LA Area Forecast Discussion

FXUS66 KLOX 261523

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
823 AM PDT Tue Sep 26 2023

.SYNOPSIS...26/220 AM.

Skies will be mostly clear through mid-week. Warming each day
today and Wednesday will bring max temperatures to above-normal
values by Wednesday. Gusty Sundowner winds over southern Santa
Barbara County will peak for tonight. Cooler conditions are
expected from the end of this week into the weekend, when there
will be a slight chance of rain.


.SHORT TERM (TDY-THU)...26/821 AM.


Both the VBG and LAX soundings early this morning showed a
surface- based inversion, with the low level flow northerly at VBG
and easterly at LAX. Pressure gradients were weakly onshore to
the E with LAX-DAG at +0.8 mb as of 14Z (-0.9 mb trend in 24
hours), while northerly pressure gradients were decently offshore
with LAX-BFL at -3.1 mb (-2.9 mb trend in 24 hours). The
northerly gradients and offshore trends helped to keep low clouds
off the coast this morning, except for patchy low clouds and fog
around Long Beach. These low clouds should dissipate by late
morning, and overall it looks like sunny skies will prevail across
the forecast area thru this afternoon. It will turn warmer for
most areas with highs reaching the 80s to low 90s for the vlys and
foothills. However, some cooler easterly flow should lower temps
for the interior SLO/SBA County vlys.

***From Previous Discussion***

There will be a strong sundowner tonight. Offshore N to S
gradients across SBA county will be in the 3 to 5 mb range which
should generate 45 to 55 mph wind gusts with local 55 to 60 mph
gusts possible in the windiest canyons and passes such as Gaviota
and Refugio. A wind advisory is out for the SBA south coast. These
strong winds will also create fire weather concerns and a Fire
Weather Watch is in effect for the area (please see LAXRFWLOX for
details) There is a low chance (20 percent probability) for a
mountain-wave in the evening. If this occurs wind gusts of 60-70
mph will be possible in any region the wave touches down.

Wednesday will be the warmest day. There should be no low
clouds and 1 to 2 degrees of warming. Most of the area will see
above normal temps. The warmest vly locations will reach into the
mid 90s.

There will be another weaker sundowner Wednesday night as
gradients will relax some.

Hi rez short range ensemble fcsts indicate that a weak eddy will
bring some low clouds to the LA coast on Thursday morning. It is
also likely that the rest of the area will not have any low
clouds. The big news Thursday will be the sudden and dramatic end
of the warming trend. A trof associated with a cold upper low over
British Columbia will lower hgts to 583 dam and bring moderate
onshore flow back to the area. Look for 4 to 8 degrees of cooling
and a return to below normal afternoon highs.

.LONG TERM (FRI-MON)...26/308 AM.

The deterministic GFS and EC are in good agreement through Sunday
and their respective ensembles also exhibit good cohesion. So
there is pretty good confidence in the fcst.

Friday will be like Thursday only more so. The trof will be
deeper. The gradients will be more onshore. The marine layer
clouds will be more extensive. Max temps will fall another 3 to 6
degrees. Max temps will end up 6 to 12 degrees blo normal.

The weekend forecast will be dominated by an atypical weather
pattern featuring a cold upper low moving into and over the state.
Hgts could fall to as low as 564 dam which is 19 dam below the
normal value. The instability and PVA assoc with the low will
interact with the marine layer any other moisture in the area to
bring a slight chc of showers to most of the coasts. valleys and
coastal slopes from Friday night through Sunday morning. Skies
will likely vary from partly cloudy to mostly cloudy through the
period as the low sweeps various cloud decks in and out. Max
temps will nose dive 4 to 8 degrees on Saturday and most high
temps will only be in the mid 60s to lower 70s. These max temps
are 10 to 20 degrees below normals. There will be a few degrees of
warming on Sunday as the coldest section of the low moves away
from the area.

Less confidence in the Monday fcst as the ensembles present a wide
assortment of solutions for the position and movement of the
upper low. Skies should be mostly clear or at worst partly cloudy.
The biggest variable in the fcst is the temperatures which depend
on the location of the low. Almost all ensembles are warmer and
blended ensemble solution suggests the most areas will see 3 to 6
degrees of warming.



