Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000
FXUS66 KLOX 221045
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
345 AM PDT Thu Apr 22 2021

.SYNOPSIS...22/223 AM.

Strong onshore flow and a deep marine layer will remain in place
today. Drizzle or light rain will be possible today. A slight
warming trend will develop for Friday and Saturday as onshore flow
weakens and the marine layer thins. A storm system originating
from Gulf of Alaska could bring rain and mountain snow to the area
between Sunday and Monday night. A warming trend is possible for
the middle portion of next week.

&&

.SHORT TERM (TDY-SAT)...22/318 AM.

The latest satellite imagery shows an upper-level trough draped
over the region this morning. A deep marine layer remains in place
across the area and clouds are well-entrenched. Clouds are
filling back in across the area, and the only cloud free areas are
the interior portions of the area and the Santa Barbara South
Coast and Santa Barbara Channel. Clouds are expected to fill in
across the channel and into the Santa Barbara area as the morning
progresses. The trough is interacting with the deep marine layer
and bringing light rain or measurable drizzle to the coastal
slopes of the San Gabriel mountains this morning. Drizzle or
light rain is possible for the southern areas today where the most
favorable flow pattern and instability is placed. Another cool
day is expected today with clouds struggling to clear from the
land mass.

Onshore flow will remain in place across the area through
Saturday, but onshore flow will weaken and the marine layer will
thin some as ridging aloft builds in. A warming and drying trend
will develop for Friday and Saturday. The best warming will take
place across the interior portions of the area. Closer to the
coast, the warming trend will be moderated some as the ridge will
likely strengthen the marine inversion, setting up a May Gray
like pattern for Friday, and maybe Saturday. The stronger marine
inversion will inhibit low clouds and fog from mixing out. Clouds
will likely hug the coast for Friday afternoon, and maybe
Saturday afternoon.

.LONG TERM (SUN-WED)...22/314 AM.

The model solutions are starting to fall inline now, and Sunday
and Monday is trending wetter. A majority of the global ensemble
members indicate rain between Sunday and Monday night across the
region. All the Canadian ensemble members have a wet forecast, a
vast majority (except for a few solutions) of the ECMWF ensemble
members are wet, and now the GEFS members are following suit. GEFS
members are still drier, but more than half have a wet forecast
for early next week. With this in mind, the forecast now mentions
either rain likely or categorical rain for between late Sunday up
north and Monday farthest south. Though still early and numbers
could change, rainfall amounts look to range between 0.25 and 0.50
inch for coast and valleys with up to 1.00 inch along the coastal
slopes of the mountains. Much less amounts, around a tenth of an
inch are expected across the desert. Only a few ensemble members
are producing amounts between 0.75 inch and 1.25 inch across the
coast and valley areas. Most are falling in the range listed
above.

Timing is still uncertain at this point, but confidence is high
for a band of light to moderate rainfall for about three to six
hours around the period when the highest PoPs are forecast. Timing
should get hammered out as we get in the window of the higher
resolution models over the next 24-48 hours. If planning to
commute to work or school on Monday, plan for a wet commute,
especially for the Southland.

Snow levels still look to remain around 6000 feet or above with
this system. Only a two GEFS members bring snow down to the
Grapevine portion of Interstate 5, while all the remaining GEFS,
GEM, and ECMWF members keep snow levels higher. Based upon the
latest QPF, early snowfall estimates would place 2-4 inches of
snow above 6500 feet with local amounts to 6 inches on the favored
peaks above 7500 feet.

Ridging aloft will build in for the middle portion of next week
and bring some warming. Onshore flow does look to strengthen
after Wednesday and bring a deeper marine layer for late next
week.

&&

.AVIATION...22/1045Z.

At 1030Z, the marine inversion at KLAX was based at 4900 feet.
The top of the inversion was 7000 feet with a temperature of
7 degrees Celsius.

Overall, moderate confidence in 12Z TAF package. MVFR CIGs
(015-025) will continue at all coastal/valley sites through the
morning. For the afternoon, expect skies to generally remain BKN
with CIGs at VFR levels. For tonight, expect near repeat with MVFR
CIGs at all coastal/valley sites.

For the desert TAFs, CAVU conditions are anticipated through the
period. Gusty westerly winds will develop late this morning and
continue into the evening hours.

KLAX...Moderate confidence in 12Z TAF. Timing of change from MVFR
to VFR CIGs could be +/- 3 hours of current 21Z forecast. No
significant easterly wind component is expected.

KBUR...Moderate confidence in 12Z TAF. Timing of change from MVFR
to VFR CIGs could be +/- 3 hours of current 21Z forecast.

&&

.MARINE...22/116 AM.

For the Outer Waters, moderate to high confidence in current
forecast. There is a 30% chance of Small Craft Advisory (SCA)
level winds this afternoon and evening. On Friday, high confidence
in winds and seas remaining below SCA levels. On Saturday, there
is a 50% chance of SCA level winds across PZZ673/676. On Sunday,
winds will diminish below SCA levels. However on Monday, there is
a 50% chance of SCA level winds across all the Outer Waters.

For the Inner Waters north of Point Sal, moderate to high
confidence in current forecast. High confidence in winds and seas
remaining below SCA levels through Sunday. On Monday, there is a
20-30% chance of SCA level winds in the afternoon and evening
hours.

For the Inner Waters south of Point Conception, moderate to high
confidence in current forecast. High confidence in winds and seas
remaining below SCA levels through Sunday. On Monday, there is a
30-40% chance of SCA level winds in the afternoon and evening
hours.

&&

.BEACHES...21/821 PM.

The first south swell of the Spring season is expected to arrive
Friday morning and will continue through the weekend. The swell
heights will be in the neighborhood of 3 to 4 feet, and along with
periods of 18-20 seconds should produce breakers of 4 to 7 feet,
highest on south facing beaches. There is a 60 percent chance of
breakers reaching the minimum criteria of a High Surf Advisory (7
feet).

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory in effect until 9 PM PDT this evening for zone
      59. (See LAXNPWLOX).
PZ...NONE.

&&

.HAZARD POTENTIAL OUTLOOK (SAT-WED).

Strong rip currents are likely and high surf is possible at area
beaches Friday and Saturday. Rain and mountain snow above 5500
feet is possible between Sunday and Monday.

&&

$$

PUBLIC...Hall
AVIATION...RAT
MARINE...RAT
BEACHES...Smith
SYNOPSIS...Hall

weather.gov/losangeles


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