Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 080106 AAA
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
506 PM PST Sun Mar 7 2021

.SYNOPSIS...07/1249 PM.

Strengthening onshore flow will bring a cooling trend through
Monday with increasing night through morning low clouds and fog.
A cold storm system will likely bring rain and low elevation snow
and gusty winds to the region late Tuesday through Thursday.

&&

.SHORT TERM (TDY-WED)...07/154 PM.

12Z models in good synoptic agreement through the short term
period. At upper levels, broad cyclonic flow will persist over
the area through Tuesday with an upper low dropping southward,
just off the Central CA coast, on Wednesday. Near the surface,
moderate onshore flow to the east will persist with some northerly
offshore flow tonight through Monday night.

Forecast-wise, tonight and Monday should be rather uneventful.
With cyclonic flow aloft and decent onshore surface gradients,
expect marine inversion to deepen overnight. So, low clouds should
be able to push into the coastal slopes by Monday morning.
Additionally, this pattern will result in some patchy drizzle
south of Point Conception with even a slight chance of measurable
rain across Los Angeles county. Other than the marine layer
clouds, varying amounts of high level clouds will continue
through Monday. Temperatures on Monday will be a few degrees
cooler all areas. Also, there will be some gusty westerly winds
across the Antelope Valley Monday afternoon and some Sundowners
Monday evening. For both these areas, there is a chance for low
end advisory-level winds.

For Monday night/Tuesday, expect gradual increase in clouds with
continued onshore flow and approaching cold front Tuesday
afternoon. The cold front is forecast to begin impacting the
Central Coast Tuesday afternoon/evening with rain becoming likely
by the evening hours north of Point Conception. South of Point
Conception, a slight chance to chance of precipitation will
develop Tuesday evening. Models indicate some instability moving
into the Central Coast Tuesday evening which will result in a
slight chance of thunderstorms. Through Tuesday evening, snow
levels will drop to 4000-4500 feet.

For Tuesday night/Wednesday, all models still indicate the upper
low will sweep a cold front across the area. So, all areas can
expect a decent amount of precipitation with this system. Steady
light to moderate rain can be expected through Wednesday afternoon
with a more showery pattern Wednesday evening. Through Wednesday
evening, most areas can expect between 0.50 and 1.00 inches of
rain with locally higher amounts in the mountains. With the cold
air aloft, a slight chance of thunderstorms will be possible for
all areas through Wednesday evening. Snow levels will continue to
drop, lowering to 2500-3500 feet by Wednesday evening. With some
gusty southwesterly winds anticipated, Winter Storm conditions
will be possible in the SBA/Ventura/LA mountains. So, will issue
a WINTER STORM WATCH from 1000 PM Tuesday evening through 1000 PM
Thursday evening (snow totals potentially 6-12" above 4500 feet
and southwest winds gusting to 45 mph), allowing for a big enough
window for future shifts to fine tune the exact timing of winter
storm conditions. With such low snow levels, there may be issues
across the Grapevine during this time period. Please see LAXWSWLOX
for the details on the WINTER STORM WATCH. As for the recent burn
areas, do not anticipate any significant issues at this time, but
the potentially heavy rainfall with any possible thunderstorm
development will need to be watched closely.

.LONG TERM (THU-SUN)...07/155 PM.

For the extended, after Thursday, forecast confidence decreases
noticeably as GFS and ECMWF have much different ideas about the
overall synoptic pattern.

For Thursday, both the GFS and ECMWF are on the same page. The
upper low will move across the area during the day, reaching the
eastern CA deserts by the evening. This pattern will keep a
post-frontal showery pattern over the area through the day. There
will be a chance of showers just about anywhere through the day.
Given the continued cold air aloft, there still is an outside
chance of isolated thunderstorms. However, do not think there is a
high enough chance for any thunderstorm mention at this time. Snow
levels will remain quite low, 2500-3000 feet in the morning then
rising to 3500-4000 feet in the afternoon. So, there will continue
to be a threat of winter weather conditions in the local mountains
(resulting in the WINTER STORM WATCH continuing through Thursday
evening).

