zones 645-670-673-676. (See LAXMWWLOX).
     Gale Warning in effect from 3 AM Sunday to 3 AM PDT Monday
      for zones 645-670-673-676. (See LAXMWWLOX).
     Gale Warning in effect until 3 AM PDT Monday for zones
      650-655. (See LAXMWWLOX).

&&

$$

PUBLIC...Hall/MW
AVIATION...Phillips
MARINE...Munroe/Lund/RK
SYNOPSIS...Hall

weather.gov/losangeles

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


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