Around 1110Z, the marine layer depth was around 250 feet deep at
KLAX. The top of the inversion was near 1700 feet with a
temperature around 23 degrees Celsius.

High confidence in the forecast for valley and desert terminals.

Low-to-moderate confidence in the current forecast for coastal
terminals. There is a moderate to high chance of LIFR to IFR
conditions at coastal terminals through 17Z and again after 08Z

KLAX...There is a 40 percent chance of LIFR to IFR conditions at
KLAX through 17Z and again after 13Z Wednesday. Any easterly winds
will remain less than 7 knots.

KBUR...VFR conditions are expected through the period. No wind
impacts are expected at this time.


.MARINE...26/343 AM.

High confidence in the current forecast through Wednesday, then
moderate confidence thereafter. There is a moderate chance that
winds could be stronger and seas much higher between Thursday and
Saturday. Confidence remains higher in winds relative to seas.

For the waters northwest through southwest of the Channel Islands,
the chances for SCA conditions will increase to a 90-100 percent
today through Thursday morning. Widespread SCA conditions with
hazardous seas are virtually certain through Thursday morning.
There is a 40-70 percent chance of Gale Force winds today,
increasing to 50-80 percent on tonight through Wednesday night.
The highest chances for Gales will be from near Point Conception
south to San Nicolas Island with the lowest chances will be north
of Point Sal beyond 20 NM offshore. There is a high-to-likely
chance of SCA conditions lingering into Friday and Saturday with a
moderate chance of Gale Force winds over the weekend.

For the nearshore waters along the Central Coast, winds and seas
will increase today. There is an 80-90 percent chance of SCA
conditions by this afternoon. Widespread SCA conditions are very
likely to virtually certain between Tuesday and Thursday,
especially during the afternoon and evening hours. There is a
30-40 percent chance for Gale Force winds each afternoon and
evening. There is a moderate-to-high chance of SCA conditions
lingering into Friday and Saturday with a low chance of Gale
Force winds over the weekend.

Inside the southern California bight, there is a 40-60 percent
chance of widespread SCA conditions (winds and seas) between
through Thursday. The highest chances are during the afternoon
and evening hours across the western portion of the Santa Barbara
Channel. Local SCA winds and choppy seas could get into the
Anacapa Passage, along the Malibu Coast, and into the San Pedro
Channel each afternoon and evening.Local Gale Force gusts are
possible across the nearshore portion between Point Conception to
Refugio State Beach and out to Santa Cruz Island. Lower confidence
exists in the current Gale Watch, mainly due to areal extent of
winds. Higher confidence exists in broader SCA conditions from a
line west of Anacapa Island to Goleta Point.


CA...High Surf Advisory in effect until 9 PM PDT Thursday for
      zones 340-346. (See LAXCFWLOX).
     Wind Advisory in effect until 5 AM PDT Thursday for zones
      349-351. (See LAXNPWLOX).
     Beach Hazards Statement in effect through Thursday evening
      for zone 354. (See LAXCFWLOX).
     Fire Weather Watch in effect from 5 PM PDT this afternoon
      through late Wednesday night for zones 349>353. (See LAXRFWLOX).
PZ...Small Craft Advisory in effect until 3 AM PDT Thursday for
      zones 645-670. (See LAXMWWLOX).
     Small Craft Advisory in effect from 2 PM this afternoon to 3
      PM PDT Wednesday for zone 650. (See LAXMWWLOX).
     Gale Watch in effect from Wednesday afternoon through late
      Wednesday night for zone 650. (See LAXMWWLOX).
     Small Craft Advisory in effect until 2 PM PDT this afternoon
      for zones 673-676. (See LAXMWWLOX).
     Gale Warning in effect from 2 PM this afternoon to 9 AM PDT
      Thursday for zones 673-676. (See LAXMWWLOX).




Experimental Graphical Hazardous Weather Outlook at:

NWS LOX Office Area Forecast Discussion