LA Area Forecast Discussion

FXUS66 KLOX 231548

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
848 AM PDT Thu Mar 23 2023

.SYNOPSIS...23/847 AM.

Some rain and mountain snow showers will linger over the area
today, and some rain and snow showers are expected on the north
mountain slopes today through Friday night. 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 next Tuesday and
Wednesday with more rain and mountain snow.


.SHORT TERM (TDY-SAT)...23/844 AM.


We are firmly in northwest flow now that the trough axis has moved
east. Still a few showers around today, especially northern
mountains and the interior portion of the Central Coast. Some of
those could spill over into the LA/Ventura valleys as well by
this afternoon but not expecting anything heavy as soundings
indicate only very minimal instability today. Snow levels today
are generally above 5000 feet so any showers over the Grapevine
should be in the form of rain. However, as mentioned below, overnight
tonight colder air does move in and there is a chance for some
snow there. And again Friday night.

***From Previous Discussion***

A broad NW flow aloft with H5 heights around 562-567 dam will
prevail over swrn CA tonight through Fri night. On Sat, a weak and
dry upper level trof will move through the area, with H5 heights
lowering to 556-559 dam.

Diminishing clouds can be expected tonight through Friday, except
for clouds lingering on the N slopes. There is also a chance of
rain and snow on the N slopes tonight, with snow falling above
4000 to 4500 feet. There could be an inch or so of snow on
Interstate 5 over the Grapevine as well. Otherwise expected dry
conditions through Fri. Mostly clear skies can then be expected in
all areas Fri night and Sat. Temps across the region will
continue on the cool side with highs for many areas in the upper
50s to mid 60s. Overnight lows will be quite cold and some of the
interior vlys of SLO/SBA Counties will likely have areas of frost
and some freezing conditions especially Fri night into Sat

An increasing northerly pressure gradient tonight will bring
strong and gusty winds NW to N winds across the Santa Ynez Mtns
and the higher mtns of SBA/VTU/L.A. Counties mtns, and gusty NW
winds into the the Antelope Vly. These winds should continue into
Fri morning as well. At this time, it appears winds will be strong
Advisory levels, and could approach Warning thresholds at times
in the mtns. Another round of Advisory level NW to N winds are
possible Fri night into Sat morning as well as strong northerly
gradients are forecast (NAM fcst LAX-BFL -5.8 mb at 12Z Sat).
These winds could also affect the S SBA County coast and Santa
Clarita and San Fernando Vlys. A Wind Advisory is in effect for
much of the mtns into the Antelope Vly for tonight through Fri
night. Please see the latest Non-Precipitation Weather Message
product (LAXNPWLOX) for further details on the Wind Advisories.

.LONG TERM (SUN-WED)...23/332 AM.

The EC and GFS deterministic and mean ensembles are in generally
good agreement with the large scale features during the extended
period, altho the EC is slower with the movement of another
Pacific storm during the Tue-Wed timeframe.

Dry weather can be expected Sun through Mon, with mostly clear
skies and milder daytime temperatures, but still at least
slightly below normal overall for many areas. It will remain quite
chilly for the overnight hours, and some frost will continue to
be possible for the SLO/SBA County interior vlys.

The mean ensembles are in good agreement that another Pacific
storm system will move into the forecast area later Mon night and
Tue with rain and mountain snow spreading across the area, altho
as mentioned above the EC is slower than the GFS. Went with the
NBM timing which was in-between the two global models.

A lingering cyclonic flow aloft and a cool and moist airmass will
keep a chance of rain and mtn snow over the region Tue night and
Wed, altho the precip may turn a bit more showery during the the
period. Cold air aloft may also lead to some convective activity
on Wed.

Indications are that most of the rain will occur over SLO/SBA
Counties with early estimates of 0.75 to 1.50 inches, except up to
2 inches over the NW Santa Lucia Mtns. For VTU/L.A. Counties, the
coast and vlys may see 0.25 to 0.50 inch, with 0.50 to 1.00 inch
possible in the mtns, highest on the S slopes. There is also the
potential for several inches of snow above 4000 to 5000 feet.



At 12Z at KLAX, there was no marine inversion but there was a deep
moist layer in place to 8000 feet.

Skies were cloudy across most of the forecast area early this
morning. There were multiple cloud layers, so cigs were highly
variable. In general cigs were mostly MVFR to low VFR, except
were IFR to VLIFR in any leftover rain, and in the foothills and
mountains. Expect any rain to end this morning, and cigs should
improve to VFR in most areas this afternoon. The exception will be
in the foothills and mountain where IFR conds may persist through
the day, and on northern slopes where low cigs may persist thru
the night. Gusty west winds will develop in the Antelope Valley
this afternoon, with gusty NW-N winds in the mountains later
today and tonight.

KLAX...Low to moderate confidence in the 12Z TAF. Cigs will vary
between BKN025-035 this morning, then more persistent VFR
conditions are  expected this afternoon as cigs rise. There is a
20-30% chance of any east wind component reaching 7 to 8 knots
thru 18Z this morning. will be under 8 kts.

KBUR...Low to moderate confidence in the 12Z TAF. Cigs will vary
between BKN025-035 this morning, then more persistent VFR
conditions are expected this afternoon as cigs rise.


.MARINE...23/341 AM.

Seas were already at or above Small Craft Advisory (SCA) levels
this morning, and fairly confidence that winds will increase to
Small Craft Advisory (SCA) levels today across most of the waters.
There is a 40%-50% chance of Gale force winds across the southern
two outer waters zones (PZZ673/676) this evening and persist at
times through Sat night. Therefore a Gale Watch has been issued.
There is a chance that the increase to gales may hold off until
late tonight or Fri.

SCA level winds are likely today through Sat night across the
SBA Channel and there is a 30% chance of Gale force winds across
western sections Fri into Sat.

Across the inner waters north of Pt Sal, and the southern inner
waters, SCA level winds are likely during the afternoon through
late tonight hours today thru Sat night.

Large, rough seas are expected throughout the waters through


CA...Wind Advisory in effect from 8 PM this evening to 6 AM PDT
      Sunday for zones 352-353-376>379-381. (See LAXNPWLOX).
     High Surf Advisory in effect until 3 PM PDT this afternoon
      for zone 354. (See LAXCFWLOX).
     High Surf Advisory in effect until 9 AM PDT this morning for
      zones 362-366. (See LAXCFWLOX).
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).
     Small Craft Advisory in effect until 9 PM PDT this evening
      for zones 673-676. (See LAXMWWLOX).
     Gale Watch in effect from this evening through late Saturday
      night for zones 673-676. (See LAXMWWLOX).




Experimental Graphical Hazardous Weather Outlook at:

NWS LOX Office Area Forecast Discussion