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000
FXUS66 KLOX 112127
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
227 PM PDT Thu Apr 11 2024

.SYNOPSIS...11/129 PM.

Warm and sunny conditions will continue today, except for some
low clouds and fog near the coast. Much cooler weather is
expected Friday through the weekend as another late season storm
moves into the region. Rain will begin Friday night with showers
lasting until Sunday. Snow is expected at higher elevations.

&&

.SHORT TERM (TDY-SUN)...11/128 PM.

Synoptically, the upper-level ridge that has been pushing into
the state from the southwest is beginning to recede in advance of
a 524 dam low system dropping down from the Gulf of Alaska. An
associated cold font will pass through the area beginning Friday
night when the low will be about 200 miles west of San Francisco.
Models are in better agreement in the track on Sunday with a more
eastward than south track, and that is the NBM solution as well.
The ridge rebuilds on Monday, but to our west and with a negative
tilt, leaving the area near the southwest edge of a conus-
spanning trough for the extended period. Heights will be back up
to about 576 dam on Tuesday and Wednesday. The pattern will become
more zonal by Thursday with heights dropping a few dam.

The shift to onshore flow and the arrival of the marine layer
pushed the cooling slightly farther inland and even into some
coastal valleys. Max temps are in the mid 70s to low 80s in the
coasts and valleys, which is a few degrees cooler than this time
yesterday.

On Friday the cooling trend will spread throughout the interior
as onshore flow strengthens ahead of another late season cold
upper low which will drop south along the West Coast. Higher
heights and onshore flow will increase the marine layer height and
the low clouds and fog will spread into the valleys Friday
morning. High temps will drop into the 60s to lower 70s.

By late Friday night the upper low is expected to be just
offshore of the Bay area with a cold front extending south through
Pt Conception. The vast majority of ensemble solutions have rain
beginning along the Central Coast Friday night and spreading into
Ventura and LA Counties from Saturday morning to afternoon.
Latest models show 500mb temperatures dropping to around -33c over
SLO County so thunderstorms are a good bet there and in northern
SB County as well with periods of heavy rain. SPC has those areas
in a general risk for thunder on Saturday, and WPC has a marginal
risk (>5%) for excessive rainfall.

Hi res models show gusty south winds developing in SLO and
northern SB Counties as well later Friday night and may need some
low end wind advisories there.

Ensembles are holding pretty steady with rain amounts, ranging
from around an inch for SLO/SB Counties (except up to 2 inches in
the mountains) to around a half inch for LA/Ventura Counties (one
inch in the mtns). Around 10-20% of the solutions are twice that
amount. Thunderstorms will boost totals in local areas, mainly
north of Pt Conception.

Snow levels will be around 6000` for the main portion of the
storm with several inches of snow possible. May need either a
winter weather advisory or possibly a winter storm watch for some
mountains. Snow levels drop rapidly Saturday night and with a
secondary upper low rotating into the area by Sunday morning. The
snow level bottoms out at around 4100`, but there`s a chance for
additional showers and thunderstorms to drop snow down to as low
as 3500`. Light snow is possible (10%) over the Grapevine on
Interstate 5 but precip will most likely fall as rain.

There will be a lull between the front and the second part of the
storm which will arrive Saturday night into Sunday. 500mb temps
remain in the -28c to -30c range and with some April surface
heating showers and thunderstorms are possible (10-20%)
everywhere. An additional quarter to half inch of rain is
possible, with higher totals near any thunderstorms that may form.
Snow levels will be lowering to near 4100 feet Sunday morning
with some light snow possible over the Grapevine on Interstate 5.

.LONG TERM (MON-THU)...11/135 PM.

The ridge rebuilds on Monday kicking off a drying and warming
pattern. The ridge axis will be to our west and with a negative
tilt, leaving the area near the inflection point between the
ridge and a conus-spanning trough. Expect partly cloudy skies.
Heights will be back up to about 576 dam on Tuesday and Wednesday.
Afternoon 80`s are possible as soon as next Wednesday in the
warmer valleys. The pattern will become more zonal by Thursday
with heights dropping a few dam, and introducing slight cooling.

&&

.AVIATION...11/1928Z.

At 1828Z, the marine layer depth was 500 feet deep with the top
of the inversion at 2300 feet with a temperature of 23 C.

Moderate confidence in TAFs. Marine layer clouds should extend
further inland tonight, reaching coastal valleys sites. Cig
heights should be a little higher than last night (near IFR), with
less prevalent dense fog. Arrival of cigs may be off by +/- 2
hours this evening.

KLAX...Arrival of OVC004-OVC008 cigs may be off by +/- 2 hours
this evening, and periods of 1/4SM vsby are possible from 08Z-14Z
Fri. No significant east wind expected.

KBUR...Arrival of OVC008-OVC015 cigs may be off by +/- 2 hours
late tonight, and there is a slight chance of periods of 1/4SM
vsby from 10Z-15Z Fri.

&&

.MARINE...11/226 PM.

Moderate confidence in the forecast. Slightly higher confidence
in winds relative to seas.

For the waters southwest through northwest of the Channel Islands
and the nearshore waters along the Central Coast, there is a 40-70
percent chance of Small Craft Advisory (SCA) level winds this
afternoon and tonight, highest for the northernmost outer waters.
Starting Friday afternoon SCA winds are likely for the waters
north of the Channel Islands. Saturday through Tuesday night,
there is a 60-80 percent chance of widespread SCA conditions
developing. There is a 20-30% chance of GALES Tuesday through
Wednesday morning, highest beyond 30 NM offshore.

Inside the southern California bight, winds and seas will likely
remain below SCA levels through Friday night, then there is a
50-70% chance of SCA level winds developing Saturday. For early
next week, SCA level winds will likely affect the western portions
of the inner waters with a 40-60 percent chance of SCA level
conditions, with the highest chances during the afternoon and
evenings.

Dense fog, with visibilities of one nautical mile or less, will
impact the coastal waters through Friday morning.

&&

.BEACHES...11/222 PM.

There is a moderate-to-high chance of low level high surf with
strong rip current activity at the beaches this weekend. Surf
will peak on Saturday night at 7 to 10 feet (local sets to 12
feet) for the Central Coast, highest on west and northwest facing
shores. For beaches south of Point Conception, surf will peak on
Sunday around 4 to 7 feet, highest on west facing shores.

Larger surf is possible for early next week as a large northwest
swell builds into the coastal waters. Early guidance suggest
breakers 9 to 12 feet along the Central Coast between Tuesday and
Wednesday. South of Point Conception, west-facing shores could
see surf of 4 to 7 feet.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory in effect until 3 AM PDT Friday for zone
      670. (See LAXMWWLOX).

&&

$$

PUBLIC...MW/jld
AVIATION...Schoenfeld
MARINE...Hall/Schoenfeld
BEACHES...Hall/Schoenfeld
SYNOPSIS...jld

weather.gov/losangeles

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