Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000
FXUS66 KLOX 190541
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
1041 PM PDT Mon Mar 18 2024

.SYNOPSIS...18/1014 PM.

Areas of overnight low clouds and fog should clear by late
Tuesday morning. In the afternoon, mountains showers are
possible, with very slight chances for valleys. Dry conditions
are expected the rest of the week before a weak system brings
wind, light showers, and cooler weather for this weekend.

&&

.SHORT TERM (MON-THU)...18/940 PM.

***UPDATE***

The upper low and associated vort max which brought scattered
showers and isolated thunderstorms to L.A. and VTU Counties this
afternoon and earlier this evening was centered near the Salton
Sea this evening and it was beginning to move east. Measurable
rain was reported in many locations in Ventura County and in
about 20-30% of L.A. County. However, due to the quick movement of
the showers/storms and dry air at low levels, only a few locations
reported more than a tenth of an inch of rain. Some small hail was
reported in Bellflower, and there were many reports of lightning.
Shower activity decreased quickly around sunset, and while
isolated showers continued across Ventura County this evening,
there should end or dissipate within the next hour or two.
Otherwise, there were just some high clouds moving southwestward
into L.A. County around the western periphery of the upper low.

The WRF shows a fairly good amount of moisture tonight, and
suggests areas of low clouds and fog later tonight/Tue morning in
coastal sections of L.A. County and possibly Ventura County,
on the Central Coast, and in the Santa Ynez Valley. There could
be some locally dense fog, mainly north of Point Conception, where
the marine inversion is lower.

Low clouds should burn off in most areas by mid to late morning
Tue. The upper low will move eastward Tue. While the WRF still
shows good instability, especially across L.A. and VTU Counties
Tue afternoon and evening. However, there will be somewhat less in
the way of moisture wrapping into the region, and there does not
look to be any mid or upper level feature (such as a strong vort)
to be a trigger for any storms. Therefore, any showers/tstorms
that might develop Tue afternoon should be mainly due to
orographic lift of the northeasterly flow into the mountains. With
N to NE flow through a deep layer, there is still a chance that
some showers could drift into the foothills and some interior
valley areas of VTU and L.A. Counties. However, expect less in
the way of shower/tstorm activity Tue, especially west of the
mountains. Increasing onshore flow may bring slight cooling on
Tue, especially to the coastal plain, but this may be somewhat
offset but height rises. Overall, max temps should be a few
degrees above normal.

***From Previous Discussion***

The upper low will likely continue to move east Tue night and
Wed, finally losing its influence on the weather in the forecast
area. Expect areas of night thru morning low clouds and fog in
coastal areas Tue night/Wed morning, then mostly sunny skies by
afternoon. Max temps may drop a bit Wed as onshore flow returns.

There will likely be areas of night/morning low clouds in coastal
and some valley areas Wed night/Thu morning. The ridge will weaken
and flatten with a large upper low moving toward the West Coast. Max
temps will likely still be above normal Thu.

.LONG TERM (FRI-MON)...18/115 PM.

The flow aloft will shift from zonal on Thu to southwesterly Fri.
There may be low clouds again Thu night/Fri morning. Increasing
mid and high level moisture pushing into the region will likely
bring an increase in clouds to all areas Fri, along with some
cooling, bringing temps close to normal levels.

Most ensemble members show measurable rain in most of the area
this weekend, but there is uncertainty with respect to amounts and
timing. In general the highest chances and rain amounts are in
northwest SLO County where up to 0.5" could fall over the weekend.
Most other areas will be between 0.1 and 0.25" except for the
Antelope Valley which will likely remain rain free.

By Monday the system should be through the area and the CWA will
see mostly clear skies and warming temps under the eastern Pacific
ridge.

&&

.AVIATION...19/0541Z.

At 0431Z at KLAX, there was a deep moist layer up to 5000 ft.

Low confidence in TAFs due to uncertainty in low clouds tonight.
There is a 30% chance of no cigs forming for KSBA, KOXR, KCMA,
KSMO, KLAX, and KLGB. Timing of development/clearing of cigs and
vsby restrictions may be off by up to 2 hours. From 20Z-04Z Tue
there is a 15% chance of thunderstorms over the mountains of LA
and Ventura Counties.

KLAX...Low confidence in TAF through 20Z Tue, due to uncertainty
in cigs. There is a 30% chance of no cigs forming tonight, and
timing might be off by up to 2 hours. Any easterly winds should
remain less than 7 knots.

KBUR...Moderate confidence in TAF. There is a 10% chance of
BKN008-BKN015 cigs between 10-17Z.

&&

.MARINE...18/1014 PM.

For the waters southwest through northwest of the Channel Islands
and along the Central Coast, there is a 60 percent chance of
Small Craft Advisory (SCA) level Tuesday afternoon and evening.
Wednesday afternoon and evening, there is a 60 percent chance of
SCA level winds for the waters around Point Conception and the
Channel Islands, and a 40% for the waters along the Central Coast.
Chances will decrease to a 30% for all these waters Thurday and
Friday.

Inside the southern California bight through Wednesday evening,
there is a 20 percent chance of Small Craft Advisory (SCA) level
winds each afternoon and evening with the highest chances for the
western portions. Thursday and Friday conditions are expected to
be below SCA level.

Widespread SCA condition are expected for all waters starting as
early as Saturday afternoon.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory in effect from 3 PM to 9 PM PDT Tuesday
      for zones 645-670-673. (See LAXMWWLOX).

&&

$$

PUBLIC...DB/jld
AVIATION...Schoenfeld
MARINE...Lund/Schoenfeld
SYNOPSIS...jld/Schoenfeld

weather.gov/losangeles

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


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