For Friday through Sunday, forecast confidence bottoms out
dramatically. GFS is more progressive with the pattern, moving the
upper low into the Midwest Friday/Saturday with another trough
impacting the area on Sunday. Conversely, the ECMWF keeps the
upper low spinning near the 4 Corners area Friday/Saturday with a
ridge moving over the area on Sunday. Either solutions keeps the
area dry Friday/Saturday, but the GFS would indicate a chance of
some light rain on Sunday. Given the uncertainty, will not get too
cute with this time period. Will indicate dry conditions with
partly cloudy to mostly clear skies and a gradual warming trend.
Hopefully, the models will come into better agreement, allowing
for a higher confidence forecast next weekend.

&&

.AVIATION...08/0104Z.

At 00Z, the marine layer depth was around 2300 feet deep at KLAX.
The top of the marine inversion was around 3300 feet with a
temperature of around 10 degrees Celsius. There was another
inversion up to around 6200 feet.

Moderate confidence in the current forecast. Higher confidence in
timing, less confidence in flight categories.

North of Point Conception, LIFR to IFR conditions are likely to
spread in between 04Z and 13Z. Conditions will improve one
category

South of Point Conception, ceilings at or below 5000 feet are
very likely for coastal and valley terminals after 02Z and clear
northwest to southwest between 12Z and 22Z. MVFR conditions will
likely develop over the area through 10Z. There is a slight chance
of IFR conditions in drizzle.

KLAX...Ceilings at or below 5000 feet will spread in between 01Z
and 04Z and very likely persist through at 17Z. There is a 40
percent chance of a later clearing as late as 20Z. There is a 80
percent chance of MVFR conditions between 06Z and 13Z. There is a
10 percent chance of IFR conditions in drizzle.

KBUR...Ceilings at or below 5000 feet will spread in between 02Z
and 05Z and very likely persist through at 19Z. There is a 40
percent chance of a later clearing as late as 22Z. There is a 80
percent chance of MVFR conditions between 06Z and 15Z. There is a
20 percent chance of IFR conditions in drizzle.

&&

.MARINE...07/156 PM.

For the Outer Waters... Small Craft Advisory (SCA) level winds
and seas will continue through late Monday night. SCA level seas
will likely continue through Thursday. There is a forty percent
chance of SCA level winds on Tuesday, otherwise winds will remain
below SCA level Tuesday through Thursday. Conditions will be below
SCA level on Friday.

For the Inner Waters north of Point Sal... SCA level winds and
seas will continue through late Monday night with a brief lull in
winds in the morning hours. Seas will diminish early on Tuesday
but then increase to SCA level again by Tuesday night and continue
through Thursday. Winds will remain below SCA level Tuesday
through Thursday and both winds and seas will be below on Friday.

For the Inner Waters south of Point Conception... SCA level winds
will likely develop late on Monday and continue on Tuesday. The
strongest winds will be in the afternoon and evening hours.
Otherwise, conditions will remain below SCA levels through
Thursday.

&&

.BEACHES...07/207 PM.

High surf conditions of 8 to 12 feet to the Central Coast have
been diminishing and will drop below advisory criteria this
afternoon. Another large swell will arrive on Monday and will
likely bring high surf to the area through the week.

The surf across the west facing beaches of Ventura County will
be elevated this afternoon and evening but will remain below
advisory criteria. Elevated surf conditions are likely again
Monday through Thursday.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Winter Storm Watch in effect from Tuesday evening through
      Thursday evening for zones 52>54. (See LAXWSWLOX).
PZ...Small Craft Advisory in effect until 3 AM PST Tuesday for
      zones 645-670-673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (WED-SUN).

High surf and dangerous rip currents are likely through the
middle of the week. Gusty west to northwest winds will create
driving and boating hazards at times through Wednesday. A winter
storm will bring rain and snow to the area Wednesday and Thursday.

&&

$$

PUBLIC...Thompson
AVIATION...Hall
MARINE...Kj
BEACHES...Kj
SYNOPSIS...RAT

weather.gov/losangeles


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