Area Forecast Discussion
Issued by NWS Los Angeles, CA

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739
FXUS66 KLOX 220304
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
804 PM PDT Fri Sep 21 2018

.SYNOPSIS...21/640 PM.

Daytime temperatures will hover around normal through the weekend
and into next week. Fair skies are expected, except for overnight
to morning low clouds and fog for the coast, and some coastal
valleys. An upper low crossing Central California will cool
temperatures some Sunday and Monday, followed by high pressure
and gradual warming starting Tuesday.

&&

.SHORT TERM (FRI-MON)...21/804 PM.

***UPDATE***

Excitement levels are very low across the district this evening.
Latest satellite/surface observations indicate some stratus along
the immediate Central Coast with clear skies elsewhere. Latest
AMDAR soundings indicate a shallow marine inversion, around 1000
feet deep.

Forecast-wise, the main concern for the immediate short term will
be the development of stratus/fog. Based on latest model forecast,
onshore flow will remain overnight, but with some offshore trends.
So, will expect the marine inversion to remain around 1000 feet
deep overnight with stratus likely across the coastal plain.
There is a chance of some very patchy stratus/fog pushing into the
lower coastal valleys. Given the shallow nature of the inversion,
there may be some patchy dense fog late tonight, especially across
the Central Coast. Other than this potential stratus, skies should
remain clear overnight.

Overall, current forecast has a good handle on expected conditions
in the immediate short term. So, no significant forecast updates
are anticipated at this time.

***From Previous Discussion***

Onshore flow returned today and brought with it a solid marine
layer for all coastal areas and some valleys. After a much warmer
night last night due to the clouds and southeast flow temps today
for coast/valleys have generally been running cooler by a degree
or two, or as much as 10-15 for the Central Coast which no longer
benefited from the warming northeast flow off the coastal hills.
After significant marine layer deepening last night the LAX
profiler and AMDAR soundings are already showing significant
warming between 1500 and 2000 feet indicating that the marine
layer depth is already getting squashed. Combine this with the
expected 1-2 mb offshore trend Saturday morning and we should be
looking at a slight rebound in temps tomorrow, generally 2-4
degrees. Still expecting a fairly solid stratus coverage but
mostly confined to coastal areas and possibly extreme lower
valleys. Likely another round of dense fog for the Central Coast
tonight.

Minimal changes going into Sunday, though by Sunday night a weak
trough will pass to the north and cause pressure gradients to
trend onshore again. This should result in a degree or two of
cooling Sunday/Monday but otherwise pretty similar weather each
day.

.LONG TERM (TUE-FRI)...21/147 PM.

Pretty quiet weather pattern through next week with no significant
day to day changes. Models generally agree that following the
Sunday night/Monday trough California will be in between an
impressive trough covering much of the eastern 2/3 of the US and a
very stable Rex block pattern over the eastern Pacific. The only
question is how much heights will build between the two systems.
The GFS is definitely favoring a ridgier/warmer pattern for our
area while the ECMWF is hanging onto some baggy troughiness
through the end of the week. Aside from that low impact dilemma
the forecast is pretty benign with light onshore flow through the
period and temps either at or slightly above normal.

&&

.AVIATION...21/2234Z.

At 2230Z, the marine inversion at KLAX was based at 1000 feet.
The top of the inversion was 3000 feet with a temperature of
24 degrees Celsius.

Overall, moderate confidence in 00Z TAF. With shallow inversion,
stratus overnight should be confined to the coastal plain.
Moderate confidence in return of stratus, but low confidence in
timing.

KLAX...Moderate confidence in 00Z TAF. Moderate confidence in
stratus/fog returning to airfield (30% chance that skies will
remain clear). However, low confidence in timing (could be +/- 4
hours of current 08Z forecast) and flight category (could be IFR
or LIFR).

KBUR...Moderate confidence in 00Z TAF. There is a 30% chance of
IFR/LIFR conditions 09Z-16Z.

&&

.MARINE...21/803 PM.

For the Outer Waters, high confidence in current forecast. There
is a 60% chance of Small Craft Advisory (SCA) level winds Sunday
across the two northern zones PZZ670 and 673 then expanding into
the NW portion of PZ676 for Monday.

For the Inner Waters north of Point Sal, high confidence in
current forecast as conditions are expected to remain below SCA
levels through Wednesday.

For the Inner Waters south of Point Conception, high confidence in
current forecast as conditions are expected to remain below SCA
levels through Wednesday.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...NONE.

&&

.HAZARD POTENTIAL OUTLOOK (MON-FRI).

No significant hazards expected.

&&

$$

PUBLIC...MW
AVIATION...RAT
MARINE...RAT
SYNOPSIS...

weather.gov/losangeles



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